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ENGINEERING MANUAL OF AUTOMATIC CONTROL

CHILLER, BOILER, AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS

391

Fig. 136. DDC Control of Large High Performance Indirect Heat Transfer Substation.

TZA+

PZA–

PZA+

TIC

TZA+

PZA–

TIC

PZA–

TSA+

PZA+

TSA+

T1
21

T1
31

PDIC

110

QIR

111

LIC

PIC

PSA+

QIR

LIC

DDC

OUTSIDE AIR

SUPPLIER

CENTRAL
SYSTEM

SUBSTATION

CONSUMER

PSF

PRF

SSF

SRF

COLD WATER

WATER SUPPLY TANK

EXPANSION TANK

M11429

HEX1

HEX12

Summary of Contents for AUTOMATIC CONTROL

Page 1: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL i HONEYWELL ENGINEERING MANUAL of AUTOMATIC CONTROL for COMMERCIAL BUILDINGS ...

Page 2: ...71 Honeywell 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 Honeywel...

Page 3: ...ems Through the years 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 manua...

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

Page 5: ...efinitions of terms are provided within individual sections For maximum usability each section of this manual is available as a separate self contained document 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...

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

Page 7: ...sychrometric Chart 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 Centeralization 89 Pneumatic Control System Example 90 Electr...

Page 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 Principles 175 Control Applications 178 Acceptance Testing 181 L...

Page 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 267 Airflow Control Applications 281 References 292 Chiller Boiler and Distribution System Control Applications 293 Introduction 297 Abbreviations 297 Definitions 297 Symbols 298 Chiller...

Page 10: ...1 Damper Selection and Sizing 451 Introduction 453 Definitions 453 Damper Selection 454 Damper Sizing 463 Damper Pressure Drop 468 Damper Applications 469 General Engineering Data 471 Introduction 472 Weather Data 472 Conversion Formulas And Tables 475 Electrical Data 482 Properties Of Saturated Steam Data 488 Airflow Data 489 Moisture Content Of Air Data 491 Index 494 ...

Page 11: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL CONTROL FUNDAMENTALS 1 CONTROL SYSTEMS FUNDMENTALS ...

Page 12: ......

Page 13: ...ntrol 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 Integral Deri...

Page 14: ...ime 29 Control Application Guidelines 29 Control System Components 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 ...

Page 15: ...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 control...

Page 16: ...int in the system or some other condition to which it is related Also the delay in response of the sensing 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 c...

Page 17: ...h the controller is set e g the desired room temperature set on a thermostat The desired control point Short cycling See Cycling Step control Control method in which a multiple switch assembly sequentially switches equipment e g electric heat multiple chillers as the controller input varies through the proportional band Step controllers may be actuator driven electronic or directly activated by th...

Page 18: ...ol 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 Tabl...

Page 19: ... heat to maintain temperature Boiler control Operates burner to maintain proper discharge steam pressure or water temperature For maximum efficiency in a hot water system water temperature should be reset as a function of demand or outdoor temperature Table 1 Functions of Central HVAC Control Loops HEATING GENERAL Building heat loss occurs mainly through transmission infiltration exfiltration and ...

Page 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...

Page 21: ...ng 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 enou...

Page 22: ...city can be controlled by unloading cylinders Absorption refrigeration systems which use heat energy directly to produce chilled water are sometimes used for large chilled water systems While heat pumps are usually direct expansion a large 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 an...

Page 23: ...o reduce 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 ...

Page 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...

Page 25: ...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 AND EQUIPMENT HANDBOOK PATH OF IO...

Page 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...

Page 27: ...osition 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 controlled var...

Page 28: ...pation 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 two position control Fig 23 Fig 23 Comparison of Basic Two Position and Timed Two Position Control HEAT ANTICIPATION In electromechanical control timed two position control can be achieved by adding a heat anticipator to a bimetal ...

Page 29: ... 1 NO LOAD TEMPERATURE 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 control is a lowering of the control point as the load on the system increases In cooling control droop is a...

Page 30: ...c pressure in a duct Fig 29 ON OFF ON OFF ON OFF ON OFF 4 3 2 1 DIFFERENTIAL THROTTLING RANGE 76 SPACE TEMPERATURE F 72 100 0 LOAD C2093 STAGES 74 SETPOINT 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 va...

Page 31: ...l and thus the discharge temperature 73 74 75 76 77 100 OPEN 50 OPEN CLOSED POSITION OF FINAL CONTROL ELEMENT ACTUATOR POSITION CONTROL POINT F THROTTLING RANGE C2095 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 ...

Page 32: ... as the load 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 Outdoor Air Discharge Air Temperature Temperature Condition F F Outdoor design temperature 0 100 Light load 70 70 100 70 0 FULL RESET 70 RESET START OUTDOOR AIR TEMPERATURE F DISCHARGE AIR TEMPERATURE SETPOINT F ...

Page 33: ...nge in compensation input x 100 Fig 35 Discharge Air Control Loop with Reset Compensation can either increase or decrease the 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 v...

Page 34: ...t 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 t...

Page 35: ...ime K T1 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 C21...

Page 36: ...ces Demand 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 Dema...

Page 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...

Page 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...

Page 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...

Page 40: ...perature pressure relative humidity and flow TEMPERATURE SENSING ELEMENTS The sensing element in a temperature sensor can be a bimetal strip a rod and tube element a sealed bellows a sealed bellows attached to a capillary or bulb a resistive wire or a thermistor Refer to the Electronic Control Fundamentals section of this manual for Electronic Sensors for Microprocessor Based Systems A bimetal ele...

Page 41: ...perature 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 small vol...

Page 42: ...onstant 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 nylon elements and can be factored into electronic sensor values if required Dew point is the temperature at which...

Page 43: ...e 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 mechanical sensor input such as a bimetal or an electric input such as a resistance element or thermocouple A microprocessor controll...

Page 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 ...

Page 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...

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

Page 47: ... 39 The Abridged Psychrometric Chart 40 Examples of Air Mixing Process 42 Air Conditioning Processes 43 Heating Process 43 Cooling Process 44 Humidifying Process 44 Basic Process 44 Steam Jet Humidifier 46 Air Washes 49 Vaporizing Humidifier 50 Cooling and Dehumidification 51 Basic Process 51 Air Washes 51 Dehumidification and Reheat 52 Process Summary 53 ASHRAE Psychrometric Charts 53 ...

Page 48: ...he air are known the dew point temperature can be plotted on the psychrometric chart Fig 4 Dry bulb temperature The temperature read directly on an ordinary thermometer Isothermal process A process in which there is no change of dry bulb temperature 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 calle...

Page 49: ... Water evaporation causes the temperature reading to be lower than the ambient dry bulb temperature by an amount proportional to the moisture content of the air The temperature re duction is sometimes called the evaporative effect When the reading stops falling the value read is the wet bulb temperature The wet bulb and dry bulb temperatures are the easiest air properties to measure When they are ...

Page 50: ...ty all lines are straight Wet bulb lines and enthalpy total heat lines are not exactly the same so care must be taken to follow the correct line The dry bulb lines are not necessarily parallel to each other and incline slightly from the vertical position The purpose of the two enthalpy scales one on the protractor and one on the chart is to provide reference points when drawing an enthalpy total F...

Page 51: ... 4 PointA the following values can be read Wet bulb temperature is 67 5F Point A Volume is 13 8 cubic feet per pound of dry air Point A Dew point is 62 5F Point B Moisture content is 0 012 pounds of moisture per pound of dry air Point C Enthalpy is 31 6 Btu per pound of dry air Point D Density is 0 0725 pounds per cubic foot reciprocal of volume 77 F DB C A D E 31 6 BTU LB 0 012 LB LB 62 5 F DP 67...

Page 52: ... the line drawn in Step 2 intersects the 62F dry bulb line Point 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 to 50F temperature range This is the temperature range immediat...

Page 53: ... the mixed air moisture content 2 3 x 0 0094 1 3 x 0 00065 0 00648pounds of moisture per pound of dry air 5 Using the enthalpy value of 19 8 and the moisture content value of 0 00648 plot the mixed air conditions Point C on Chart No 1 Figure 9 by drawing a horizontal line across the chart at the 0 00648 moisture content level and a diagonal line parallel to the enthalpy lines starting at the 19 8 ...

Page 54: ...rcentage relative humidity at 70F than at 90F Calculate the total heat removed as follows B A C1836 90 F DB 50 RH SUPPLY FAN COOLING COIL AIRFLOW 70 F DB 95 RH 37 9 BTU LB 33 3 BTU LB 70 F DB 95 RH 90 F DB 50 RH Fig 12 Total heat at Point A total heat at Point B total heat removed 37 9 33 3 4 6 Btu per pound of dry air This is all sensible heat since there is no change in moisture content HUMIDIFY...

Page 55: ...ound of dry air 3 The moisture required is 0 0056 0 0006 0 005 pounds of moisture per pound of dry air Line A B Figure 15 represents this humidifying process on the psychrometric chart C1838 A 70 F DB 4 5 RH 0 0006 LB LB FROM CHART 2 Fig 15 The space contains the following volume 30 x 40 x 8 9600 cubic feet Two air changes per hour is as follows 2 x 9600 19 200 cubic feet per hour This amount of a...

Page 56: ...urrounded by a steam jacket The jacket is filled with 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 212F or higher The enthalpy includes the heat needed to raise the water temperature from 32 t...

Page 57: ...F DB 92 F DB 50 RH 0 0164 LB LB 0 0065 LB LB 1150 THIS LINE IS PARALLEL TO THE SOLID LINE C B ON THE PSYCH CHART CONSTRUCTION LINE C1841 S E N S IBLE HEAT T O T AL HEAT H S H T 1 0 0 8 0 6 0 5 0 4 0 3 0 2 0 1 5 0 0 0 3 0 0 0 2 0 0 0 1500 1000 5 0 0 1 0 0 0 0 1 0 3 0 5 1 0 2 0 4 0 1 0 2 0 ENTHALPY HUMIDITY RATIO h W 4 0 0 ...

Page 58: ...ENTHALPY STEAM ENTHALPY 1150 REFERENCE POINT 50 RH C1842 Fig 18 The remaining 0 9 Btu is sensible heat The actual moisture added per pound of dry air is 0 0099 pounds The specific volume of the entering air at Point B is 14 cubic feet per pound For a 10 000 cubic feet per minute system the weight of the air passing through is 10 000 14 714 3 pounds per minute The weight of the moisture added is 71...

Page 59: ... adiabatic and is illustrated by Figure 21 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 temper...

Page 60: ...d because of the heat in the water VAPORIZING HUMIDIFIER Vaporizing and water spray humidifiers operate on the principal of breaking water up into small particulates so they are evaporated directly into the air This process is essentially adiabatic since the enthalpy lines of the water vapor for 32 and 212F are so close The enthalpy of water at 32F is zero and at 212F it is 180 Btu per pound If ai...

Page 61: ...ing air the total moisture removed per pound of dry air can be read on the humidity ratio scale and is determined as follows 1 The entering air condition is 85F dry bulb and 63 percent rh Point A The moisture content is 0 0166 pounds of moisture per pound of dry air 2 The leaving air condition is 60F dry bulb and 93 percent rh Point C The moisture content is 0 0100 pounds of moisture per pound of ...

Page 62: ...ss line follows the Constant Enthalpy Line A C The water assumes the wet bulb temperature of the air as the process line extends Note that whenever 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 r...

Page 63: ... a constant moisture line When latent heat is added or removed a process line always crosses the constant moisture lines LATENT HEAT CHANGE SENSIBLE HEAT CHANGE C1851 Fig 31 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 HUMIDIFY...

Page 64: ...PSYCHROMETRIC CHART FUNDAMENTALS 54 ENGINEERING MANUAL OF AUTOMATIC CONTROL Fig 33 ASHRAE Psychrometric Chart No 1 ...

Page 65: ...PSYCHROMETRIC CHART FUNDAMENTALS 55 ENGINEERING MANUAL OF AUTOMATIC CONTROL Fig 34 ASHRAE Psychrometric Chart No 2 ...

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

Page 67: ... Sensing Elements 63 Bimetal 63 Rod and Tube 64 Remote Bulb 64 Averaging Element 64 Throttling Range Adjustment 64 Relays and Switches 65 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...

Page 68: ...80 Positive Positioning Relay 80 Ratio Relay 81 Pneumatic 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 T...

Page 69: ...er 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 the ...

Page 70: ...haft 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 3 and 15 psi Setpoint The value on th...

Page 71: ... into 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 18 to 22 psi For two pres...

Page 72: ...quired 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 escaping the branchline pressure increases proportionally When the spring tension preve...

Page 73: ... 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 of springs and valves A spring in the tube continually tries to force the ball ...

Page 74: ...ion 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 sensor is similar to the remote bulb ...

Page 75: ...rt as shown If the pilot pressure falls below the relay setpoint the diaphragm moves down blocks the normally disconnected X port and connects the normally connected port O to the common port GENERAL A pneumatic control system requires a supply of clean dry compressed air The air source must be continuous because many pneumatic sensors controllers relays and other devices bleed air A typical air s...

Page 76: ...oint 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 relationships at various air pressures refer to the General Engineeri...

Page 77: ...ith 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 12F dew point at 20 psi mainline pressur...

Page 78: ...CING 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 are the air filter and the PRV AIR FILTER The air filter Fig 16 re...

Page 79: ...ing at 20 and 25 psi are sometimes used to eliminate the need and expense of the second PRV Thermostats are of four basic types A low capacity single temperature thermostat is the basic nozzle flapper bleed type control described earlier It is a bleed one pipe proportional thermostat that is either direct or reverse acting A high capacity single temperature thermostat is a low capacity thermostat ...

Page 80: ...perature 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 1 degree F could result in a branchline pressure change of only 1 psi GENERAL A controller is the same as a thermostat except that it may have a remote sensing element A controller typically measures and controls temperature humid...

Page 81: ...ure controllers measure and control high pressures or vacuums measured in pounds per square inch or in inches of mercury e g steam or water pressures in an air conditioning system Low pressure controllers measure and control low pressures and vacuums measured in inches of water e g pressure in an air duct High and low pressure controllers have different size diaphragms In both types one side of th...

Page 82: ... 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 applica...

Page 83: ...n and operate on a force balance principle similar to a wall thermostat The low pressure sensor measures 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 c...

Page 84: ...ve 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 linkage for a butterfly valve Valve actuator strokes typically are between one quarter and one and one half in...

Page 85: ...mber 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 spring moves the diaphragm down toward its normal position and the valve stem tow...

Page 86: ...nstant 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 12 inches depending on the differential close off rating of the valve For other applications hig...

