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ENGINEERING MANUAL OF AUTOMATIC CONTROL

CONTROL FUNDAMENTALS

24

Reset error correction time is proportional to the deviation

of the controlled variable. For example, a four-percent deviation
from the setpoint causes a continuous shift of the proportional
band at twice the rate of shift for a two-percent deviation. Reset
is also proportional to the duration of the deviation. Reset
accumulates as long as there is offset, but ceases as soon as the
controlled variable returns to the setpoint.

With the PI controller, therefore, the position of the final

control element depends not only upon the location of the
controlled variable within the proportional band (proportional
band adjustment) but also upon the duration and magnitude of
the deviation of the controlled variable from the setpoint (reset
time adjustment). Under steady state conditions, the control
point and setpoint are the same for any load conditions, as shown
in Figure 37.

PI control adds a component to the proportional control

algorithm and is described mathematically by:

Where:

V = output signal
K = proportionality constant (gain)

E

= deviation (control point - setpoint)

T

1

= reset time

K/T

1

= reset gain

dt = differential of time (increment in time)

M = value of the output when the deviation

is zero

Integral windup, or an excessive overshoot condition, can

occur in PI control. Integral windup is caused by the integral
function making a continued correction while waiting for
feedback on the effects of its correction. While integral action
keeps the control point at setpoint during steady state conditions,
large overshoots are possible at start-up or during system upsets
(e.g., setpoint changes or large load changes). On many systems,
short reset times also cause overshoot.

Integral windup may occur with one of the following:

— When the system is off.
— When the heating or cooling medium fails or is not

available.

— When one control loop overrides or limits another.

Integral windup can be avoided and its effects diminished.

At start-up, some systems disable integral action until measured
variables are within their respective proportional bands. Systems
often provide integral limits to reduce windup due to load
changes. The integral limits define the extent to which integral
action can adjust a device (the percent of full travel). The limit
is typically set at 50 percent.

The reset action of the integral component shifts the

proportional band as necessary around the setpoint as the load
on the system changes. The graph in Figure 36 shows the shift
of the proportional band of a PI controller controlling a normally
open heating valve. The shifting of the proportional band keeps
the control point at setpoint by making further corrections in
the control signal. Because offset is eliminated, the proportional
band is usually set fairly wide to ensure system stability under
all operating conditions.

T1

T2

T3

T4

CLOSED

VALVE

POSITION

OPEN

SETPOINT

TIME

C2098

DEVIATION

FROM

SETPOINT

INTEGRAL ACTION

CONTROL POINT (LOAD CHANGES)

PROPORTIONAL CORRECTION     

Fig. 36. Proportional Band Shift Due to Offset.

Reset of the control point is not instantaneous. Whenever

the load changes, the controlled variable changes, producing
an offset. The proportional control makes an immediate
correction, which usually still leaves an offset. The integral
function of the controller then makes control corrections over
time to bring the control point back to setpoint (Fig. 37). In
addition to a proportional band adjustment, the PI controller
also has a reset time adjustment that determines the rate at which
the proportional band shifts when the controlled variable
deviates any given amount from the setpoint.

Fig. 37. Proportional-Integral Control

Response to Load Changes.

V = KE + 

K

T

1

∫

Edt + M

Integral

34

37

40

43

46

CLOSED

50% OPEN

100% OPEN

SETPOINT (

°

C)

PROPORTIONAL BAND

FOR SEPARATE LOAD

CONDITIONS

HEATING

VALVE

POSITION

0%

LOAD

50%

LOAD

100%

LOAD

     = CONTROL POINT
THROTTLING RANGE = 5 KELVINS

C3985

Содержание AUTOMATIC CONTROL SI Edition

Страница 1: ...AUTOMATIC CONTROL for ENGINEERING MANUAL of COMMERCIAL BUILDINGS SI Edition ...

Страница 2: ...well Europe S A 3 Avenue du Bourget 1140 Brussels Belgium Honeywell Asia Pacific Inc Room 3213 3225 Sun Hung Kai Centre No 30 Harbour Road Wanchai Hong Kong Home and Building Control Honeywell Limited Honeywell Limitée 155 Gordon Baker Road North York Ontario M2H 3N7 Honeywell Latin American Region 480 Sawgrass Corporate Parkway Suite 200 Sunrise FL 33325 Home and Building Control Honeywell Inc Ho...

Страница 3: ... Honeywell has been dedicated to assisting consulting engineers and architects in the application of automatic controls to heating ventilating and air conditioning systems This manual is an outgrowth of that dedication Our end user customers the building owners and operators will ultimately benefit from the efficiently designed systems resulting from the contents of this manual All of this manual ...

Страница 4: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL iv ...

Страница 5: ...the control information To enhance understanding definitions of terms are provided within individual sections Building management systems have evolved into a major consideration for the control engineer when evaluating a total heating ventilating and air conditioning system design In response to this consideration the basics of building management systems configuration are presented The control re...

Страница 6: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL vi ...

Страница 7: ...ASHRAE Psychrometric Charts 53 Pneumatic Control Fundamentals 57 Introduction 59 Definitions 59 Abbreviations 60 Symbols 61 Basic Pneumatic Control System 61 Air Supply Equipment 65 Thermostats 69 Controllers 70 Sensor Controller Systems 72 Actuators and Final Control Elements 74 Relays and Switches 77 Pneumatic Control Combinations 84 Pneumatic Centralization 89 Pneumatic Control System Example 9...

Страница 8: ... Programming 142 Typical Applications 145 Indoor Air Quality Fundamentals 149 Introduction 151 Definitions 151 Abbreviations 153 Indoor Air Quality Concerns 154 Indoor Air Quality Control Applications 164 Bibliography 170 Smoke Management Fundamentals 171 Introduction 172 Definitions 172 Objectives 173 Design Considerations 173 Design Priniples 175 Control Applications 178 Acceptance Testing 181 L...

Страница 9: ...ing System Control Process 246 Year Round System Control Processes 248 ASHRAE Psychrometric Charts 261 Building Airflow System Control Applications 263 Introduction 265 Definitions 265 Airflow Control Fundamentals 266 Airflow Control Applications 280 References 290 Chiller Boiler and Distribution System Control Applications 291 Introduction 295 Abbreviations 295 Definitions 295 Symbols 296 Chiller...

Страница 10: ...izing 437 Damper Selection and Sizing 445 Introduction 447 Definitions 447 Damper Selection 448 Damper Sizing 457 Damper Pressure Drop 462 Damper Applications 463 General Engineering Data 465 Introduction 466 Conversion Formulas and Tables 466 Electrical Data 473 Properties of Saturated Steam Data 476 Airflow Data 477 Moisture Content of Air Data 479 Index 483 ...

Страница 11: ...SMOKE MANAGEMENT FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL 1 CONTROL SYSTEM FUNDAMENTALS ...

Страница 12: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL SMOKE MANAGEMENT FUNDAMENTALS 2 SMOKE MANAGEMENT FUNDAMENTALS ...

Страница 13: ...iables 15 Control Loop 15 Control Methods 16 General 16 Analog and Digital Control 16 Control Modes 17 Two Position Control 17 General 17 Basic Two Position Control 17 Timed Two Position Control 18 Step Control 19 Floating Control 20 Proportional Control 21 General 21 Compensation Control 22 Proportional Integral PI Control 23 Proportional Integral Derivative PID Control 25 Enhanced Proportional I...

Страница 14: ...onents 30 Sensing Elements 30 Temperature Sensing Elements 30 Pressure Sensing Elements 31 Moisture Sensing Elements 32 Flow Sensors 32 Proof of Operation Sensors 33 Transducers 33 Controllers 33 Actuators 33 Auxiliary Equipment 34 Characteristics and Attributes of Control Methods 35 ...

Страница 15: ...mize building comfort safety and efficiency DEFINITIONS The following terms are used in this manual Figure 1 at the end of this list illustrates a typical control loop with the components identified using terms from this list Analog Continuously variable e g a faucet controlling water from off to full flow Automatic control system A system that reacts to a change or imbalance in the variable it co...

Страница 16: ...ng element of a control due to the time required for the sensing element to sense a change in the sensed variable Load In a heating or cooling system the heat transfer that the system will be called upon to provide Also the work that the system must perform Manipulated variable The quantity or condition regulated by the automatic control system to cause the desired change in the controlled variabl...

Страница 17: ...rol point range through which the controlled variable must pass to move the final control element through its full operating range Expressed in values of the controlled variable e g Kelvins or degrees Celsius percent relative humidity kilopascals Also called proportional band In a proportional room thermostat the temperature change required to drive the manipulated variable from full off to full o...

Страница 18: ...ontrol loops and can be divided into central system and local or zone control loops For maximum comfort and efficiency all control loops should be tied together to share information and system commands using a building management system Refer to the Building Management System Fundamentals section of this manual The basic control loops in a central air handling system can be classified as shown in ...

Страница 19: ...ON 20 C C3971 Control Loop Classification Description Ventilation Basic Coordinates operation of the outdoor return and exhaust air dampers to maintain the proper amount of ventilation air Low temperature protection is often required Better Measures and controls the volume of outdoor air to provide the proper mix of outdoor and return air under varying indoor conditions essential in variable air v...

Страница 20: ...el Figure 4 shows an air handling system with a hot water coil A similar control scheme would apply to a steam coil If steam or hot water is chosen to distribute the heat energy high efficiency boilers may be used to reduce life cycle cost Water generally is used more often than steam to transmit heat energy from the boiler to the coils or terminal units because water requires fewer safety measure...

Страница 21: ...g the process is reversed by tilting the pipe the other way Controls may be pneumatic electric electronic digital or a combination Satisfactory control can be achieved using independent control loops on each system Maximum operating efficiency and comfort levels can be achieved with a control system which adjusts the central system operation to the demands of the zones Such a system can save enoug...

Страница 22: ...heat pump may be in the form of a chiller Air is typically the heat source and heat sink unless a large water reservoir e g ground water is available Initial and operating costs are prime factors in selecting cooling equipment DX systems can be less expensive than chillers However because a DX system is inherently two position on off it cannot control temperature with the accuracy of a chilled wat...

Страница 23: ... infiltration While ventilation is required in nearly all buildings the design of a ventilation system must consider the cost of heating and cooling the ventilation air Ventilation air must be kept at the minimum required level except when used for free cooling refer to ASHRAE Standard 62 Ventilation for Acceptable Indoor Air Quality To ensure high quality ventilation air and minimize the amount r...

Страница 24: ...of particles to be removed and acceptable maintenance requirements High efficiency particulate air HEPA mechanical filters Fig 16 do not release the collected particles and therefore can be used for clean rooms and areas where toxic particles are released HEPA filters significantly increase system pressure drop which must be considered when selecting the fan Figure 17 shows other mechanical filter...

Страница 25: ...example of closed loop control would be the temperature of discharge air in a duct determining the flow of hot water to the heating coils to maintain the discharge temperature at a controller setpoint AIRFLOW AIRFLOW ALTERNATE PLATES GROUNDED INTERMEDIATE PLATES CHARGED TO HIGH POSITIVE POTENTIAL THEORETICAL PATHS OF CHARGES DUST PARTICLES POSITIVELY CHARGED PARTICLES SOURCE 1996 ASHRAE SYSTEMS AN...

Страница 26: ...use pressure or volume changes that are applied directly to the diaphragm or bellows in the valve or damper actuator Many complete control systems use a combination of the above categories An example of a combined system is the control system for an air handler that includes electric on off control of the fan and pneumatic control for the heating and cooling coils Various control methods are descr...

Страница 27: ...two position control works well for many applications For close temperature control however the cycling must be accelerated or timed Basic Two Position Control In basic two position control the controller and the final control element interact without modification from a mechanical or thermal source The result is cyclical operation of the controlled equipment and a condition in which the controlle...

Страница 28: ...o position control However the controller responds to gradual changes in the average value of the controlled variable rather than to cyclical fluctuations Overshoot and undershoot are reduced or eliminated because the heat anticipation or time proportioning feature results in a faster cycling rate of the mechanical equipment The result is closer control of the variable than is possible in basic tw...

Страница 29: ...ditions maintain the preset 10 minute total cycle 10 7 5 5 2 5 0 SELECTED CYCLE TIME MINUTES 100 75 50 25 0 LOAD ON OFF C2090 Fig 24 Time Proportioning Control Because the controller responds to average temperature or humidity it does not wait for a cyclic change in the controlled variable before signaling corrective action Thus control system lags have no significant effect Droop in heating contr...

Страница 30: ... floating control is the regulation of static pressure in a duct Fig 29 SPACE OR RETURN AIR THERMOSTAT ACTUATOR SOLENOID VALVES FAN DISCHARGE AIR DIRECT EXPANSION COILS MULTISTAGE ELECTRIC HEAT STEP CONTROLLER STAGE NUMBERS 6 5 4 3 2 1 C2716 D X D X Fig 28 Step Control with Sequenced DX Coils and Electric Heat A variation of step control used to control electric heat is step plus proportional cont...

Страница 31: ...nd thus the discharge temperature Fig 31 Proportional Control Loop In proportional control the final control element moves to a position proportional to the deviation of the value of the controlled variable from the setpoint The position of the final control element is a linear function of the value of the controlled variable Fig 32 T1 T2 T3 T4 T5 T6 TIME NO LOAD FULL LOAD CLOSED OPEN DAMPER POSIT...

Страница 32: ...d condition increases from 50 percent offset increases toward cooler As the load condition decreases offset increases toward warmer The opposite occurs in a cooling application Where V output signal K proportionality constant gain E deviation control point setpoint M value of the output when the deviation is zero Usually the output value at 50 percent or the middle of the output range The generate...

Страница 33: ...setpoint as the compensation input increases Increasing the setpoint by adding compensation on an increase in the compensation variable is often referred to as positive or summer compensation Increasing the setpoint by adding compensation on a decrease in the compensation variable is often referred to as negative or winter compensation Compensation is most commonly used for temperature control but...

Страница 34: ...able When one control loop overrides or limits another Integral windup can be avoided and its effects diminished At start up some systems disable integral action until measured variables are within their respective proportional bands Systems often provide integral limits to reduce windup due to load changes The integral limits define the extent to which integral action can adjust a device the perc...

Страница 35: ...reset gain dt differential of time increment in time TD rate time time interval by which the derivative advances the effect of proportional action KTD rate gain constant dE dt derivative of the deviation with respect to time error signal rate of change M value of the output when the deviation is zero SETPOINT T1 T2 T3 T4 T5 T6 C2099 CONTROL POINT OFFSET TIME SETPOINT T1 T2 T3 T4 T5 T6 C2100 CONTRO...

Страница 36: ...emand disturbances Setpoint changes Ambient environmental variable changes Supply disturbances are changes in the manipulated variable input into the process to control the controlled variable An example of a supply disturbance would be a decrease in the temperature of hot water being supplied to a heating coil More flow is required to maintain the temperature of the air leaving the coil Demand di...

Страница 37: ...ed by a Thermostat Lag also occurs between the release of heat into the space the space warming and the thermostat sensing the increased temperature In addition the final control element requires time to react the heat needs time to transfer to the controlled medium and the added energy needs time to move into the space Total process lag is the sum of the individual lags encountered in the control...

Страница 38: ... tank exerts a stabilizing effect and does not immediately react to changes such as variations in the rate of the flow of steam or liquid minor variations in the heat input and sudden changes in the ambient temperature LIQUID IN HEATING MEDIUM IN LIQUID OUT HEATING MEDIUM OUT C2076 Figure 45 shows a high velocity heat exchanger which represents a process with a small thermal capacitance The rate o...

Страница 39: ...increases the temperature difference and or flow required to maintain heat transfer If the fins on a coil become dirty or corroded the resistance to the transfer of heat from one medium to the other medium increases Dead Time Dead time which is also called transportation lag is the delay between two related actions in a continuous process where flow over a distance at a certain velocity is associa...

Страница 40: ... rates of heat expansion the curvature of the bimetal changes with changes in temperature The resulting movement of the bimetal can be used to open or close circuits in electric control systems or regulate airflow through nozzles in pneumatic control systems Winding the bimetal in a coil Fig 49 enables a greater length of the bimetal to be used in a limited space Fig 49 Coiled Bimetal Element The ...

Страница 41: ...nd to temperature changes more rapidly than bimetal or sealed fluid sensors The resistance change is detected by a bridge circuit Nickel A BALCO and platinum are typical materials used for this type of sensor In thermocouple temperature sensing elements two dissimilar metals e g iron and nickel copper and constantan iron and constantan are welded together The junction of the two metals produces a ...

Страница 42: ...and decreasesastemperatureincreases Humiditysensorsalsorespond tochangesintemperature Iftherelativehumidityisheldconstant the sensor reading can be affected by temperature changes Because of this characteristic humidity sensors should not be used in atmospheres that experience wide temperature variations unless temperature compensation is provided Temperature compensation is usually provided with ...

Страница 43: ...ntroller compares the input signal with the desired condition or setpoint and generates an output signal to operate a controlled device A sensor may be integral to the controller e g a thermostat or some distance from the controller Controllers may be electric electronic microprocessor or pneumatic An electric electronic controller provides two position floating or modulating control and may use a...

Страница 44: ... to the control signal The positive positioning relay receives the controller output signal reads the actuator position and repositions the actuator according to the controller signal regardless of external loads on the actuator Electric actuators can provide proportional or two position control action Figure 56 shows a typical electric damper actuator Spring return actuators return the damper to ...

Страница 45: ...Integral sensor controller Simple sequence of control Broad environmental limits Complex modulating actuators especially when spring return Precise control Solid state repeatability and reliability Sensor may be up to 300 feet from controller Simple remote rotary knob setpoint High per loop cost Complex actuators and controllers Precise control Inherent energy management Inherent high order propor...

Страница 46: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTROL FUNDAMENTALS 36 ...

Страница 47: ...Process 42 Air Conditioning Processes 43 Heating Process 43 Cooling Process 44 Humidifying Process 44 Basic Process 44 Steam Jet Humidifier 46 Air Washers 49 Vaporizing Humidifier 50 Cooling and Dehumidification 51 Basic Process 51 Air Washers 51 Dehumidification and Reheat 52 Process Summary 53 ASHRAE Psychrometric Charts 53 CONTENTS Psychrometric Chart Fundamentals ENGINEERING MANUAL OF AUTOMATI...

Страница 48: ...t of measure for energy work and heat This section uses joule as a unit of heat where 4 2 joules will raise the temperature of 1 gram of water 1 kelvin Latent heat Heat that changes liquid to vapor or vapor to liquid without a change in temperature or pressure of the moisture Latent heat is also called the heat of vaporization or condensation When water is vaporized it absorbs heat which becomes l...

Страница 49: ...they can be used to determine other air properties on a psychrometric chart DESCRIPTION OF THE PSYCHROMETRIC CHART The ASHRAE Psychrometric Chart is a graphical represen tation of the thermodynamic properties of air There are five different psychrometric charts available and in use today Chart No 1 Normal temperatures 0 to 50 C Chart No 2 Low temperatures 40 to 10 C Chart No 3 High temperatures 10...

Страница 50: ...ogram of dry air The chart also contains a protractor nomograph with the following scales Enthalpy humidity ratio scale Sensible heat total heat ratio scale When lines are drawn on the chart indicating changes in psychrometric conditions they are called process lines With the exception of relative humidity all lines are straight Wet bulb lines and enthalpy total heat lines are not exactly the same...

Страница 51: ...e is 0 86 cubic meters per kilogram of dry air Point A Dew point is 17 C Point B Moisture content is 12 0 grams of moisture per kilogram of dry air Point C Fig 4 Figure 5 is the same as Figure 4 but is used to obtain latent heat and sensible heat values Figures 4 and 5 indicate that the enthalpy total heat of the air is 56 0 kilojoules per kilogram of dry air Point D Enthalpy is the sum of sensibl...

Страница 52: ...int C EXAMPLE B Plotting values when both Chart No 1 and Chart No 2 are required In this example a ventilating system Fig 7 is used to illustrate how to plot data on Chart No 2 and transfer values to Chart No 1 Chart No 2 is similar to Chart No 1 except that it covers the 40 C to 10 C temperature range This is the temperature range immediately below that of Chart No 1 Note that there is an overlap...

Страница 53: ...ng the enthalpy value of 28 2 kJ kg and the moisture content value of 6 5g plot the mixed air conditions Point C on Chart No 1 Figure 9 by drawing a horizontal line across the chart at the 6 5g moisture content level and a diagonal line parallel to the enthalpy lines starting at the 28 2 kilojoulesper kilogram of dry air enthalpy point Point C yields 12 C dry bulb and 9 5 C wet bulb temperature 6 ...

Страница 54: ... percentage relative humidity at 21 C than at 32 C Calculate the total heat removed as follows Fig 12 Total heat at Point A total heat at Point B total heat removed 70 5 59 0 11 5 kilojoules per kilogram of dry air This is all sensible heat since there is no change in moisture content HUMIDIFYING PROCESS BASIC PROCESS The humidifying process adds moisture to the air and crosses constant moisture l...

Страница 55: ...is 0 55 grams of moisture per kilogram of dry air 3 The moisture required is 5 5 g kg 0 55 g kg 4 95 grams of moisture per kilogram of dry air Line A B Figure 15 represents this humidifying process on the psychrometric chart Fig 15 The space contains the following volume 9m x 12m x 2 5m 270 cubic meters Two air changes per hour is as follows 2 x 270m3 540 cubic meters per hour or 540 60 x 60 150 l...

Страница 56: ...h steam then the steam is fed through nozzles and sprayed into the air stream The jacket minimizes condensation when the steam enters the pipe with the nozzles and ensures dry steam for humidification The steam is sprayed into the air at a temperature of 100 C or higher The enthalpy includes the heat needed to raise the water temperature from 0 to 100 C or 419 kJ plus 2256 kJ to change the water i...

Страница 57: ... 32 C DB 33 C DB 50 RH 16 g kg 6 5 g kg CONSTRUCTION LINE M15331 REFERENCE POINT 2675 kJ kg THIS LINE IS PARALLEL TO THE SOLID LINE C B ON THE PSYCH CHART TOTAL HEAT SENSIBLE HEAT Hs Ht h W ENTHALPY HUMIDITY RATIO 1 0 1 0 0 10 0 5 0 4 0 0 4 0 6 0 8 0 2 3 0 2 5 2 0 1 0 0 2 0 2 0 4 0 4 0 2 0 1 0 0 5 5 0 ...

Страница 58: ...eight of the air passing through is 4 72 m3 s 0 874 m3 kg 5 4 kilograms per second The weight of the moisture added is 5 4 kg s x 9 5 g kg 51 3 grams per second of moisture The steam raised the temperature of the air from 32 C dry bulb to 33 C dry bulb To find the latent heat added by the steam humidifier to the air determine the enthalpy at Point D the enthalpy of the heated air without added moi...

Страница 59: ... Point A is the entering condition of the air Point B is the final condition and Point C is the temperature of the water Since the water is recirculating the water temperature becomes the same as the wet bulb temperature of the air Fig 21 The next two psychrometric charts Fig 22 and 23 illustrate the humidifying process using a heated air washer The temperature to which the water is heated is dete...

Страница 60: ...alpy of the air is increased because of the heat in the water VAPORIZING HUMIDIFIER Vaporizingandwatersprayhumidifiersoperateontheprincipal ofbreakingwaterupintosmallparticulatessotheyareevaporated directly into the air This process is essentially adiabatic since the enthalpy lines of the water vapor for 0 and 100 C are so close The enthalpy of water at 0 C is zero and at 100 C it is 419 kilojoule...

Страница 61: ...entering air condition is 30 C dry bulb and 61 percent rh Point A The moisture content is 16 5 grams of moisture per kilogram of dry air 2 The leaving air condition is 15 C dry bulb and 93 percent rh Point C The moisture content is 10 grams of moisture per kilogram of dry air 3 The moisture removed is 16 5 g kg 10 g kg 6 5 grams of moisture per kilogram of dry air The volume of air per kilogram at...

Страница 62: ...ever the washer water temperature is between the dew point Point B and the dry bulb Point D temperature of the air moisture is added and the dry bulb temperature of the air falls If the water temperature is above the dry bulb temperature of the air to the right of Point D both the air moisture and the dry bulb temperature increase Whenever the water temperature is below the dew point temperature P...

Страница 63: ... based on a kilogram of dry air Zero moisture is the bottom line of the chart A C B D E F G H SUMMARY OF ALL PROCESSES CHARTABLE PROCESS MOVEMENT IN THE DIRECTION OF A HEATING ONLY STEAM HOT WATER OR ELECTRIC HEAT COIL B HEATING AND HUMIDIFYING STEAM HUMIDIFIER OR RECIRCULATED HOT WATER SPRAY C HUMIDIFYING ONLY AIR WASHER WITH HEATED WATER D COOLING AND HUMIDIFYING WASHER E COOLING ONLY COOLING CO...

Страница 64: ...TROL PSYCHROMETRIC CHART FUNDAMENTALS 54 Fig 33 ASHRAE Psychrometric Chart No 1 TOTAL HEAT SENSIBLE HEAT H s H t h W ENTHALPY HUMIDITY RATIO 1 0 1 0 0 10 0 5 0 4 0 0 4 0 6 0 8 0 2 3 0 2 5 2 0 1 0 0 2 0 2 0 4 0 4 0 2 0 1 0 0 5 5 0 M15336 ...

Страница 65: ...RING MANUAL OF AUTOMATIC CONTROL 55 Fig 34 ASHRAE Psychrometric Chart No 2 0 TOTAL HEAT SENSIBLE HEAT 4 0 2 0 1 0 8 6 4 2 0 2 5 1 0 2 0 1 0 1 0 1 2 1 4 1 6 1 8 2 0 4 0 4 0 0 9 0 8 0 7 0 6 0 5 0 4 0 2 H s H t h W ENTHALPY HUMIDITY RATIO M15335 ...

Страница 66: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL PSYCHROMETRIC CHART FUNDAMENTALS 56 ...

Страница 67: ... Sensing Elements 63 Bimetal 63 Rod and Tube 64 Remote Bulb 64 Averaging Element 64 Throttling Range Adjustment 64 Relays and Switches 64 Air Supply Equipment 65 General 65 Air Compressor 65 Air Drying Techniques 66 General 66 Dry Air Requirement 66 Condensing Drying 67 High Pressure Drying 67 Refrigerant Drying 67 Desiccant Drying 67 Pressure Reducing Valve Station 68 Air Filter 68 Pressure Reduc...

Страница 68: ...eumatic Potentiometer 81 Hesitation Relay 82 Electrical Interlocking Relays 82 Electric Pneumatic Relay 82 Pneumatic Electric Relay 82 Electronic Pneumatic Transducer 83 Pneumatic Switch 83 Manual Positioning Switch 84 Pneumatic Control Combinations 84 General 84 Sequence Control 85 Limit Control 85 Manual Switch Control 86 Changeover Control for Two Pressure Supply System 87 Compensated Control S...

Страница 69: ...ngeover The point at which the compensation effect is reversed in action and changes from summer to winter or vice versa The percent of compensation effect authority may also be changed at the same time Compensation control A process of automatically adjusting the control point of a given controller to compensate for changes in a second measured variable such as outdoor air temperature For example...

Страница 70: ...and extends the shaft on a decrease in pressure Sensing element A device that detects and measures the controlled variable e g temperature humidity Sensor A device placed in a medium to be measured or controlled that has a change in output signal related to a change in the sensed medium Sensor Span The variation in the sensed media that causes the sensor output to vary between 20 to 100 kPa Setpoi...

Страница 71: ...a storage tank at high pressure Fig 2 A pressure switch turns the compressor on and off to maintain the storage tank pressure between fixed limits The tank stores the air until it is needed by control equipment The air dryer removes moisture from the air and the filter removes oil and other impurities The pressure reducing valve PRV typically reduces the pressure to 125 to 150 kPa For two pressure...

Страница 72: ...htly against the nozzle To create a branchline pressure a restrictor Fig 3 is required The restrictor and nozzle are sized so that the nozzle can exhaust more air than can be supplied through the restrictor when the flapper is off the nozzle In that situation the branchline pressure is near zero As the spring tension increases to hold the flapper tighter against the nozzle reducing the air escapin...

Страница 73: ...is being reduced Since modern nozzle flapper devices consume little air feed and bleed systems are no longer popular The feed and bleed system consists of a feed valve that supplies main air to the branch line and a bleed valve that exhausts air from the branch line Fig 5 Each valve consists of a ball nested on top of a tube Some pneumatic controllers use pressure balance diaphragm devices in lieu...

Страница 74: ...the diaphragm chamber The expansion causes the diaphragm pad to push the pin toward the lever which moves the flapper to change the branchline pressure Fig 9 Remote Bulb Temperature Sensor Remote bulb temperature sensors are used in bleed type controllers Capillary length of up to 2 5 meters are normally used for inserting the bulb in duct tank or pipe AVERAGING ELEMENT The averaging element senso...

Страница 75: ...TER Fig 11 Typical Air Supply The controlling pressure is connected at the pilot port P and pressures to be switched are connected at the normally connected port O or the normally disconnected port X The operating point of the relay is set by adjusting the spring pressure at the top of the relay When the pressure at the pilot port reaches the relay operating point it pushes up on the diaphragm in ...

Страница 76: ...h When air is compressed and cooled below its saturation point moisture condenses Draining the condensate from the storage tank causes some drying of the air supply but an air dryer is often required An air dryer is selected according to the amount of moisture in the air and the lowest temperature to which an air line will be exposed For a chart showing temperature and moisture content relationshi...

Страница 77: ...e with a desiccant dryer The desiccant requires about one third of the process air to regenerate itself or it may be heated To regenerate desiccant dryers may require a larger compressor to produce the needed airflow to supply the control system and the dryer It may be necessary to install a desiccant dryer after the refrigerant dryer in applications where the 11 C dew point at 138 kPa mainline pr...

Страница 78: ...D DRY AIR OUT H G F E AIR FROM COMPRESSOR SOLENOID PRESSURE REDUCING VALVE STATION The pressure reducing valve station is typically furnished with an air filter The filter high pressure gage high pressure relief valve pressure reducing valve PRV and low pressure gage are usually located together at one point in the system and may be mounted directly on the compressor The most important elements ar...

Страница 79: ...manually switch a heating cooling system In many applications requiring two pressure reducing valves a single pressure reducing valve is also required to supply single pressure controllers which do not perform well at low pressures Higher dual pressure systems operating at 140 and 170 kPa are sometimes used to eliminate the need and expense of the second PRV THERMOSTATS Thermostats are of four bas...

Страница 80: ... the nozzle the force of the bimetal is reduced This reduction requires a greater temperature change at the bimetal to throttle the flapper over the nozzle The result is a wider throttling range or very low sensitivity For example a temperature change of 0 5 kelvins could result in a branchline pressure change of only 7 kPa CONTROLLERS GENERAL A controller is the same as a thermostat except that i...

Страница 81: ...High pressure controllers measure and control high pressures or vacuums measured in kilopascals or pascals e g steam or water pressures in an air conditioning system Low pressure controllers measure and control low pressures and vacuums measured in kilopascals or pascals e g pressure in an air duct High and low pressure controllers have different size diaphragms In both types one side of the diaph...

Страница 82: ...nd 22 the sensors are fed restricted main air from the controllers Where sensors are located extremely remote from the controller a remote restrictor may be required Fig 22 Dual Input Controller with Manual Remote Setpoint PROPORTIONAL INTEGRAL PI CONTROLLERS Variations of single input and dual input controllers can provide proportional integral PI control PI controllers are used in critical appli...

Страница 83: ...s duct static pressure and differential pressure When the duct static pressure or the pressure differential increases branchline pressure increases VELOCITY SENSOR CONTROLLER The velocity sensor controller combines a highly sensitive air velocity sensor with a pneumatic controller to detect and control airflow regardless of system static pressure It is used in air terminal units and other air hand...

Страница 84: ...Fig 27 Pneumatic Actuator and Damper ACTUATORS GENERAL Pneumatic actuators position damper blades and valve stems A damper actuator typically mounts on ductwork or on the damper frame and uses a push rod and crank arm to position the damper blades rotary action A valve actuator mounts on the valve body and positions the valve stem directly linear action for a globe valve or rotary action via linka...

Страница 85: ...e bottom surface of the diaphragm An increase in air pressure in the diaphragm chamber increases force F1 causing the actuator diaphragm to move upward and open the valve Motion continues until the increase in pressure on the diaphragm plus the controlled medium force F3 is balanced by the increase in spring compression force F2 On a decrease in air pressure in the diaphragm chamber the compressed...

Страница 86: ...nt total flow is maintained through the common inlet or outlet port Two and three way butterfly valves can be operated by long stroke pneumatic actuators and appropriate linkage Fig 31 One or two low pressure actuators powered directly by branchline pressure can operate butterfly valves up to about 300 millimeters depending on the differential close off rating of the valve For other applications h...

Страница 87: ... and the normally connected port O are connected on a fall in pilot pressure P below the relay setpoint and the normally disconnected port X is blocked Fig 34 On a rise in pilot pressure above the relay setpoint C and X are connected and O is blocked Fig 34 Relay Port Connections SWITCHING RELAY A switching relay requires a two position pilot signal and is available with either single pole double ...

Страница 88: ... the relay setpoint the normally disconnected port X is blocked and the normally connected port O connects to the common port C to connect the valve actuator to the room thermostat C2360 SNAP ACTING RELAY VAV TERMINAL UNIT DAMPER ACTUATOR N O HEATING VALVE DA OUTDOOR AIR THERMOSTAT DA ROOM THERMOSTAT M P C X O B M B M M C2362 SNAP ACTING RELAY LOCKOUT RELAY BLEED OUTDOOR AIR DAMPER ACTUATOR MIXED ...

Страница 89: ... to operate final control elements Fig 41 The relay contains multiple diaphragms and control nozzles Each input pressure connects to two diaphragms Fig 41 Load Analyzer Relay in Multizone Air Unit Application In Figure 41 the load analyzer relay selects the lowest pressure signal from the thermostat in the coldest zone and transmits that signal to a normally open heating valve The relay transmits ...

Страница 90: ...DAMPER ACTUATOR CAPACITY RELAY C2365 DAMPER ACTUATOR DAMPER ACTUATOR M P B E EXH M M Fig 44 Positive Positioning Relay with Damper and Valve Actuators When the relay is connected to an actuator the feedback spring produces a force proportional to the actual valve or damper position The relay positions the actuator in proportion to the branchline input If the connected load attempts to unbalance th...

Страница 91: ...l systems to sum two input signal values average two input pressures or as an adjustable flow restriction The potentiometer is a linear restricted air passage between two input ports The pressure at the adjustable output port is a value based on the inputs at the two end connections and the location of the wiper between them Figure 47 shows a pneumatic potentiometer providing an average of two inp...

Страница 92: ...associated electrical circuit ELECTRIC PNEUMATIC RELAY The electric pneumatic E P relay is a two position three way air valve Depending on the piping connections to the ports the relay performs the same functions as a simple diverting relay A common application for the E P relay is to exhaust and close an outdoor air damper in a fan system when the fan motor is turned off as shown in Figure 51 M F...

Страница 93: ...ut to the controller which provides all of the system adjustments and logic requirements for control The controller output of 2 to 10 volts dc is input to the electronic pneumatic transducer which converts the signal to a 20 to 100 kPa output to position the heating valve PNEUMATIC SWITCH The pneumatic switch is available in two or three position models Fig 54 Rotating the switch knob causes the p...

Страница 94: ...controls Figure 57 shows a basic control combination of a thermostat and one or more control valves A normally open control valve assembly is selected when the valve must open if the air supply fails A normally open control valve requires a direct acting thermostat in the heating application shown in Figure 57 Cooling applications may use normally closed valves and a direct acting thermostat The t...

Страница 95: ...alve and damper actuators without positioners have various spring ranges To perform the sequencing application in Figure 59 without positioners select a heating valve actuator that has a 13 to 48 kPa spring range and a cooling valve actuator that has an 55 to 90 kPa spring range Although this method lessens precise positioning it is usually acceptable in systems with lower pressure differentials a...

Страница 96: ...stat can supply it thus overriding the thermostat M M B DA THERMOSTAT N O VALVE C2350 DA LOW LIMIT CONTROLLER MANUAL SWITCH CONTROL Common applications for a diverting switch include on off automatic control for a heating or a cooling valve open closed control for a damper and changeover control for a two pressure air supply system Typical applications for a proportional switch include manual posi...

Страница 97: ... 124 kPa air according to a preset schedule The system then provides the scheduled water temperature to the convectors fan coil units or other heat exchangers in the system Fig 67 Compensated Supply Water System Using Dual Input Controller ELECTRIC PNEUMATIC RELAY CONTROL Figure 68 shows one use of an E P relay in a pneumatic control circuit The E P relay connects to a fan circuit and energizes wh...

Страница 98: ...as the thermostat branchline pressure reaches 49 kPa Relay 2 starts Fan 2 when the controller branchline pressure reaches 84 kPa On a decrease in branchline pressure Relay 2 stops Fan 2 at 70 kPa branchline pressure and Relay 1 stops Fan 1 at 35 kPa branchline pressure Figure 71 shows two spdt P E relays starting and stopping a two speed fan to control condenser water temperature Fig 71 Two Speed ...

Страница 99: ...xhaust configuration PNEUMATIC CENTRALIZATION Building environmental systems may be pneumatically automated to any degree desired Figure 73 provides an example of the front of a pneumatic automation panel This panel contains pneumatic controls and may be local to the controlled HVAC system or it may be located centrally in a more convenient location In this example the on off toggle switch starts ...

Страница 100: ...hour operation GRAVITY RELIEF RETURN AIR RETURN FAN SUPPLY FAN EAST ZONE DISCHARGE AIR WEST ZONE MIXED AIR OUTSIDE AIR EXHAUST M10298 Control Requirements Maintain design outside air airflow during all levels of supply fan loading during occupied periods Use normally open two way valves so system can heat or cool upon compressed air failure by manually running pumps and adjusting water temperature...

Страница 101: ...1 2 X2 2 1M EXHAUST FAN 480V X1 1 X2 1 TN 1TC 1CR NIGHT STAT 2EP 1EP 1M 1M OL SMOKE DETECTOR SUPPLY RETURN LOW TEMPERATURE THERMOSTAT HIGH STATIC PRESSURE CUTOUT X1 1 X2 1 1M 2M 2M OL X1 2 X2 2 A H A H 2CR 2CR 2M 1CR 2TC 3M 3M OL X1 3 X2 3 A H H FIRE EXHAUST 1 CR 2 TC 1 TC TIME CLOCKS INTERVAL TIMER AFTER HOURS N 120 VOLT CONTROL CIRCUIT M10303 2 CR EARLY START CLOCK OCCUPANCY CLOCK Interval Timer...

Страница 102: ...To prevent unnecessary hunting by the return fan at start up the supply fan control signal should be slow loading such that the supply fan goes from zero or a minimum to maximum load over three minutes Shut down should not be restricted WARM UP HEATING COIL CONTROL SEQUENCE Any time the Supply Fan Fig 78 runs and the return air temperature is below 20 5 C Temperature ControllerTC 1 trips Snap Acti...

Страница 103: ...e Electric Pneumatic Relay 1EP starts the outside air system Fig 79 Mixing Damper and Discharge Air Temperature Control M M Y 2 EP 2 EP M Z X P C X O P C X O M P C X O P C X O SR 1 SR 3 SR 2 RA 20 C B S M TC 1 2 EP DA 32 C B S M TC 2 SA 1 C X 21 C C O 22 C SNAP ACTING RELAY RETURN AIR RETURN FAN OUTSIDE AIR TO COOLING CONTROLS TS 1 FROM COOLING CONTROLS 20 55 kPa N O SIGNAL TO OPEN ALL INTERIOR VA...

Страница 104: ...C 3 setpoint Controller TC 3 is a PI proportional plus integral controller NOTE In this constant 1 9 m3 s outside air system if the return air is 22 C and the outside air is 25 C the mixed air temperature will drop below 13 C if theAHU airflow drops below 52 percent of the design airflow OFF FAILURE MODE CONTROL SEQUENCE If compressed air fails both control valves open the outside air damper close...

Страница 105: ...imit Control 102 Series 80 Control Circuits 102 Application 102 Equipment 102 Controllers 102 Relays and Actuators 102 Operation 102 Control Combinations 103 High Limit Control 103 Low Limit Control 103 Series 60 Two Position Control Circuits 103 Application 103 Equipment 103 Controllers 103 Actuators 103 Operation 104 Control Combinations 105 Two Position Control of Steam Valve 105 Summer Winter ...

Страница 106: ...ontrol 110 Control Combinations 111 Low Limit Control 111 High Limit Control 111 Two Position Limit Control 112 Manual and Automatic Switching 112 Closing the Actuator with a Manual Switch 112 Transferring Actuator Control from One Thermostat to Another 112 Reversing for Heating and Cooling Control 112 Transferring Controller from One Actuator to Another 113 Unison Control 113 Manual Minimum Posit...

Страница 107: ...s sense when the motor is stalled at the end of the stroke Actuator gear trains are generally factory lubricated for life so no additional lubrication is necessary Actuators may attach to the valve stem or damper shaft through a linkage or be direct coupled connecting directly to the stem or shaft In some actuators the motor is electrically reversible by the controller A Solenoid brake is commonly...

Страница 108: ... action dependent on the condition of the controlled variable Floating controllers Fig 3D are spdt devices with a center off position Refer to SERIES 60 FLOATING CONTROL CIRCUITS for a discussion of floating control operation Potentiometer controllers Fig 3E move the wiper R toward B on a fall and toward W on a rise in the controlled variable This action varies the resistance in both legs of the p...

Страница 109: ...s each of which has unique characteristics These control circuits are identified by Series Numbers 10 20 40 60 70 80 and 90 Table 1 Series 10 and 20 are no longer used Series 70 is electronic control and is covered in the Electronic Control Fundamentals section The construction of individual control devices conforms to the requirements for the basic series for which it is intended However there ar...

Страница 110: ...lers 2 Pressure controllers 3 Humidity controllers 4 Other two position devices that have a normally open or normally closed contact action such as a line voltage relay In these controllers either snap acting or mercury switch contacts close and open the circuit In most cases Series 40 controllers are snap acting Series 40 controllers can be used in low voltage circuits but low voltage controllers...

Страница 111: ...e actuator drives to the open limit where it is held by the solenoid brake When the controller switch is open the actuator returns to its spring return position Series 80 controllers cannot be used with actuators having a line voltage control circuit Fig 6 Series 40 Control Circuit CONTROL COMBINATIONS UNIT HEATER CONTROL In unit heater control Fig 7 it is usually necessary to keep the heater fan ...

Страница 112: ... Temperature controllers 2 Humidity controllers 3 Any low voltage device with a minimum of one normally open contact such as a low voltage relay A Series 80 controller cannot switch line voltage directly A relay must be used between the controller and a line voltage load However Series 40 or Series 80 controllers can be used with Series 80 actuators A Series 80 controller has snap acting contacts ...

Страница 113: ... control of valves or dampers The basic Series 60 circuit contains a Series 60 actuator and a Series 60 controller Limit controllers can be added where required EQUIPMENT CONTROLLERS 1 Temperature controllers 2 Humidity controllers 3 Pressure controllers 4 Any single pole double throw controller such as a relay or switch Series 60 two position controllers are line voltage rated devices and have a ...

Страница 114: ...rop in temperature or pressure the controller contacts close R to B and open R to W Fig 13 The OPEN winding is energized and the actuator shaft rotates cw until it reaches the limit of travel and opens the OPEN limit switch Fig 14 The actuator remains in this position until a rise in temperature or pressure causes the controller contacts R to B to open and R to W to close The CLOSE coil is then en...

Страница 115: ...n and R to B close calling for winter operation The low limit controller located in the return water line senses the return water temperature If the water temperature is above the setpoint of the low limit controller the R to B circuit completes and the actuator positions the diverting valve to send the return water to the boiler If the low limit controller senses that the return water is too cool...

Страница 116: ...sure controllers 3 Simulated Series 60 floating control using two Series 40 or 80 controllers Series60floatingcontrollersarethree wire line orlow voltage devices with a spdt switching action and a center off position ACTUATORS The actuators discussed in SERIES 60 TWO POSITION CONTROL are also used for floating control In addition actuator assemblies are available with two single direction motors d...

Страница 117: ...ust the output of the valve or damper Series 90 circuits combine any Series 90 controller with an actuator usable for proportioning action Limit controls can also be added EQUIPMENT CONTROLLERS Temperature controllers Humidity controllers Pressure controllers Manual positioners Series 90 controllers differ from controllers of other series in that the electrical mechanism is a variable potentiomete...

Страница 118: ...ersed at either the actuator or the controller The actuator then drives toward the closed position as the potentiometer wiper at the controller moves toward B on a fall in the controlled variable and toward the open position as the potentiometer wiper moves toward W on a rise in the controlled variable These connections are typically used in a cooling application NOTE Most Honeywell Series 90 cont...

Страница 119: ...lf of the 140 ohm unbalance has to go on each side of the bridge to rebalance the circuit the feedback potentiometer will move 70 ohms to the left The table then appears as follows Left Leg RightLeg Controller potentiometer 140 0 Feedback potentiometer 0 140 Total 140 140 When the feedback potentiometer reaches the new position shown dotted the bridge is rebalanced the right triac turns off and th...

Страница 120: ...half of the 70 ohm unbalance has to go on each side of the bridge to rebalance the circuit the feedback potentiometer moves 35 ohms to the left The table then appears as follows Left Leg RightLeg Controller potentiometer 0 140 Low limit potentiometer 70 0 Feedback potentiometer 105 35 Total 175 175 When the feedback potentiometer reaches the new position shown dotted the bridge is rebalanced the r...

Страница 121: ...MBINATIONS The following illustrates common applications of Series 90 controls including low and high limit controls from an application viewpoint LOW LIMIT CONTROL Figure 25 illustrates a typical Series 90 circuit for a heating application with a room controller motorized valve and a low limit controller located in the discharge air to the space The temperature of the space can rise rapidly as a ...

Страница 122: ...ening the cooling valve to reduce humidity also lowers the temperature of the air and may result in occupant discomfort Fig 27 Diagram of Series 90 Circuit with Two Position High Limit Humidity Controller MANUAL AND AUTOMATIC SWITCHING Figures 28 through 31 illustrate various uses of manual switches or relays in Series 90 circuits Substitute a relay with the same switching action as a manual switc...

Страница 123: ... B to B and W to W to the heating actuator which operates normally and the cooling actuator is positively closed by a R to W connection at the actuator Fig 31 Circuit for Transferring Controller from One Actuator to Another UNISON CONTROL Figure 32 illustrates a circuit for controlling up to six Series 90 actuators in unison from one Series 90 controller The B to W terminals of the controller are ...

Страница 124: ...OL CIRCUITS APPLICATION Motor control circuits are used to 1 Start and stop motors 2 Provide electric overload and low voltage protection 3 Provide interlocks for human safety equipment protection and integration with the temperature control system EQUIPMENT STARTERS The starter is a motor load switching device having one or more load switching contacts and optional auxiliary pilot duty contacts A...

Страница 125: ...control N C and N O momentarily actuated relay contacts under computer control are added to the start and stop contacts circuit The N C contact is in series with the stop contact and the N O contact is in parallel with the start contact An overload in any of the motor coils causes the associated overloads OL to heat up and open the OL contacts opening the holding circuit and stopping the motor Ove...

Страница 126: ...id F for the fast windings Pressing the SLOW button closes a circuit energizing starter solenoid S for the slow windings The holding circuits and the push button contacts are mechanically interlocked to prevent energizing both sets of windings at the same time Pressing the STOP button opens both holding circuits and stops the motor Where a mechanical interlock does not exist between the holding ci...

Страница 127: ...F AUTO SWITCH MOTOR CONTROL PUSH BUTTON START STOP MOTOR CONTROL CONTROL COMBINATIONS There are many different control combinations for motor control circuits Figure 38 illustrates a return fan interlocked with the supply fan In this circuit the supply fan starts when the START button is pressed energizing starter solenoid 1M The return fan will not start until supply airflow is proven A relay can...

Страница 128: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL ELECTRIC CONTROL FUNDAMENTALS 118 ...

Страница 129: ...25 Resistance Relative Humidity Sensor 125 Capacitance Relative Humidity Sensor 125 Temperature Compensation 126 Condensation and Wetting 126 Quartz Crystal Relative Humidity Sensor 126 Pressure Sensors 127 Controller 127 Input Types 127 Temperature Controllers 128 Relative Humidity Controllers 128 Enthalpy Controllers 128 Universal Controllers 128 Control Modes 128 Output Control 128 Output Devic...

Страница 130: ...A resistance temperature input and a 2 to 10V dc output are used for purposes of discussion Electric circuits are defined in Electric Control Fundamentals A detailed discussion on control modes can be found in the Control Fundamentals section DEFINITIONS NOTE For definitions of terms not in this section see the Control Fundamentals section Authority CompensationAuthority or ResetAuthority A settin...