Page 87: ... SWITCHES In the following illustrations common C 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...

Page 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 ...

Page 89: ... input to the branch port Figure 40 shows a low pressure selector relay controlling the heating coil valve from the thermostat that calls for the most heat Fig 40 Typical Application for Low Pressure Selector Relay LOAD ANALYZER RELAY The load analyzer relay is a bleed type diaphragm logic pressure selector The relay selects the highest and lowest branch pressure from multiple inputs to operate fi...

Page 90: ...ay is typically used for large actuators for sequencing or in applications requiring precise control 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...

Page 91: ...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 input...

Page 92: ...actuate an air valve in an associated pneumatic circuit The pneumatic electric relay uses control air pressure to make or break an 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...

Page 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 3 to 15 psi 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 por...

Page 94: ...everal 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 56 Cooling applications may use normally closed valves and a direct acting thermosta...

Page 95: ...without positioners have various spring ranges To perform the sequencing application in Figure 59 without positioners select a heating valve actuator that has a 2 to 7 psi spring range and a cooling valve actuator that has an 8 to 13 psi spring range Although this method lessens precise positioning it is usually acceptable in systems with lower pressure differentials across the valve or damper and...

Page 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...

Page 97: ... 18 psi 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 whe...

Page 98: ...ation as the thermostat branchline pressure reaches 7 psi Relay 2 starts Fan 2 when the controller branchline pressure reaches 12 psi On a decrease in branchline pressure Relay 2 stops Fan 2 at 10 psi branchline pressure and Relay 1 stops Fan 1 at 5 psi 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 Sp...

Page 99: ... exhaust configuration 0 10 2 0 3 0 1 0 0 9 0 8 0 7 0 60 50 40 3 0 20 1 0 0 PSI DISCHARGE AIR TEMPERATURE OPEN ON RETURN AIR SUPPLY FAN OUTSIDE AIR AHU 6 ON OFF COOLING COIL M10297 4 11 PSI NORMALLY OPEN 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 c...

Page 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 temperatur...

Page 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...

Page 102: ...acceptable but is complex if varying exhaust is worked into the control scheme 2 Exercise care in selecting location of the inside pick up and in selection of the pressure controller Location of the reference pick up above the roof is recommended by ASHRAE 3 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 go...

Page 103: ...r vice versa in unison to maintain design outside air at 4000 cfm M Y Z M X P C X O SR 4 P C X O SR 5 2 EP DA 55 F B S M TC 3 L B M H P F RA OUTSIDE AIR 2 EP 1 EP TO WARM UP CONTROLS TS 1 6 11 PSI N O 4 11 PSI N O M M P E B RR FROM WARM UP CONTROL AIR DURING COLD RETURN M10302 SUPPLY FAN P O TO 20 B 20 TO 0 6 11 PSI CHW OPEN TO CLOSED AIR WHEN FAN ON TO HEATING COIL CONTROL AND TO CHILLER PLANT CO...

Page 104: ...TC 3 setpoint Controller TC 3 is a PI proportional plus integral controller NOTE In this constant 4000 cfm outside air system if the return air is 72F and the outside air is 5F the mixed air temperature will drop below 55F if the AHU 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 closes ...

Page 105: ...it Control 101 Low Limit 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 Valv...

Page 106: ...ge Circuit with Low Limit Control 110 Bridge Circuit with High Limit Control 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 fr...

Page 107: ...ters 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 commo...

Page 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...

Page 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...

Page 110: ...e controllers 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 co...

Page 111: ...uator 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 from ...

Page 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 ...

Page 113: ...losed 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 ha...

Page 114: ... a drop 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 the...

Page 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...

Page 116: ...ssure 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 ...

Page 117: ...djust 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 potentiome...

Page 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...

Page 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...

Page 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...

Page 121: ...OMBINATIONS 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...

Page 122: ...opening 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 withTwo Position High Limit HumidityController 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...

Page 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 ...

Page 124: ...nd then permits the step controller to recycle to the position called for by the thermostat Fig 34 Typical Step Controller System Step controllers can also be actuated by Series 60 floating controllers MOTOR CONTROL 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 p...

Page 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 Ov...

Page 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...

Page 127: ...FF 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 ca...

Page 128: ...ENGINEERING MANUAL OF AUTOMATION CONTROL ELECTRIC CONTROL FUNDAMENTALS 118 ...

Page 129: ...e 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 Devices 128 Two Position 128 Modulating 128 Transducer 129...

Page 130: ...tionar egeneral Aresistance temper atur e input and a 2 to 10V dc output are used for purposes of discussion Electr ic circuits ar e defined in Electr ic Contr ol Fundamentals A detailed discussion on contr ol modes can be foundintheControlFundamentalssection DEFINITIONS NOTE For definitions of ter ms not in this section see the ControlFundamentalssection Authority Compensation Authority or Reset ...

Page 131: ...dvariablemustpasstodr ivethefinalcontr ol elementthroughitsfulloperatingrange Proportional band is e xpressed in per cent of the main sensor span A commonl y used equi valent is thr ottling r ange whichisexpressedinvaluesofthecontr olledvariable Proportional control P A contr ol algorithm or method in which the final contr ol element mo ves to a position propor tional to the de viation of the v al...

Page 132: ...atisonorof f Thedigitalsensorpr ovidesthecontr ollerwith a discrete signal such as open or closed contacts Some electr onic sensor s use an inher ent a ttr ibute of their mater ial e g wire resistance to pr ovide a signal and can be directly connected to the electr onic contr oller Other sensor s requir e conversion of the sensor signal to a type or le vel tha t can be used b y the electr onic con...

Page 133: ... of 6 39 ohms Mft is used the 50 feet of wire has a total dc resistance of 0 319 ohms If the sensor is a 100 ohm platinum sensor with a temperature coefficient of 0 69 ohms per degree F the 50 feet of wire will introduce an error of 0 46 degrees F If the sensor is a 3000 ohm platinum sensor with a temperature coefficient of 4 8 ohms per degree F the 50 feet of wire will introduce an error of 0 066...

Page 134: ...ion Impr oved pac kaging and f ilm isolationha veeliminatedthesepr oblemsresultinginincr eased useofplatinumRTDsoverwir ewoundandNTCther mistor s LADDER NETWORK OF METALLIC FILM RESISTOR LASER TRIM INDICATEDBY GAPS IN LADDER NETWORK CONNECTION PADS C3098 Fig 4 Platinum Element RTD Sensor Solid State Resistance Temperature Devices Figure5showsexamplesofsolid sta teresistancetemper atur e sensorshav...

Page 135: ...utdoor exhaust dampers to maintain acceptable air quality levels 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 h...

Page 136: ...asure 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 relative humidity ...

Page 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...

Page 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...

Page 139: ...tric to Pneumatic Transducer Fig 20 Indicating Devices INTERFACE WITH OTHER SYSTEMS It is often necessary to interface an electronic control device to a system such as a microprocessor based building management 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 ...

Page 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...

Page 141: ...ecise and Accurate Control 135 Reliability 135 Controller Configuration 135 Types of Controllers 136 Zone Level Controller 136 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...

Page 142: ...ing 143 Data File Programming 143 Custom Control Programming 143 Analyze Control Application 144 Partition Into Control Loops 144 Determine Inputs and Outputs 144 Design Write and Compile Program 145 Debug Install Enter Data Files and Test 145 Typical Applications 145 Zone Level Controller 145 Example 1 VAV Cooling Only 145 Example 2 VAV Cooling with Sequenced Electric Reheat 145 System Level Cont...

Page 143: ...nfigurable controller A controller with a set of selectable programs with adjustable parameters but without the ability to modify the programs Digital to analog D A converter The part of a micropro cessor based controller that changes digital values from a software program to analog output signals for use in the control system The analog signals are typically used to position actuators or actuate ...

Page 144: ... various input devices such as the electronic temperature humidity and pressure sensors described in the section on Sensors Based on the digitized equivalents of the voltage or current signals produced by the inputs the control software calculates the required state of the output devices such as valve and damper actuators and fan starters The output devices are then moved to the calculated positio...

Page 145: ...for seasonal changes is eliminated These items are discussed in the Control Fundamentals section RELIABILITY Digital controllers should be conservatively designed and should incorporate self checking features so they notify the operator immediately if anything goes wrong Input and output circuits should be filtered and protected from extraneous signals to assure reliable information to the process...

Page 146: ...el Controllers ZONE LEVEL CONTROLLER Zone level controllers typically control HVAC terminal units that supply heating and cooling energy to occupied spaces and other areas in the building They can control VAV terminal units fan coil units unit ventilators heat pumps space pressurization equipment laboratory fume hoods and any other zone control or terminal unit device Design of a zone level contro...

Page 147: ...e the interrupt request is processed all data is returned to the proper registers and the program resumes where it left off Multiple levels or prioritized interrupts are provided The effect of these interrupts is transparent to the application that the controller is controlling APPLICATION SOFTWARE Application software includes direct digital control energy management lighting control and event in...

Page 148: ...n a different scale Analog controlled digital output Allows a digital output to change when an analog input reaches an assigned value Also has an assignable dead band feature Digital controlled analog output Functionally similar to a signal switching relay One state of the digital input selects one analog input as its analog output the other state selects a second analog input as the analog output...

Page 149: ...ystems during Night Purge to reduce energy usage Outdoor temperature outdoor RH or dewpoint and space temperature are analyzed One hundred percent outdoor air is admitted under the following typical conditions 1 Outdoor air above a summer winter changeover point such as 50F 2 Outdoor temperature below space temperature by a specified RH or determined differential 3 Outdoor air dewpoint less than 6...

Page 150: ...er unloads to maintain the raised setpoint d As the chilled water temperature increases the discharge air temperature increases e The space temperature control opens the valves to maintain the space temperature setpoint This response takes several minutes in space temperature control f The most demanding AHU valve opens to greater than 80 percent but less than 95 percent g The other AHU valves ope...

Page 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 FULL ON FULL OFF 70 73 75 78 TYPICAL SPACE TEMPERATURE RANGE F HEATING REGION ZERO ENERGY BAND COOLING REGION HEATING COOLING VENTILATION ONLY C2431 TOTAL COMFORT RANGE Fig 11 Zero Energy Band M10358 AUTO 46 68 73 74 77 79 70 64 69 79 74 ...

Page 152: ... 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 also be accumulate...

Page 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...

Page 154: ...chart should be drawn showing all relationships influencing the controlled variable between the controller and actuators START ANALYZE CONTROL APPLICATION REQUIREMENTS PARTITION INTO CONTROL LOOPS SYSTEM DRAWINGS AND SEQUENCES OF OPERATION DETERMINE INPUTS AND OUTPUTS FOR EACH LOOP DESIGN WRITE AND COMPILE PROGRAM RUN DEBUG AND SIMULATION PROGRAMS INSTALL PROGRAM AND ASSOCIATED DATA FILES STEP 1 S...

Page 155: ...e monitored 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 se...

Page 156: ...is entered or displayed in non BMS applications by a portable operator s terminal or by a keypad when display is integral with the controller A five step approach can be used to define DDC programs 1 Develop a system flow schematic as a visual representa tion of the process to be controlled The schematic may be provided as a part of the plans and specifications for the job If not a schematic must ...

Page 157: ...ated to maintain a converter leaving water temperature according to a varying setpoint 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 5 Write the program See the Air Handling System Control Applications section and the Chiller Boiler and Distribution System Control Applications sec...

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

Page 159: ...minant 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 Particulate C...

Page 160: ... 163 ASHRAE Guideline 1 1989 164 Indoor Air 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 ...

Page 161: ...ctively removes impurities from the air Includes particle filters gas phase filters and electronic devices Air quality standard A government mandated regulation which specifies the maximum contaminant concentration beyond which health risks are considered to be unacceptable Allergen A substance that can trigger immune responses resulting in an allergic reaction also known as antigen Bacteria One c...

Page 162: ...hat can affect not only the lungs but also the gastrointestinal tract central nervous system and kidneys Materials Safety Data sheets MSDSs OSHA required documents supplied by manufacturers of potentially hazardous products MSDSs contain information regarding potentially significant airborne contaminants precautions for inspection health effects odor description volatility expected contaminants fr...

Page 163: ...heric pressure In indoor air VOCs are generated by such sources as tobacco smoke building products furnishings cleaning materials solvents polishes cosmetics deodorizers and office supplies ABBREVIATIONS The following abbreviations are used throughout this section in the text and drawings AHU Air Handling Unit ASHRAE American Society of Heating Refrigerating and Air Conditioning Engineers ANSI Ame...

Page 164: ...dian Concentrations for TSP NO2 O3 CO 1979 a AIR CONTAMINANTS Air contaminants are categorized by location and type Location of contaminants is divided between outdoor and indoor Outdoor air contamination results from natural or man made phenomena that occur outdoors or indoors Contaminant types include particulate gas vapor radionuclide CONTAMINANT SOURCES Outdoor Contaminant Sources Outdoor cont...

Page 165: ...ntrations 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 Concentration µg m3 mg m3 Location TSP annual average b NO2 1 hr average O3 1 hr average CO 1 hr average Pittsburgh 88 162 2...

Page 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...

Page 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 ...

Page 168: ...upants complaining of a problem that subsides after exiting the building Complaints often result from discomfort from temperature or humidity rather than IAQ problems Building Related Illness is the term applied to a specific identifiable medical condition of know etiology that is documented by physical signs and laboratory tests Multiple Chemical Sensitivity is the term applied to an illness resu...

Page 169: ... remove viruses and bacteria Portable and fixed installation HEPA filters are also available in the residential and light commercial market Gas Contaminant Remediation Gas phase filtration is used to reduce and control gas and vapor contaminants Gas phase filtration systems utilizing virgin coconut shell carbon activated to 60 percent carbon tetrachloride activity should be capable of removing par...

Page 170: ...es prohibit humidification above 30 percent space levels in the winter except for special occupancy uses Refer toASHRAE Standard 55 1992 Thermal Environmental Conditions for Human Occupancy for more information Fig 2 Effect Of Changes in Relative Humidity on Various Items The relative humidity in the supply air duct after the humidifier will approach 100 percent and condense unless controlled Cond...

Page 171: ...cceptable Indoor Air Quality be consulted before using any of the data Table 4 Minimum Ventilation Requirements INDOOR AIR QUALITY DESIGN PROCEDURE The Indoor Air Quality Procedure 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...

Page 172: ...approach utilized for the Ventilation Rate Procedure monitors the load or airflow of all the VAV terminal boxes and the outdoor air flow of the supply fan calculates the required ventilation fraction and resets the outdoor airflow to the minimum outdoor air that will satisfy the critical space or spaces See the latest version of ASHRAE Standard 62 for additional information on critical zone reset ...