Страница 131: ...inal control element through its full operating range Proportional band is expressed in percent of the main sensor span A commonly used equivalent is throttling range which is expressed in values of the controlled variable Proportional control P A control algorithm or method in which the final control element moves to a position proportional to the deviation of the value of the controlled variable...

Страница 132: ...as a pump that is on or off The digital sensor provides the controller with a discrete signal such as open or closed contacts Some electronic sensors use an inherent attribute of their material e g wire resistance to provide a signal and can be directly connected to the electronic controller Other sensors require conversion of the sensor signal to a type or level that can be used by the electronic...

Страница 133: ...0 96 ohms per km is used the 16 meters of wire has a total dc resistance of 0 335 ohms If the sensor is a 100 ohm platinum sensor with a temperature coefficient of 1 24 ohms per kelvin the 16 meters of wire will introduce an error of 0 27 degrees C If the sensor is a 3000 ohm platinum sensor with a temperature coefficient of 8 6 ohms per kelvin the 16 meters of wire will introduce an error of 0 03...

Страница 134: ...tamination Improved packaging and film isolation have eliminated these problems resulting in increased use of platinum RTDs over wire wound and NTC thermistors LADDER NETWORK OF METALLIC FILM RESISTOR LASER TRIM INDICATEDBY GAPS IN LADDER NETWORK CONNECTION PADS C3098 Fig 4 Platinum Element RTD Sensor Solid State ResistanceTemperature Devices Figure 5 shows examples of solid state resistance tempe...

Страница 135: ... Since electronic controllers are capable of handling voltage amperage or resistance inputs temperature transmitters are not usually used as controller inputs within the ranges of HVAC systems due to their high cost and added complexity RELATIVE HUMIDITY SENSOR Various sensing methods are used to determine the percentage of relative humidity including the measurement of changes of resistance capac...

Страница 136: ...frequency to measure relative humidity Fig 13 can use a quartz crystal coated with a hygroscopic material such as polymer plastic When the quartz crystal is energized by an oscillating circuit it generates a constant frequency As the polymer material absorbs moisture and changes the mass of the quartz crystal the frequency of oscillation varies and can be measured by an electronic circuit Most rel...

Страница 137: ... ENLARGED VIEW POLYMER COATING TO CONTROLLER OSCILLATING CIRCUIT FREQUENCY MEASURING CIRCUIT C3088 PRESSURE INLET E G AIR WATER FLEXIBLE DIAPHRAGM AMPLIFIER STRAIN GAGE ASSEMBLY DOTTED LINE SHOWS FLEXING GREATLY EXAGGERATED C3102 AMPLIFIER CONNECTION FINE SERPENTINE WIRE THIN FILM METAL FLEXIBLE BASE PRESSURE INLET E G AIR WATER FLEXIBLE DIAPHRAGM FLEXIBLE PLATE TOP PORTION OF CAPACITOR FIXED PLAT...

Страница 138: ...rements Control modes include two position proportional and proportional integral Other control features include remote setpoint the addition of a compensation sensor for reset capability and override or limit control OUTPUT CONTROL Electronic controllers provide outputs to a relay or actuator for the final control element The output is not dependent on the input types or control method The simple...

Страница 139: ...essor basedbuildingmanagement system An example is an interface that allows a building management system to adjust the setpoint or amount of reset compensation for a specific controller Compatibility of the two systems must be verified before they are interconnected ELECTRONIC CONTROLLER FUNDAMENTALS GENERAL The electronic controller is the basis for an electronic control system Figure 21 shows th...

Страница 140: ... discharge air temperature drops to the control range of the low limit setpoint A minimum discharge air temperature is maintained regardless of space temperature When the outdoor temperature is below the selected reset changeover point set on C1 the controller is in the winter compensation mode As the outdoor air temperature falls the space temperature setpoint is raised When the outdoor temperatu...

Страница 141: ...System Level Controller 136 Controller Software 137 Operating Software 137 Application Software 137 Direct Digital Control Software 137 Energy Management Software 138 Optimum Start 138 Optimum Stop 138 Night Cycle 138 Night Purge 139 Enthalpy 139 Load Reset 139 Zero Energy Band 141 Distributed Power Demand 142 Building Management Software 142 Controller Programming 142 General 142 Programming Cate...

Страница 142: ...C FUNDAMENTALS 132 ENGINEERING MANUAL OF AUTOMATIC CONTROL Typical Applications 145 Zone Level Controller 145 Example 1 VAV Cooling Only 145 Example 2 VAV Cooling with Sequenced Electric Reheat 145 System Level Controller 146 ...

Страница 143: ...oller periodically updates a process as a function of a set of measured control variables and a given set of control algorithms Microprocessor based controller A device consisting of a microprocessor unit digital input and output connec tions A D and D A converters a power supply and software to perform direct digital control and energy management routines in a HVAC system Operating software The m...

Страница 144: ...s digital computation The microprocessor unit MPU in the controller provides the computation Therefore the term digital in DDC refers to digital processing of data and not that HVAC sensor inputs or control outputs from the controller are necessarily in digital format Nearly all sensor inputs are analog and most output devices are also analog In order to accept signals from these I O devices A D a...

Страница 145: ...e basic elements of a microprocessor based or micro processor controller Fig 3 include The microprocessor A program memory A working memory A clock or timing devices A means of getting data in and out of the system In addition a communications port is not only a desirable feature but a requirement for program tuning or interfacing with a central computer or building management system Timing for mi...

Страница 146: ... and mix of inputs and outputs to be variable Several different packaging approaches have been used Fixed I O configuration Universal I O configuration Card cage with plug in function boards Master slave I O modules Universal I O allows software to define the function of each set of terminals Zone and system level controllers should be equipped with a communications port This allows dynamic data s...

Страница 147: ...using different programs to match the application An existing building for example might require energy management software to be added to the existing control system A new building however might require a combination of direct digital control and energy management software DIRECT DIGITAL CONTROL SOFTWARE DDC software can be defined as a set of standard DDC operators and or high level language sta...

Страница 148: ...tdoor air dampers and ventilation fans should be inactive during preoccupancy warmup periods For weekend shutdown periods the program automatically adjusts to provide longer lead times This program adapts itself to seasonal and building changes Optimum Stop The optimum stop program Fig 6 uses stored energy to handle the building load to the end of the occupancy period Based on the zone temperature...

Страница 149: ...igital control apart from pneumatic and traditional control The application uses VAV box loadings to determine VAVAHU requirements for air static pressure and temperature uses reheat valve loadings to determine hot water plant requirements for temperature and pressure and uses chilled water valve positions to determine chilled water plant requirements for temperature and pressure These adjustments...

Страница 150: ...tabilize in time The chiller loop is usually set for a fast response and the discharge air loop is set for a slow response The events of the first scenario occur within seconds because both loops leaving water temperature controlling the chiller load and discharge air temperature controlling chilled water flow are close coupled and fast Because the two loops oppose each other a chilled water tempe...

Страница 151: ...e for cooling On multizone fan systems with simultaneous heating and cooling load capability zone load reset controls the hot and cold deck temperature setpoints Fig 11 Zero Energy Band FULL ON FULL OFF 21 23 24 25 5 TYPICAL SPACE TEMPERATURE RANGE C HEATING REGION ZERO ENERGY BAND COOLING REGION HEATING COOLING VENTILATION ONLY C4314 TOTAL COMFORT RANGE M15138 AUTO 8 68 73 74 77 79 70 64 69 79 74...

Страница 152: ... are stored in the controller Communications module Controls transmissions between controllers and between controllers and a central computer based on an established bus protocol Global points Allows designated points to share their data with other bus connected devices Run time Accumulates equipment on or off time and trans mits totals periodically to the central system On off cycle counting can ...

Страница 153: ...nction or variable function device Zone level controllers are typically fixed function since the applications and control sequences are generally standardized In these controllers the input terminals are dedicated to a specific sensor type and range and the output terminals are dedicated to a control relay or specific type of actuator The need for data files is minimized The processor always knows...

Страница 154: ...ULATION PROGRAMS INSTALL PROGRAM AND ASSOCIATED DATA FILES STEP 1 STEP 2 STEP 3 STEP 4 STEP 5 STEP 6 C2440 END CONTROL ALGORITHM SETPOINT D A ERROR CORRECTIVE SIGNAL FINAL CONTROL ELEMENT ACTUATOR MANIPULATED VARIABLE PROCESS DISTURBANCE LOAD CHANGE FEEDBACK CONTROLLED VARIABLE SENSING ELEMENT CONTROLLER C2441 Fig 14 Simple Control Loop A typical central fan system may require several control loop...

Страница 155: ...onitored live in their actual executing environment with inputs outputs and intermediate signal values updating continuously TYPICAL APPLICATIONS ZONE LEVEL CONTROLLER Zone level controllers can be applied to a variety of types of HVAC unitary equipment Several control sequences can be resident in a single zone level controller to meet various application requirements The appropriate control seque...

Страница 156: ...ent System Fundamentals section Where the examples indicate that user entered values are furnished e g setpoint or that key parameters or DDC operator outputs will have display capability this represents sound software design practice and applies whether or not the controller is tied into a central building management system Data is entered or displayed in non BMS applications by a portable operat...

Страница 157: ...water temperature setpoint varies linearly from 50 C to 77 C as the outside air temperature varies from 16 C to 20 C The converter steam valve is modulated to maintain a converter leaving water temperature according to a varying reset schedule The steam valve closes anytime hot water pumping is not proven and anytime the valve actuator loses motive power Step 4 Develop the detailed flowchart Step ...

Страница 158: ...MICROPROCESSOR BASED DDC FUNDAMENTALS 148 ENGINEERING MANUAL OF AUTOMATIC CONTROL ...

Страница 159: ...ed Contaminant Sources 157 Contaminant Types 157 Particulate Contaminants 157 Gas and Vapor Contaminants 158 Radionuclide Contaminants 158 Indoor Air Contaminant Indicators 158 Human Responses to Contaminants 158 Building Responses to Contaminants 158 Design Considerations 158 General 158 Eliminating Contaminant Sources 158 Eliminating Contaminant Paths 158 Remediating Contaminant Levels 159 Parti...

Страница 160: ...Quality Control Applications 164 General 164 Flow Tracking Control System 165 Flow Tracking System with Mixing Box Static Pressure Control 166 Rooftop Unit Control System 167 Operator Interface 167 Graphic Displays 168 Bibliography 170 Referenced Publications 170 Related Publications 170 ...

Страница 161: ... impurities from the air Includes particle filters gas phase filters and electronic devices Airqualitystandard Agovernment mandatedregulationwhich specifies the maximum contaminant concentration beyond which health risks are considered to be unacceptable Allergen Asubstancethatcantriggerimmuneresponsesresulting in an allergic reaction also known as antigen Bacteria Onecelledorganismswhicharemember...

Страница 162: ... airborne contaminants precautions for inspection health effects odor description volatility expected contaminants from combustion reactivity and procedures for spill cleanup Micro organisms Life forms too small to be seen with the unaided eye Mitigation A procedure or strategy aimed at reducing or eliminating an indoor air problem through source control ventilation control exposure reduction and ...

Страница 163: ...e used throughout this section in the text and drawings AHU Air Handling Unit ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers ANSI American National Standards Institute BOCA Building Owners and Code Administrators BMS Building Management System DNR Department of Natural Resources C Celsius CDC Center for Disease Control CO Carbon monoxide CO2 Carbon dioxide DOP Dioc...

Страница 164: ...ble 1 Annual Median Concentrations for TSP NO2 O3 CO 1979 a AIR CONTAMINANTS Aircontaminantsarecategorizedbylocationandtype Location of contaminants is divided between outdoor and indoor Outdoor air contamination results from natural or manmade phenomena that occur outdoors or indoors Contaminant types include particulate gas vapor radionuclide CONTAMINANT SOURCES Outdoor Contaminant Sources Outdo...

Страница 165: ...ations have been measured No averaging times are given NA indicates it is not appropriate to list a concentration For a detailed discussion of air contaminants refer to ASHRAE Fundamentals Handbook 1997 Chapter 9 Indoor Environmental Health and Chapter 12 Air Contaminants Pollutant Averaging Time Primary Standard Levels Secondary Standard Levels Particulate matter Annual geometric mean 75 µg m3 60...

Страница 166: ...om cooling towers humidifiers dehumidifiers and showers is also a source Pollutant Sources of Indoor Pollution Possible Indoor Concentrations Indoor Outdoor Concentration Ratio Location Asbestos Fireproofing 106 fiber m3 1 Homes schools offices Carbon Dioxide CO2 Combustion humans pets 3000 ppm 1 Homes schools offices Carbon Monoxide CO Combustion equipment engines faulty heating systems 100 ppm 1...

Страница 167: ...resistant TB Tobacco smoke is a major contaminant Its use has declined in most occupancies except for a concern for residences and bars The human tracheo bronchial system serves somewhat as a pollution control device by acting like a saturated adsorber by removing a portion of contaminants such as VOCs For a detailed discussion of odors refer to ASHRAE Fundamentals Handbook 1997 Chapter 13 Odors C...

Страница 168: ... a specific identifiablemedicalconditionofknowetiologythatisdocumented by physical signs and laboratory tests Multiple Chemical Sensitivity is the term applied to an illness resulting from exposure to multiple chemicals none of which by itself would cause a problem in most people BUILDING RESPONSES TO CONTAMINANTS Building responses to indoor air contamination include visual signs of fungus mold m...

Страница 169: ...on tetrachloride activity shouldbecapableofremovingpartsperbillionofVolatileOrganic Compounds ozone nitrogen dioxide and sulfur dioxide According to the EPA one half the population of the United States lives in areas that do not meet the National Ambient Air Quality Standards with ozone being the most prevalent contaminant Electronic air cleaners are high efficiency filter devices that produce ozo...

Страница 170: ...r will approach 100 percent and condense unless controlled Condensation in the duct promotes the growth of mold and fungi andhasbeenthesourceofairqualityproblemsinmanybuildings Proper maintenance is essential for the control of contaminants and bioaerosols Assuming that return air relative humidity is the same as space relative humidity is a common mistake They are the same only if the two tempera...

Страница 171: ...e provides a direct solution by restricting the concentration of all known contaminants of concern to specified acceptable levels This procedure lists acceptable levels for CO2 chlordane ozone and radon gas and references many other potential contaminants without defined limits The use of CO2 as an indicator of IAQ is inferred The limit of 1000 ppm is recommended to satisfy comfort and odor criter...

Страница 172: ...ile others are concerned only with IAQ These agencies and their jurisdictions are listed in Table 5 M10482 GENERAL EXHAUST AIR CLEANER LOCATION VENTILATION AIR INFILTRATION LOCAL OCCUPIED SPACE EXFILTRATION RETURN AIR ALTERNATE AIR CLEANER LOCATIONS OUTDOOR AIR MAKEUP AIR SUPPLY AIR ENERGY RECOVERY UNIT Fig 3 Possible Location for Filtration in an HVAC System Recirculation Requirements Recirculati...

Страница 173: ...d operating rooms in these facilities The American Society of Heating Refrigeration Air Conditioning Engineers ASHRAE created design Standard 62 1989 Ventilation for Acceptable IAQ This was adopted by theAmerican National Standards Institute ANSI and has been incorporated into several state building codes Even where 62 1989 has not been adopted into code it exerts a powerful influence because it e...

Страница 174: ...quires the involvement of operating and maintenance personnel in the Acceptance process to ensure understanding of the design intent and operational requirements of the systems Personnel turnover requires extensive additional training Assuming adequate funding of the operations and maintenance staff the systems will deliver the design performance throughout the intended life cycle Any alternations...

Страница 175: ...s per fan system The sample VAV terminal unit shown is a fan powered unit but the units could be non fan powered Without an air flow station in the outdoor air this system might not deliver the minimum air flow at all fan volumes because the mixing box negative static pressure and therefore the OA airflow varies with the supply fan load If mixed air temperature is used to calculate the percentage ...

Страница 176: ...re constant at the filter inlet This is accomplished by separating the control of the outdoor air damper from the control of the return and relief dampers Note that the OA damper minimum position and the MA static pressure setpoint must be determined in conjunction with the air balancing contractor Refer to VAV AHU WITH RETURN FAN AND FLOW TRACKING in the Air Handling System Control Applications s...

Страница 177: ... M10488 SUPPLY FAN EXHAUST FAN CT RA TEMPERATURE MA TEMPER ATURE HEATING STAGE COOLING VALVE SA FAN SA FAN STATUS HUMIDIFIER VALVE SA TEMPER ATURE SA RELATIVE HUMIDITY ROOM TEMPER ATURE EXHAUST FAN STATUS SA PRESSURE AFTER HOURS OA TEMPER ATURE OA DAMPER RETURN AND RELIEF DAMPER STATIC PRESSURE OPERATOR INTERFACE Modern Building Management Systems BMS utilizing distributeddirectdigitalcontrollersa...

Страница 178: ...mation on system configuration network communications and specifying graphics refer to the Building Management System Fundamentals section GRAPHIC DISPLAYS Figure 7 provides a sample of an operator graphic showing the functional software relationships that control the system Actual values for the temperatures air flows and valve and damper positions and percent fan loads are all shown for the oper...

Страница 179: ... and review results in real time This is one of many operator displays that can be designed to facilitate operator understanding and control of IAQ Fig 8 Operator Graphic with Dynamic Data embedded in the Text Sequence PROGRAM IF OR LESS VAV BOXES ARE FULL OPEN DECREMENT THE STATIC PRESSURE SETPOINT kPa EVERY MINUTES IF OR MORE VAV BOXES ARE FULL OPEN INCREMENT THE STATIC PRESSURE SETPOINT kPa EVE...

Страница 180: ...echanical Code 8 Uniform Mechanical Code 9 BOCA Mechanical Code 10 Southern Mechanical Code 11 OSHA Standards 12 NIOSH IDLH Listing RELATED PUBLICATIONS 1 HRA 84 14 500 Guideline for Construction and Equipment of Hospital and Medical Facilities 2 SMACNA HVAC Systems Commissioning Manual 3 SMACNA HVAC Systems Testing Adjusting and Balancing 4 SMACNA IAQ Guidelines for Occupied Buildings Under Const...

Страница 181: ... Standards 174 Design Priniples 175 Causes of Smoke Movement 175 Stack Effect 175 Buoyancy 175 Expansion 176 Wind Velocity 176 HVAC 177 Control of Smoke 177 Pressurization 177 Airflow 178 Purging 178 Contr ol Applica tions 178 Zone Pressurization Control 179 Stairwell Pressurization Control 180 Control of Malls Atria and Large Areas 181 Acce ptanceTesting 181 Leaka ge Ra ted Damper s 181 Bibliogra...

Страница 182: ...ch or zoning in which the floors adjacent to the fire floor are pressurized and the fire floor is exhausted DEFINITIONS AHJ Authority Having Jurisdiction There may be more than one authority ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers Inc Atrium A large volume space within a floor opening or series of floor openings connecting two or more stories covered at the ...

Страница 183: ...objectives of the system 2 The smoke management system must be designed as a complete mechanical control system that is able to function satisfactorily in the smoke management mode The smoke management system should be designed independently of the HVAC system and then integrated where feasible without sacrificing functionality of the smoke control system 3 The smoke management system must be desi...

Страница 184: ...icated smoke control systems Controls that meet UL Standard 864 are listed under UL Category UUKL Standby power and electrical supervision items listed in UL864 are optional for smoke control systems According to NFPA 92A control sequences should allow smoke control modes to have the highest priority however some control functions should not be overridden Examples of these functions are duct stati...

Страница 185: ...f air upward within the building This is called normal stack effect Stack effect is greater for a tall building than for a low building however stack effect can exist in a one story building With normal stack effect air enters the building below the neutral plane approximately midheight and exits above the neutral plane See Figure 2 Air neither enters nor exits at the neutral plane a level where t...

Страница 186: ...use infiltration negative pressures on the leeward side cause exfiltration The higher the wind velocity the greater the pressure on the side of the building In general wind velocity increases with the height from the ground The effects of wind on a tightly constructed building can be negligible However the effects can be significant for loosely constructed buildings or buildings with open doors or...

Страница 187: ...truction and the doors the toxicity of the smoke the airflow rates and the volume of the protected space Occasional variances of up to 50 percent of the maximum design pressure difference can be allowed in most cases Table 2 lists values for the maximum pressure differences across doors These values should not be exceeded so that the doors can be used when the pressurization system is in operation...

Страница 188: ... an area Where this is not possible the HVAC system can be designed to have a purge mode The principle of dilution can be applied to zones where smoke has entered and is being purged Purging dilutes the contaminated air and can continue until the level of obscuration is reduced and thespaceisreasonablysafetoenter Thefollowingequationallows determining a concentration of contaminant in a compartmen...

Страница 189: ...llustrates typical arrangements of smoke control zones The minus sign indicates the smoke zone The plus signs indicate pressurized nonsmoke zones In the event of a fire the doors are closed to the fire or smoke control zone and the adjacent zones are pressurized In the example in Figures 7A and 7B the floors above and below the smoke zone are pressurized The application in Figure 7B is called a pr...

Страница 190: ...oor To ensure proper stairwell pressurization system design a means should be included to modulate either the supply or the exhaust relief dampers Also a means should be included to provide multiple supply injection points at a minimum of every three floors unless design analysis can justify a greater spacing to provide uniform pressurization According to NFPA 92A Recommended Practice for Smoke Co...

Страница 191: ...AMPER FIRE AREA FIRE SPRINKLER Fig 10 Control of Smoke in Malls Atria and Other Large Areas 1 Any fire alarm initiates smoke control mode 2 System turns on exhaust fans 3 System enables damper operation as appropriate for smoke control mode 4 Operator verifies operation as appropriate e g action of airflow proving sail switch 5 Operator cancels smoke control mode as long as initiating panel is not...

Страница 192: ... Smoke Management Systems in Malls Atria and Large Areas 1995 Edition 5 NFPA 101 Life Safety Code 1994 Edition 6 Smoke Control in Fire Safety Design A G Butcher and A C Parnell E F N Spon Ltd 11 New Fetter Lane London EC4P 4EE 1979 7 Smoke Control Technology Code 88146 ASHRAE 1989 8 UL 555 Standard for Fire Dampers and Ceiling Dampers Fifth Edition 1995 Revision 9 UL 555S Standard for Leakage Rate...

Страница 193: ...ions Protocol 187 Peer Communications Protocol 188 Communications Media 188 Twisted Copper Pair 188 Fiber Optic 188 Phone Lines 188 System Functions 189 General 189 Zone Level Controller Functions 189 System Level Controller Functions 189 Operations Level Functions 189 General 189 Hardware 189 Software 189 Standard Software 189 Communications Software 189 Server 190 Security 190 Alarm Processing 1...

Страница 194: ...ontrol Applications the Building Airflow System Control Applications and the Chiller Boiler and Distribution System Control sections The examples used throughout this section are typical of what is available and not necessarily representative of any given installation DEFINITIONS Building Control System BCS A system that controls the comfort and safety of a buildings assets and environment Buildin...

Страница 195: ...management information and user access provided by the BMS host Equipment is operated at a minimum cost and temperatures are controlled for maximum efficiency within user defined comfort boundaries by a network of controllers Energy strategies are global and network communications are essential Load leveling and demand control along with starting and loading of central plant based upon the demands...

Страница 196: ...evel processors Operations level processors System level controllers Zone level controllers The actual levels used in a given system depend on the specific needs of the building or complex of buildings The zone level may incorporate intelligent microprocessor based sensors and actuators The discussions that follow begin with zone level controllers ZONE LEVEL CONTROLLERS Zone level controllers are ...

Страница 197: ...on custom programming see the Microprocessor Based DDC Fundamentals section Graphics Builds custom graphic displays incorporating dynamic system data Bar chart and curve plot software may be included Standard reports Provides automatic scheduled and by request reports of alarm and operator activity Also provides a broad range of system and category points in alarm disabled points etc summary repor...

Страница 198: ...ance are possible Serial bus and star wiring configurations Fig 2 and 3 permit efficient wiring layouts COMMUNICATIONS BUS BMS CENTRAL SYSTEM ZONE LEVEL CONTROLLER C1862 SYSTEM ZONE LEVEL CONTROLLER SYSTEM ZONE LEVEL CONTROLLER SYSTEM ZONE LEVEL CONTROLLER SYSTEM ZONE LEVEL CONTROLLER Fig 4 Dialup to Remote Controllers COMMUNICATIONS BUS BMS CENTRAL C1863 SYSTEM ZONE LEVEL CONTROLLER SYSTEM ZONE L...

Страница 199: ...trollers OPERATIONS LEVEL FUNCTIONS GENERAL The operations level is the third tier of the BMCS configuration Building or facility operations and management personnel interact on a day to day basis through this level The hardware and software for this tier is dedicated to interfacing with operating personnel rather that with mechanical systems as the controllers do in the lower tiers of the BMCS co...