Page 173: ...rooms and 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 beca...

Page 174: ...equires the involvement of operating and maintenance personnel in theAcceptance 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...

Page 175: ...ts 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...

Page 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...

Page 177: ...ith meaningful real time dynamic data displays can enable building operators to understand how the building is operating CO2 VOC airflow DP SP filter and drain pan alarms can all provide operator information required to maintain IAQ Further trend logging and dynamic displays can allow the designer and operator to analyze the building performance historically or in real time And a real time predict...

Page 178: ... which allow the operator to look at additional data Clicking on one of the buttons produces an operator display similar to Figure 8 Fig 7 Sample Minimum Operator Graphic Display 63 83 58 OA SA RA EA ON 9610 56 1300 PERCENT LOAD PERCENT LOAD SUPPLY FAN RETURN FAN OUTSIDE AIR MINIMUM SIGNAL M10489 NORMAL EXHAUST DIFFERENTIAL CFM SELECTOR 22 60 UNOCCUPIED OVERRIDE STATUS DURATION MINUTES ON IN 74 76...

Page 179: ...d 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 INCHES EVERY MINUTES IF OR MORE VAV BOXES ARE FULL OPEN INCREMENT THE STATIC PRESSURE SETPOINT INCHES ...

Page 180: ...al Mechanical 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 C...

Page 181: ...moke Movement 175 Stack Effect 175 Buoyancy 175 Expansion 176 Wind Velocity 176 HVAC 177 Control Of Smoke 177 Pressurization 177 Airflow 178 Control Applications 178 Purging 178 Zone Pressurization Control 179 Stairwell Pressurization Control 180 Control of Malls Atria And Large Areas 181 Acceptance Testing 181 Leakage Rated Dampers 181 Bibliography 182 Referenced Publications 182 Additional Relat...

Page 182: ...h 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 andAir 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 to...

Page 183: ...s route for the handicapped DESIGN CONSIDERATIONS GENERAL Four points must be stressed in developing a smoke management system 1 The smoke management system can be properly designed only with agreement on the 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 ...

Page 184: ...ts for Fire Protective Signaling Systems Compliance with this UL standard for engineered smoke control systems requires the following Compliance with NFPA 92A Recommended Practice for Smoke Control Systems End of process verification of each control sequence Annunciation of any failure to confirm equipment operation Automatic testing of dedicated smoke control systems Controls that meet UL Standar...

Page 185: ...ire Protective Signaling Systems UL Category UUKL DESIGN PRINCIPLES CAUSES OF SMOKE MOVEMENT The movement or flow of smoke in a building is caused by a combination of stack effect buoyancy expansion wind velocity and the HVAC system See Figure 1 These items basically cause pressure differences resulting in movement of the air and smoke in a building Fig 1 Factors Affecting the Movement of Smoke Be...

Page 186: ...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 windows If a window breaks on the windward side of...

Page 187: ...ggested Minimum Design Pressure Differences Across Smoke Barriers Fig 3 Pressurization Used to Prevent Smoke Infiltration Guidelines for pressurization values are found in NFPA 92A Recommended Practice for Smoke Control Systems Table 1 indicates minimum design pressure differences across smoke barriers The design pressure difference listed is the pressure difference between the smoke zone and adja...

Page 188: ...rge 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 the space is reasonably safe to enter The following equation allows determining a concentration of contaminant in ...

Page 189: ... floors other than the fire floor Exhausting the smoke zone also aids stairwell pressurization systems by minimizing buoyancy and expansion effects Shutting off providing supply air to or leaving under temperature control all supplies other than those adjacent to the fire floor A smoke control zone can consist of one or more floors or a portion of a floor Figure 7 illustrates typical arrangements ...

Page 190: ...urization 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 Control Systems the intake of supply a...

Page 191: ...0 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 in alarm and FSCS is not in manual ...

Page 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...

Page 193: ...nt Level Processors 188 Communications Protocol 188 Peer Communications Protocol 189 Communications Media 189 Twisted Copper Pair 189 Fiber Optic 189 Phone Lines 189 System Functions 190 General 190 Zone Level Controller Functions 190 System Level Controller Functions 190 Operations Level Functions 190 General 190 Hardware 190 Software 190 Standard Software 190 Communications Software 191 Server 1...

Page 194: ...TROL BUILDING MANAGEMENT SYSTEM FUNDAMENTALS 184 Operation 193 Specifying Graphics I O Summaries 194 Control Graphics 195 Data Penetration 195 Integration of Other Systems 197 General 197 Surface Integration 197 In Depth Integration 197 ...

Page 195: ...trol 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 Building ...

Page 196: ...agement 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 of...

Page 197: ...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 ...

Page 198: ...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...

Page 199: ...rom 16 to 24 gage are the most commonly used and the best economic choice as the communications media for single building applications Bus lengths up to 4000 feet are common without use of extenders or repeaters When repeaters are used extensions up to three or four times this distance are possible Serial bus and star wiring configurations Fig 2 and 3 permit efficient wiring layouts Fig 3 Typical ...

Page 200: ...vement with access control and card readers For a detailed description of system level controllers refer to Microprocessor Based DDC Fundamentals section Processed point data at the system controller level is used directly by the resident DDC EMS and time event programs The data is also available for readout at local control panels portable terminals and can be communicated up to the operations le...

Page 201: ...r LAN is down the processors operate from their own database Security System security software prevents unauthorized system access and can limit authorized personnel to geographic areas as well as function acknowledge alarms issue commands modify database etc Top level operators assign security passwords and enter security parameters for other operators If no keyboard or mouse activity occurs for ...

Page 202: ...served for Normal On and yellow may be reserved for Normal Off Strong color conventions unclutter graphics by needing less explanatory text for example a yellow filter may be clean a red filter dirty and a red and blinking filter dirty and unacknowledged Buildings ducts and piping valves and dampers floor plans and most text on graphics are typically static Graphics consist of artwork text and dyn...

Page 203: ...oints to indicate status of control command to each chiller system 2 AUTO OFF command point for each chiller 2 Chiller status indicators 2 Maximum load commandable current limiting points 2 maximum current indicator for each chiller 2 Alarm status indicator for each chiller 2 Commandable chilled water temperature minimum and maximum setpoints 1 Current chilled water temperature setpoint indicator ...

Page 204: ... message SPECIFYING GRAPHICS I O SUMMARIES When writing the control sequence of operation sketch the graphic Fig 7 and note the necessary inputs and outputs required for control Develop an Input Output I O Summary Fig 8 where the X axis lists generic types of points and the Y axis lists the specific points Publishing the graphic sketch with all hardware and software points and symbols is an excell...

Page 205: ...ROL SMOKE CONTROL SETPOINT DISPLAY ADJUST 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 MA...

Page 206: ...ents the specified points setpoint min max airflow damper position etc on a terminal unit graphic All system points should be positioned on graphics and certain points should be specified on multiple graphics 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...

Page 207: ...d by the building control and related control industries Theses standards such as BACnet and LonMark will make in depth integration of products and systems from multiple vendors and from multiple industries much easier resulting in lower cost and more functional integrations Fig 11 In Depth Integrated System Information from other subsystems such as fire alarm security access control or lighting c...

Page 208: ...stems 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 LonMark and BACnet points may be positioned on or added to standard system graphics The disadvantage of this type of integration is that care must be taken in configuring the system to be sure that transmission speeds are adequate fo...

Page 209: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL BUILDING MANAGEMENT SYSTEM FUNDAMENTALS 199 CONTROL SYSTEMS APPLICATIONS ...

Page 210: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL BUILDING MANAGEMENT SYSTEM FUNDAMENTALS 200 ...

Page 211: ... 216 Economizer Cycle 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 222 Heating Control Processes 223 Control From Supply Air 223 Control From Space...

Page 212: ...239 Cold Deck System With Zone Damper Control 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 Free Cooling and Humidification 246 Year Round System Control Processes 248 Heating Cooling and Economizer 248 Multizone Unit 250 Heating Cooling Humidific...

Page 213: ...uded 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 Defini...

Page 214: ... provide with capacity tanks where necessary to eliminate surges and pulsations 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 SPA...

Page 215: ... circulate RA e Stopping fan if 100 percent OA system f Initiating low temperature alarms g Stopping fan if steam is not present 2 Providing failure alarms for pump coils and other heating systems components 12 ALLOWAIR HANDLINGAND 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 spac...

Page 216: ...elated 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 on ...

Page 217: ...Steam humidifier Closes Closes 1 Return air dampers need no springs if the associated fan is delayed upon start up to allow the RA damper to properly position to assure that the fan does not start with both RA and OA dampers closed 2 If a duct temperature sensor is located near a hot water or steam coil leaving the coil under control with a setpoint of 80 F to 100 F during equipment shutdown can p...

Page 218: ...MPERATURE 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 ...

Page 219: ...atic fan system control subject to commandable ON OFF AUTO software point 7 Control program turns supply return and exhaust fan on and off dependent upon optimized time schedule unoccupied space temperatures and occupant override requests The following applications show various ways of controlling ventilation in an air conditioning system FAN SYSTEM START STOP CONTROL FUNCTIONAL DESCRIPTION 8 Occu...

Page 220: ...o 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 te...

Page 221: ...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 LIMITATIONS The MA temperatur...

Page 222: ...tart up load is minimal since the building is not warm and the VAV boxes start at or near their minimum 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 linearl...

Page 223: ...at the design OA airflow is maintained 9 OA temperature operator information FEATURES 1 The proper proportions 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...

Page 224: ...controller is set at 60 F 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 60 F C2545 1 60 F DB MA CONTROLLER SETPOINT RA 75 F DB 59 5 F WB MA OA 40 F DB 35 F WB 3 2 1 The following results are obtained Item No Explanation 1 As OA temperature varies between 30 F and 60 F the MA ...

Page 225: ...rally be located at least six feet above the ground in the shade North side in a perforated enclosure away from exhausts Following are several popular strategies with guidelines of when each is appropriate ECONOMIZER CYCLE DECISION OUTDOOR AIR DRY BULB CONTROL Functional Description Item No Function 1 OA sensor senses OA temperature 2 Economizer decision mode selector including OA temperature setp...

Page 226: ...mizer mode ECONOMIZER CYCLE DECISION OUTDOOR AIR ENTHALPY CONTROL Functional Description 16 8 OA MA RA EA 27 0 1 22 ON ECONOMIZER MODE SELECTOR OA MINIMUM SETPOINT NOTE THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22 OTHER INPUTS AND OUTPUTS ECONOMIZER STATUS ENTHALPY BTU PER POUND M10455 4 7 5 9 3 6 83 8 1 2 83 CONTROL PROGRAM 1 AUTO BASED UPON OA ENTHALPY BELOW BTU PER POUND 72 0...

Page 227: ...er a simple economizer decision It gives the user four economizer control software selectable options an automatic OA enthalpy based economizer decision an automatic OA dry bulb based economizer decision for use if the OA RH sensor is bad a manual economizer ON command for use if the chiller plant is not ready to run for any reason and a manual economizer OFF command for use if the outdoor air is ...

Page 228: ...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 49 52 29 0 4 5 78 45 Item No Function 1 Sensor senses OA temperature 2 Sensor senses OA humidity 3 OA enthalpy calculated from OA temperature and humidity 4 Sensor senses RA temperature 5 Sensor senses RA humidity 6 RA enthalpy ...

Page 229: ...erform satisfactorily with OA enthalpy only If RA moisture varies similarly on severalAHUs a single comparison and decision may be globally shared among them NOTE The OA RA enthalpy comparison decision is best on systems where the return air experiences wide swings in humidity when the OA temperatures are between approximately 60 F and 80 F The size of the AHU should also be considered since savin...

Page 230: ... to assist in cooling 10 Control program coordinates MA minimum ventilation and economizer control of mixing dampers FEATURES 1 The proper proportions of OA and RA are admitted to maintain the desired MA temperature during economizer operation periods 2 A minimum quantity of OA determined by the software adjustable setpoint value is assured at all times 3 The OA economizer changeover program retur...

Page 231: ... F WB for summer 6 Other components exist in the complete system which hold the RA at the desired condition 7 The desired MA temperature can be maintained during economizer periods until the OA temperature falls below the temperature at which only minimum OA is admitted if the OA is less than 55 F C2546 1 MA WINTER RA WINTER 75 F DB 59 5 F WB RA SUMMER 80 F DB 65 5 F WB MA SUMMER OA SUMMER 100 F D...

Page 232: ... ventilation damper position 12 Determines when OA is suitable to assist in cooling 13 Space temperature setpoint and PID function PID output 0 100 inputs to reset schedule 14 Control program coordinates space temperature SA temperature minimum ventilation fan interlock and economizer control of mixing dampers FEATURES 1 The system admits only the minimum quantity of OA required for ventilation wh...

Page 233: ...control 6 Control program coordinates temperature control and fan interlock FEATURES 1 Air is discharged at a minimum temperature 2 Valve opens upon loss of motive force electricity or compressed air and closes upon fan shutdown CONDITIONS FOR SUCCESSFUL OPERATION 1 A multiple inline coil arrangement should be used if a high temperature rise is required 2 Heating medium and flow must be available ...

Page 234: ... coil entering air rises CONDITIONS FOR SUCCESSFUL OPERATION A multiple inline coil arrangement if a high temperature rise is required SPECIFICATIONS See FAN SYSTEM START STOP CONTROL 1 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 SA temperature setpoint shall be reset from no lower than 55 F to no greater ...

Page 235: ...Use multiple inline coil arrangement should be used if a high temperature rise is required SPECIFICATIONS See FAN SYSTEM START STOP CONTROL 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 60 F to 100 F as the OA temperature varies from 60 F t...

Page 236: ...4 90 72 90 83 74 EAST OFFICE WEST OFFICE 10 4 CONTROL PROGRAM NORMAL NO 56 PERCENT OPEN TO HOT DECK 80 15 AS THE DEMAND FOR HEAT FROM THE ZONE WITH THE GREATEST DEMAND FOR HEAT VARIES FROM TO 100 THE HOT DECK TEMPERATURE SETPOINT SHALL VARY FROM TO DEGREES 80 105 55 15 55 Item No Function 1 2 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 3 4 Zone mixing dampers m...

Page 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 ...

Page 238: ...preheat process heats the air in preparation for subsequent conditioning Preheat is sometimes necessary when high percentages of low temperature OA must be handled by the system Considerations before a preheat component is 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...

Page 239: ...tion 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 35 F and shall control to maintai...

Page 240: ... preferable to have the hot water valve position to approximately 25 open rather 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 Anytim...

Page 241: ...EN NORMAL COIL NO 2 COIL NO 1 COIL NO 3 11 N O 60 N O V1 V2 V3 100 ON N O 64 10 64 1 12 40 35 VALVE 2 PERCENT OPEN COIL 1 TEMPERATURE 0 100 9 40 35 OA TEMPERATURE VALVE 1 PERCENT OPEN 0 100 Item No Function 1 2 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 3 OA damper opens when fan runs 4 6 Supply air PID control loop modulates the coil 3 valve to maintain const...

Page 242: ... be sized for the balance of the heating load 3 Follow good piping practices to avoid freezing steam coils 4 On large systems fan start signal should open the OA damper and a damper end switch should start the fan to prevent the ductwork from collapsing before the damper can open SPECIFICATIONS See FAN SYSTEM START STOP CONTROL Anytime the supply fan runs heating control shall be enabled and the O...

Page 243: ...ED BY SUPPLY SYSTEM CONTROL 3 6 Item No Function 1 2 Fans start and enable pump control upon HVAC demand for ventilation See FAN SYSTEM START STOP CONTROL 3 4 Dampers close upon fan shutdown 5 Pump runs when temperature conditions are suitable for beneficial results 6 10 The OA and RA temperature difference determines when pump operation is beneficial 2 Coil No 2 valve is closed 3 Coil No 3 is mod...

Page 244: ...e 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 run a...

Page 245: ...umidistat 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 65 F 5 Check recommended applications for specific humidifier furnished 6 Where humidifiers have a separate steam jacket a separate valve may be added t...

Page 246: ...ED WATER COIL THREE WAY VALVE Functional Description M10469 MA SA 4 5 50 ON 1 CONTROL PROGRAM 3 2 80 SUPPLY FAN 80 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 coil as needed to furnis...

Page 247: ... system is from the ECONOMIZER CYCLE DECISION application This system operates on 35 percent OA during the cooling cycle 4 Coil discharge temperature is 55 F C2558 2 OA 95 F DB 75 F WB RA 78 F DB 50 RH SA 55 F DB 2 1 MA TWO POSITION CONTROL OF DIRECT EXPANSION COIL SYSTEM Functional Description The following results are obtained Item No Explanation 1 Mixed air temperature at cooling design conditi...

Page 248: ...rol program it shall remain on at least eight minutes and when it is commanded off or drops off during power interruptions it shall remain off at least ten minutes C2559 1 SA OA 95 F DB 75 F WB 3 2 1 4 55 F DB RA 78 F DB 50 RH MA On a rise in space temperature to the setpoint the refrigerant liquid line valve shall open and a relay shall enable the compressor to start under it s controls When the ...

Page 249: ...tect compressor from short cycling 10 Control program coordinates temperature compressor and fan interlock control FEATURES 1 The proportions of air passing through and around the coil are varied by modulating face and bypass dampers 2 Lowering air velocity through the coil lowers the moisture content of air leaving the coil thus producing lower space RH than systems that only cycle the refrigerat...

Page 250: ... Cooled air from the coil is mixed with bypass air to provide the necessary DA temperature In the following chart it is assumed that 1 Desired RA condition is 80 F DB and 50 RH 66 5 F WB 2 Design OA condition is 95 F DB and 75 F WB C2560 2 SA OA 95 F DB 75 F WB RA 80 F DB 66 5 F WB 3 4 2 1 DX COIL DISCHARGE 55 F DB MA 3 Air entering the system is from the ECONOMIZER CYCLE DECISION application The ...

Page 251: ...n is turned on See FAN SYSTEM START STOP CONTROL 2 4 Zone mixing dampers modulate to maintain space temperature setpoint 5 6 Chilled water valve modulates to maintain cold deck temperature setpoint 7 Mixed air temperature determines cold deck temperature setpoint at zero cooling load 8 Control program coordinates zone demand temperature and fan interlock control 9 Dynamic graphic sequence display ...

Page 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 78 F DB and 50 RH 65 F WB 2 Design OA condition is 95 F DB and 75 F 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 z...

Page 253: ...ion on a rise to 60 RH and off on a drop to 55 RH Modulating dehumidification control of a chilled water valve which delays moisture removal until the chilled water flow gets high enough to cause condensation is also satisfactory 3 Hot water flow is available for reheat or the space will get very cold and humid during periods when dehumidification is demanded and the cooling load is light SPECIFIC...

Page 254: ... entering the cooling 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 The final leaving air temperature necessary to satisfy space requirements will be maintained by reheating along a constant moisture line 4 Heating coil discharge 5 ...

Page 255: ...ty high 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 shal...

Page 256: ... 6 5 28 NC HEAT N O N C ON 1 CONTROL PROGRAM 4 3 45 88 52 52 16 2 13 55 80 SUPPLY AIR TEMPERATURE SETPOINT SPACE COOLING DEMAND 100 0 17 83 00 NORMAL ECONOMIZER DECISION REFER TO PREVIOUS ECONOMIZER OPTIONS OA MINIMUM SETPOINT NOTE THE TEST AND BALANCE INITIAL VALUE FOR PROPER VENTILATION IS 22 18 12 8 20 CONTROL PROGRAM 22 19 14 CONTROL PROGRAM 105 55 SUPPLY AIR TEMPERATURE SETPOINT SPACE HEATING...

Page 257: ...varies from 0 to 100 the SA heating PI loop setpoint shall be reset from 55 F to 105 F The hot water valve shall be modulated as required to maintain the SA temperature setpoint Anytime the fan runs the mixing dampers shall position to a minimum ventilation setting As the space cooling load varies from 0 to 100 the SA cooling PI loop setpoint shall be reset from 80 F to 55 F The outdoor and return...

Page 258: ...SPACE TEMPERATURE 15 59 64 11 9 10 74 76 2 0 8 76 SETPOINT 13 72 SETPOINT 100 0 CHILLED WATER COOLING SETPOINT FREE COOLING SETPOINT PLUS FREE COOLING SETPOINT 1 5 MINIMUM 12 2 0 HEATING SETPOINT FREE COOLING SETPOINT MINUS 1 5 MINIMUM Item No Function 1 3 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 4 6 Mixing dampers modulate to maintain minimum ventilation va...

Page 259: ...osition to minimum ventilation position during scheduled occupancy periods 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 The space temperature shall have a free cooling PID loop setpoint selected to provide optimum occupant comfor...

Page 260: ...S THE COLD DECK TEMPERATURE FROM TO DEGREES AS REQUIRED TO MAINTAIN ITS SPACE TEMPERATURE DEGREES ABOVE SETPOINT 2 0 2 0 78 55 55 97 Item No Function 1 2 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 3 4 Mixing dampers position to minimum position during occupied fan operation and modulate for cooling 5 8 Zone mixing dampers modulate to maintain space temperature...

Page 261: ...ng dampers 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 ...

Page 262: ...Function 1 3 Control system energizes when fan is turned on See FAN SYSTEM START STOP CONTROL 4 6 Manual positioning value determines minimum ventilation mixing damper position 7 Operator information outdoor air temperature 8 Economizer enables free cooling when OA is suitable 9 Operator information MA temperature 10 27 Heating coil valve modulates to keep reheat coil entering air from getting too...

Page 263: ...control loop shall be disabled anytime there is no hot water flow or temperature 5 As the SA PI cooling demand varies from 100 to 45 the cooling SA PI loop setpoint shall vary from 55 F to 75 F 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 52 F to 105 F 7 The heating coil hot water valve shall modu...

Page 264: ...midification 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 2 F DB RA rise is discussed in the ...

Page 265: ...4 ANYTIME ALL VAV BOX DAMPERS ARE LESS THAN 90 OPEN DECREMENT THE AHU DUCT STATIC PRESSURE SETPOINT INCHES EVERY MINUTES ANYTIME ANY VAV BOX DAMPER IS FULL OPEN INCREMENT THE AHU DUCT STATIC PRESSURE SETPOINT INCHES EVERY MINUTES 0 1 0 1 4 0 4 0 1 8 Item No Function 1 3 Control system energizes when supply fan is turned on See FAN SYSTEM START STOP CONTROL 4 6 Supply fan loads to maintain duct sta...

Page 266: ...dification and allows the chiller to operate at an efficient loading less than 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 ade...

Page 267: ... shall be modulated in sequence to maintain the SA temperature setpoint Anytime the optimum start perimeter zone space temperature sensor is less than 70 F at start up time the SA temperature setpoint shall be 90 F until the RA temperature rises to 74 F at which time the SA temperature setpoint shall be lowered to 55 F The EPID shall be invoked at the switching of the setpoint to 55 F with a start...

Page 268: ...the return air damper the value of which will be overridden 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 63 83 55 1 8 1 8 58 ON OA SA RA EA ON ON 55 2700 360 1300 PERCENT LOAD PERCENT LOAD SA TEMPERATURE SETPOINT OA TEMPERATURE EXHAUST FAN WARM UP MODE M10467...

Page 269: ...l be enabled Also anytime 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 non economizer occupied periods the RA damper...

Page 270: ...g air temperature 50 F 4 80 OA The following results are obtained Item No Explanation 1 RA mixes with 20 percent 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 content is reduced as the air is cooled This process involves both latent and sensible cooli...

Page 271: ...ENGINEERING CMANUAL OF AUTOMATION CONTROL AIR HANDLING SYSTEM CONTROL APPLICATIONS 261 ASHRAE PSYCHROMETRIC CHARTS ASHRAE Psychrometric Chart No 1 ...

Page 272: ...ENGINEERING CMANUAL OF AUTOMATION CONTROL AIR HANDLING SYSTEM CONTROL APPLICATIONS 262 ASHRAE Psychrometric Chart No 2 ...

Page 273: ...Building Pressure Balance 270 Containment Pressurization 271 Wind Pressure Effects 271 Stack Effect 271 Characteristics Of Fans And Fan Laws 272 General 272 Fan Types 272 Fan Performance Terms 273 Fan Laws 273 Fan Horsepower 273 Duct System Curves 274 Fan Curve And System Curve Comparison 274 Characteristics Of Airflow In Ducts 274 General 274 Pressure Changes Within A Duct 274 Effects of Fittings...

Page 274: ...oop Control 283 Direct Building Static Control 283 Airflow Tracking Control 284 Duct Static Control 284 Relief Fan Control For VAV Systems 284 Return Damper Control For VAV Systems 285 Sequencing Fan Control 286 Other Control Modes 286 Warm Up Control 286 Smoke Control 286 Night Purge Control 286 Zone Airflow Control 286 Airflow Tracking Space Static Pressure 286 Multiple Fan Systems 287 Exhaust S...

Page 275: ...anes or variable pitch blades depending on the fan type Centrifugal fan A fan where airflow within the wheel is substantially radial to the shaft 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 duc...

Page 276: ...ty 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 Peak Velocity The greatest air velocity occurring in an increment of a duct cross section Peak velocity is denoted VPK Velocity Pressure The pressure created by air moving at a velocity due to its kinetic ...

Page 277: ... 000 cfm and the return fan is 25 000 cfm The 5 000 cfm difference is lost through kitchen and restroom exhaust fans 2 000 cfm and exfiltration 3 000 cfm Thus 5 000 cfm of outdoor air must be brought in through the supply fan to make up the difference Depending on mixed air system pressure drops even is all dampers in the mixed air system NEED FOR AIRFLOW CONTROL Proper control of airflow is impor...

Page 278: ...m design provides sufficient capacity to deliver supply air to the space for design load conditions In many systems reheat coils allow individual space control for each zone and provide heating when required for perimeter zones with different exposure 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...

Page 279: ...to prevent non economizer occupied mode ventilation from varying with the cooling load This may be accomplished in several ways The dampers may be set at design load as for a constant air volume system and the filter inlet pressure noted Then the noted filter inlet negative pressure can be maintained by modulating the return air damper Keeping this pressure constant keeps the OA airflow constant T...

Page 280: ...ide sources Areas within a building such as laboratories can use negative pressure to prevent contamination and exfiltration to adjacent spaces and zones Proper building pressurization must also consider the effects of outdoor wind pressure 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 d...

Page 281: ...ute temperature in degrees Rankin R 460 F h Height of building in feet ft Ks Coefficient 7 46 Rearranging the equation to calculate the differential pressure results in the following EXAMPLE Calculate the differential pressure for a 3 ft wide x 7 ft high door that has a 30 lb opening force a 10 lb force to overcome the door closer and 0 25 ft between the door knob and the door edge Similarly the m...

Page 282: ...ng requirements FAN TYPES Two main types of fans are used in airflow systems centrifugal and axial Centrifugal Fans A centrifugal fan Fig 4 has airflow within the wheel that is substantially radial to the shaft or away from the axis of the shaft The air from an in line centrifugal fan does not have to turn before being C5153 NEUTRAL PLANE REVERSE STACK EFFECT NORMAL STACK EFFECT NOTE ARROWS INDICA...

Page 283: ...ng to the fan outlet velocity FAN LAWS Fan laws Table 1 are simple and useful when dealing with changing conditions Three important laws deal with speed changes 1 Airflow varies directly with the fan speed For example doubling the fan speed rpm doubles the airflow cfm delivery 2 Static pressure varies as the square of the fan speed For example doubling the fan speed rpm develops four times the sta...

Page 284: ...ms Any pressure The quantity of air flowing in a duct can be variable or constant depending on the type of system See TYPES OF AIRFLOW SYSTEMS PRESSURE CHANGES WITHIN A DUCT For air to flow within a duct a pressure difference must exist The fan must overcome friction losses and dynamic turbulent losses to create the necessary pressure difference Friction losses occur due to air rubbing against duc...

Page 285: ...he examples use U tube manometers to read pressure The sensor connected to the U tube determines the type of pressure measured V 4005 VP Fig 8 Relationships of Total Static and Velocity Pressures for Positive and Negative Duct Static Pressures TOTAL PRESSURE STATIC PRESSURE AIRFLOW FAN A PRESSURE IN THIS DUCT ABOVE ATMOSPHERIC PRESSURE TOTAL PRESSURE VELOCITY PRESSURE B PRESSURE IN THIS DUCT BELOW...

Page 286: ...in half increases the velocity and the friction loss increases In most low pressure airflow systems the velocity component of the total pressure may be ignored because of its relative size For example if a supply fan delivers 10 000 cfm at 2 in wc static pressure in a supply duct that is 3 ft x 4 ft or 12 ft2 the Velocity V Q A is 10 000 cfm 12 ft2 or 833 fpm The Velocity Pressure VP V 4005 2 is 8...

Page 287: ...nts of these units that actually determines the airflow in the main supply duct In this type of system the supply fan is controlled to maintain a constant static pressure at a point in the duct system so there is sufficient supply air for all of the air terminal units MEASUREMENT OF AIRFLOW IN DUCTS GENERAL Total pressure and static pressure can be measured directly velocity pressure cannot Veloci...