Страница 200: ...uration or continuously Fast medium or slow beep rate Option Automation Graphic Display Present button for operator graphic display request Present alarm status on graphics point red if in alarm blinking if unacknowledged The alarm archive may be queried at any time to analyze historical alarm activity Reports BMS Software includes many system reports for display and printout in addition to alarm ...

Страница 201: ...er Support A major portion of the BMS Software is the definition and maintenance of system level controller software The software allows viewing and editing setpoints and parameters up or down loading controller databases adding and editing points and programs and executing diagnostics OPERATION Operator access to the system is usually positioning the cursor via a mouse on a graphic display of a s...

Страница 202: ...derstand and need to know Selecting a commandable point presents analog or digital command options to be executed via dialog boxes radio buttons up down arrows etc Selecting an analog input allows modification of alarm limit values Selecting an alarm point allows entry and modification of the alarm message 100 SYMBOL LEGEND DYNAMIC VALUE TEMPERATURE HUMIDITY COMMANDABLE ANALOG VALUE COMMANDABLE AN...

Страница 203: ... all hardware and software points and symbols is an excellent alternative to the I O summary 0 0 100 33 33 100 33 7 00 13 0 26 7 3 13 30 ON OFF 100 100 78 NORMAL ENABLED ENABLED BY REMOTE CONTROLS OPERATING MODE ALARM STATUS MAX CURRENT STATUS NORMAL 00 AUTO MINIMUM CHILLED WATER SETPOINT MAXIMUM ACTUAL AUTO 1 AUTO AUTO 7 8 11 100 PRESSURE CHOKE VALVE CHILLER CONTROL SETPOINTS SEQUENCES 365 TO AHU...

Страница 204: ... RUNTIME TOTALIZATION CALCULATED VALUE GRAPHIC PENETRATION TIMED START STOP OPTIMUM START STOP ECONOMIZER CHANGEOVER ENTHALPY CHANGEOVER DEMAND LIMITING ZERO ENERGY BAND NIGHT CYCLE NIGHT PURGE LOAD RESET NOTES COOLINGTOWER FAN ISOLATIONVALVES LEAVINGWATER LEAVINGWATER COMMON CHILLER LEAVING COND WATER CONDENSER PUMP CHILLER CONTROL COMMAND STATUS STATUS MAX CURRENT CURRENT AMPS ALARM LEAVING CHIL...

Страница 205: ...etc on a terminal unit graphic All system points should be positioned on graphics and certain points should be specified on multiple graphics Fig 9 Typical Graphic to Aid System Fine Tuning in the Field MINIMUM CHILLED WATER SETPOINT ANYTIME ANY AHU VALVE IS OPEN GREATER THAN FOR MORE THAN MINUTES AND THE TIME IS BEFORE THE LEAD CHILLED WATER PUMP STARTS ANYTIME BOTH CHILLERS ARE RUNNING AND THE C...

Страница 206: ...e the need to replace functioning equipment The disadvantages of surface integration are Higher first cost because of duplicated equipment and increased installation to connect the two systems Interconnection between systems is not supervised and could fail without notifying the central Independent operations staffs may be required for monitoring each subsystem IN DEPTH INTEGRATION Figure 11 shows...

Страница 207: ...HIRD PARTY PROCESSOR FA FIRE ALRM PROCESSOR INPUTS OUTPUTS Fig 11 In Depth Integrated System The advantages of an in depth integrated system are First costs and ongoing operating costs are usually lower Interdependence between subsystems such as smoke control can be easily accommodated since there is only one processor Independent operating centers at remote locations can be provided Third party L...

Страница 208: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL BUILDING MANAGEMENT SYSTEM FUNDAMENTALS 198 ...

Страница 209: ...SMOKE MANAGEMENT FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL 199 CONTROL SYSTEM APPLICATIONS ...

Страница 210: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL SMOKE MANAGEMENT FUNDAMENTALS 200 SMOKE MANAGEMENT FUNDAMENTALS ...

Страница 211: ...ycle Decision Outdoor Air Return Air Enthalpy Comparison 218 Economizer Cycle Decision Outdoor Air Return Air Dry Bulb Temperature Comparison 219 Mixed Air Control with Economizer Cycle Ventilation System Only 220 Economizer Cycle Control of Space Temperature with Supply Air Temperature Setpoint Reset 221 Heating Control Processes 223 Control From Supply Air 223 Control From Space with Supply Temp...

Страница 212: ...ol 241 Dehumidification Control Processes 243 Direct Expansion or Water Coil System Control 243 Water Coil Face and Bypass System Control 244 Heating System Control Process 246 Space Control of Heating Economizer Free Cooling and Humidification 246 Year Round System Control Processes 248 Heating Cooling and Economizer 248 Multizone Unit 250 Heating Cooling Humidification and Dehumidification Contr...

Страница 213: ...at the end of this section for reference For further understanding of the basics of psychrometric charts refer to the Psychrometric Chart Fundamentals section For additional detailed information on air handling systems refer to the ASHRAE 1996 HVAC Systems and Equipment Handbook ABBREVIATIONS The following abbreviations are used throughout this section in the text and drawings Refer to Definitions...

Страница 214: ...ss than 2 5 and no more than 9 meters downstream of the humidifier REQUIREMENTS FOR EFFECTIVE CONTROL Effective control system performance requires careful design of the mechanical system and selection of components Consideration needs to be given to the following by the mechanical system designer and the control engineer 1 PROPERLY DESIGN DISTRIBUTION SYSTEM TO DELIVER AIR TO THE SPACE a Extend d...

Страница 215: ...ing low temperature alarms g Stopping fan if steam is not present 2 Providing failure alarms for pump coils and other heating systems components 12 ALLOW AIR HANDLING AND CONTROL SYSTEM DESIGN TO PROVIDE ENERGY CONSERVATION a Use space sensors rather than OA sensors to determine reset schedules For example use the damper signal from space PI control loops to reset multizone unit hot and cold deck ...

Страница 216: ... related control loops If a PC station is not required the data points required for control and operation should still be specified for the operator by listing the points or including a graphic sketch Values setpoints gains timings etc shown in these examples are general and actual values should be determined on a project to project basis The following applications were selected for this section o...

Страница 217: ...reference Multizone hot deck cold areas Opens Opens Opens Multizone hot deck hot areas Closes Closes Closes Closes Valves AHU chilled water Closes Opens Closes Stays same Terminal reheat Preheat in OA below 1 5ℑC Opens2 Opens2 Opens Preheat in OA above 1 5ℑC Closes Closes Other hot water Closes2 Closes2 Stays same AHU steam heating Closes Closes Steam humidifier Closes Closes 1 Return air dampers ...

Страница 218: ...PERATURE LOW LIMIT HIGH LIMIT MANUAL RESET NOTATION INSERTION TEMPERATURE SENSOR TEMPERATURE SENSOR AVERAGING TEMPERATURE CONTROLLER MANUAL RESET SAFETY LOW LIMIT MANUAL MULTI STATE COMMAND ON OFF AUTO STATUS POINT VALUE POINT LOAD COMMANDABLE VALUE 3 WAY VALVE WITH ACTUATOR 2 WAY VALVE WITH ACTUATOR DAMPER WITH ACTUATOR SMOKE DETECTOR NFPA SYMBOL PROPELLER EXHAUST FAN SOLENOID VALVE PUMP FILTER H...

Страница 219: ...pied space temperatures and occupant override requests 8 Occupant override switch provides after hours operation when pressed 9 Duration of operation for override request 10 Space temperature perimeter zone inputs to optimum start stop unoccupied purge and low limit programs 11 Setpoint at which unoccupied low limit program executes 12 OA temperature input to optimum start stop program 13 Return f...

Страница 220: ...operate 2 On large 100 OA systems and systems where OA and RA dampers both close upon fan shutdown dampers should be enabled prior to fan start and the fan should start only after damper end switches prove dampers are in safe positions SPECIFICATIONS Air handling system shall be under program control subject to SA and RA smoke detectors SA high pressure cutout and heating coil leaving air low temp...

Страница 221: ... on fan startup closes on fan shutdown FEATURES 1 A fixed quantity of OA is admitted when the fan is operating 2 This system is composed of a minimum of ventilation and control equipment CONDITIONS FOR SUCCESSFUL OPERATION 1 The system provides the desired proportions of OA and RA a manual RA damper shown is usually required 2 The system is designed so that coils are not subject to freezing LIMITA...

Страница 222: ...mum airflow setpoint It is therefore very predictable that the fan will accelerate rapidly the duct pressure will rise rapidly and with PID will overshoot and unsafe conditions may occur Recognizing this EPID starts the fan at a minimum loading senses the error and ramps the error slowly and linearly into PID control usually over a 30 to 90 second period adjustable to any value Thus the fan loads ...

Страница 223: ...tions of OA and RA above minimum OA setting are admitted to prevent the MA temperature from dropping below the desired MA temperature 2 A minimum quantity of OA determined by the setting of the minimum position signal is assured at all times CONDITIONS FOR SUCCESSFUL OPERATION 1 Adequate mixing of OA and RA which may be obtained using a special mixing chamber 2 The temperature sensor is located wh...

Страница 224: ...ntroller is set at 16 C 5 The desired MA temperature can be maintained until the OA temperature falls below the temperature at which only minimum OA is admitted and until the OA is greater than 16 C The following results are obtained Item No Explanation 1 As OA temperature varies between 1 5 C and 16 C the MA condition lies on the 16 C DB line 2 As OA temperature rises above 16 C DB 100 percent OA...

Страница 225: ...Economizer decision status operator information 4 Setpoint for minimum OA damper position 5 Actuator positions OA and RA dampers 6 Actuator positions EA dampers 7 Control program coordinates occupancy temperature smoke and ventilation controls 9 OA MA RA EA 22 1 22 ON ECONOMIZER MODE SELECTOR OA MINIMUM SETPOINT NOTE THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22 OTHER INPUTS AND ...

Страница 226: ...ATION IS 22 OTHER INPUTS AND OUTPUTS ECONOMIZER STATUS ENTHALPY kJ PER KILOGRAM M15155 4 7 5 9 3 6 83 8 1 2 83 CONTROL PROGRAM 1 AUTO BASED UPON OA ENTHALPY BELOW kJ kg 22 0 2 AUTO BASED UPON OA DB TEMPERATURE BELOW DEGREES 3 MANUAL ECONOMIZER ON 4 MANUAL ECONOMIZER OFF NOTE THE SYSTEM IS LOCKED OUT OF THE ECONOMIZER MODE ANYTIME THE OA DRY BULB IS ABOVE DEGREES 9 52 27 5 the OA is between approxi...

Страница 227: ...nimum OA based upon an OA enthalpy calculation setpoint except the system shall be locked out of the economizer mode anytime the OA DB is higher than 27 5 C Software shall also be provided to allow the user to switch with an appropriate commandable setpoint the decision to be based upon OA dry bulb or to lock the system into or out of the economizer mode NOTE The preceding graphic is an example of...

Страница 228: ...TION IS 22 OTHER INPUTS AND OUTPUTS ENTHALPY kJ PER KILOGRAM ENTHALPY kJ PER KILOGRAM M15156 7 9 11 3 8 6 83 10 1 2 83 CONTROL PROGRAM 1 AUTO BASED UPON OA RA ENTHALPY COMPARISON 22 0 2 AUTO BASED UPON OA DB BELOW DEGREES 3 MANUAL ECONOMIZER ON 4 MANUAL ECONOMIZER OFF NOTE THE SYSTEM IS LOCKED OUT OF THE ECONOMIZER MODE ANYTIME THE OA DRY BULB IS ABOVE DEGREES 9 52 49 0 4 5 26 45 27 5 OA DB CONTRO...

Страница 229: ...at least 3 accuracy and long term stability should be selected 2 Periodic maintenance of the humidity sensors is provided 3 In some cases only certain AHUs which have varying latent loads need RA enthalpy sensors and calculations and others will be perform satisfactorily with OA enthalpy only If RA moisture varies similarly on severalAHUs a single comparison and decision may be globally shared amo...

Страница 230: ...n when OA is not suitable CONDITIONS FOR SUCCESSFUL OPERATION 1 Adequate mixing of OA and RA Mixing may be obtained using a special mixing chamber The temperature sensor should be in the fan discharge when possible The fan in a blow through system usually provides adequate mixing 2 An MA averaging element sensor is used on draw through units LIMITATIONS If the manual positioning value is set to ad...

Страница 231: ...results are obtained Item No Explanation 1 At OA temperatures below 26 C DB 25 percent OA set by manual positioning setpoint value the MA condition lies to the left of the 13 C DB line 2 As the OA temperature varies between 26 C and 13 C MA conditions lie on the 13 C DB line 3 As the OA temperature varies between 13 C and 24 C 100 percent OA is admitted and the MA lies in the area between 13 C and...

Страница 232: ...ule setpoints 3 A minimum quantity of OA determined by the software adjustable setpoint value is assured at all times CONDITIONS FOR SUCCESSFUL OPERATION 1 Adequate mixing of OA and RA Mixing may be obtained using a special mixing chamber The temperature sensor should be in the fan discharge when possible The fan in a blow through system usually provides adequate mixing 2 A satisfactory schedule o...

Страница 233: ...e FAN SYSTEM START STOP CONTROL Anytime the supply fan runs the hot water valve shall be modulated by an SA PID control loop to maintain the SA temperature setpoint The hot water valve shall close upon fan shutdown and open upon loss of motive force PSYCHROMETRIC ASPECTS 1 The SA temperature remains constant until the entering air temperature exceeds the desired SA temperature 2 In the following c...

Страница 234: ...shall be modulated by an SA PID control loop to maintain the SA temperature setpoint The SA temperature setpoint shall be reset from no lower than 13 C to no greater than 38 C as the space temperature PID demand for heating varies from 0 to 100 2 The N O hot water valve shall close upon fan shutdown PSYCHROMETRIC ASPECTS The supply condition of the air depends on the condition of the entering air ...

Страница 235: ... Anytime the supply fan runs heating control shall be enabled A SA PID control loop shall modulate the hot water valve to maintain the SA temperature setpoint The SA temperature setpoint shall be reset from 16 C to 38 C as the OA temperature varies from 16 C to 15 C PSYCHROMETRIC ASPECTS The SA condition depends on the entering air condition and the temperature rise needed to satisfy the space hea...

Страница 236: ...k temperature based upon operator inputs 10 Control program coordinates load reset temperature and fan interlock programs 33 SA MA ON 23 46 HOT DECK ZONE MIXING DAMPERS AS THE DEMAND FOR HEAT FROM THE ZONE WITH THE GREATEST DEMAND FOR HEAT VARIES FROM ZERO TO THE HOT DECK TEMPERATURE SETPOINT SHALL VARY FROM THE MIXED AIR TEMPERATURE TO DEGREES AS THE DEMAND FOR HEAT FROM EACH ZONE VARIES FROM TO ...

Страница 237: ...t may be allowed to go out of control storage rooms etc should not be connected to the load reset program 3 Each zone duct should have a balancing damper following the mixing dampers to ensure design volume to each zone NOTE See the Microprocessor Based DDC Fundamentals section for a description of the load reset program LIMITATIONS 1 If only selected zones are connected to the load reset program ...

Страница 238: ... installed in an air conditioning system are 1 Preheat coils are often exposed to subfreezing temperatures Provision to prevent freezing the coils must be made Item No Function 1 2 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 3 OA damper opens on fan startup closes upon fan shutdown in some cases the OA damper may be part of a mixed air system 4 OA temperature d...

Страница 239: ...eat section is usually dictated by the downstream AHU temperature controls SPECIFICATIONS See FAN SYSTEM START STOP CONTROL Anytime the supply fan runs heating control shall be enabled and the OA dampers shall open for ventilation requirements The heating coil valve shall open upon loss of actuator motive force shall close upon fan shutdown if the OA temperature is above 1 5 C and shall control to...

Страница 240: ...ther than full open upon fan shutdown in freezing weather This saves pump energy and often prevents the need for multiple pumps LIMITATIONS If too high a temperature rise is used the valve may short cycle or slow down the water in the coil and allow the coil to freeze SPECIFICATIONS See FAN SYSTEM START STOP CONTROL Anytime the supply fan runs heating control shall be enabled and the OA dampers sh...

Страница 241: ...nitoring is desired FEATURES 1 The multiple inline coil system heats below freezing air with little danger of freezing the coils or overheating the space 2 The supply temperature is constant or may be dictated by other HVAC controls 3 In this sequence individual Coil 1 and 2Valves are opened fully just before freezing air enters to prevent freezing 4 The low temperature control Item 2 is intended ...

Страница 242: ...rce shall close upon fan shutdown if the OA temperature is above 1 5 C and shall open upon fan shutdown if the OA temperature is below 1 5 C Heating Coils 2 and 3 valves shall open upon loss of actuator motive force and shall close upon fan shutdown The Heating CoilValve 3 shall be modulated by a PID control loop to maintain the leaving air temperature setpoint The valve to Coil No 1 nearest enter...

Страница 243: ...nded by the HVAC control system Mixing valve also keeps water entering the exhaust coil from dropping below freezing to prevent the coil from frosting 8 9 HVAC system SA temperature setpoint determines valve position in winter 11 Operator information 12 Dynamic graphic sequence display permits the operator to adjust program setpoints 100 OA SA RA EA ON ON ON N C PERCENT OPEN TO SUPPLY COIL N C N C...

Страница 244: ...een the water and OA SPECIFICATIONS OA and exhaust fans shall start their OA dampers open and the water flow and temperature controls shall be enabled anytime the HVAC system requires OA In the cooling season the recirculating pump shall run with full flow in the coils anytime the OA temperature is greater than six degrees above the RA temperature In the heating season the recirculating pump shall...

Страница 245: ...the required amount of moisture The best humidifier location is after a heating coil 3 The high limit humidistat is set relatively high about 90 percent relative humidity 4 If the digital controller is in a network and the OA temperature value is available the comfort humidification system is disabled when the OA temperature is above a summer value 18 C 5 Check recommended applications for specifi...

Страница 246: ...S The following are common control arrangements for cooling CONTROL OF MODULATING CHILLED WATER COIL THREE WAY VALVE Functional Description Item No Function 1 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 2 3 Space temperature PID control loop modulates the three way valve to maintain space temperature setpoint 4 Chilled water valve directs flow through or around...

Страница 247: ...re content of leaving air increases as the sensible cooling load lightens In the following chart it is assumed that 1 Desired space and RA condition is 25 C DB and 50 RH 18 C WB 2 Design OA temperature is 35 C DB and 24 C WB 3 Air entering the system is from the ECONOMIZER CYCLE DECISION application This system operates on 35 percent OA during the cooling cycle 4 Coil discharge temperature is 13 C...

Страница 248: ...ety controls must be incorporated into the control system SPECIFICATIONS See FAN SYSTEM START STOP CONTROL The DX control system shall be enabled anytime the fan operates Cooling system shall be cycled by a temperature control loop with a 1 4 kelvins adjustable differential to maintain the space temperature setpoint When the system is commanded on by the control program it shall remain on at least...

Страница 249: ...e following results are obtained Item No Explanation 1 Mixed air temperature at cooling design condition 2 Air entering the coil is cooled along a line of constant moisture content until saturation is approached Near saturation the moisture content is reduced as the air is cooled This process involves both latent and sensible cooling 3 When the space thermostat has the DX cooling energized coil le...

Страница 250: ...e PI control loop shall modulate DX coil face and bypass dampers to maintain setpoint Anytime the face damper modulates up to 80 open the refrigerant valve shall open and a relay shall enable the compressor to start under compressor controls When the compressor system is commanded on it shall remain on at least eight minutes and when it is commanded off or drops off during power interruptions it s...

Страница 251: ...des individual zone control Three zones shown 2 A single cooling coil or group of coils furnishes cooling for the entire system 3 A constant volume of air is delivered to each zone 4 Cold deck temperature is maintained just low enough to satisfy the zone requiring the greatest amount of cooling which provides efficient operation when used in conjunction with a hot deck coil control multizone syste...

Страница 252: ...zone with the greatest cooling demand varies from 50 to 100 PSYCHROMETRIC ASPECTS In the following chart it is assumed that 1 RA condition is 26 C DB and 50 RH 18 5 C WB 2 Design OA condition is 35 C DB and 24 C WB 3 Air entering the system is from the ECONOMIZER CYCLE DECISION application The system operates on 35 percent OA during the cooling cycle 4 One zone is calling for full cooling 5 Other ...

Страница 253: ...um dehumidification In this mode the heating space temperature setpoint shall be midpoint between the heating and cooling setpoints and the hot water valve shall be modulated to prevent the dehumidification cycle from overcooling the space 4 The dehumidification cycle shall be disabled anytime there is no hot water flow or temperature PSYCHROMETRIC ASPECTS In comfort air conditioning dehumidificat...

Страница 254: ... is turned on See FAN SYSTEM START STOP CONTROL 2 4 Space temperature PI control loops have heat and cool setpoints with deadband 5 6 Space humidity sensor and setpoint enable dehumidification 7 9 Heating and cooling valves and face and bypass dampers position for heating cooling and dehumidifying cycles 10 Stages chilled water and face and bypass damper loading 11 Control program coordinates cool...

Страница 255: ...igh limit PI loop demand whichever demand is greater for cooling varies from 0 to 60 percent the chilled water valve shall position from closed to open As the space temperature or the humidity PI loop demand whichever demand is greater for cooling varies from 10 to 100 percent demand the face and bypass dampers shall position from closed to open to the coil face The dehumidification cycle shall be...

Страница 256: ...modulates to maintain SA temperature setpoint 14 Control program coordinates space and SA heating control and fan interlock 15 16 Space temperature cooling PI loop inputs to SA temperature cooling reset schedule 17 Mixing dampers modulate to maintain SA temperature setpoint 18 Economizer decision program determines when OA is suitable to assist with cooling demand 19 Mixing dampers minimum ventila...

Страница 257: ...ted as required to maintain the SA temperature setpoint Anytime the fan runs the mixing dampers shall position to a minimum ventilation setting Asthespacecoolingloadvariesfrom0to100 theSAcooling PI loop setpoint shall be reset from 27 C to 13 C The outdoor andreturn andreliefifapplicable airdampersshallbemodulated as required to maintain the SA temperature setpoint Cooling damper control shall be ...

Страница 258: ...s Software has a minimum 0 8 kelvins heating and cooling deadband 14 Heat demand varies SA temperature setpoint M15176 OA EA RA SA 3 2 ON ON 1 100 5 100 16 19 4 20 NORMAL ECONOMIZER DECISION REFER TO PREVIOUS ECONOMIZER OPTIONS OA MINIMUM SETPOINT NOTE THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22 7 6 22 CONTROL PROGRAM 22 96 17 14 18 41 13 SUPPLY AIR TEMPERATURE SETPOINT SPACE H...

Страница 259: ...iods Anytime the economizer decision program determines that OA is suitable to assist in cooling the temperature controls shall be enabled to override the dampers minimum ventilation position for free cooling as required ThespacetemperatureshallhaveafreecoolingPIloopsetpoint selected to provide optimum occupant comfort temperature The space temperature shall have a chilled water cooling PI loop se...

Страница 260: ...izer enables free cooling when OA is suitable 15 Fan leaving air temperature for operator information 16 Control program coordinates cooling heating ventilation and fan interlock control M15178 OA RA SA 2 ON 1 22 78 14 4 3 NORMAL ECONOMIZER DECISION REFER TO PREVIOUS ECONOMIZER OPTIONS OA MINIMUM SETPOINT NOTE THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22 CONTROL PROGRAM 22 13 8 ...

Страница 261: ...ampers shall be returned to their minimum ventilation position PSYCHROMETRIC ASPECTS In the summer zone space temperature is maintained by mixing air from the hot deck with cold deck air the temperature of which is dictated by the zone with the greatest demand for cooling The zone with the greatest demand for cooling gets 100 cold deck air In the winter zone space temperature is maintained by mixi...

Страница 262: ...mixing dampers as required to maintain SA PI setpoint 19 Chilled water coil leaving air temperature lowered if required for dehumidification 20 26 Space humidity PI control loop modulates humidifier valve to maintain space relative humidity subject to an SA high limit humidity PI loop 27 Control program coordinates ventilation heating cooling humidification dehumidification and fan interlocks M151...

Страница 263: ...g demand varies from 100 to 45 the cooling SA PI loop setpoint shall vary from 13 C to 24 C 6 As the SA PI cooling demand varies from 40 to 0 the reheat coil hot water valve SA PI loop setpoint chilled water and economizer shall vary from 11 C to 41 C 7 The heating coil hot water valve shall modulate to prevent the cooling coil leaving air temperature from dropping below 11 C PSYCHROMETRIC ASPECTS...