Page 288: ...eral readings across the duct a traverse are normally needed to obtain an accurate average velocity 3 Accurate pressure readings cannot occur in locations with varying swirls eddies or impinged air Because of this The pitot tube must be inserted into the air stream at least 10 duct diameters downstream from elbows and five duct diameters upstream of bends elbows or other obstructions which cause t...

Page 289: ...al rectangular areas are taken The velocities are then mathematically totaled and averaged Fig 17 Pitot Tube Locations for Traversing Round and Rectangular Ducts The principle behind the manual pitot tube transverse is simple and straightforward However care must be taken to obtain accurate readings without inadvertent violation of the formal traverse pattern With the manual pitot tube traverse in...

Page 290: ...NIFOLD ASSEMBLY TOTAL PRESSURE CONNECTION STATIC PRESSURE CONNECTION AIRFLOW Fig 19 Averaging Flow Measuring Station C2660 Fig 20 Air Straighteners Sensors and Manifolds 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 21...

Page 291: ...e control loop This avoids the assumption that branches and multisensor locations have identical requirements The sensed point having the lowest duct pressure relative to its own setpoint should control the supply fan When a long straight duct 10 diameters is available a single point static sensor or pitot tube can be used When long duct sections are not available use static or airflow measuring s...

Page 292: ... close or ducts are blocked especially during initial system start up Fan shut down and controlling high limit are two techniques used to limit duct static Both techniques sense duct static at the supply fan discharge DUCT STATIC PRESSURE SENSORS C2621 SUPPLY FAN AIR TERMINAL UNITS DUCT STATIC HIGH LIMIT SENSOR SMOKE DAMPERS SMOKE DAMPERS DUCT STATIC PRESSURE SENSORS Fig 25 Duct Static High Limit ...

Page 293: ... control sequence where the outdoor air damper is closed e g night cycle or morning warm up open loop control should not be used Excessive negative pressurization will occur in the duct between the return and supply fans Direct Building Static Control In direct building static control the return fan responds directly to the building space static pressure referenced to the static pressure outside o...

Page 294: ...t fan total airflow If controlling the space returns from airflow tracking using dampers the exhaust fan volume must be included in RELIEF FAN SUPPLY FAN BUILDING SPACE EXHAUST FAN C2626 OA RA RELIEF DAMPER RELIEF FAN STATIC PRESSURE CONTROLLER BUILDING SPACE STATIC PRESSURE OUTDOOR STATIC PRESSURE C2627 the tracking control system for constant building and space pressurization If controlling the ...

Page 295: ...amper controls minimum outdoor airflow or building pressurization Airflow tracking or direct building static pressure control can be used to control the return damper depending on which parameter is most important See Figure 35 for airflow tracking and Figure 36 for direct building static pressure control C2631 STATIC PRESSURE CONTROLLER BUILDING SPACE STATIC PRESSURE OUTDOOR STATIC PRESSURE OA SU...

Page 296: ...e 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 accomplished when usi...

Page 297: ...door static pressure sensor should be at least 15 feet 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 ...

Page 298: ...ral exhausts route contaminants into common ducts which connect to a common exhaust fan If the airflow is manually balanced the exhaust fan runs at a fixed level However if the airflow is controlled at each entry to vary the airflow in response to the local need duct pressurization control of the exhaust fan is required It may also be necessary to introduce outdoor air prior to the general exhaust...

Page 299: ...low in individual fumehoods to be reduced when sensors determine no one is present at the face of the hood The subject of the correct face velocity is still debated However most research now indicates that 80 100 feet per minute fpm at the sash opening provides a zone of maximum containment and operating efficiency provided that the supply air delivery system is designed to minimize cross drafts V...

Page 300: ...pens Figure 47 shows a laboratory example with a single fume hood a single door 36 in wide x 80 in high 20 ft2 and a crack area estimated at 0 5 ft2 If the fixed airflow tracking differential is 200 cfm the average velocity through the cracks would be 400 fpm which is more than adequate for containment However when the door opens the average velocity in this example decreases to 9 8 fpm which is m...

Page 301: ... exhaust flow Replacement air for the space that is being exhausted migrates from adjacent areas through the doorway and cracks The supply system for the adjacent area must replace this air in order to maintain a positive building pressurization The significant issues are 1 how fast can the room pressurization system respond to upset a door opening or several hoods being closed at once and 2 what ...

Page 302: ...ng and Air Conditioning Engineers Inc 1791 Tullie Circle N E Atlanta GA 30329 Trane Air Conditioning Manual The Trane Company Educational Department 3600 Pammel Creek Road LaCrosse WI 54601 Engineering Fundamentals of Fans and Roof Ventilators Plant Engineering Library Technical Publishing 1301 S Grove Avenue P O Box 1030 Barrington IL 60010 Industrial Ventilation Manual Committee on Industrial Ve...

Page 303: ... 303 System Controls Which Influence The Chiller 303 Safety Controls 303 Chiller BMCS Interface 303 Chilled Water Systems 304 Central Cooling Plants 304 Single Centrifugal Chiller Control 304 Single Centrifugal Chiller Control Application 305 Multiple Chiller System Control Applications 308 Dual Centrifugal Chillers Control Application 309 Similar Multiple Centrifugal Chillers Control Applications...

Page 304: ...ers 331 Boiler Controls 332 Boiler Output Control 332 Combustion Control 332 Flame Safeguard Control 332 Flame Safeguard Instrumentation 333 Application Of Boiler Controls 333 Multiple Boiler Systems 334 General 334 Dual Boiler Plant Control 335 Modular Boilers 337 Hot And ChilledWater Distr ibution Systems Contr ol 337 Introduction 337 Classification Of Water Distribution Systems 337 Typical Wate...

Page 305: ...ot Water Converters 360 Hot Water Piping Arrangements 361 General 361 Primary Secondary Pumping 362 Control Of Hot Water Systems 362 General 362 Modulating Flow Control 362 Supply Hot Water Temperature Control 363 Supply Hot Water Temperature Control With Flow Control 363 Hot Water Reset 363 Hot Water Converter 363 Three Way Valve 366 Coordinating Valve Selection and System Design 366 Hot Water Co...

Page 306: ...Converter Control 379 HTW Coils 380 HTW Space Heating Units 380 Storage Converters 380 Multizone Space Heating HTW Water Converters 381 HTW Steam Generators 381 District Heating Applications 382 Introduction 382 Heat Sources 382 The Distribution Network 382 The Substation 383 Abbreviations 383 Definitions 384 Symbols 384 System Configuration 385 Heat Generation 385 Heat Distribution Network 385 Ho...

Page 307: ...Speed Drive WB Wet Bulb DEFINITIONS 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 le...

Page 308: ...o the pressure of the vapor Surge A condition where refrigerant reverses flow approximately every two seconds creating excessive noise vibration and heat Surge is caused by insufficient pumping head 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 other...

Page 309: ... 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 t...

Page 310: ...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...

Page 311: ... power than air cooled condensers However condenser water temperature must not be allowed to go too low or there will not be enough 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 Cylinde...

Page 312: ...s the refrigerant Use of water as a refrigerant requires that the system be sealed all the air removed and an absolute pressure of 0 25 in Hg be maintained Under these conditions the refrigerant water boils at 40F which allows the refrigerant to cool the chilled water to 44F Fig 7 Absorption Chiller Operating Cycle Schematic WEAK ABSORBENT STRONG ABSORBENT REFIRGERANT LIQUID REFIRGERANT VAPOR KEY ...

Page 313: ...illers can be reduced to as low as 10 percent Mostchillerswithmodulatingcapacitycontroluseproportional integralcontrol andoftenreceivetheirchilledwatersetpointfrom a BMCS to optimize building energy efficiency Whenchilledwaterdischargetemperaturecontrolisused offset can be reduced and control improved by using return water temperature to reset the supply setpoint upward at light loads to reduce th...

Page 314: ...r or chiller combination in multiple chiller plants to satisfy the current load at minimum operating cost The influence of refrigerant head 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...

Page 315: ...TROL APPLICATION FUNCTIONAL DESCRIPTION Item No Function 1 Indicates when chiller system is required by fan system 2 Chilled water pump ON OFF AUTO function In AUTO pump runs when fan systems need chilled water 3 Chiller ON OFF AUTO function In ON and AUTO chilled water flow required for chiller to run 4 Condenser pump status Pump started by chiller controls when chilled water needed 5 6 Chiller l...

Page 316: ...impler to pipe If all two way valves are provided on single pump systems chilled water flow or pressure controls See DUAL CENTRIFUGAL CHILLERS are provided to maintain the required flow varies with chiller manufacturers through the chiller Do not use three way valves when diversity is used in the chiller system design NOTE Little pumping energy can be saved on a single pump single chiller system b...

Page 317: ... to 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 Withou...

Page 318: ...13 illustrate that for the chillers operating at design condition with a 43F 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 31F and that the first chiller can be loaded to 11...

Page 319: ...RM STATUS CHILLER CONTROL SETPOINTS SEQUENCES 1 CHILLER 1 LEADS 2 CHILLER 2 LEADS 3 ALTERNATES CONTROL PROGRAM FLOW PRESSURE CONTROL TOWER CONTROL MORNING LEAD CHILLER SELECTOR CHILLER 1 CHILLER 2 MINIMUM CURRENT MAXIMUM CHILLED WATER SETPOINT M10497 CURRENT PERCENT LOAD MAX 1 42 50 AUTO AUTO AUTO 100 100 AUTO ON ENABLED DISABLED NORMAL NORMAL 55 0 42 1 12 19 4 9 13 1 3 15 8 11 17 4 14 5 2 11 2 10...

Page 320: ...ditions 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 T...

Page 321: ...l 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...

Page 322: ... 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 Where ...

Page 323: ...5 0 GPM PC TRP DECOUPLER LINE 45 8 13 10 12 11 15 9 21 6 14 19 16 2 4 1 3 17 8 18 5 7 20 M10502 Item No Function 1 2 Secondary pump speeds 3 Icon for selection of secondary control details 4 Secondary pump leaving water temperature operator information 5 Four chiller pump status indicators green on yellow off red alarm typical 6 Four Icons for selection of chiller detail graphic 7 Four chiller sta...

Page 324: ...friendly monitoring and adjustment 3 Flow calculations without costly and maintenance prone flow meters see SPECIFICATION 4 Chiller that has been off longest is next 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 Int...

Page 325: ...ing 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 load expected should be dynamically modified based upon manufacturers data...

Page 326: ... Absorption Centrifugal Chiller System 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 CHI...

Page 327: ...arging 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...

Page 328: ...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 control A variable speed fan ...

Page 329: ...lder weather Specification On a rise in condenser water temperature to 80F the cooling tower fan shall start and on a drop in condenser water temperature to 73F 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...

Page 330: ...mum 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 application...

Page 331: ...ordinated with the chiller manufacturer 3 Good OA RH sensor and WB calculation 4 Proper project specific setpoint and parameter settings 5 If tower must operate with OA temperature below freezing the diverting valve must be controlled two position during freezing conditions Specification Cooling tower controls shall be enabled anytime the condenser water pump runs The cooling tower fan speed shall...

Page 332: ...t for 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 ISOL...

Page 333: ...ntain 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 speed of 25...

Page 334: ...and opening to the tower after a 3 degree differential If after both valves position open to the tower for 2 minutes the temperature rises to the valve control setpoint plus 4F 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 valu...

Page 335: ...OWER FOR MULTIPLE CHILLERS THIS IS REPLACED BY CAPACITY CONTROL OF HEAT REJECTION CHILLER C2696 TEMPERATURE AT T1 F 110 105 100 95 ACTION OFF IF T3 T2 THEN T1 CONTROLS V1 CONDENSER HEAT ON OPEN OA DAMPER COOLING CLOSED CLOSED V2 CONTROLLED BY T1 OPEN FOR MULTIPLE CHILLERS THIS IS REPLACED BY CAPACITY CONTROL OF HEAT REJECTION CHILLER SHUT OFF OA COOLING ON FAN UNITS HEAT SOURCE T1 LOAD HOT WATER G...

Page 336: ...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 COMPRESSOR EV...

Page 337: ...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 cooling to...

Page 338: ... 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 ...

Page 339: ...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 Firetube boilers are manu...

Page 340: ...ater temperature activates each stage of heating as required to heat the building Fig 40 Electrode Steam boiler BOILER RATINGS AND EFFICIENCY Boilers can be rated in several ways Figure 41 shows commonly used ratings and terms The terms Btuh Btu per hour and MBtuh or MBH thousand Btuh indicate boiler input rate Input ratings are usually shown on the boiler or burner nameplate The terms hp boiler h...

Page 341: ...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 1 000 000 Btuh 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 ...

Page 342: ...t 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 1 000 000 Btuh capacity The oil or gas burner cycles on and off to maintain steam pressure or water temperature Cycling control causes...

Page 343: ...lumn Steam flow with totalizer or hot water Btu 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 60F for more than 30 minutes and an AH...

Page 344: ...o 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 145F minimum entering water temperature required prior to high fire water flow must be maintained when the...

Page 345: ...SYSTEM ON VALVES DISPLAY OPEN TO SECONDARY RETURN OUTSIDE AIR TEMPERATURE DECOUPLER CROSSOVER OUT BOILER BOILER NO NC PID SP IN 2 1 26 27 25 12 C P1 P2 7 5 F PUMP P1 ON OFF AUTO SELECTOR PUMP P2 ON OFF AUTO SELECTOR SECONDARY PUMP SYSTEM ON OFF AUTO SELECTOR BOILER 1 OFF AUTO SELECTOR BOILER 2 OFF AUTO SELECTOR PS 4 3 9 2 18 24 21 15 17 1 16 8 19 6 11 23 10 22 13 14 20 135 155 155 OFF 145 160 85 A...

Page 346: ...ntering water 3 Variable flow secondary system with full boiler flow 4 Automatic boiler staging 5 User friendly monitoring and adjustment Conditions For Successful Operation 1 Control network software and programming to advise heating plant controller of secondary fan and water flow demands 2 Interlock and control wiring coordinated with the boiler manufacturer 3 Control in accord with boiler manu...

Page 347: ...ntrol sensor 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 PU...

Page 348: ...y 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 the...

Page 349: ... 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 head in feet versus gallons per minute gpm...

Page 350: ... Pump Curve Pump Performance Curves Commercial pumps have performance curves showing the following data for a given pump speed Total head in ft versus flow in gpm Total head versus flow for various impeller diameters Pump efficiency at various operating points Brake horsepower BHP or motor horsepower required Net positive suction head NPSH NPSH is the absolute pressure psia required at the suction...