Страница 264: ...ification control is set at 50 percent The following results are obtained Item No Explanation 1 Heating coil leaving air temperature will be as high as required to satisfy the space temperature controller 2 Humidification will be provided to satisfy space humidification requirements 3 The space heating and humidifying load varies with people and weather 4 The 1 kelvin DB RA rise is discussed in th...

Страница 265: ... operator information 21 SA temperature setpoint switches from cooling to heating value during warm up modes 22 Control program coordinates temperature control ventilation and fan interlock 63 83 13 0 45 OA RA ON ON SUPPLY AIR TEMPERATURE SETPOINT MAXIMUM SETPOINT PROPELLER EXHAUST FAN PERIMETER ZONE PERCENT LOAD SPACE SA TO VAV BOXES WARM UP MODE M15181 2 5 6 3 7 23 22 18 4 15 21 14 12 11 17 1 9 ...

Страница 266: ...n 100 CONDITIONS FOR SUCCESSFUL OPERATION 1 Airflow element and transducer must be kept clean and calibrated 2 OA fan must provide adequate OA shaft pressure Alternatively if there is no OA fan the OA airflow setpoint may be maintained by modulating the RA damper which would have to be added 3 A controller network and adequate software and programmingprovidedtosupportcommunicationbetween the box c...

Страница 267: ...shall be modulated in sequence to maintain the SA temperature setpoint Anytime the optimum start perimeter zone space temperature sensor is less than 21 C at start up time the SA temperature setpoint shall be 32 C until the RA temperature rises to 23 C at which time the SA temperature setpoint shall be lowered to 13 C The EPID shall be invoked at the switching of the setpoint to 13 C with a start ...

Страница 268: ... will be overriden to maintain a constant mixing box negative static pressure and thus a constant OA airflow 16 OA determines SA temperature setpoint 17 Economizer enables free cooling when OA is suitable 18 Mixed air temperature is for operator information 63 83 13 0 45 0 45 58 ON OA SA RA EA ON ON 13 1 274 360 0 613 PERCENT LOAD PERCENT LOAD SA TEMPERATURE SETPOINT OA TEMPERATURE EXHAUST FAN WAR...

Страница 269: ...the supply fan runs during scheduled occupancy periods mixing dampers shall position to minimum ventilation position and the exhaust fan shall start Anytime the economizer mode is enabled the temperature controls shall be enabled to override theAHU mixing dampers minimum ventilation setpoint for free cooling as required During noneconomizer occupied periods the RA damper shall be modulated to main...

Страница 270: ... minimum position outdoor air to obtain mixed air condition 2 Air entering the coil is cooled along a line of constant moisture content until saturation is approached Near saturation the moisture con tent is reduced as the air is cooled This process involves both latent and sensible cooling 3 Mixed air is cooled and dehumidified by cooling coil to obtain cooling coil leaving air condition 4 Reheat...

Страница 271: ...NG SYSTEM CONTROL APPLICATIONS 261 ASHRAE PSYCHROMETRIC CHARTS ASHRAE Psychrometric Chart No 1 TOTAL HEAT SENSIBLE HEAT H s H t h W ENTHALPY HUMIDITY RATIO 1 0 1 0 0 10 0 5 0 4 0 0 4 0 6 0 8 0 2 3 0 2 5 2 0 1 0 0 2 0 2 0 4 0 4 0 2 0 1 0 0 5 5 0 M15336 ...

Страница 272: ...IR HANDLING SYSTEM CONTROL APPLICATIONS 262 ASHRAE Psychrometric Chart No 2 0 TOTAL HEAT SENSIBLE HEAT 4 0 2 0 1 0 8 6 4 2 0 2 5 1 0 2 0 1 0 1 0 1 2 1 4 1 6 1 8 2 0 4 0 4 0 0 9 0 8 0 7 0 6 0 5 0 4 0 2 H s H t h W ENTHALPY HUMIDITY RATIO M15335 ...

Страница 273: ...68 Pressurization 270 Building Pressure Balance 270 Containment Pressurization 270 Wind Pressure Effects 271 Stack Effect 271 Characteristics of Fans and Fan Laws 271 General 271 Fan Types 272 Fan Performance Terms 272 Fan Laws 273 Fan Power 273 Duct System Curves 273 Fan Curve and System Curve Comparison 273 Characteristics of Airflow in Ducts 274 General 274 Pressure Changes Within a Duct 274 Ef...

Страница 274: ...op Control 281 Direct Building Static Control 282 Airflow Tracking Control 282 Duct Static Control 283 Relief Fan Control for VAV Systems 283 Return Damper Control for VAV Systems 283 Sequencing Fan Control 285 Other Control Modes 285 Warm Up Control 285 Smoke Control 285 Night Purge Control 285 Zone Airflow Control 285 Airflow Tracking Space Static Pressure 285 Multiple Fan Systems 287 Exhaust Sy...

Страница 275: ...haft and the air must make two turns before being expelled from the fan housing Centrifugal fan airflow can be controlled by speed variable inlet vanes or less commonly by dampers Constant Air Volume CAV system A central fan system in which airflow in the duct is maintained at a constant volume Differential The difference between supply and return airflows necessary to maintain a positive or a neg...

Страница 276: ...enoted V and is measured in meters per second m s See General Engineering Data section Average Velocity The sum of the air velocities from equal area increments of a duct cross section divided by the number of increments Average velocity denoted VAVG is derived Where N Number of duct increments Turndown Max Flow Min Flow Max Flow x 100 VAVG V1 V2 V3 VN N V VP 2 Da V VP 2 1 2 V 1 3 VP AIRFLOW CONTR...

Страница 277: ...posure The CAV system shown in Figure 2 has the same interior and perimeter zone load requirements as theVAV system in Figure 1 The CAV system however does not use static pressure sensors and flow measuring stations since the airflow is constant In a CAV system the supply and return fans are manually set to meet the total airflow needs The cooling coil discharge temperature can be reset as a funct...

Страница 278: ...low Therefore the instantaneous load of the VAV system central equipment is not the sum of the maximum loads from all air terminal units Instead the maximum instantaneous load on the central equipment of a VAV system is a percentage of the sum of all maximum individual loads This percentage can vary for different buildings In Figure 1 for a single duct VAV system the maximum air terminal unit load...

Страница 279: ...nother positive method is to provide a small OA injection fan set to inject the required OA into the AHU mixing box during occupied periods the OA damper remains closed The fan airflow quantity may be controlled by fan speed adjustment or inlet damper setting and sensed by an airflow measuring station for closed loop modulating control This basic method is positive and relatively maintenance free ...

Страница 280: ...sure and stack effect or vertical air differences BUILDING PRESSURE BALANCE The pressures in a building must be balanced to avoid airflow conditions which make it difficult to open and close doors or conditionswhichcausedrafts Buildingshaveallowablemaximum and minimum static pressures that control these conditions A force of 130 through 220 newtons is considered the maximum reasonable force to ope...

Страница 281: ...y distributed the neutral plane is at midheight In general the neutral plane for tall buildings varies from 0 3 through 0 7 of total building height Stack effect can be calculated from the following equation C5153 NEUTRAL PLANE REVERSE STACK EFFECT NORMAL STACK EFFECT NOTE ARROWS INDICATE DIRECTION OF AIR MOVEMENT Where DP Pressure difference in pascals Pa To Outdoor absolute temperature in degree...

Страница 282: ...es of Axial Fans Propeller fans are low pressure high airflow noisy fans They work up to a maximum static pressure of 190 Pa Tubeaxial fans are heavy duty propeller fans arranged for duct connection They discharge air with a motion that causes high friction loss and noise They work up to a maximum static pressure of 0 75 kPa Vaneaxial fans are basically tubeaxial fans with straightening vanes adde...

Страница 283: ...re of the fan speed For example doubling the fan speed rpm develops four times the static pressure Pa 3 Power varies as the cube of the fan speed For example doubling the fan speed rpm requires eight times the fan power Po Table 1 Fan Laws FAN POWER The theoretical fan power Po required to drive a fan is the fan power required if there were no losses in the fan 100 percent efficiency The fan power...

Страница 284: ...ic pressures When static pressure is above atmospheric pressure it is positive and when below atmospheric pressure it is negative The examples use U tube manometers to read pressure The sensor connected to the U tube determines the type of pressure measured Fig 7 Combination of Fan and System Curves The fan curves shown are for a fan running at two speeds 400 rpm and 600 rpm Also two system curves...

Страница 285: ...nds solely on the duct size The pressure loss due to friction TOTAL PRESSURE STATIC PRESSURE TOTAL PRESSURE VELOCITY PRESSURE VELOCITY PRESSURE ATMOSPHERIC PRESSURE DIRECTION OF AIRFLOW AIR DUCT OPEN END OF DUCT C2644 Fig 9 Theoretical Changes in Pressure with Changes in Duct Area appears to be a static pressure loss However in reality the total pressure decreases because the pressure loss due to ...

Страница 286: ...n excessive friction losses unless prevented Turning vanes are often used in elbows to reduce the friction loss In addition they provide more uniform and parallel flow at the outlet of the elbow In transitions to and from equipment an attempt is made to spread the air evenly across the face of the equipment If the diverging section into the equipment has too great an angle splitters are often used...

Страница 287: ...increases The total pressure reading drops off gradually and then more rapidly as θ increases Modern Developments in Fluid Dynamics Volume 1 Dover Publications Copyright 1965 1 2 1 1 1 0 0 9 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 C2656 10 20 30 40 50 60 Po P Po PRESSURE WHEN θ 0 STATIC TUBE TOTAL PRESSURE TUBE ONLY P PRESSURE AT INCLINATION θ ANGLE OF INCLINATION θ DEGREES θ θ Fig 16 Error Caused by ...

Страница 288: ...en along at least two diameters perpendicular to each other In rectangular ducts readings at the centers of equal rectangular areas are taken The velocities are then mathematically totaled and averaged EQUAL CONCENTRIC AREAS CENTERS OF AREA OF THE EQUAL CONCENTRIC AREAS 0 316 R 0 548 R 0 707 R 0 837 R 0 949 R ROUND DUCT 16 64 EQUAL RECTANGULAR AREAS CENTERS OF AREAS RECTANGULAR DUCT C2657 PITOT TU...

Страница 289: ...OW Fig 19 Averaging Flow Measuring Station C2660 Electronic flow stations use the tube type construction with thermal velocity sensors instead of static and total pressure sensors Other flow sensing arrangements use holes in round tubing Fig 21A and 21B or airfoil designs Fig 21C It is important to consult the manufacturer of each type of flow station for specifications calibration data and applic...

Страница 290: ... return damper closes further outdoor air increases above minimum These conditions are used for free cooling economizer cycle control and when minimum air must be greater than the difference between supply and return fan airflow rates Fig 23 Central Fan Control with Net Airflow Balance SUPPLY FAN CONTROL FOR VAV SYSTEMS General The supply fan control system provides adequate duct static pressure t...

Страница 291: ...e is lowest in cost but should not be used with smoke control systems where continued fan operation is required DUCT STATIC PRESSURE SENSORS C2621 SUPPLY FAN AIR TERMINAL UNITS DUCT STATIC HIGH LIMIT SENSOR SMOKE DAMPERS SMOKE DAMPERS DUCT STATIC PRESSURE SENSORS A controlling high limit application is used when the fan system must continue to run if duct blockage occurs but its operation is limit...

Страница 292: ...ttling range for stable accurate and responsive operation C2624 CONTROLLER FLOW MEASURING STATIONS RETURN FAN SUPPLY FAN Since building static is controlled directly the pressure remains constant even when exhaust fan airflow changes Minimum outdoor airflow varies with changes in exhaust fan airflow and building infiltration exfiltration In a control sequence where the outdoor air damper is closed...

Страница 293: ...er cycles In Figure 31 a relief damper is located after the relief fan and is controlled to open fully whenever the relief fan operates Direct building static pressure or airflow tracking controls the relief fan In direct building static pressure control Fig 32 the same guidelines apply as for return fan control During minimum ventilation cycles and when the outdoor air damper is closed the relief...

Страница 294: ... for direct building static pressure control C2631 STATIC PRESSURE CONTROLLER BUILDING SPACE STATIC PRESSURE OUTDOOR STATIC PRESSURE OA SUPPLY FAN OA RELIEF FAN RA MIXED AIR TEMPERATURE CONTROLLER AIRFLOW CONTROLLERS SELECTOR C2632 FLOW MEASURING STATION FLOW MEASURING STATION SUPPLY FAN Fig 37 Mixed Air Control Cycle with Relief Fan Control Using Airflow Tracking Fig 38 Mixed Air Control Cycle wi...

Страница 295: ... operating fan s is modulated to minimum output when the next fan is turned on This sequence is used to avoid a stall of the starting fan When all requested fans are running they are modulated upward to satisfy duct static setpoint OTHER CONTROL MODES Warm Up Control If warm up control is used it is not necessary to provide outdoor air The following control actions should be accom plished when usi...

Страница 296: ...oor static pressure sensor should be at least 5 meters above the building depending on surrounding conditions and be specifically designed to accommodate multidirectional winds For zone control using airflow tracking or direct space static pressure return fan control should hold duct pressure constant at a point about two thirds of the duct length upstream of the return fan Fig 41 This control is ...

Страница 297: ... minimum discharge velocity SASH OPEN STANDARD SASH OPEN AUXILIARY AIR SASH OPEN BYPASS SASH CLOSED SASH CLOSED SASH CLOSED C1484 FUME HOODS Fume hoods are the primary containment devices in most chemical based research venues The lab envelope itself becomes the secondary containment barrier In all cases the basic use of the fume hood is for the safety of the worker researcher Because no air is re...

Страница 298: ... properties but contributes to excessive energy usage Figure 45 illustrates a face velocity chart showing the comparative face velocities which may be experienced with different types of hoods using either constant volume or variable volume control strategies The variable volume hood with face velocity controls in this example shows increased air velocities at the low aspect of sash closure becaus...

Страница 299: ...h a single fume hood a single door 1m wide x 2m high 2m2 and a crack area estimated at 0 05 m2 If the fixed airflow tracking differential is 0 1 m3 s the average velocity through the cracks would be 2 0 m s which is more than adequate for containment However when the door opens the average velocity in this example decreases to 0 05 m s which is marginal to inadequate for containment However the ab...

Страница 300: ... stability volumetric tracking control is becoming the more accepted method of pressurization control in lab spaces Direct pressure control remains a viable alternative especially in lab spaces that are sealed tightly where there is sufficient building supply air and good lab operation protocols REFERENCES The following references were useful in preparing this section on Building Airflow System Co...

Страница 301: ...gal Chiller Control Application 303 Multiple Chiller System Control Applications 305 Dual Centrifugal Chillers Control Application 307 Similar Multiple Centrifugal Chillers Control Applications 309 Equal Sized Centrifugal Chillers Control 309 Multiple Centrifugal Chiller Sequencing 311 Dissimilar Multiple Centrifugal Chillers Control 313 Alternative Multiple Decoupled Chiller Control 313 Combinati...

Страница 302: ...tribution Systems 336 Centrifugal Pumps Used in Hot and Chilled Water Systems 336 Pump Performance 337 Pump Power Requirements 338 Pump Performance Curves 338 Pump Efficiency 338 Pump Affinity Laws 339 Matching Pumps to Water Distribution Systems 340 System Curves 340 Plotting a System Curve 340 Combining System and Pump Curves 340 Variable Speed Pumps 342 Pumps Applied to Open Systems 343 Multipl...

Страница 303: ...ystem Design 364 Hot Water Control Method Selection 364 Chilled Water Distribution Systems 364 General 364 System Objectives 365 Control of Terminal Units 365 Dual Temperature Systems 365 Changeover Precautions 365 Multiple Zone Dual Temperature Systems 365 Steam Distribution Systems and Control 366 Introduction 366 Advantages of Steam Systems Vs Hot Water Systems 366 Steam System Objectives 366 P...

Страница 304: ...Steam Generators 379 District Heating Applications 380 Introduction 380 Heat Sources 380 The Distribution Network 380 The Substation 381 Abbreviations 381 Definitions 381 Symbols 382 System Configuration 382 Heat Generation 382 Heat Distribution Network 382 Hot Water System Control 382 Steam System Vs Hot Water System 383 Hot Water Pipeline System 383 Booster Pump Station 383 Pressure Reducing Sta...

Страница 305: ...ITIONS Approach 1 The temperature difference in a cooling tower between outdoor wet bulb and condenser water leaving the tower 2 The temperature difference in an air cooled condenser between the liquid refrigerant leaving the condenser and the entering air dry bulb 3 The temperature difference in a conduction heat exchanger between the entering working fluid and the leaving treated fluid Central p...

Страница 306: ...essive noise vibration and heat Surge is caused by insufficient pumping pressure to meet the rise in pressure from evaporator to condenser Symmetrical loading Diversity in multiple load systems where individual loads operate at the same time and same percentage loading as the others Variable speed pumping VSP A pumping system where the flow pressure is varied by changing the pump speed Diversity f...

Страница 307: ...evaporator Fig 4 isusedwithpositivedisplacementcompressors In both cases the condenser is a large pressure cylinder shell with tubes connected to inlet and outlet headers In the flooded shell and tube type evaporator the shell is about 80 percent filled with refrigerant and the chilled water flows through the tubes Heat from the water evaporates the refrigerant surrounding the tubes which cools th...

Страница 308: ...ondense the refrigerant vapor An evaporative condenser is similar to the air cooled condenser where the refrigerant flows through a coil Water is sprayed over the coil and then air is blown over the coil to evaporate the water and condense the refrigerant Evaporative condensers are rarely used because of the additional maintenance compared with an air cooled condenser CENTRIFUGAL COMPRESSOR Centri...

Страница 309: ...pressure difference to circulate the refrigerant Reciprocating chiller capacity is controlled in stages steps Methods of capacity control include the following Unloading cylinders On off cycling of multiple compressors Hot gas bypass Hot gas through evaporator Cylinder unloading or multiple compressor on off cycling is sequenced by automatic controls The cylinder inlet valves are held open so no c...

Страница 310: ...trong absorber Heatsourcesmaybehotwater hightemperaturehotwater steam or a gas flame direct fired Light loads require a reduced concentration of strong absorbent absorbent retains more refrigerant or less flow of the strong absorbent The amount of heat required for a given cooling load is proportional to the temperature difference between condensing water and chilled water refrigerant pressure It ...

Страница 311: ...ntrol andoftenreceivetheirchilledwatersetpointfrom a BMCS to optimize building energy efficiency When chilled water discharge temperature control is used offset can be reduced and control improved by using return water temperature to reset the supply setpoint upward at light loads to reduce the supply to return chilled water temperature difference Proportional integral PI control improves the accu...

Страница 312: ...hiller or chiller combination in multiple chiller plants to satisfy the current load at minimum operating cost The influence of refrigerant pressures and chiller efficiency curves must be considered 3 Using rejected heat when a heating load exists at the same time as a cooling load 4 Using thermal storage to store day time rejected heat and or night time cooling Thermal storage can also reduce the...

Страница 313: ...r to run 4 Condenser pump status Pump started by chiller controls when chilled water needed 5 6 Chiller leaving water temperature and setpoint 7 Icon to select chiller control dynamic sequence display Fig 10 8 BMCS commandable load limiting function 9 14 Operator information 15 Control program coordinates chiller control 16 Icon to select cooling tower control displays 6 5 MINIMUM CURRENT MAXIMUM ...

Страница 314: ... and are operating under a reduced maximum airflow setpoint during all unoccupied cooling modes see theAir Handling System Control Applications to save fan energy and place the chiller operation in the maximum efficiency range 6 Chilled water temperature reset fromAHU chilled water valve position requires a No valve always full open b Maximum of 30 to 40 valves With too many valves the probability...

Страница 315: ...save energy and require that the system be able to operate with the reduced flow The check valves prevent reverse flow through the shut down chiller Use of a common pump and isolation valves require that the operating chiller be able to withstand full system flow The isolation valves allow the operating chiller to supply only the chilled water temperature required to meet system demands Without th...

Страница 316: ...operating at design condition with a 24 kelvins temperature differential T between chilled and condenser water the second chiller must be added when the first chiller reaches 100 percent load 50 percent of chiller system capacity The next set of curves C and D show the chiller is more efficient because of the smaller T 17K and that the first chiller can be loaded to 110 percent 55 percent of syste...

Страница 317: ...illed water setpoint reset dynamic sequence display Fig 15 8 BMCS commandable load limiting functions 9 Lead chiller selector function 10 17 Operator information 18 Control program coordinates chiller staging and control 19 Icon to select cooling tower control displays 20 Icon to select chilled water flow and pressure control displays 26 32 5 8 ON 78 OFF 00 29 5 BY REMOTE CONTROLS OPERATING MODE S...

Страница 318: ...onditions For Successful Operation 1 Control network software and programming advises chiller controller of AHU chilled water demands 2 Interlock and control wiring coordinated with the chiller manufacturer ANYTIME ANY AHU VALVE IS OPEN GREATER THAN FOR MORE THAN MINUTES AND THE TIME IS BEFORE THE LEAD CHILLED WATER PUMP STARTS ANYTIME THE LEAD CHILLER HAS RUN LONGER THAN MINUTES THE CHILLED WATER...

Страница 319: ...be proven in the ON mode Provide control and interlock wiring per the chiller manufacturers recommendation Upon a call for chilled water the chiller controls shall start the condenserwaterpumpandenergizethecoolingtowerfancontrols When condenser water flow is proven via a condenser water pump current sensing relay the chiller shall start operate and load under chiller factory controls to maintain t...

Страница 320: ...ow Stop a chiller anytime the decoupler forward flow exceeds that of the next chiller to be shed SOFTWARE PARTITIONING From an operational and control perspective the physical configuration of chiller plant digital controllers is usually transparent The configuration varies depending upon Chiller staging algorithm Redundant backup control requirements Condenser water system configuration NOTE Wher...

Страница 321: ...ng 12 Decoupler flow the difference between primary and secondary flows 13 16 Temperatures for calculating secondary flow 17 Status of optional AUTO MANUAL toggle switch 18 Four chiller CHWS temperature indicators 19 Operator information from secondary system 20 Icon for selection of chilled water setpoint details display 21 Icon for selection of chiller sequencing display Fig 20 29 5 CT 4 CT 3 CT...

Страница 322: ... to start 5 Constant flow through chillers with a variable flow secondary water system Conditions For Successful Operation 1 Control network software and programming to advise chiller plant controller of AHU chilled water demands 2 Interlock and control wiring coordinated with the chiller manufacturer 3 Appropriate cooling tower and control 4 Two way AHU control valves provide variable flow second...

Страница 323: ...aging approach measures the secondary load via flow and differential temperature and stage the chillers on and off to match the demand Since the leaving chilled water temperature and the entering condenser water temperature are frequently optimized and chiller capacity varies with changes in either temperature the per chiller expected should be dynamically modified based upon manufacturers data re...

Страница 324: ...ystem Water Piping Figure 23 compares the steam consumption of individual chillers to a combination system showing the savings using the combination system The range of centrifugal cutout points indicates where most centrifugal chillers are shut down and the absorption chiller provides all cooling required by the system CONDENSER COMPRESSOR EVAPORATOR CONDENSER CHILLER 1 LOAD C2689 ABSORBER EVAPOR...

Страница 325: ...rging cycle is scheduled to start when low cost cooling is available The charging cycle is stopped when storage is sufficient for the next days load or when the storage capacity is filled The storage discharge cycle is controlled to meet load conditions If storage capacity is not large enough for the next day the chiller supplements the use of stored cooling as necessary The control sequences for ...

Страница 326: ... supply temperature in mild weather A tower bypass valve is used to further limit cooling when the fans are off Fig 27 On off fan control is very difficult at light loads because at light load the OAWB is usually well below design which increases the tower capacity producing short fan on periods Controlling the air volume with dampers blade pitch or fan speed provides much closer and more stable c...

Страница 327: ...er Specification On a rise in condenser water temperature to 27 C the cooling tower fan shall start and on a drop in condenser water temperature to 23 C the cooling tower fan shall stop When started the cooling tower fan shall run a minimum of five minutes When the OA temperature is above freezing the bypass valve shall modulate if required to prevent the condenser water from falling below 21 5 C ...

Страница 328: ...ps to a minimum safe speed below which results in motor overheating If the tower capacity is still excessive at minimum fan speed the fan control mode reverts to on off During this mode disable the PI function or when the fan is restarted it will start at a speed greater than the minimum although the minimum speed was too great This produces an undesirable short on time The following is a possible...