Page 351: ...mpeller delivers 80 ft of head with a 7 21 inch impeller it would deliver 65 ft of head It is calculated as follows Table 3 Pump Affinity Laws Fig 55 Pump Curve for 1750 RPM Operation C1051 CAPACITY IN GALLONS PER MINUTE 45 55 60 68 68 65 60 55 45 3HP 2HP 1 1 2HP 1HP 3 4HP 1 2HP 7 6 1 2 6 5 1 2 5 0 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 TOTAL HEAD IN FE...

Page 352: ...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 ride the...

Page 353: ...ps and the control valve represented by line B makes the difference about 36 ft Similarly at 50 percent flow the valve drop represented by line C accounts for about 63 ft C1055 1 SYSTEM CURVE 9 1 2 8 3 4 8 7 1 4 5 HP 7 1 2 HP 10 HP 12 HP 15 HP OPERATION WITH 8 3 4 IMPELLER DESIGN OPERATING POINT BALANCED OPERATING POINT WITH 9 1 2 IMPELLER 100 90 80 70 60 50 40 30 20 10 0 0 100 200 300 400 500 600...

Page 354: ...ical 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...

Page 355: ...VE SYSTEM CURVE INDICATED OPERATING POINT Fig 64 System Curve for Open Circuit with Static Head MULTIPLE PUMPS Multiple pumps are used when light load conditions could overload a single pump These conditions normally occur when two way control valves are used 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 ...

Page 356: ...mp pressure drops to I at which time the cycle repeats See PLOTTINGA 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 curve is ...

Page 357: ...ied 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 40 gpm is the same as the sum of the flows through the three coil circuits 10 12 18 40 gpm 2 Design pressure drop head loss includes the drop through the heating or cooling source supply piping return piping and the highest of ...

Page 358: ...n system control solutions vary dependent upon 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 an...

Page 359: ...or a reverse return system Fig 71 as for the direct return system Fig 70 The return flow is reversed 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 6 ft drop If the AHUs and source were positioned in a c...

Page 360: ... are often not available therefore small three way valves tend to be oversized Consider using two way control valves for all applications of Cv 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...

Page 361: ...actuator close off requirements and the inherent leakage will not be a significant factor DIFFERENTIAL PRESSURE SENSOR LOCATION As previously stated the chiller design flow is 1200 gpm at 12 ft of head and requires a minimum flow of 1080 gpm At 1080 gpm the pump curve shows a head of 50 ft From the formula Fig 73 Typical Example Loads Single Pump Pressure Bypass Direct Return Figure 74 analyzes Fi...

Page 362: ...3 PD 8 2 PD 4 1 PD 48 54 0 4 1 4 1 PD 12 3 PD 8 44 PD 16 4 24 48 10 2 5 18 46 5 0 0 PD 8 44 PD 10 2 5 6 1 5 PD 6 1 5 PD 6 DROP TOTAL TOP NUMBERS FULL FLOW BOTTOM NUMBERS HALF FLOW EACH COIL PD PRESSURE DROP NUMBERS IN CIRCLES GAUGE PRESSURES PUMP INLET ZERO FOR SIMPLICITY 8 2 PD M15061 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 B...

Page 363: ...ss valve 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 head still rises to 54 ft and the control valve drop still rises to 44 ft For 90 percent flow control the pump still operates at a 50 foot headwiththesensorlocatedasfarawayfromthepumpaspractical to t...

Page 364: ...ngle pump chiller operation During periods of dual pump chiller operation the 34 foot setpoint controller is used alone AHU Valve High Differential Pressure Control As noted in the discussion of Figure 75 the differential pressure 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 acr...

Page 365: ... 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 28 ft Fig 74 and pressure bypassing occurs at 34 ft The maximum setpoint for DP 2 Fig 78 should be about 29 or 30 ft This initial setpoint is then slowly...

Page 366: ...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 28 feet With each AHU at one third flow the speed is ...

Page 367: ...ustable NOTES 1 From Figure 81 pump head is 36 feet if allAHUs require full flow therefore the 30 foot 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 pres...

Page 368: ...REATER THAN 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 PSI 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 55 88 100 65 8 5 0 8 0 8 8 5 25 55 MANUAL AUTO SELECTOR PERCENT...

Page 369: ... 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...

Page 370: ...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 laminar range b Keep water veloci...

Page 371: ...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...

Page 372: ...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...

Page 373: ...xcept that it is impractical to provide a different hot water temperature to each heating coil or piece of radiation in a building Varying supply water temperature as a function of outdoor temperature provides a good compromise Fig 92 Supply Water Temperature vs Heat Output at Constant Flow HOT WATER UNIT HEATER RADIANT PANEL CONVECTORS AND RADIATORS 100 90 80 70 60 50 40 30 20 10 0 80 100 150 200...

Page 374: ...e small 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 sequen...

Page 375: ... 1 Technicians and users capable of understanding and tuning the control strategy 2 Proper settings and timings of all control parameters Specification Converter Control Anytime the pump does not prove operation the converter valves shall close Control The control system shall be enabled anytime steam pressure is available The hot water pump shall start anytime the OA is below 58F subject to a sof...

Page 376: ... flow The 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 wat...

Page 377: ...ransfer Characteristic of a Cooling Coil Supplied with Chilled Water FLOW IN GPM TOTAL HEAT REMOVED C2403 Fig 99 Two Pipe Dual Temperature System The three way valves on the chiller and boiler are used for 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 outs...

Page 378: ...condensate flow PROPERTIES OF STEAM One Btu added to one pound of water raises the water temperature one degree Fahrenheit When water temperature reaches 212F at sea level 14 7 psia it contains 180 Btu lb 212 32 180 However it takes another 970 Btu to convert the one pound of water to a vapor steam The total heat of the vapor is 180 Btu lb 970 Btu lb 1150 Btu per pound The 970 Btu lb is the latent...

Page 379: ... will be exposed to the higher temperature To correct for superheated steam 1 Btu lb is added for each Fahrenheit degree of superheat EXAMPLE 1000 MBtuh of 10 psi steam is required From Table 6 10 psi steam has a latent heat of 953 Btu lb If condensate leaves at 180F the steam gives up 1012 Btu lb 953 Btu lb condensing the steam and 59 Btu lb cooling the condensate from 239F to 180F If the 10 psi ...

Page 380: ...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 Thermostatic ...

Page 381: ...74 Reprinted by permission from the ASHRAE Handbook 1996 Systems and Equipment Fig 107 Orifice Trap 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 chambe...

Page 382: ...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 ...

Page 383: ...ure created by the condensation of steam in the system This means that steam is continuously supplied to the radiator at a decreasing temperature until the limit of induced vacuum is reached Table 7 shows reduced heat output from radiators in a vacuum system To operate successfully the system must be air tight Variable vacuum systems use nonreturn vents which allow air to leave the system but none...

Page 384: ... signaled to the valve to cut heat output in half the coil is still full of steam and the heat output is only reduced by 5 percent The reduction is because of the difference in temperature of 4 psi steam compared to 1 psi steam assuming 50F air temperature entering the coil The trap drop is 0 9 psi Most of the pressure drop between the supply and the return mains is now across the steam valve The ...

Page 385: ...uts off at 8 in Hg of vacuum The pressure difference between supply and return mains can vary from a minimum of 4 psi to a maximum of 10 psi as the boiler and vacuum pump cycle This means a 60 percent variation in capacity of the control valves in the building as the pressure fluctuates Control valves correctly sized for 4 psi are 60 percent too large during periods when a 10 psi difference exists...

Page 386: ...transfer units is returned to the HTW generator Several major design characteristics are typical of HTW systems 1 The HTW boiler is controlled by pressure rather than temperature to eliminate flashing if heating load fluctuates 2 Multiple boiler systems must be designed so that loads are divided between the boilers Generally it is less costly to operate two boilers at part load than one at full lo...

Page 387: ... Fig 117 Typical Nitrogen Pressurized High Temperature Water System Controls can be pneumatic electric or digital The low mass of electronic temperature sensors thermocouple or resistance bulb provides faster response than fluid filled or bimetal elements Pneumatic actuators generally have the faster response higher temperature ratings and greater reliability required for HTW applications Standard...

Page 388: ... rings are available in industrial valves and acceptable to 450F A valve with a deep packing gland is normally required VALVE FLOW CHARACTERISTICS The flow characteristics of a valve is the relationship between fluid flow expressed in percent of flow and valve stem travel expressed in percent of travel Always use equal percentage characteristic valves for HTW control Equal percentage valves compen...

Page 389: ...er as close to the converter as possible 2 A stainless steel well that matches the element with heat conductive compound in the well must be used 3 A primary control must be used that has integral action and integral cutout to allow a wider throttling range for stability with minimum deviation from setpoint and to eliminate integral windup A control arrangement for a typical zone supplied with HW ...

Page 390: ...nd opens the valve on sensing a freezing temperature Use of a glycol solution as shown in Figure 120 is recommended Fig 121 HTW for Mixed Air Reheat HTW SPACE HEATING UNITS Unit heaters convectors radiation and radiant panels can be supplied directly with HTW This allows use of smaller units and smaller piping and eliminates intermediate heat exchangers Most of the additional control cost is in th...

Page 391: ...tral HTW boilers for steam production is not recommended The HTW system is best used to produce steam by locating steam generators at the point of need The steam generator Fig 125 is designed so that the minimum water level covering the tubes takes up 60 percent or less of the volume of the shell The remaining 40 percent for steam is sufficient to avoid water carry over A water eliminator at the s...

Page 392: ... 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 or steam...

Page 393: ... pressure depend on the structure and dimensions of the network and the heat source The water temperature is generally limited to 265F on the supply side In fact manynetworksnowkeepthesupplytemperatureunder180F allowing use of lower cost equipment and fewer safety devices See HOT WATER DISTRIBUTION SYSTEMS and HIGH TEMPERATURE WATER HEATING SYSTEM CONTROL Outdoor Air Temperature Control reduces th...

Page 394: ...vertor transfers heat from the primary network to a secondary network Heat Surface Factor A value corresponding to the effectiveness of radiating surface The value depends upon the shape size and color HeatTransfer Station Controls flow pressure and temperature in sections of a primary network Primary Network Supply and return pipe for heating medium hot water or steam from the heat power plant to...

Page 395: ...rature and pipe insulation Because of the many variables a combination of both Outdoor Air Temperature Control and Variable Flow Control or Variable Temperature Control is often used STEAM SYSTEM VS HOT WATER SYSTEM Steam networks differ mainly in the following points from hot water systems No pumps are required the pressure difference between boiler and consumer drives the movement of the steam C...

Page 396: ...f a branch line is shut down the pressure ratio in the entire network is affected To prevent pressure spikes in the main system the shutdown must be performed slowly and carefully Often two different sized surge tanks in parallel are used to damp the pressure peak during shutdown Usually key point temperatures and pressures are monitored Fig 128 Principle Of A Mixing Station Fig 129 Typical Key Po...

Page 397: ...Substation for Multiple Family Buildings Table 9 Description of Figure 131 Reference Points Fig 130 Two And Three Way Valve Configurations for a Heat regulation Unit Jet pumps use the effect of injection making a mechanical pump unnecessary thereby saving electrical energy However adapting and dimensioning jet pump applications to fit operating conditions is difficult Control loops used in a direc...

Page 398: ...water facilities Secondary side Functional principle The primary side of the substation Fig 132 contains the differential pressure control and a normally closed temperature control valve with safety spring return if the secondary medium temperature exceeds 212F The differential pressure control is used in large networks where over time significant pressure differences exist The primary supply flow...

Page 399: ...ange from small substations to large heat exchanger substations supplying several blocks of buildings As described before there are usually three main parts to the substation Primarysideincludingpressure flowregulatingequipment Heat exchanger or hot water storage tank chargeable for DHW and heat flow regulating equipment for heating Circulating pumps for secondary side heating and for DHW The prim...

Page 400: ... PLC S9000 Supervisory Control TZA 26 Safety temperature limit SSF HEX 1 locked PSA 52 Safety pressure limit refill pipe TZA 36 High temperature limit SSF HEX 12 locked PSA 58 Safety pressure limit SSF TZA 41 Safety temperature limit SSF total high PZA 24 Safety pressure limit high Y 11 Actuator valve Primary Supply Flow PSF PZA 34 Safety pressure limit high Y 17 Y 18 Actuator control valve PDPC P...

Page 401: ...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 ...

Page 402: ...ined 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 56maintainstheexpansiontankwaterlevel NormallyPRF water throughValveY 51 provides make up water in cases of a high quantity water loss PumpY 64 pumps make up water from the water s...

Page 403: ...re Y 23 Circulating pump TIC 22 SSF temperature Fig 139 SSF Temperature Reset Schedule 270 255 240 235 220 205 190 175 160 5 25 45 65 OUTSIDE AIR TEMPERATURE F SSF TEMPERATURE F M10673 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...

Page 404: ...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 ...

Page 405: ...Pumps 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 213 356 320 284 248 212 176 140 13 6 1 9 16 23 30 37 45 52 59 66 SSF SETPOINT TEMPERATURE F OUTSIDE AIR TEMPERATURE F M11441 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 S...

Page 406: ...2 control the SSF temperature The SSF setpoint is reset based on outdoor air temperature Fig 143 If the primary return flow PRF exceeds the TI 14 temperature limit the SSF 1 temperature reset schedule is adjusted to a lower temperature schedule If the SSF temperature exceeds the high limit setpoint of hard wired thermostat TZA 21 power to valve Y 12 is shut off closing the valve 2 DHW temperature ...

Page 407: ...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...

Page 408: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL CHILLER BOILER AND DISTRIBUTION SYSTEM CONTROL APPLICATIONS 398 ...

Page 409: ...8 Dual Duct ATU 410 Dual Duct Pressure Independent VAV ATU 410 Dual Duct Pressure Independent Constant Volume ATU 411 Unitary Equipment Control 412 General 412 Natural Convection Units 412 Radiant Panels 413 Unit Heaters 413 General 413 Control 414 Two Position Control 414 Down Blow Unit Heater 414 Modulating Control 414 Gas Or Oil Fired Unit Heater 415 Unit Ventilators 415 General 415 Control 416...

Page 410: ...22 Power Failure 422 Coil Freeze Up 422 Fan Coil Units 422 General 422 Two Pipe Heating Cooling 423 Two Pipe Heating Cooling Single Coil 423 Four Pipe Heating Cooling Split Coil 424 Four Pipe Heating Cooling Single Coil 424 Heat Pumps 425 General 425 Operation 425 Control Loops 426 Individual Room Control Automation 427 Hot Water Plant Considerations 428 ...