Страница 329: ... less than 7 minutes duration If after cycling the fan on for 3 minutes the temperature rises above the back on setpoint by 1 kelvin the EPID function shall be reinstated with a start value of 25 and a ramp duration of 90 seconds The tower diverting valve shall modulate to divert tower water to the sump if required to prevent the condenser water temperature from dropping below the minimum temperat...

Страница 330: ...common condenser water temperature control 11 Optimum condenser water temperature calculation based upon OA WB 12 22 Operator information 23 Isolates towers if required 24 Icon for dynamic control and setpoint display 25 Icon to select tower low load control dynamic sequence display CHILLER CONTROL 100 0 33 100 0 33 V1T V2T V1S V2S TOWER ISOLATION SELECTOR 0 NO TOWERS ISOLATED 1 TOWER 1 ISOLATED 2...

Страница 331: ...e to maintain a fixed minimum temperature setpoint of the minimum value the chiller can tolerate or the tower free cooling setpoint in the tower free cooling mode of operation Single pump operation with above freezing OA temperature For both towers valves shall position open to the tower and closed to the sump and the tower fans shall modulate in unison under EPID control down to a minimum fan spe...

Страница 332: ...tower after a 1 5 kelvins differential If after both valves position open to the tower for 2 minutes the temperature rises to the valve control setpoint plus 2 kelvins control shall revert back to alternately cycling the fans on at minimum speed as before If after a fan is running greater than 2 minutes at minimum speed in the on off mode of operation the water temperature rises to a value equal t...

Страница 333: ...ater reset is used stop the reset action when the coolingtowerisoff Thisprovidesrecoverysystemheattoalower outdoor temperature before it is necessary to use fuel for heating FREE COOLING TOWER COOLING When the condenser water temperature from an evaporative cooling tower is equal to or lower than chilled water load requirements mechanical refrigeration is not needed During these times free cooling...

Страница 334: ...ence should change the tower water controller setpoint first then change the heat exchanger valves when temperatures are proper for the new mode of operation Following is a tower free cooling example using plate frame heat exchangers for the dual chiller system shown in the DUAL CENTRIFUGAL CHILLER example The DUAL COOLING TOWERVARIABLE SPEED FAN CONTROL example is also relevant CONDENSER COMPRESS...

Страница 335: ...tus 20 Operator information 21 Prevents tower from cooling water below minimum value that chiller can tolerate during chiller cooling mode 22 23 Tower fans modulate to maintain condenser water setpoint 24 CHILLER AUTO TOWER software mode selection function 25 Prevents chilled water temperature setpoint from dropping below the design minimum 26 45 Operator information see chiller control and coolin...

Страница 336: ... cooling mode during the condenser water warm up period the cooling tower fans shall remain on at no less than minimum speed to prevent short cycling and the condensers entering water temperature shall be controlled by the low limit condenser water temperature pump inlet valves A software CHILLER AUTO TOWER selection function shall be provided to lock the system in either mode if desired Features ...

Страница 337: ...ET M11415 Steel boilers come in a large variety of configurations They are factory assembled and welded and shipped as a unit Figure 38 illustrates a firetube boiler The fire and flue gases are substantially surrounded by water The products of combustion pass through tubes to the back then to the front and once more to the back before finally exiting at the front This makes it a four pass boiler F...

Страница 338: ...ng elements immersed in but electrically insulated from the water and are manufactured in sizes up to 3000 kW Electric elements and electrodes are grouped to provide four or more stages of heating A step controller responding to steam pressure or hot water temperature activates each stage of heating as required to heat the building Fig 40 Electrode Steam boiler BOILER RATINGS AND EFFICIENCY Boiler...

Страница 339: ...the dewpoint of the flue gas to prevent condensation on the fireside of the boiler FLUE GAS ANALYSIS Combustion can be monitored by flue gas analysis For large boilers over 300 kW the analysis is typically continuous For small boilers flue gas is analyzed periodically using portable instruments Flue gas composition analysis routinely measures the percent of CO2 carbon dioxide or O2 oxygen but not ...

Страница 340: ...otstat must be manually reset BOILER CONTROLS BOILER OUTPUT CONTROL There are three ways to control the output of a commercial boiler 1 On off cycling control 2 High fire low fire control 3 Modulating control On off cycling control is most common for small boilers up to 300 kW capacity The oil or gas burner cycles on and off to maintain steam pressure or water temperature Cycling control causes lo...

Страница 341: ...umn Steam flow with totalizer or hot water flow with totalizer Oil and or gas flow with totalizer Stack smoke density APPLICATION OF BOILER CONTROLS Boilers have to provide steam or hot water whenever heat is needed A conventional BMCS is often set to provide a continuous hot water or steam supply between October and May at anytime the OA temperature drops to 16 C for more than 30 minutes and an A...

Страница 342: ...the boiler in the return line There several variations are possible with this type system but the process is the same There is no minimum boiler water flow limit in this example The Dual Boiler Plant Control example following is a dual boiler plant with high fire low fire controlled boilers 63 C minimum entering water temperature required prior to high fire water flow must be maintained when the b...

Страница 343: ...rmation 24 Icon selects the Boiler System Control dynamic display Fig 49 25 26 Software signal selection functions allows valve to control secondary HW temperature subject to boiler low limits 27 OA reset valve control PID AUTO 43 82 13 15 HOT WATER TEMPERATURE RESET SCHEDULE OUTSIDE AIR TEMPERATURE HOT WATER TEMPERATURE SET POINT SECONDARY HOT WATER RETURN SECONDARY HOT WATER SUPPLY SETPOINT SPEE...

Страница 344: ...heating plant shall be disabled anytime the OA temperature rises to 18 C for greater than 1 minute and after May 1 Anytime the boiler plant is enabled the lead boiler primary pump shall start and as flow is proven the boiler shall fire under its factory controls to maintain 82 C If the lead boiler status does not change to on or if flow is not proven within 5 minutes the lag boiler shall be enable...

Страница 345: ...cycles the boilers in sequence If the load increases beyond the capacity of the boilers on line an additional boiler is started The lead cycling boiler can be rotated on a daily or weekly basis to equalize wear among all boilers or when using digital control the program can start the boiler that has been off the longest HOT WATER SUPPLY SENSOR PRIMARY PUMP MODULAR BOILERS SECONDARY PUMPS HWS HWR H...

Страница 346: ...ny varieties of centrifugal pumps are available as shown in Table 2 Figure 52 shows a typical base mounted pump M15053 HEAT COOL COIL 3 RETURN HEAT COOL COIL 2 HEAT COOL COIL 1 AIR SEPARATION HEAT COOL SOURCE MAKE UP WATER EXPANSION TANK PUMP SUPPLY PRESSURE REGULATING VALVE The expansion tank is charged with compressed air to place the system under the minimum pressure required at the inlet to th...

Страница 347: ...oupled Horizontal Vertical inline Single suction One Volute Flexible or close coupled Vertical Vertical turbine Single suction One to twenty Diffuser Flexible coupled Vertical Source ASHRAE Handbook 1996 Systems and Equipment Fig 52 Typical Cross Section of an End Suction Pump PUMP PERFORMANCE The performance of a given pump is expressed in a curve showing pump pressure versus flow Figure 53 shows...

Страница 348: ...urves Commercial pumps have performance curves showing the following data for a given pump speed Total pressure in kPa versus flow in L s Total pressure versus flow for various impeller diameters Pump efficiency at various operating points Net positive suction pressure Net positive suction pressure is the absolute pressure in kPa required at the suction inlet to prevent cavitation due to boiling a...

Страница 349: ...m impeller it would deliver 196 kPa It is calculated as follows Table 3 Pump Affinity Laws Fig 55 Pump Curve for 1750 RPM Operation New pressure Old pressure x New Diameter Old Diameter 2 240 190 210 2 196 kPa C4091 CAPACITY L s 45 55 60 68 68 65 60 55 45 2000W 1500W 1000W 750W 500W 400W 180mm DIA 165mm DIA 140mm DIA 150mm DIA 125mm DIA 0 60 90 120 150 180 0 0 6 1 2 1 8 2 4 3 0 3 6 4 2 4 8 5 4 6 0...

Страница 350: ... two way AHU control valves flow rides the pump curve The system curve is plotted assuming that the control valves are full open which in any system only occurs at the full load As control valves throttle and loads are turned off the system becomes non proportional and the system curve rises between no load and design With variable speed pumps the system control objective is to have the pump curve...

Страница 351: ...ol valve represented by line B makes the difference about 105 kPa Similarly at 50 percent flow the valve drop represented by line C accounts for about 220 kPa C4093 SYSTEM CURVE 240mm 220mm 200mm 185mm 4000W 5500W 7500W 9000W 11000W OPERATION WITH 220mm IMPELLER DESIGN OPERATING POINT BALANCED OPERATING POINT WITH 240mm IMPELLER 300 215 240 210 180 150 120 90 60 30 0 0 6 25 12 5 18 75 25 31 25 37 ...

Страница 352: ... Variable Speed Pump Performance Range Table 4 and Figure 61 show the Figure 58 system with all the control valves remaining full open and the load controlled by varying the pump speed This is the ideal system wherein the loads of all AHUs vary in unison and the pump speed is controlled to satisfy the valve with the greatest demand This is usually accomplished via differential pressure control aut...

Страница 353: ...ed in the control system Two way control valves sharply reduce flow when they begin to close Figure 65 shows that in a single pump system over pressure can result at low flow At one third flow the pump pressure has increased the source and piping drop is reduced to one ninth of the design drop and the control valve drop has increased greatly Bypass variable speed or throttling valve pressure relie...

Страница 354: ...ial pump pressure drops to I at which time the cycle repeats See PLOTTING A SYSTEM CURVE for statement on use of ideal system curve for determining setpoints when coil loading may not be proportional Again a reminder to exercise caution when using the ideal system curves for switching pumps on and off The ideal curves are valid only at full and no load conditions the rest of the time the actual cu...

Страница 355: ... Simplified Water Distribution System In Figure 68 the flow and pressure considerations are 1 The flow through the heating or cooling source the supply piping and the return piping 2 5 L s is the same as the sum of the flows through the three coil circuits 0 6 0 8 1 1 2 5 L s 2 Design pressure drop includes the drop through the heating or cooling source supply piping return piping and the highest ...

Страница 356: ... whetherthedesignerchoseadirectorreversereturnpipingsystem Systems are sometimes configured as a combination of both a high rise building could for example be reverse return on the riser and direct return on the floor run outs Direct return systems are usually lower cost and used in smaller installations Reverse return systems are used in both small and large installations flow2 flow1 2 p2 p1 0 37...

Страница 357: ...or a reverse return system Fig 71 asforthedirectreturnsystem Fig 70 Thereturnflowisreversed such that the return piping increases in size between AHUs 1 2 3 4 5 and 6 A full size return line is run back to the source room from AHU 6 In this example the pump is the same as the direct return since the return line fromAHU 6 also takes a 18 kPa drop IftheAHUsandsourcewerepositionedinacircularorhexpatt...

Страница 358: ... are often not available therefore small three way valves tend to be oversized Consider using two way control valves for all applications of KV 4 0 and less where the quantity of two way valves will have little effect on the total system flow Constant Flow in Mains Constant flow provides nearly constantpressuredifferential drop acrossacoilandvalve Pumping Cost A three way valve system uses full pu...

Страница 359: ...r DIFFERENTIAL PRESSURE SENSOR LOCATION As previously stated the chiller design flow is 75 L s at 36 kPa and requires a minimum flow of 66 L s At 66 L s the pump curve shows a pressure of 150 kPa From the formula Fig 73 Typical Example Loads Single Pump Pressure Bypass Direct Return Figure 74 analyzes Figure 70 pumping system at full flow and at half flow The flow reduction at half flow is taken e...

Страница 360: ... 3 PD 36 9 PD 24 132 PD 48 12 72 144 30 7 5 54 139 5 0 0 PD 24 132 PD 30 7 5 18 4 5 PD 18 4 5 PD TOP NUMBERS FULL FLOW BOTTOM NUMBERS HALF FLOW EACH COIL PD PRESSURE DROP IN kPa NUMBERS IN CIRCLES GAUGE PRESSURES kPa PUMP INLET ZERO kPa FOR SIMPLICITY 24 6 PD M15286 18 kPa DROP TOTAL RETURN SYSTEM STRAINER HEAT COOL COIL 1 V1 B1 HEAT COOL COIL 2 V2 B2 HEAT COOL COIL 3 V3 B3 HEAT COOL COIL 4 V4 B4 ...

Страница 361: ...operation Single Pump Pressure Bypass Reverse Return A reverse return system analysis equivalent to the direct return analysis of Figure 74 would show that at half flow and no bypass the pump pressure still rises to 162 kPa and the control valve drop still rises to 132 kPa For 90 percent flow control the pump still operates at 150 kPa with the sensor located as far away from the pump as practical ...

Страница 362: ...iller operation During periods of dual pump chiller operation the 103 5 kPa setpoint controller is used alone AHUValve High Differential Pressure Control AsnotedinthediscussionofFigure75 thedifferentialpressure controlled bypass valve in constant speed pumping systems is adequate to maintain a high flow through chillers but does little to prevent high differential pressures across theAHU load cont...

Страница 363: ...H I L L E R 2 HEAT COOL COIL 1 V1 B1 HEAT COOL COIL 2 V2 B2 HEAT COOL COIL 3 V3 B3 HEAT COOL COIL 4 V4 B4 HEAT COOL COIL 5 V5 B5 HEAT COOL COIL 6 V6 B6 SUPPLY V7 V8 DP 1 DP 2 M15065 In these examples the design differential pressure across Load 1 is 84 kPa Fig 74 and pressure bypassing occurs at 103 5 kPa The maximum setpoint for DP 2 Fig 78 should be about 87 or 90 kPa This initial setpoint is th...

Страница 364: ...tem is to operate satisfactorily with non symmetrical loading DP 1 located at the variable speed drive VSD is the most convenient place It requires the DP 2 setpoint plus the friction losses between the pump and AHU 1 Figure 80 shows the operating curve of the system with the differential pressure sensor located in the DP 2 position and set for 84 kPa With each AHU at one third flow the speed is 1...

Страница 365: ...e NOTES 1 From Figure 81 pump pressure is 108 kPa if all AHUs require full flow therefore the 90 kPa value is an arbitrary compromise 2 This relaxes the control demands for smooth stability after the response to the initial load Figure 81 shows the ideal performance of the load reset setpoint control with eachAHU demanding one third flow All control valves are full open and the differential pressu...

Страница 366: ...N 95 OPEN VALVE V 1 DP SETPOINT IS INCREMENTED UP AT THE SAME RATE WHEN ALL V 1 VALVES ARE LESS THAN 75 OPEN THE VARIABLE SPEED PUMPING SYSTEM DP SETPOINT IS DECREMENTED DOWN kPa EVERY MINUTES WHEN ANY V 1 VALVE IS GREATER THAN 95 OPEN VALVE V 1 DP SETPOINT IS INCREMENTED UP AT THE SAME RATE MANUAL PERCENT OPEN VALUE AUTO 88 88 100 450 380 380 175 8 5 5 5 5 5 8 5 MANUAL AUTO SELECTOR PERCENT OPEN ...

Страница 367: ... causesAHU 1 water flow loop to draw significantly more than design flow because it is nearer the pump where the differential pressure is higher This will slightly starve the other loads 2 Cool down periods for other than AHUs 1 and 2 will be extended With all valves full open until AHUs 1 and 2 are satisfied the other AHUs will be starved 3 Industrial valves may be required to maintain acceptable...

Страница 368: ...twater The control objectives for a hot water distribution system providing space heating are 1 Provide adequate hot water flow to all heating units 2 Maintain a stable pressure difference between supply and return mains at all load conditions 3 Match hot water temperature to the heating load based on outdoor air temperature and or occupancy a Avoid heat exchanger flow velocities dropping into the...

Страница 369: ...urns the water to the main where it is mixed with the supply water The next unit will be supplied with slightly lower temperature water One pipe systems are typically used in small buildings with only one or two zones SINGLE INPUT CONTROL STEAM TO HOT WATER CONVERTER HOT WATER SENSOR SUPPLY RETURN PUMP STEAM SUPPLY C2831 CONDENSATE RETURN LOAD LOAD LOAD LOAD LOAD LOAD FLOW DIVERTING FITTINGS BOILE...

Страница 370: ...9 can be used in large or high rise buildings to reduce the zone temperature pressure requirements from those of the mains EXPANSION TANK CONVERTER HIGH OR MEDIUM TEMP MAINS RETURN SUPPLY C2915 1 LOAD LOAD LOAD LOAD Fig 89 Converter Used to Supply Zones from a Larger System CONTROL OF HOT WATER SYSTEMS General Heating terminal units used in hot water heating systems are Radiant Panels Radiators or...

Страница 371: ...iously discussed reset of hot water supply temperature is the most effective method of controlling heat output of a water supplied heating coil panel radiator or convector Heat output of most water supplied heating is relatively linear with respect to supply water temperature Water temperature reset can be provided by a steam to hot water converter a three way valve or boiler water temperature res...

Страница 372: ...mall valve handles light loads preventing a single large valve from throttling down to the point where the valve plugapproachesthevalveseatwherenoiseandseaterosionoccur and the large valve is sequenced in after the small valve is full open At the point where the 2 3 sized valve starts opening the same noise and erosion is possible With digital systems the valves may be staged rather than sequenced...

Страница 373: ...is available The hot water pump shall start anytime the OA is below 14 5 C subject to a software on off auto command Control During early morning periods AHUs in warm up mode the hot water HW temperature setpoint shall vary from 68 C to 90 5 C as the OA varies from 16 C to 20 C During occupied periods any AHU in occupancy mode the HW temperature setpoint shall vary from 54 C to 77 C as the OA vari...

Страница 374: ...result is a relatively linear heat output as a function of stem position Fig 97 The heat output is relatively constant providing optimized controllability of heat exchangers such as converters fan coils and induction units Fig 96 Radiators with Scheduled Water Temperature Using Three Way Valve Coordinating Valve Selection and System Design A prerequisite to good modulating control of water systems...

Страница 375: ...r changeover The valve on the chiller is controlled two position The three way boiler valve is controlled modulating for heating so that the hot water supply temperature may be reset from the outside temperature Boiler minimum flow or temperature may require system modifications Changeover from heating to cooling can be based on outdoor air temperature solar gain outdoor wet bulb temperature or a ...

Страница 376: ...onvert the one kilogram of water to a vapor steam The total heat of the vapor is 420 kJ kg 2257 kJ kg 2677 kJ kg The 2257 kJ kg is the latent heat required to vaporize water One kilogram of water in the liquid state occupies about 0 001 cubic meters at 0 C When converted to vapor at 100 C it occupies 1 673 cubic meters or 1673 times as much space as the liquid One kilogram of steam water vapor whe...

Страница 377: ...am downstream will be at 170 C not 111 C This is 59 kelvins of superheat and downstream valves and piping will be exposed to the higher temperature To correct for superheated steam 4 kJ kg is added for each kelvin of superheat EXAMPLE 300 kW of 150 kPa steam is required From Table 6 150 kPa steam has a latent heat of 2226 kJ kg If condensate leaves at 80 C the steam gives up 2356 kJ kg 2226 kJ kg ...

Страница 378: ...il the element cools BOILER BLOWDOWN VALVE LOW WATER CUTOFF PUMP CONTROL AND GAUGE GLASS TO RECEIVER TANK STEAM PRESSURE GAUGE PRESSURE CONTROLS F T TRAP STEAM MAIN STOP VALVE RELIEF VALVE F T TRAP HIGH LEVEL SPILL CONDENSATE RETURNS RECEIVER TANK PUMP CHECK VALVE SOLENOID VALVE OPTIONAL STOP VALVE C2923 Reprinted by permission from the ASHRAE Handbook 1996 Systems and Equipment Fig 103 Thermostat...

Страница 379: ...4 Reprinted by permission from the ASHRAE Handbook 1996 Systems and Equipment Fig 107 OrificeTrap The piston trap Fig 108 relies on a pressure change caused by steam or condensate entering the trap to open or close the piston or port A small amount of condensate bleeds through an orifice in the control disc into the control chamber When steam or condensate that flashes to steam enters the chamber ...

Страница 380: ...te C2925 MANUAL OR AUTOMATIC VALVES THERMOSTATIC AIR VENT THERMOSTATIC AIR VENT STEAM SUPPLY RETURN F T TRAP AT END OF MAIN AND BOTTOM OF EACH RISER C2924 MANUAL OR AUTOMATIC VALVES STEAM SUPPLY RETURN TRAP AT EACH TERMINAL UNIT Fig 112 Open Return System A vacuum return system requires a vacuum pump assembly to discharge noncondensable gases to the atmosphere and to force the condensate into the ...

Страница 381: ...the steam mains and in the returns to ensure air removal from the system These vents are larger than radiator vents and are referred to as quick vents VARIABLE VACUUM RETURN SYSTEMS In a variable vacuum steam system also called a sub atmospheric steam system the operating pressures range from 34 kPa absolute to 200 kPa The principle of water boiling at reducedtemperaturesinavacuumisthebasisofavari...

Страница 382: ...d return mains 2 Heat output changes little due to pressure change within the coil as long as the coil is full of steam 3 Heat output changes little until the valve assumes most of the pressure drop between supply and return mains 4 Heat output from the coil is reduced by starving a part of the coil surface of steam and allowing the surface to cool off NOTE Steam distributing coils allow reduced o...

Страница 383: ...cuum pump cycle This means a 60percentvariationincapacityofthecontrolvalvesinthebuilding as the pressure fluctuates Control valves correctly sized for 28 kPa are 60 percent too large during periods when a 65 kPa difference exists across the supply and return mains SYSTEM DESIGN CONSIDERATIONS FOR STEAM COILS Figure 116 shows the optimum design conditions and piping arrangement for a steam supplied...

Страница 384: ...te with supply water temperatures of 120 to 230 C and pressures from 500 to 3000 kPa HTW is typically generated by boilers however experimental systems utilizing geothermal or solar energy have been built First costs are similar for steam and high temperature water systems however maintenance and operating costs are generally lower for HTW systems The use of the same boiler for both HTW and steam ...

Страница 385: ... valves An industrial controller or a digital system may be required where local recording of a control value is specified The control system selected should 1 Function from zero to full load 2 Close the HTW valve if there is failure in the control system loss of power or air or shutdown of the system being controlled HTW VALVE SELECTION Valves for HTW must be selected to ensure suitability for hi...

Страница 386: ...lve Selection and Sizing section The pressure drop across a control valve should be between 50 and 80 percent of the drop across that part of the piping system in which flow will vary as a result of valve action Always use a 35 kPa or greater pressure drop across the valve VALVE LOCATION Always locate a HTW valve on the return side of the converter coil steam generator or other equipment because i...

Страница 387: ...ithin the shell cannot controlV1 in a stable manner The use of an instantaneous converter Fig 120 for heating water supplied directly to an air heating coil provides fast response Control system selection problems are the same as for the control of a coil supplied with low or medium temperature water except that a high quality valve with fast control response is required for HTW Fig 120 Instantane...

Страница 388: ...PS OPTIONAL RESET LINE FROM OUTDOOR CONTROLLER DISCHARGE AIR TEMP CONTROLLER RELAY OPENS VALVE ON LOW TEMPERATURE RELAY CLOSES OA DAMPER WHEN FAN STOPS DAMPER ACTUATOR HTWS LOW TEMP LIMIT HTWR VALVE C2584 N O N C RA N O N C OA DAMPER ACTUATOR DISCHARGE AIR DAMPER ACTUATOR TEMPERATURE CONTROL STORAGE CONVERTER HTWR HTWS RELIEF VALVE MAKE UP WATER 50 C C4625 TO BUILDING FROM BUILDING STORAGE CONVERT...

Страница 389: ...ning 40 percent for steam is sufficient to avoid water carry over A water eliminator at the steam exit removes most water from the steam Flash converters convert HTW to steam by reducing the pressure They are not satisfactory steam generators because water is carried with the steam and control is less stable Control of a steam generator is simpler because pressure changes are sensed immediately an...

Страница 390: ...factories and other facilities from a central source The basic structure of District Heating Systems is shown in Figure 126 A DH System consists of one or more heat generating facilities a widely spread heat distribution network and substations between the distribution network and the consumer Heat is generated by the heat source s and transferred to an appropriate heating medium such as hot water...

Страница 391: ...res up to 200 C and pressures up to 20 bars 2000 kPa The optimum operating conditions temperature and pressure depend on the structure and dimensions of the network and the heat source The water temperature is generally limited to 130 C on the supply side In fact many networks now keep the supply temperature under80 Callowinguseoflowercostequipmentandfewersafety devices See HOT WATER DISTRIBUTION ...

Страница 392: ... is absorbed by the heat transfer medium hot water or steam at the source and delivered to the consumer Primary networks are one or two pipe distribution systems In a two pipe system the hot pipe or supply line transports the water or steam to the substation heat is drawn from the network at the substation and transferred to the consumer s side then the cooled water or condensate flows through the...

Страница 393: ...ferential pressure in the network produces heavier pump loads Every network has a different optimum value for the supply and return pipelines Use of friction reducing chemicals to decrease the friction losses in the pipeline can reduce the pump power required Extracting as much heat at the substations as possible also reduces pumping costs Additionally the water in the entire district heating syst...

Страница 394: ...tations link district heating networks with the consumer The consumer side can be either another network or the end user Heat transfer can be either direct and indirect Direct transfer uses mixing valves jet pumps or two way valves to supply the heating medium directly to the consumer Indirect substations use heat exchangers and physically decoupled or independent heating circuits Direct Heat Tran...

Страница 395: ...urn if the secondary medium temperature exceeds 100 C The differential pressure control is used in large networks where over time significant pressure differences exist The primary supply flow from the district heating network enterstheheatexchanger transferstheheattothesecondarysupply flow and returns to the heat source through the primary return In large networks with distributed pressure and te...

Страница 396: ...y be necessary depending upon the pressure and temperature level in each circuit The second method uses treated tap water Use of untreated water is not recommended as it can coat system with minerals precipitated from the water and dissolved oxygen can corrode the piping This method can also be used as a back up to the first method Hybrid Heat Transfer Substations This combines direct heating with...

Страница 397: ...rential pressure TIC 28 SSF temperature HEX 1 PDIC 45 Secondary differential pressure TIC 38 SSF temperature HEX 12 PI 13 PSF pressure TIC 44 SSF temperature PI 16 PRF pressure internal TSA 22 High temperature limit Primary Return Flow Heat exchanger 1 PRF HEX 1 PI 46 SRF pressure TSA 32 High temperature limit PRF HEX 12 PI 110 PRF pressure outdoor TSA 25 High temperature limit SSF HEX 1 PIC 57 SS...

Страница 398: ...27 TIC 28 TIC 38 PZA 37 TSA 25 TSA 35 PZA 24 PI 13 TI 12 TI 01 Y 11 PZA 34 TSA 22 TSA 32 T1 21 T1 31 PDIC 14 PDIC 45 Y 19 PI 110 QIR 111 Y 18 M Y 51 Y 55 M Y 17 M Y 61 M Y 54 LIC 56 PIC 57 PSA 58 PSA 52 QIR 53 Y 48 M Y 49 QIR 62 LIC 63 Y 64 PI 46 TI 47 M Y 23 M Y 33 M Y 39 M Y 29 TI 15 PI 16 M DDC OUTSIDE AIR SUPPLIER CENTRAL SYSTEM SUBSTATION CONSUMER PSF PRF SSF SRF COLD WATER WATER SUPPLY TANK ...

Страница 399: ... defined range to avoid too low pressure vaporization and too high pressure pump overload Vent valveY 54 maintains the high limit and compressor Y 55 maintains the low limit 5 Expansion Tank Water Level Control WLC Loop LIC 56 maintains the expansion tank water level Normally PRF water throughValveY 51 provides make up water in casesofahighquantitywaterloss PumpY64pumpsmake up water from the water...

Страница 400: ...emperature Y 23 Circulating pump TIC 22 SSF temperature Fig 139 SSF Temperature Reset Schedule Reference Description Reference Description DDC Controller TIC 16 PRF temperature PI 11 PSF pressure TIC 21 DHW temperature supply flow PI 17 PRF Pressure TIC 31 SSF temperature PI 22 DHW pressure supply flow TIC 34 SRF temperature PI 24 DHW pressure return flow Y 13 Actuator valve SSF temperature contro...

Страница 401: ...er and Heating TIC 21 PI 22 TI 12 PI 11 Y 23 M Y 13 TIC 215 PI 24 M Y 31 TIC 32 PIC 33 M Y 310 Y 39 QIR 214 PI 213 Y 38 QIR 15 TIC 16 PI 17 M QIR 02 Y 27 Y 26 Y 25 Y 14 M DDC TI 01 OUTSIDE AIR CENTRAL SYSTEM DISTRIBUTION SUBSTATION CONSUMER ELEC POWER Y 36 PIC 35 TIC 34 Y 29 Y 210 Y 211 Y 212 Y 37 PI 28 HEX1 HEX2 HEX3 PSF PRF DHW DHW SSF SRF COLD WATER M11431 RECIRCULATED ...

Страница 402: ...Y 38 and Y39 throughValveY 310 provide make up water from the PRF 5 DHW Pressure Control Booster Pumps Y29 Y210 Y211 and Y212 boost the cold water pressure to the pressure at PI 213 Y 12 TI 11 M Y 33 DDC TI 01 OUTSIDE AIR QIR 02 COLD WATER Y 34 TIC 32 TIC 31 Y 24 CENTRAL SYSTEM DISTRIBUTION SUBSTATION CONSUMER Y 49 TZA 21 TIC 22 TI 14 QIR 15 TIC 13 HW STORAGE TANK COLD WATER DHW SUPPLY DHW RECIRCU...

Страница 403: ... tank water temperature Thermostat TIC 32 supplies the HW storage tank loading cycle start point During the loading cycle SSF water heats HEX 2 other loads are switched off and the pumps Y 24 Y 34 load the HW storage tank Temperature sensor TIC 31 turns loading operation off 3 DHW Circulating pump control Circulating pumpY 33 is time schedule controlled to maintain the DHW temperature at the end o...

Страница 404: ...rculation pumps ValveY 33 on the return pipe provides a limited amount of flow control As the valve varies from full open to 30 flow through the jet pump varies from full flow When the valve is less than 30 open SSF flow cannot be guaranteed TI 32 controlsY33 to maintain the SRF temperature as reset from outdoor air 2 Heat exchanger HEX 1 Transfers heat to the isolated domestic hot water system DH...

Страница 405: ...4 Dual Duct ATU 406 Dual Duct Pressure Independent VAV ATU 406 Dual Duct Pressure Independent Constant Volume ATU 407 Unitar y Equipment Contr ol 408 General 408 Natural Convection Units 408 Radiant Panels 409 Unit Heaters 409 General 409 Control 410 Two Position Control 410 Modulating Control 410 Down Blow Unit Heater 410 Gas or Oil Fired Unit Heater 411 Unit Ventilators 411 General 411 Control 4...

Страница 406: ...8 General 418 Two Pipe Heating Cooling 419 Two Pipe Heating Cooling Single Coil 419 Four Pipe Heating Cooling Split Coil 420 Four Pipe Heating Cooling Single Coil 420 Heat Pumps 421 General 421 Operation 421 Control Loops 422 Individual Room Control Automation 423 Hot Water Plant Consider ations 424 ...

Страница 407: ...ints should still be availableforoper atorsandtec hniciansviaapor tableterminal Simple systems suc h as unit hea ters are also shown in Electr ic ControlFundamentalssection Lar ge air handling units and c hiller plants typicall y use general purpose digital controllers while rooms typically use contr ollers designed for r oom contr ol Thus a VAV box contr ollerma ybeconfiguredtocontr olavar ietyof...

Страница 408: ...ERATURE LOW LIMIT HIGH LIMIT MANUAL RESET NOTATION INSERTION TEMPERATURE SENSOR TEMPERATURE SENSOR AVERAGING TEMPERATURE CONTROLLER MANUAL RESET SAFETY LOW LIMIT MANUAL MULTI STATE COMMAND ON OFF AUTO STATUS POINT VALUE POINT LOAD COMMANDABLE VALUE 3 WAY VALVE WITH ACTUATOR 2 WAY VALVE WITH ACTUATOR DAMPER WITH ACTUATOR SMOKE DETECTOR NFPA SYMBOL PROPELLER EXHAUST FAN SOLENOID VALVE PUMP FILTER HE...

Страница 409: ...de ener gy savings by reducing the load on the central fan when cooling loads are less than design and avoid reheating cooled air Asystemdesignedtor educeoverallsystemairf lowas ATUs shut do wn offers the greatest ener gy savings because system fansandf anmotor soperateatlighterloads Thesepar agraphs descr ibe the oper ation of VAVATUs in single duct and dual ductairhandlingsystems PRESSURE DEPEND...

Страница 410: ...s the simplest and least expensive ATU A room controller controls the operation of the damper actuator using PI control The throttling VAV ATU usually has software minimum and or maximum damper position limits for limiting air volume Because the unit is pressure dependent volume at any given damper position varies with the inlet duct static pressure Maintaining a stable duct static pressure at the...

Страница 411: ...ll module can be dir ected tomultiplecontr ollerstocontr olmultiple ATUswiththesame ordifferingvolumer atings Figure 4 shows a reheat coil added to a thr ottling VAVATU In this application the temperature controller sequences the operationofthedamperactua torandthecontr olvalveorr eheat coil The coil can be r eplaced b y single or m ultiple sta ges of electricresistancehea t Thedampermodula tesund...

Страница 412: ... PI gains the heating loop PI gains reheat airflow setpoint unoccupied space temperature setpoint standby temperature setpoint temper atur esensorcalibr ationoffset bypasspush b uttonsta tus bypasspush b uttono verridetimeinmin utes smokepur gemode of maximum airflow setpoint smoke pressurization mode of maximum airflow setpoint and unoccupied mode of maximumairflowsetpoint NOTE On offelectr ichea...

Страница 413: ... OFF OFF OFF OFF OFF OFF OFF OFF 0 071 LOBBY ROOM 102 ROOM 103 ROOM 104 0 165 0 260 0 165 MINIMUM MAXIMUM AIRFLOW SETPOINTS m3 s CURRENT AIRFLOW m3 s DAMPER PERCENT OPEN HEATER STATUS HEATING DEADBAND TEMPERATURE COOLING SETPOINT M15307 MINIMUM AIRFLOW REHEAT AIRFLOW MAXIMUM AIRFLOW LOW HIGH LOW HIGH SPACE HEATING LOAD HEATING SETPOINT COOLING SETPOINT SPACE COOLING LOAD DEADBAND MAXIMUM AIRFLOW H...

Страница 414: ...g load g oes to zero ther eheatvalvecloses thenthef anstops Afterthespace temperature rises through a deadband as the cooling load increases thepr imar yairf lowincreasestomaxim um Ser ies F an ATU The ser ies fan ATU Fig 9 delivers a constant v olume of dischar geairwithav ariablevolumeof AHUsuppl yair Inthis ATU thefanisoncontin uouslydur ingoccupiedhour s Primar y airismodula tedtomeetspacedema...

Страница 415: ...TPOINTS m3 s HEATING DEADBAND COOLING SETPOINT TEMPERATURE WALL MODULE PLENUM AIR RHC MAX REHEAT VALVE PRIMARY AIRFLOW MIN OPEN CLOSED ZERO FULL M15309 0 FAN 0 FULL HEATING LOAD REHEAT VALVE PRIMARY AIRFLOW HEATING SETPOINT COOLING SETPOINT COOLING LOAD DEADBAND ADJUSTABLE ON OFF PRIMARY AIR M15310 24 0 165 0 445 0 543 24 MINIMUM AIRFLOW SETPOINT m3 s MAXIMUM AIRFLOW SETPOINT m3 s CURRENT AIRFLOW ...

Страница 416: ...ual Duct Pressure Independent VAV Air Terminal Unit Dual Duct Pr essur e Inde pendent VAV ATU Figure 10 shows a dual duct pressure independentATU The airflow sensor in the outlet of the ATU controls the cold duct inlet damper in the cooling mode from the cooling maximum airflow to the minimum ventilation airflow through the dead band and to the heating setpoint As the heating load increases the ho...

Страница 417: ...owsetpoints Dual Duct Pressure Independent Constant VolumeATU Figure11showsaconstantv olumepr essureindependentdual duct ATU Modula ting the hot duct damper up to a total f low nottoexceedthemaximumairflowsetpointmaintainstheroom temper atur e A constant total airf low is nor mally maintained by modula ting the cold duct damper With this conf igur ation thereisnodeadbandandcomfortismaintainedbymix...

Страница 418: ... convection circulation of air Baseboard A unit installed at the base of a wall Hot water or steam circulates through a finned tube or a cast iron enclosure Air circulates through the unit by convection Typically a na tur al convection unit is contr olled man ually or b y a room ther mosta t contr olling a valve or electr ic heat coil Figure 12 shows the contr ol loops for indi vidual r oom contr ...

Страница 419: ... ceiling panels T he actual hotwatertemper atur emaybehigher Radiant heat panels that use electric resistance heating elements ar e contr olled by a two position ther mosta t As the space temper atur e drops below the ther mosta t setpoint and differential thether mostatclosesaswitchtoallowcurrentflow to heat the elements Whenaradiantpanelisusedforcooling thetemperatureof the water cir culating th...

Страница 420: ... or just the valve and let the low limit cycle the fan Figure16showsthatcontr olofanelectr ic heatunithea teris similar to steam or hot w ater tw o position contr ol except tha t thether mostatcyclesthefanandther elayorcontactorener gizes the electr ic heating elements w hen the f an is r unning Fig 16 Unit Heater Two Position Control Electric Heat C3026 UNIT HEATER LOW LIMIT ROOM THERMOSTAT COIL ...

Страница 421: ...ms conference r ooms A unit ventilatorcontr olsystemvariesheating ventilating andcooling if available while the f an r uns contin uously Figure 20 shows a blow through unit ventilator Dampers at the bottom of the unit control the amounts of outdoor air and return air brought into the unit The air passes through the filter section and enters the fan section where the fan blows it across the coil CE...

Страница 422: ...E control cycles may be implemented by pneumatic electric electronic or digital control STANDBY WARMUP STAGE Duringcoldr oomper iods allthr eecyclespositionthev alves and damper s the same Figure 23 shows the standb y warmup stageinwhichtheunitv entilatorfanisshutdo wn man uallyor bytimeclock Theoutdoorairdamperisc losed andther etur n airdamperisfullopen Thehea tingcoilvalveisopen Thecoil acts as...

Страница 423: ...nto the room below 13 C Fig 24 Unit Ventilator Cycle I Control CYCLE II FIXED MINIMUM PERCENTAGE OF OUTDOOR AIR Cycle II contr ol Fig 25 pr ovides a fixed minim um percentageofoutdoorair usually10to33percent adjustable from 0 to 100 percent Atlowspacetemper atur es theoutdoorairdamperisc losed andthehea tingcoilvalveandfacedamperar efullopen Asspace temper atur erises theoutdoorairdampermo vestoit...

Страница 424: ...can be oper ated at lower setpoints dur ing unoccupied hour s to save ener gy Two commonl y used da y night systems ar e individual r oom day night contr ol and z one day night control Pneumatic actuation is preferred for unit ventila tor contr ol because it oper ates smoothl y and c hang es modesofoperationthroughasimplepressurechange Individual r oom day night contr ol uses a da y night r oom th...

Страница 425: ...l including PID control enhanced digital control and graphicdispla y Figur e 27 is of a DDC ASHRAE Cyc le III basic system Unlessthespacetemper atur eisbelowsetpointthef andischar ge temper atur e is constant a t 13 C The space sensor modula tes the HW valve for comfort control Other than PI control and friendly displa y of values and setpoints this figur e is the standar dcycleIII Figure 28 utili...

Страница 426: ...In the unoccupied mode the valve is contr olled in a tw o positionmannertomaintainanunoccupiedcon vectionhea ting roomtemperaturesetpoint Iftheroomtemperaturecannotbe maintainedb yconvectionhea ting thefaniscycledtomaintain the unoccupied hea ting fan on setpoint The face damper is open and the O A damper is c losed Figure 29 adds a chilled water coil to F igure 28 RA FAN M15315 OA CONTROL PROGRAM...

Страница 427: ...SETPOINT HEATING LOAD PERCENT FREE COOLING LOAD PERCENT COOLING LOAD PERCENT 100 100 100 0 0 0 FREE COOLING SETPOINT HOT WATER VALVE O U T S I D E A I R D A M P E R C H I L L E D W A T E R V A L V E H O T W A T E R V A L V E FAN ON OCCUPIED MODE OPEN ON CLOSED OFF FAN ON SETPOINT CONVECTION SETPOINT FACE DAMPER FAN UNOCCUPIED MODE OA DAMPER CLOSED 13 41 0 100 0 100 DISCHARGE TEMPERATURE SETPOINT H...

Страница 428: ...ughthecoils Coilscanalsofr eezewhenlow temper atur eoutdoorairleaks thr ough def ective damper s Frequent inspection of damper s should be made to detect bent and br oken damper linka ges war ped damper b lades and def ective or missing b lade seals tha t can contr ibute to coil fr eeze up Low temper atur e switches to stop the f an and c lose the OA dampershouldbepr ovidedwherefreezingOAcondition...

Страница 429: ... coil As space temper atur e rises the ther mosta t contr ol signal modula tes the valve to decr ease the amount of flow thr ough the coil and incr ease the b ypass flow around the coil At the upper end of the ther mosta t thr ottling r ange the valve is in the coil b ypass position elimina ting flow thr ough the coil The fan r uns contin uously or is stopped as space temper atur erisesabovesetpoi...

Страница 430: ...hen space temper atur e is satisfied The fan can be oper ated b y a local fan switch or a centr al time c lock FOUR PIPE HEATING COOLING SINGLE COIL Figure35showsthesingle coilmethodf orfour pipehea ting cooling Ather mosta tcontr olstwothr ee wayvalvestoregulate the flow of chilled or hot w ater into a single coil Fig 34 Four Pipe Heating Cooling Fan Coil Unit with a Split Coil C3030 1 DISCHARGE ...

Страница 431: ...vemultipleunits F ig 37 Thissystemr elieson loaddiversification Someunitsma ybecoolingwhileotherz ones operateinthehea tingcycle Inthiscase thewaterloopisasour ce toheatingunitsandasinktocoolingunits transferringheatfrom onetotheother Water looptemper atur esaremaintainedbetw een 21 C and32 C topr ovideanadequa teheatsour ceorhea tsink A centr alboilerto getherwithac hillerand orcoolingto wertempe...

Страница 432: ...he compressor in either the heating or cooling mode In others thechangeovervalveremainsinthehea tingorcoolingposition aslongasspacetemperatureisintheappropriaterange Whereacentr alwaterplantpr ovidesheating coolingsour ce water for the hea t pumps water contr ol is often pr ovided to conser ve water w hen the hea t pump c ycles off and w hen the water temper atur e is excessive for the load Valves...

Страница 433: ...temper atur es Selectingan yVAVboxwouldpr oduceagraphic of tha t box similar to those pr eviously shown in this section and all specif ied da ta suc h as space temper atur e setpoints minimumandmaximumairflowsetpoints etc Fig 39 ATU System Floor Plan Graphic VAV BOX MEN ELEVATOR LOBBY M10532 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V 23 7 V ...

Страница 434: ...rsandfancoilunitsandtheirassocia tedhea ting andcoolingplantsshouldbestartedbyaglobaloptimumstart programwiththeO Adamperc loseduntiloccupanc ytime See Chiller Boiler and Distr ibution System Contr ol Applica tions section f or ad ditional inf ormation on hot w ater systemcontrol Because unit v entila tor s have lar ge OA damper s in close proximity to the w ater coils the hot w ater pump should r...

Страница 435: ...SMOKE MANAGEMENT FUNDAMENTALS ENGINEERING MANUAL OF AUTOMATIC CONTROL 425 ENGINEERING INFORMATION ...

Страница 436: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL SMOKE MANAGEMENT FUNDAMENTALS 426 SMOKE MANAGEMENT FUNDAMENTALS ...

Страница 437: ...d Media 431 Valve Selection 432 Globe Valve 433 Ball Valve 433 Butterfly Valve 433 Two Way Valve 434 Quick Opening Valve 434 Linear Valve 434 Equal Percentage Valve 435 Three Way Valves 436 Mixing Valve 436 Diverting Valve 436 Valve Sizing 437 Water Valves 437 Quantity of Water 438 Water Valve Pressure Drop 438 Water Valve Sizing Examples 439 Steam Valves 441 Quantity of Steam 442 Steam Valve Pres...

Страница 438: ...p to contact the valve disc when closing off flow of the controlled fluid Stem The shaft that runs through the valve bonnet and connects an actuator to the valve plug Trim All parts of the valve that contact the controlled fluid Trim includes the stem packing plug disc and seat it does not include the valve body VALVE FLOW CHARACTERISTICS Directionofflow Thecorrectflowofthecontrolledfluidthrough t...

Страница 439: ...wing relationships Av 0 0000278 Kv Av 0 0000240 Cv Kv 0 865 Cv The flow coefficient Av is in cubic meters per second and can be determined from the formula Where Q volumetric flow in cubic meters per second ρ fluid density in kilograms per cubic meter p static pressure loss across the valve in pascals The flow coefficient Kv is water flow in cubic meters per hour with a static pressure loss across...

Страница 440: ...orrelation between safe permissible flowing fluid pressure and flowing fluid temperature of the valve body exclusive of the packing disc etc The nominal valve body rating is the permissible pressure at a specific temperature EXAMPLE A cast iron screwed end valve with a nominal rating of 850 kPa could have an actual rating of 850 kPa at 180 C and 1200 kPA at 65 C Maximum pressure and temperature Th...

Страница 441: ...force than a double seated valve Three way valve A valve with three ports The internal design of a three way valve classifies it as a mixing or diverting valve Three way valves control liquid in modulating or two position applications and do not provide tight shut off Two way valve A valve with one inlet port and one outlet port Two way valves control water or steam in two position or modulating a...

Страница 442: ...y closed valves or a variety of other control schemes Lower cost and more powerful normally open valve assemblies may be used with the close on shutdown feature and allow in the case of pneumatic systems the capability to provide heating or cooling in the event of air compressor failure Converter control valves should be normally closed and outdoor air preheat valves should be normally open Is tig...

Страница 443: ... at the half open position Fig 5 Two Way Globe Valves BALL VALVE Ball valves are available for two position applications either manual hand or power operated or for modulating applications with direct coupled electric actuators Ball valves are relatively low cost and provide tight close off and available in two way and three way configurations As with all other valves ball valves must be properly ...

Страница 444: ...l percentage valve is appropriate to balance the system so that resultant performance is linear SUPPLY LOAD RETURN C2329 TWO WAY VALVE 100 0 100 NONLINEAR SYSTEM RESPONSE RESULTANT LINEAR SYSTEM CONTROL EQUAL PERCENTAGE CONTROL VALVE TEMPERATURE PERCENTAGE OF FULL COOLING C2330 100 0 100 STEM TRAVEL FLOW C2331 90 20 QUICK OPENING CONTROL VALVE Fig 9 Flow vs Stem Travel Characteristic of a Quick Op...

Страница 445: ...tage Valve An equal percentage valve is used for proportional control in hot water applications and is useful in control applications where wide load variations can occur Typically in hot water applications large reductions in flow through the load e g coil cause small reductions in heat output An equal percentage valve is used in these applications to achieve linear control For example Figure 11 ...

Страница 446: ...imum pressure of 170 kPa on one inlet port maximum pressure of 140 kPa on the other inlet port and minimum downstream pressure of 70 kPa on the outlet port The close off pressure is 170 kPa 70 kPa 100 kPa The application requires a mixing valve with at least a 100 kPa close off rating The actuator selected must have a high enough force to operate satisfactorily In globe mixing valve applications t...

Страница 447: ... required Kv When the required Kv is not available in a standard valve select the next closest and calculate the resulting valve pressure differential at the required flow to verify to verify acceptable performance After determination of the valve Kv calculation of the flow of any medium through that valve can be found if the characteristics of the medium and the pressure drop across the valve are...

Страница 448: ...emoved in kJ kg Includes both sensible and latent heat 1 02 A scaling constant Tw Temperature difference of water entering and leaving the coil WATER VALVE PRESSURE DROP To determine valve pressure drop 1 For two way valves consider the following guidelines for valve pressure drop a Include the pressure drop in the design of the water circulating system In systems with two way valves only it is of...

Страница 449: ...o the three way valve input b The valve pressure drop should be equal to or greater than the drop through the boiler and the fittings If the valve drop is much smaller than the boiler pressure drop at design effective control is obtained only when the disc is near one of the two seats The mid portion of the valve lift will be relatively ineffective c A manual balancing valve may be installed in th...

Страница 450: ...water specific gravity of water and pressure drop in the Kv formula shows that the Valve V5 should have a Kv of 223 Fig 16 Chiller Bypass Application EXAMPLE 3 Sizing water valves for heating coils is especially critical In Figure 17 a valve with a Kv of 10 will have 30 percent of the available pressure drop when full open while a valve with a Kv of 4 4 will have 70 percent of the available pressu...