Page 411: ...yed data points should still be available for operators and technicians via a portable terminal Simple systems such as unit heaters are also shown in Electric Control Fundamentals section Large air handling units and chiller plants typically use general purpose digital controllers while rooms typically use controllers designed for room control Thus a VAV box controller may be configured to control...

Page 412: ...EMPERATURE 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...

Page 413: ...ings by reducing the load on the central fan when cooling loads are less than design and avoid reheating cooled air A system designed to reduce overall system airflow asATUs shut down offers the greatest energy savings because system fans and fan motors operate at lighter loads These paragraphs describe the operation of VAV ATUs in single duct and dual duct air handling systems PRESSURE DEPENDENT ...

Page 414: ...g 3 is 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 a...

Page 415: ... be directed to multiple controllers to control multiple ATUs with the same or differing volume ratings M10538 75 74 00 24 75 77 MINIMUM DAMPER POSITION MAXIMUM DAMPER POSITION 2 5 HEATING DEADBAND CURRENT TEMPERATURE SPACE TEMPERATURE SETPOINT SCHEDULE OPEN ACTUATOR POSITION CLOSED MINIMUM POSITION REHEAT POSITION MAXIMUM POSITION LOW HIGH VALVE DAMPER RHC LOW HIGH SPACE HEATING LOAD HEATING SETP...

Page 416: ...5 and 6 show several inputs outputs and setpoints many more parameters are available and necessary to allow technicians to adapt the standard program to a unique room and set of equipment These additional parameters usually addressable and commandable from the BMS or portable terminal include the cooling loop PI gains the heating loop PI gains reheat airflow setpoint unoccupied space temperature s...

Page 417: ...104 350 550 350 MINIMUM MAXIMUM AIRFLOW SETPOINTS CFM CURRENT AIRFLOW CFM DAMPER PERCENT OPEN HEATER STATUS HEATING DEADBAND TEMPERATURE COOLING SETPOINT M10540 MINIMUM AIRFLOW REHEAT AIRFLOW MAXIMUM AIRFLOW LOW HIGH LOW HIGH SPACE HEATING LOAD HEATING SETPOINT COOLING SETPOINT SPACE COOLING LOAD DEADBAND MAXIMUM AIRFLOW HEATER 2 ON HEATER 1 ON HEATER 2 OFF HEATER 1 OFF ZERO AIRFLOW SPACE PRIMARY ...

Page 418: ...ATU dampers with a small centrifugal fan to recirculate return air at a constant volume after primary air decreases The fan acts as the first stage of reheat after primary flow is at minimum or can be switched on at a low primary flow threshold while primary flow goes to zero The reheat coil is optional The operation cycle in Figure 8 shows that when space temperature is below the heating setpoint...

Page 419: ... PLENUM AIR RHC MAX REHEAT VALVE PRIMARY AIR AIRFLOW MIN OPEN CLOSED ZERO FULL M10542 0 FAN 0 FULL HEATING LOAD REHEAT VALVE PRIMARY AIR AIRFLOW HEATING SETPOINT COOLING SETPOINT COOLING LOAD DEADBAND ADJUSTABLE ON OFF PRIMARY AIR Fig 8 Parallel Fan Air Terminal Unit Fig 9 Series Fan Air Terminal Unit M10543 75 350 943 1150 75 MINIMUM AIRFLOW SETPOINT CFM MAXIMUM AIRFLOW SETPOINT CFM CURRENT AIRFL...

Page 420: ...r from respective ducts mixes the air as directed by a sensor in the controlled space and discharges the mixed air into the space This basic dual duct mixing system is not economical because air is cooled and heated much of the year DDC systems are still sometimes used with digital hot and cold duct load reset to minimize the energy waste during mixing periods Adapting dual duct systems to VAV con...

Page 421: ... minimum airflow setpoints Dual Duct Pressure Independent Constant Volume ATU Figure 11 shows a constant volume pressure independent dual duct ATU Modulating the hot duct damper up to a total flow not to exceed the maximum airflow setpoint maintains the room temperature A constant total airflow is normally maintained by modulating the cold duct damper With this configuration there is no deadband a...

Page 422: ...ion 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 natural convection unit is controlled manually or by a room thermostat controlling a valve or electric heat coil Figure 12 shows the control loops for individual room control As space temperatu...

Page 423: ... panels The actual hot water temperature may be higher Radiant heat panels that use electric resistance heating elements are controlled by a two position thermostat As the space temperature drops below the thermostat setpoint and differential the thermostat closes a switch to allow current flow to heat the elements When a radiant panel is used for cooling the temperature of the water circulating t...

Page 424: ...ust the valve and let the low limit cycle the fan Figure 16 shows that control of an electric heat unit heater is similar to steam or hot water two position control except that the thermostat cycles the fan and the relay or contactor energizes the electric heating elements when the fan is running Fig 16 Unit Heater Two Position Control Electric Heat C3026 UNIT HEATER LOW LIMIT ROOM THERMOSTAT COIL...

Page 425: ...lled ventilation e g classrooms conference rooms A unit ventilator control system varies heating ventilating and cooling if available while the fan runs continuously 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 fa...

Page 426: ...d by pneumatic electric electronic or digital control STANDBY WARM UP STAGE During cold room periods all three cycles position the valves and dampers the same Figure 23 shows the standby warm up stage in which the unit ventilator fan is shut down manually or by time clock The outdoor air damper is closed and the return air damper is full open The heating coil valve is open The coil acts as a conve...

Page 427: ... F Fig 24 Unit Ventilator Cycle I Control CYCLE II FIXED MINIMUM PERCENTAGE OF OUTDOOR AIR Cycle II control Fig 25 provides a fixed minimum percentage of outdoor air usually 10 to 33 percent adjustable from 0 to 100 percent At low space temperatures the outdoor air damper is closed and the heating coil valve and face damper are full open As space temperature rises the outdoor air damper moves to i...

Page 428: ...rs can be operated at lower setpoints during unoccupied hours to save energy Two commonly used day night systems are individual room day night control and zone day night control Pneumatic actuation is preferred for unit ventilator control because it operates smoothly and changes modes of operation through a simple pressure change Individual room day night control uses a day night room thermostat t...

Page 429: ...tor control including PI control enhanced digital control and graphic display Figure 27 is of a DDC ASHRAE Cycle III basic system Unless the space temperature is below set point the fan discharge temperature is constant at 55F The space sensor modulates the HW valve for comfort control Other than PI control and friendly display of values and setpoints this figure is the standard cycle III Figure 2...

Page 430: ...s with the hot water valve open the face damper open and the OA damper closed and as the room warms to a vent recirculate setpoint the OA damper opens to a minimum ventilation position As the heating load drops the face and bypass dampers modulate to maintain the room heating temperature setpoint As the room temperature rises to a value midpoint between the heating and cooling setpoints the heatin...

Page 431: ...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 55 105 0 100 0 100 DISCHARGE TEMPERATURE SETPOINT ...

Page 432: ...stem and flow through the coils Coils can also freeze when low temperature outdoor air leaks through defective dampers Frequent inspection of dampers should be made to detect bent and broken damper linkages warped damper blades and defective or missing blade seals that can contribute to coil freeze up Low temperature switches to stop the fan and close the OA damper should be provided where freezin...

Page 433: ...ough the coil As space temperature rises the thermostat control signal modulates the valve to decrease the amount of flow through the coil and increase the bypass flow around the coil At the upper end of the thermostat throttling range the valve is in the coil bypass position eliminating flow through the coil The fan runs continuously or is stopped as space temperature rises above setpoint Cooling...

Page 434: ...rature is satisfied The fan can be operated by a local fan switch or a central time clock FOUR PIPE HEATING COOLING SINGLE COIL Figure 35 shows the single coil method for four pipe heating cooling A thermostat controls two three way valves to regulate the flow of chilled or hot water into a single coil Fig 34 Four Pipe Heating Cooling Fan Coil Unit with a Split Coil C3030 1 DISCHARGE AIR THERMOSTA...

Page 435: ...his system relies on load diversification Some units may be cooling while other zones operate in the heating cycle In this case the water loop is a source to heating units and a sink to cooling units transferring heat from one to the other Water loop temperatures are maintained between 70 and 90F to provide an adequate heat source or heat sink A central boiler together with a chiller and or coolin...

Page 436: ...h the compressor in either the heating or cooling mode In others the changeover valve remains in the heating or cooling position as long as space temperature is in the appropriate range Where a central water plant provides heating cooling source water for the heat pumps water control is often provided to conserve water when the heat pump cycles off and when the water temperature is excessive for t...

Page 437: ...4 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 V 74 6 TENTH FLOOR SOUTH The Figure 39 example shows a graphic of the southern half of a floor with 30 VAV boxes and their associated space temperatures Selecting anyVAV box would produce a graphic of that box similar to those previously shown in this section and all ...

Page 438: ...il units and their associated heating and cooling plants should be started by a global optimum start program with the OA damper closed until occupancy time See Chiller Boiler and Distribution System Control Applications section for additional information on hot water system control Because unit ventilators have large OA dampers in close proximity to the water coils the hot water pump should run an...

Page 439: ...ENGINEERING MANULA OF AUTOMATIC CONTROL INDIVIDUAL ROOM CONTROL APPLICATIONS 429 ENGINEERING INFORMATION ...

Page 440: ...ENGINEERING MANULA OF AUTOMATIC CONTROL INDIVIDUAL ROOM CONTROL APPLICATIONS 430 ...

Page 441: ... Ball Valve 437 Butterfly Valve 437 Two Way Valve 438 Quick Opening Valve 438 Linear Valve 439 Equal Percentage Valve 439 Three Way Valves 440 Mixing Valve 440 Diverting Valve 441 Valve Sizing 441 Water Valves 441 Quantity Of Water 442 Water Valve Pressure Drop 443 Water Valve Sizing Examples 443 Steam Valves 445 Quantity Of Steam 445 Steam Valve Pressure Drop 447 Proportional Applications 447 Two...

Page 442: ...dy The shaped end controls fluid flow through the valve with respect to stem travel A V port plug has a cylinder called a skirt that rides up and down in the valve seat ring The skirt guides the plug and varies the flow area with respect to stem travel via its shaped openings A quick opening plug is flat and is either end guided or guided by wings riding in the valve seat ring The flat plug provid...

Page 443: ...ol valve for specified conditions Currently in the control valve industry one of three flow coefficients British Av North American Kv or United States Cv is used depending upon the location and system of units The flow coefficients have the following 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 formul...

Page 444: ... that the nominal body rating is not the same as the actual body rating Body rating actual The correlation 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 From Figure 2 a valve with an ANSI rating of 150 psi ANSI Class 150 has...

Page 445: ...gm or piston chamber Reduced Port valve A valve with a capacity less than the maximum for the valve body Ball butterfly and smaller globe valves are available with reduced ports to allow correct sizing for good control Screwed end connection A valve with threaded pipe connections Valve threads are usually female but male connections are available for special applications Some valves have an integr...

Page 446: ...gives some indication of whether the valve requires a screwed end or a flanged end connection Does the application require two position control or proportional control Does the application require a normally open or normally closed valve Should the actuator be direct acting or reverse acting In its state of rest the valve is normally open or closed depending on the load being controlled the fluid ...

Page 447: ...ors with linear motion to operate globe valves are available for operation with many control signals 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...

Page 448: ...e provides a small increase in cooling A nonlinear system has varying sensitivity For example a small increase in temperature can provide a large increase in cooling in one part of the operating range and a small increase in another part of the operating range To achieve linear control the combined system performance of the actuator control valve and load must be linear If the system is linear a l...

Page 449: ...rtional to changes in the stem travel Thus a linear valve is used in linear applications to provide linear control EQUAL PERCENTAGE VALVE An equal percentage valve includes a contoured plug or contoured V port shaped so that similar movements in stem travel at any point in the flow range change the existing flow an equal percentage regardless of flow rate Stem Flow Change Position Rate Change 30 o...

Page 450: ...ream pressure of 10 psi on the outlet port The close off pressure is 25 psi 10 psi 15 psi The application requires a mixing valve with at least a 15 psi close off rating The actuator selected must have a high enough force to operate satisfactorily HEAT OUTPUT HEAT OUTPUT C2333 100 0 100 FLOW 90 10 100 0 100 STEM TRAVEL FLOW 90 100 0 100 STEM TRAVEL 90 10 GRAPH A GRAPH B GRAPH C 50 50 50 10 50 50 5...

Page 451: ...p across the valve can cause it to slam shut with resulting loss of control EXAMPLE A diverting valve application has 20 psi maximum on the inlet port one outlet port discharging to the atmosphere and the other outlet port connecting to a tank under 10 psi constant pressure The pressure difference between the inlet and the first outlet port is 20 psi and between the inlet and second outlet port is...

Page 452: ... coil Q Btu hr K x TD w 2 For hot water coil valves Where cfm Airflow through the coil 1 08 A scaling constant See Note TDa Temperature difference of air entering and leaving the coil K Value from Table 3 based on temperature of water entering the coil pounds per gallon x 60 minutes per hour TDw Temperature difference of water entering and leaving the coil NOTE Thescalingconstant1 08isderivedas fo...

Page 453: ...to equalize the load drop and the bypass drop 3 When selecting pressure drops for three way mixing valves in boiler bypass applications Fig 13 consider the following a Determine the design pressure drop through the boiler including all of the piping valves and fittings from the bypass connection through the boiler and up to the three way valve input b The valve pressure drop should be equal to or ...

Page 454: ... section Substituting the flow of water specific gravity of water and pressure drop in the Cv formula shows that the Valve V5 should have a Cv of 235 Fig 16 Chiller Bypass Application 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 V5 PUMP SUPPLY DP SETPOINT 34 180 GPM PER AHU COIL DP M10605 CHILLER 12 9 6 36 40 4 48 50 PD 4 3 2 4 ...

Page 455: ...em indicate three inch supply and return mains From an elbow equivalent table and pipe friction chart found in the ASHRAE Handbook or other reference manuals the calculated pressure drop through a three inch tee and the piping from the valve and the tee to the exchanger is 0 09 psi Heat exchanger pressure drop is 1 41 ft of water or 1 41 ft x 0 433 psi ft 0 61 psi Total pressure drop from bypass c...

Page 456: ... follows Simplifying the equation Where Btu hr Heat output 1000 Btu lb A scaling constant representing the approximate heat of vaporization of steam 2 For sizing steam coil valves Where cfm Cubic feet per minute ft3 min of air from the fan TDa Temperature difference of air entering and leaving the coil 1 08 A scaling constant See NOTE 1000 Btu lb A scaling constant representing the approximate hea...