Страница 451: ...pressure drop through a 80 mm tee and the piping from the valve and the tee to the exchanger is 0 62 kPa Heat exchanger pressure drop is 4 2 kPa Total pressure drop from bypass connection through the heat exchanger and to the hot water input of the three way valve is 4 2 kPa 0 62 kPa or 4 82 kPa Select a linear valve providing close control with a capacity index of 73 STEAMVALVES Calculate the req...

Страница 452: ...eturn in kPa absolute Where Heat output Heat output in kJ kg 2325 kJ kg The approximate heat of vaporization of steam 2 For sizing steam coil valves Where m3 s Volume of air from the fan in cubic meters per second Ta Temperature difference of air entering and leaving the coil 4330 A scaling constant 2325 kJ kg The approximate heat of vaporization of steam 3 For sizing steam to hot water converter ...

Страница 453: ...ine capacity index for Valve V1 as follows Where Q The quantity of steam required to pass through the valve is found using the converter valve formula Q L s Tw 6 462 Where L s 5 2 L s water flow through exchanger Tw 10 kelvins temperature difference 6 462 A scaling constant Substituting this data in the formula Q 329 7 kilograms per hour P The pressure drop across a valve in a modulating applicati...

Страница 454: ...and pressure drop in the Kv formula shows that Valve V1 should have a Kv of 22 3 or the next higher available value Kv Q 0 224 P P o Kv Q 0 224 P P o Kv 325 0 224 48 102 325 0 224 x 69 97 20 7 Kv 325 0 224 18 132 29 8 Select a linear valve providing close control with a capacity index of 22 3 and meeting the required pressure and temperature ratings EXAMPLE 3 Figure 20 shows the importance of sele...

Страница 455: ...ection Dampers 451 Baffles 451 Typical Damper Construction 452 Performance Data 452 Leakage Ratings 452 Torque Requirements 454 Velocity Ratings 454 Temperature Ratings 454 Pressure Ratings 454 UL Classification Fire Smoke 454 Application Environment 454 Velocity 454 Static Pressure 455 Temperature 455 Corrosion 455 Turbulence 455 Nuclear Seismic Applications 455 Actuators and Linkages 455 Normall...

Страница 456: ...stic 458 Installed Characteristic 458 Determining Damper Size 459 Other Damper Sizing Considerations 461 Two Position Control 461 Modulating Control 461 Oversized Damper Characteristics 461 Damper Performance 461 Control System Sensitivity 461 Damper Pressure Drop 462 Damper Applications 463 Mixed Air Control 463 Face and Bypass Control 464 Throttling Control 464 ...

Страница 457: ...damper or control valve in a control system Baffle An orifice placed in the duct to reduce the duct size to the damper size Damper seals Construction features used to minimize the leakage through a damper Dampersystem Thedamperplustheseriesresistancethatrelates to it e g duct work mixing boxes diffusers and coils Damper A device used to regulate the flow of air in an HVAC system by modulating or t...

Страница 458: ...ducts in sizes similar to rectangular ducts The smallest sizes of round dampers have a butterfly type blade while larger ones might be multiblade Fig 3 Round Damper LOW LEAKAGE DAMPERS Low leakage dampers minimize the amount of leakage through a fully closed damper This can increase the energy efficiency of the control system the comfort level in occupied spaces and the safe operation of control e...

Страница 459: ... foil blades also reduce noise and provide lower full open airflow resistance at higher velocities C2397 Fig 9 Reinforced Standard Damper Blade C2387 BLADE EDGE SNAP ON SEAL WORKS WITH COMPRESSION AND OR AIR PRESSURE Fig 7 Inflatable Blade Edge Seal Blade side seals minimize leakage between the ends of the blades and the frame Fig 8 One type of side seal is a stainless steel or coated spring steel...

Страница 460: ...aximum B and Maximum A Maximum B Damper testing includes meeting material construction requirements cycling temperature degradation dust loading salt spray exposure leakage and operation at maximum pressure and velocity In testing for temperature degradation the damper is heated in the closed position for 30 minutes and then cycled to see that it operates as intended Temperature classifications in...

Страница 461: ...necting damper blade linkage for a multiple section damper As a multiple section damper assembly increases in size additional precautions are required to withstand pressure drop forces including Increased bracing at intersecting corners of individual dampers Additional external supports from the damper frame near the center of the assembly to other solid structural members adjacent to the assembly...

Страница 462: ...305m high x 1 22m wide However there is significantly more leakage with the 1 2m high x 0 305m wide damper due to the increased number of blades Using the leakage performance graph in Figure 18 the range of leakage for these two dampers 0 37 m2 each at 0 249 kPa is Leakage Area x Rating m2 Minimum Leakage 0 37 x 0 05 min 0 018 m3 s Maximum Leakage 0 37 x 0 13 max 0 47 m3 s Performance characterist...

Страница 463: ...ER DEPENDS UPON THE HEIGHT AND WIDTH RELATIONSHIP AS WELL AS THE AREA THE SHADED AREA SHOWS THE RANGE OF LEAKAGE FOR A GIVEN AREA NOTE TORQUE APPLIED TO DAMPER 6 Nm m2 OF DAMPER AREA M15302 A DIMENSION LEAKAGE L s B DIMENSION LEAKAGE L s A DIMENSION B DIMENSION TOTAL LEAKAGE B DIMENSION LEAKAGE A DIMENSION LEAKAGE WHERE A DIMENSION OUTSIDE DIMENSION PARALLEL TO THE DAMPER BLADES B DIMENSION OUTSID...

Страница 464: ...itions PRESSURE RATINGS The pressure rating of a control damper is the maximum static pressure differential which may be applied across the assembly when the blades are closed Excessive leakage caused by deflection of blades and abnormally high operating torque due to forces on blades and loads on bearings and linkages can result fromhighdifferentialpressure Inextremecases physicaldamage to the da...

Страница 465: ...preferred in many cases Optionally protective finishes are available The requirement for corrosion resistant dampers usually necessitates a custom built damper TURBULENCE The flow of air in an air handling system is turbulent Excessive turbulence or pulsations can have the same effects on dampers as increasing air velocity There is a direct relationship between air velocity and the turbulence caus...

Страница 466: ...tor position the feedback mechanism causes the actuator to correct its position It also minimizes any effect of hysteresis inherent in the actuator It is not recommended to use more than one positive positioner per bank of dampers multiple sections connected together MULTIPLE ACTUATORS Multiple actuators can drive sections of a multiple section damper Fig 22 in unison Multiple sections should be a...

Страница 467: ...oversized dampers which produce undesirable system control results Proper selection and sizing of dampers provides the following benefits Lower installation cost because damper sizes are smaller In addition smaller actuators or a fewer number of them are required Reduced energy costs because smaller damper size allows less overall leakage Improved control characteristics rangeability because the r...

Страница 468: ...ARACTERISTIC The inherent characteristic is based on a constant pressure drop across the damper This is frequently not the case in practical applications Series resistance elements such as duct resistance coils and louvers cause the pressure drop to vary as the damper changes position Fig 26 and 27 The resulting installed characteristic Fig 28 is determined by the ratio of series resistance elemen...

Страница 469: ...1 20 10 or For parallel blade dampers Damper resistance 29 of total resistance or For opposed blade dampers or damper resistance 9 of total resistance For example if a coil Fig 31 with a pressure drop of 0 140 kPa is located in series with an opposed blade damper the damper should have a pressure drop of 0 014 kPa 10 percent of 0 140 0 014 2 5 100 damper resistance 1 10 100 damper resistance 1 9 1...

Страница 470: ...io 1 0 0859 x pressure drop 0 3903 For pressure drops Step 3 57 1 Pa Ratio 1 0 3214 x pressure drop 0 2340 5 Calculate damper area m2 For parallel blade dampers Damper area m2 Duct area m2 x ratio x 1 2897 0 9085 For opposed blade dampers Damper area m2 Duct area m2 x ratio x 1 4062 0 9217 a The free area of a damper is the open portion of the damper through which air flows The free area ratio is ...

Страница 471: ...stem pressure drop across the damper The oversized damper characteristic is based upon a majority of the system pressure drop being across the series resistance rather than the damper The actual curve can approach the linear curve if the proper initial resistance ratio for the damper has been selected See Figure 32 An oversized parallel blade damper causes a greater deviation from the linear chara...

Страница 472: ...following Steps 2 Calculate the free area ratioa For parallel blade dampers the free area ratio is found Ratio 0 0798 x damper area m2 0 1007 x Damper area m2 Duct area m2 For opposed blade dampers the free area ratio is found Ratio 0 0180 x damper area m2 0 0849 x Damper area m2 Duct area m2 3 Using the ratio from Step 1 calculate the pressure drop at 5 08 m s For ratios 0 5 Pressure drop Pa 11 6...

Страница 473: ...door air and exhaust air provide a more linear characteristic for these systems The return damper is still the primary source of pressure drop in its system so a parallel blade damper is used to minimize pressure drop yet maintain a linear characteristic Control Application Damper Type Return Air Parallel Outdoor Air or Exhaust Air with Weather Louver or Bird Screen Opposed without Weather Louver ...

Страница 474: ...37 shows a face and bypass damper application The system pressure drop is relatively constant across the bypass damper so a parallel blade damper is used for minimum pressure drop at full flow The system pressure drop across the face damper shifts from the coil to the damper as the damper closes so an opposed blade damper is used for more linear control The face damper should be equal to the coil ...

Страница 475: ...perature 468 Heat Transfer 470 Velocity 470 Flow 470 Power 471 Work Energy 471 Enthalpy 472 Force 472 Torque 472 Density 472 Electrical Data 473 Electrical Distribution Systems 473 General 473 Single Phase System 473 Three Phase Three Wire Wye System 474 Three Phase Four Wire Wye System 474 Three Phase Delta System 474 Electric Motors 475 Voltage Conversion 475 Properties of Saturated Steam Data 4...

Страница 476: ...0 2 0 01 milli m 10 3 0 001 micro µ 10 6 0 000 001 nano n 10 9 0 000 000 001 Psi kPa Psi kPa 1 2 3 4 5 7 14 21 28 34 16 17 18 19 20 110 117 124 131 138 6 7 8 9 10 41 48 55 62 69 21 22 23 24 25 145 152 159 165 172 11 12 13 14 15 76 83 90 97 103 26 27 28 29 30 179 186 193 200 207 Desired Unit Existing Unit Pounds per Sq In psi Kilo pascals kPa Ounces per Sq In Millimeters of Mercury Kilogram force p...

Страница 477: ...g Unit Inches in Feet ft Meters m Millimeters mm Miles mi Kilometers km Inches in 0 083 0 0254 25 4 0 0000158 0 0000254 Feet ft 12 0 3048 304 80 0 0001894 0 0003048 Meters m 39 37 3 281 1 000 0 0006214 0 001 Millimeters mm 0 03937 0 003281 0 001 0 0000006 0 00001 Miles mi 63 360 5 280 1 609 344 1 609 344 1 6093 Kilometers km 39 370 3 281 1 000 1 000 000 0 6214 Centimeters cm x 10 millimeters mm Mi...

Страница 478: ...nce Fahrenheit and Celsius scales coincide at 40 the following alternate formulas may be used Temperature in degrees F 9 5 x degrees C 40 40 Temperature in degrees C 5 9 x degrees F 40 40 NOTE A temperature range or span does not require the factors to adjust the zero reference of the temperature scales A range or span is denoted as Degrees Fahrenheit or Degrees Kelvin K and converted as follows D...

Страница 479: ... 20 28 89 29 44 30 00 30 56 31 11 31 67 32 22 32 78 33 33 33 89 10 23 33 3 89 24 44 25 00 25 56 26 11 26 67 27 22 27 78 28 33 0 17 78 18 332 18 89 19 44 20 00 20 56 21 11 21 67 22 22 22 78 For Temperatures Above 0F Temp F 0 1 2 3 4 5 6 7 8 9 0 17 78 17 22 16 67 16 11 15 56 15 00 14 44 13 89 13 33 12 78 10 12 22 11 67 11 11 10 56 10 00 9 44 8 89 8 33 7 78 7 22 20 6 67 6 11 5 56 5 00 4 44 3 89 3 33 ...

Страница 480: ...0 016667 Meters per second m s 196 8 3 281 60 Desired Unit Existing Unit Cubic Feet per minute cfm Cubic Feet per seconds cfs Cubic Meters per second m3 s Liters per second L s Cubic Feet per minute cfm 0 016667 0 0004719 0 4719 Cubic Feet per second cfs 60 0 02832 28 32 Cubic meters per second m3 s 2119 35 31 1000 Liters per second L s 2 119 0 03531 0 001 Desired Unit Existing Unit Cubic feet per...

Страница 481: ... has the potential to do work One ft lb is the work required to raise a weight of one pound one foot or the potential energy possessed by that weight after being raised in reference to its former position See TORQUE for pound foot Desired Unit Existing Unit British Thermal Unit Hour Btuh British Thermal Unit Minute Btu min Foot Pounds Minute ft lb min Foot Pounds Second ft lb s Horse power hp Boil...

Страница 482: ...a Pound Force Foot lbf ft a Pound Force Inch lbf in a Newton Meter Nm Kilogram Force Meter kgf m 1388 7 7 2329 86 795 9 8067 Ounce Force Inch Ozf in a 0 00072 0 00521 0 0625 0 0070618 Pound Force Foot lbf ft a 0 138257 192 0 12 0 1 3557 Pound Force Inch lbf in a 0 01152 16 0 0 0833 0 1130 Newton Meter Nm 0 10197 141 61 0 7376 8 850 a Torque is a turning effort caused by a force acting normal to a ...

Страница 483: ... capacitors are often added to balance the inductance of motor and fluorescent light loads and bring the PF closer to one Powerdistributedtoaloadiseithersingle phaseorthree phase Thesystemsforsmallloadsareusuallysingle phase Thesystems for heavy loads are usually three phase Three phase systems are three single phase circuits arranged such that each phase reaches its peak at a different time Fig 2...

Страница 484: ...ase power for heavier loads The single phase power is the same as described in SINGLE PHASE and the three phase power is the same as described in THREE PHASE THREE WIRE WYE SYSTEM C1813 120V 120V 120V E3 120V E6 208V E5 208V E1 120V A B N C E4 208V E2 120V The total power is the sum of the power in the three coils Fig 5 Three Phase Four Wire Wye Connected Transformer THREE PHASE DELTA SYSTEM The l...

Страница 485: ...eld connected in series Operates on dc or ac with approximately the same speed and torque Where either ac or dc may be available Used for portable tools vacuum cleaners electric typewriters etc Split Phase Starting Uses a pair of field windings for starting with one winding slightly lagging One winding is disconnected by a centrifugal switch when running speed is reached Where starting torque and ...

Страница 486: ... 800 900 1000 1100 1200 170 41 175 36 179 88 184 07 187 96 0 2403 0 2148 0 1943 0 1774 0 1632 0 4902 0 4635 0 4408 0 4212 0 4040 400 0 450 0 500 0 550 0 600 0 720 94 742 64 762 61 781 13 798 43 2667 5 2772 1 2776 2 2779 7 2782 7 2667 5 2772 1 2776 2 2779 7 2782 7 1300 1400 1500 1600 1700 191 61 195 04 198 29 201 37 204 31 0 1511 0 1407 0 1317 0 1237 0 1166 0 3887 0 3751 0 3629 0 3517 0 3415 650 0 ...

Страница 487: ...0 96 1 02 1 09 1 15 1 23 1 31 1 39 1 48 1 58 1 69 1 80 1 93 20 1 00 1 06 1 12 1 19 1 27 1 35 1 44 1 54 1 64 1 75 1 87 2 00 30 1 03 1 09 1 16 1 23 1 31 1 40 1 49 1 59 1 69 1 81 1 93 2 07 40 1 06 1 13 1 20 1 28 1 36 1 44 1 54 1 64 1 75 1 87 2 00 2 13 50 1 10 1 17 1 24 1 32 1 40 1 49 1 59 1 69 1 81 1 93 2 06 2 20 60 1 13 1 20 1 28 1 36 1 44 1 54 1 64 1 74 1 86 1 99 2 12 2 27 70 1 17 1 24 1 31 1 40 1 ...

Страница 488: ... 432 50 26 807 557 50 30 435 1200 00 44 652 60 00 9 985 185 00 17 532 310 00 22 695 435 00 26 884 560 00 30 503 1225 00 45 115 62 50 10 190 187 50 17 650 312 50 22 787 437 50 26 961 562 50 30 571 1250 00 45 573 65 00 10 392 190 00 17 768 315 00 22 877 440 00 27 038 565 00 30 639 1275 00 46 027 67 50 10 590 192 50 17 884 317 50 22 968 442 50 27 115 567 50 30 707 1300 00 46 476 70 00 10 785 195 00 1...

Страница 489: ...s Figure 7 is used to determine the maximum water vapor content of compressed air at various temperatures and pressures EXAMPLE Assume ambient conditions are 25 C and 80 percent rh The air is compressed and stored in a tank at 310 kPa and 30 C Air is delivered to the controls at 240 kPa 4 6 8 10 14 16 18 20 22 24 26 28 30 32 34 36 38 12 2 40 15 10 5 0 5 10 15 20 25 30 35 40 45 COMPRESSED AIR TEMPE...

Страница 490: ...isture per kilogram of dry air This means that 0 8 grams of moisture per kilogram of dry air condenses and collects in low places in the tubing As the compressed air temperature is reduced further as it passes through air at a lower ambient temperature additional moisture will condense This may plug filters and restrictors in controllers or collect in valve or damper actuators The problem is contr...

Страница 491: ...81 RELATIVE HUMIDITY Fig 8 Relative Humidity for Normal Dry Bulb and Wet Bulb Temperatures DRY BULB TEMPERATURE C TEMPERATURE DIFFERENCE TEMP DB TEMP WB KELVINS 2 0 4 0 5 0 6 0 8 0 9 0 5 0 0 1 2 3 4 5 6 7 8 5 15 10 M15328 3 0 7 0 1 0 R E L A T I V E H U M I D I T Y 0 ...

Страница 492: ...EERING DATA 482 Fig 9 Relative Humidity for Low Dry Bulb and Wet Bulb Temperatures R E L A T I V E H U M I D I T Y 0 40 30 30 5 10 15 20 10 0 5 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 90 DRY BULB TEMPERATURE C TEMPERATURE DIFFERENCE TEMP DB TEMP WB KELVINS M15329 ...

Страница 493: ...INDEX ENGINEERING MANUAL OF AUTOMATIC CONTROL 483 INDEX ...

Страница 494: ...l 204 Ventilation control processes 209 Year round system control processes 248 Air Mixing Process 42 Air quality standard 151 Air Supply Equipment 65 Air Terminal Unit Constant Air Volume 402 Control 399 Dual Duct Pressure Independent 406 407 Dual Duct 406 Induction VAV 402 Parallel Fan 404 Pressure Independent Constant Volume 407 Dual Duct 406 Pressure Dependent 399 Series Fan 404 Single Duct VA...

Страница 495: ...uilding pressure balance 270 Butterfly Valve 431 433 C Capacity index 429 Capacity Relay 79 Celsius Fahrenheit Conversion Tables 469 Central Cooling Plants 302 Central plant 295 Centrifugal Chiller Control Application 303 307 Multiple Dissimilar 313 Multiple Similar 309 Single 302 Centrifugal Chiller Control with Absorption Chiller 313 Centrifugal Compressor 295 298 Changeover Control 87 Character...

Страница 496: ...olled medium 5 Controlled Variable 5 15 59 Controller 5 33 98 Configuration 133 DDC Configuration 135 Microprocessor Based 135 Programming 142 System Level 134 146 Zone level 133 145 Electric Classification 99 High Limit 101 103 111 Low Limit 102 103 111 Series 40 100 Series 60 Floating 106 Series 60 Two Position 103 Series 80 102 Series 90 107 Spdt 106 Electronic 121 127 Enthalpy 128 Relative Hum...

Страница 497: ...50 Damper Control 105 Damper Selection and Sizing 445 Dampers 76 Data File Programming 143 Data Penetration 195 DDC 6 Deadband 6 295 Definitions Chiller Boiler And Distribution System Control 295 Dehumidification 12 Dehumidification and Reheat 52 Dehumidification control processes 243 Dehumidifier Air Washer 51 Density 38 Density Conversion Multipliers 472 Desiccant Drying 67 Design considerations...

Страница 498: ... 473 Three Phase Delta System 474 Three Phase Four Wire Wye System 474 Three Phase Three Wire Wye System 474 Electronic Indicating Devices 129 Output Control 128 Output Devices 128 Power Supply 129 System Application 130 Transducer 129 Electronic Control 6 120 Electronic Control Fundamentals 119 Electronic Control Systems 120 Electronic Controller 121 129 Electronic Pneumatic Transducer 83 Electro...

Страница 499: ... Exchanger Substation 381 Heat pump 11 421 Operation 421 Heat Recovery System 323 Heat Surface Factor 381 Heat Transfer Station 381 Heating 9 Heating Anticipation 102 Heating coil 10 Heating control processes 223 Heating Process 43 Heating system control processes 246 HEPA filter 152 Hesitation Relay 82 Hierarchical Configuration 184 High Temperature Water Control Selection 375 Heating System Cont...

Страница 500: ...ipulated variable 6 15 60 Manual Minimum Positing of Outdoor Air Damper 113 Manual Positioning Switch 84 Manual Switch Control 86 Materials safety data sheets 152 Measured variable 6 Metric Prefixes 466 Microprocessor based control 6 Microprocessor Based Controller 133 135 Microprocessor Based DDC Fundamentals 131 Microprocessor Based Systems 120 Mixed Air 60 Mixing Valve 436 Modulating 6 60 Modul...

Страница 501: ...Dual Duct 407 VAV ATU Dual Duct 406 Pressure Reducing Stations District Heating 383 Pressure Reducing Valve Station 68 369 Pressure Reducing Valves 69 Pressure Sensor Electronic 127 Pressure sensors 277 Pressure Dependent ATU 399 Pressure Independent ATU 399 Primary Network 381 Process 6 Processor Management Level 184 Operations Level 184 Programming Configuration 138 Custom Control 138 Data File ...

Страница 502: ...80 Snap Acting 78 Switching 77 Series 40 100 Relays and Switches 64 77 Remote Setpoint 121 Requirements for effective control 204 Reset from Outdoor air temperature 225 Hot deck temperature 226 Hot Water 361 Negative 121 Positive 121 Supply Air Temperature 221 224 225 Reset Authority 23 120 Reset Changeover 59 Reset Control 7 22 60 87 121 Resistance Temperature Devices 122 124 Restrictor 60 62 Ret...

Страница 503: ...plication 133 137 Building Management 142 Direct Digital Control 137 Operating 133 134 Solenoid Brake 97 100 101 Solenoid Valve 128 Specific Volume 39 Spring Range 74 Stack effect 271 Starters 114 Steam Heating Devices 371 Pressure Temperature and Density 367 Properties 366 Quality 367 System Objectives 366 Steam Coil Low Temperature Protection 373 Performance Modulating 371 System Design Consider...

Страница 504: ...tronic to Pneumatic 129 Transformer 99 Transmission 9 Transmitter Electronic 121 125 127 Turndown 429 Twisted Copper Pair 188 Two Pipe Steam Systems 370 Two Position Control 7 17 105 Electric 107 Two Pressure Reducing Valve 69 Two Way Valve 431 434 U Unbalanced loading 295 Unit Heater 10 409 Control 101 410 Modulating 410 Two Position 410 Down Blow 410 Gas Fired 411 Oil Fired 411 Unit Ventilator 1...

Страница 505: ...pumping VSP 296 Variable Vacuum Return Systems 371 Velocity Conversion Multipliers 470 Velocity Pressure 478 Velocity Sensor Controller 73 Ventilation 10 13 Ventilation control processes 209 Volatile organic compound 153 Voltage Conversion 475 Volume Conversion Multipliers 468 W Warmup control 285 Water Valves Sizing 437 Weight Mass Conversion Multipliers 467 Wet Bulb Temperature 39 Wind pressure ...

Страница 506: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL INDEX 496 NOTES ...

Страница 507: ...INDEX ENGINEERING MANUAL OF AUTOMATIC CONTROL 497 NOTES ...

Страница 508: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL INDEX 498 NOTES ...

Страница 509: ...INDEX ENGINEERING MANUAL OF AUTOMATIC CONTROL 499 NOTES ...

Страница 510: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL INDEX 500 NOTES ...

Страница 511: ...INDEX ENGINEERING MANUAL OF AUTOMATIC CONTROL 501 NOTES ...

Страница 512: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL INDEX 502 NOTES ...

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