Page 457: ...ur h The pressure drop across a valve in a modulating application is h 80 x Pm Pr Where Pm Upstream pressure in supply main is 80 psig Pr Pressure in return is atmospheric pressure or 0 psig Substituting this data in the pressure drop formula h 0 80 x 80 0 0 80 x 80 64 psi Average Radiator of Convector Temperature Deg F Cast Iron Radiator Btu Hr EDRa Convector Btu Hr EDRb 215 240 240 200 209 205 1...

Page 458: ...steam will be superheated in most cases and must be considered EXAMPLE 2 In Figure 19 a linear valve V1 is needed for accurate flow control of a steam coil that requires 750 pounds per hour of steam Upstream pressure in the supply main is 5 psig and pressure in the return is 4 in Hg vacuum minimum 80 47 4 2 80 23 6 56 4 psig Cv 1 0 00075 x 0 x 808 5 x 2 63 5 47 4 1745 6 63 5 x 6 88 4 6 VALVE VI C2...

Page 459: ...20 130 140 337 9 344 1 350 0 355 2 360 9 3 888 3 595 3 337 3 12 2 923 1 972 1 896 1 827 1 766 1 710 57 4 62 3 67 4 72 3 77 4 150 160 170 180 190 366 2 370 6 375 5 379 6 383 9 2 746 2 602 2 462 2 345 2 234 1 657 1 613 1 569 1 531 1 495 82 3 87 4 92 3 97 4 102 3 63 5 A scaling constant s 0 Substituting the quantity of steam specific volume of steam and pressure drop in the Cv formula shows that Valv...

Page 460: ...4 2 421 8 2 134 1 918 1 742 1 595 1 472 1 461 1 385 1 320 1 263 1 213 107 4 119 8 132 4 145 0 157 4 350 400 450 500 550 435 6 448 1 459 5 470 0 479 7 1 272 1 120 0 998 0 900 0 818 1 128 1 058 0 999 0 949 0 904 182 4 207 4 232 4 257 4 282 4 600 650 700 800 900 1000 488 8 497 3 505 4 520 3 533 9 546 3 0 749 0 690 0 639 0 554 0 488 0 435 0 865 0 831 0 799 0 744 0 699 0 659 307 4 332 4 357 4 407 4 457...

Page 461: ...affles 457 Typical Damper Construction 458 Performance Data 458 Leakage Ratings 458 Torque Requirements 460 Velocity Ratings 460 Temperature Ratings 460 Pressure Ratings 460 UL Classification Fire Smoke 460 Application Environment 460 Velocity 460 Static Pressure 461 Temperature 461 Corrosion 461 Turbulence 461 Nuclear Seismic Applications 461 Actuators and Linkages 461 Normally Open Normally Clos...

Page 462: ...stic 464 Installed Characteristic 464 Determining Damper Size 465 Other Damper Sizing Considerations 467 Two Position Control 467 Modulating Control 467 Oversized Damper Characteristics 467 Damper Performance 467 Control System Sensitivity 467 Damper Pressure Drop 468 Damper Applications 469 Mixed Air Control 469 Face and Bypass Control 470 Throttling Control 470 ...

Page 463: ... 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 Damper system The damper plus the series resistance that relates 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 modula...

Page 464: ...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...

Page 465: ... 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...

Page 466: ...lade length ThethreedampersizestestedbyULareMaximumA Minimum B Minimum A Maximum 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...

Page 467: ...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...

Page 468: ...a damper 12 in high x 48 in wide However there is significantly more leakage with the 48 in high x 12 in 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 4 0 ft2 each at 1 0 in wc is Leakage Area x Rating ft2 Minimum Leakage 4 0 x 10 0 min 40 ft3 min Maximum Leakage 4 0 x 26 0 max 104 ft3 min Performance c...

Page 469: ...10 0 0 6 12 18 24 30 36 42 48 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 A DIMENSION LEAKAGE SCFM B DIMENSION LEAKAGE SCFM A DIMENSION B DIMENSION LEAKAGE VS DAMPER SIZE APPLIED TORQUE 50 LB IN ACTUAL TEST DATA 1 IN WC STATIC 2 IN WC STATIC 3 IN W C STATIC 4 IN W C STATIC 5 IN W C STATIC 6 IN W C STATIC TOTAL LEAKAGE B DIMENSION LEAKAGE A DIMENSION LEAKAGE WHERE A DIMENSION OUTSIDE DIMENSION PAR...

Page 470: ...t conditions 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 from high differential pressure In extreme cases physical dama...

Page 471: ... is 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 ...

Page 472: ...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...

Page 473: ...versized 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 ra...

Page 474: ...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...

Page 475: ... 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 55 in wc is located in series with an opposed blade damper the damper should have a pressure drop of 0 06 10 percent of 0 55 0 06 Characteristic ratio Fig 29 and 30 series resistance damper resistance 2 5 100 damper resistance 1 10 100 damper resist...

Page 476: ... 21 3265 x pressure drop 0 3903 For pressure drops Step 3 0 23 Ratio 1 79 7448 x pressure drop 0 2340 5 Calculate damper area in2 For parallel blade dampers Damper area in2 Duct area in2 x ratio 0 37 0 9085 For opposed blade dampers Damper area in2 Duct area in2 x ratio 0 3810 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 the op...

Page 477: ... 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 character...

Page 478: ... Calculate the free area ratioa For parallel blade dampers the free area ratio is found Ratio 0 00005149 x damper area in2 0 1007 x Damper area in2 Duct area in2 For opposed blade dampers the free area ratio is found Ratio 0 00001159 x damper area in2 0 0849 x Damper area in2 Duct area in2 3 Using the ratio from Step 1 calculate the pressure drop at 1000 fpm For ratios 0 5 Pressure drop in wc 0 04...

Page 479: ...e drop shifts from the louvers screens to the dampers as they go from open to closed Opposed blade dampers for outdoor 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...

Page 480: ...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 ...

Page 481: ... Heat Transfer 479 Flow 479 Velocity 479 Power 480 Work Energy 480 Enthalpy 481 Force 481 Torque 481 Density 481 Electrical Data 482 Electrical Distribution Systems 482 General 482 Single Phase System 482 Three Phase Three Wire Wye System 483 Three Phase Four Wire Wye System 483 Three Phase Delta System 483 Electrical Conductors 484 Conduit Size And Fill 485 Electric Motors 485 Voltage Conversion ...

Page 482: ...r a given location and da y the highest recordedtemper atur eis74Fandthelo westrecorded temper atur eis46F Thenthedail ymeantemper atur eis Therefore the n umber of hea ting de gree days for the g iven day is 65 60 5 heating de gree days Table 1 gives heating degree days and Table 2 gives cooling degree days in a normal year based on the years 1961 through 1990 for some selected cities Table 1 inc...

Page 483: ... Los Angeles AP CA 258 215 224 158 96 54 9 5 22 32 127 258 1458 43 63 0 Los Angeles C O CA 222 170 169 128 72 35 0 0 10 17 105 226 1154 40 66 0 Miami FL 88 51 14 0 0 0 0 0 0 0 6 41 200 47 75 9 Milwaukee WI 1429 1176 983 618 338 82 14 27 123 456 819 1259 7324 4 46 1 Minneapolis St Paul MN 1649 1319 1054 558 244 41 11 22 167 502 954 1460 7981 12 44 9 New York La Guardia NY 1045 890 729 405 144 8 0 0...

Page 484: ...7 727 77 67 Los Angeles C O CA 14 32 36 77 97 176 293 316 271 162 45 18 1537 86 69 Miami FL 156 149 221 306 425 492 546 552 507 412 264 168 4198 89 77 Milwaukee WI 0 0 0 0 16 82 197 160 24 0 0 0 479 84 71 Minneapolis St Paul MN 0 0 0 0 43 137 278 192 32 0 0 0 682 86 71 New York La Guardia NY 0 0 0 0 44 191 353 322 125 17 0 0 1052 87 72 Oklahoma City OK 0 0 9 38 136 351 527 499 255 44 0 0 1859 95 7...

Page 485: ... 000 000 000 mega M 106 1 000 000 kilo k 103 1 000 hecto h 102 100 deca da 101 10 deci d 10 1 0 1 centi c 10 2 0 01 milli m 10 3 0 001 micro µ 10 6 0 000 001 nano n 10 9 0 000 000 001 Desired Unit Existing Unit Pounds per Sq In psi Kilo pascals kPa Ounces per Sq In Milli meters of Mercury Kilogram force per cm 2 Inches of Water Inches of Mercury Feet of Water Bar Pounds per Sq In psi 6 8948 16 0 5...

Page 486: ...t Existing 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 millimet...

Page 487: ... 32 Since 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 fol...

Page 488: ... 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 ...

Page 489: ...8 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 p...

Page 490: ...orsepower hp 2546 4 42 44 33 000 550 0 07605 0 2121 0 7457 Boiler Horsepower hp boiler 33520 558 7 433 880 7231 13 15 2 793 9 803 Tons of Refrigeration 12000 200 0 155 640 2594 4 715 0 358 3 516 Kilowatts kW 3414 2 56 92 44 260 737 6 1 341 0 1020 0 2844 Desired Unit Existing Unit British Thermal Unit Btuh 15 6C Watt hour Wh Kilowatt hour kWh Calorie Cal Foot pound ft lb a Joule J British Thermal U...

Page 491: ...nd 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 radiu...

Page 492: ... 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...

Page 493: ...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...

Page 494: ...m Ohm Mft 18 16 14 1620 2580 4110 0 106 0 118 0 131 0 0088 0 0109 0 0135 0 146 0 158 0 204 0 0167 0 0196 0 0327 0 089 0 100 0 105 0 0062 0 0079 0 0087 7 95 4 89 3 14 8 45 5 29 3 26 13 1 8 21 5 17 12 10 8 6530 10 380 16 510 0 148 0 168 0 245 0 0172 0 0222 0 0471 0 221 0 242 0 328 0 0384 0 0460 0 0845 0 122 0 153 0 218 0 0117 0 0184 0 0373 1 98 1 24 0 778 2 05 1 29 0 809 3 25 2 04 1 28 6 4 3 26 240 ...

Page 495: ...phase motors since starting rotational torque is inherent in three phase motors A three phase motor can be reversed by switching any two phases Table 23 Single Phase Motor Characteristics and Applications Motor Type Characteristics Application Universal Series Armature and field connected in series Operates on dc or ac with approximately the same speed and torque Where either ac or dc may be avail...

Page 496: ... Rotor Indicating Code Letters Table 25 Motor Current Ratings Cross Types TF Types TFN Approximate dc Resistance at 167F 75C section TW THW Types RHW RHH THWN THHN Copper Wire Size AWG of copper Circular Mills Approx imate Dia in Approx imate Area in2 Approx imate Dia in 2 Approx imate Area n 2 Approx imate Dia in Approx imate Area in2 Uncoated Ohm Mft Coated Ohm Mft Aluminum Ohm Mft 18 16 14 1620...

Page 497: ... 20 12 10 10 10 10 12 10 10 10 10 12 10 10 10 10 20 00 21 25 22 50 23 75 25 00 50 60 60 60 60 40 45 45 50 50 40 45 45 50 50 35 35 40 40 40 35 35 40 40 40 35 35 40 40 40 25 30 30 30 30 25 30 30 30 30 22 24 26 28 32 10 10 8 8 8 10 10 8 8 8 10 10 8 8 8 27 50 30 00 32 50 35 00 40 00 70 80 80 90 100 60 60 70 70 80 60 60 70 70 80 45 50 60 60 70 45 50 60 60 70 45 50 60 60 70 35 40 40 45 50 35 40 40 45 50...

Page 498: ...8 0 200 5 203 0 205 4 207 7 209 9 958 8 957 2 955 5 954 0 952 5 951 1 1156 8 1157 7 1158 5 1159 4 1160 2 1161 0 12 15 20 25 30 40 243 7 249 8 258 8 266 8 274 0 286 7 15 35 13 87 12 00 10 57 9 463 7 826 3 918 3 724 3 464 3 251 3 076 2 797 13 4 14 8 17 4 19 8 22 4 27 4 212 1 214 2 227 4 235 6 243 0 255 9 949 7 948 3 939 5 934 0 928 9 919 9 1161 8 1162 5 1166 9 1169 6 1171 9 1175 8 50 60 70 80 90 100...

Page 499: ...1 1 03 1 05 1 07 1 09 1 11 1 13 70 1 00 1 02 1 04 1 06 1 08 1 10 1 12 1 14 1 16 1 18 1 20 80 1 02 1 04 1 06 1 08 1 10 1 12 1 14 1 16 1 18 1 20 1 22 100 1 06 1 08 1 10 1 12 1 14 1 16 1 18 1 20 1 22 1 25 1 27 120 1 09 1 11 1 13 1 16 1 18 1 20 1 22 1 24 1 27 1 29 1 31 140 1 13 1 15 1 17 1 20 1 22 1 24 1 26 1 29 1 31 1 34 1 36 160 1 17 1 19 1 21 1 24 1 26 1 28 1 31 1 33 1 35 1 38 1 41 180 1 21 1 23 1 ...

Page 500: ...1 26 1 27 4442 4460 4478 4496 4513 1 74 1 75 1 76 1 77 1 78 5283 5298 5313 5328 5343 2 25 2 26 2 27 2 28 2 29 6008 6021 6034 6047 6061 5 10 5 20 5 30 5 40 5 50 9045 9133 9220 9307 9393 0 26 0 27 0 28 0 29 0 30 2042 2081 2119 2157 2194 0 77 0 78 0 79 0 80 0 81 3514 3537 3560 3582 3604 1 28 1 29 1 30 1 31 1 32 4531 4549 4566 4584 4601 1 79 1 80 1 81 1 82 1 83 5358 5373 5388 5403 5418 2 30 2 31 2 32 ...

Page 501: ...1 5 1 0 5 M10494 Fig 7 Moisture in Compressed Air Versus Temperature and Pressure EXAMPLE Assume ambient conditions are 80F and 80 percent rh The air is compressed and stored in a tank at 30 psi and 90F Air is delivered to the controls at 20 psi See Psychrometric Chart Fundamentals section for use of the psychrometric chart and Psychrometric Charts No 1 and No 2 77 0031 and 77 0031 A MOISTURE IN C...

Page 502: ...nly 0 0091 pounds of moisture per pound of dry air This means that 0 0008 pounds of moisture per pound 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...

Page 503: ... 33 34 35 37 38 39 40 41 42 43 44 44 45 46 47 48 48 49 50 50 51 51 52 53 53 54 55 56 57 57 58 59 60 61 61 62 62 63 64 64 65 65 66 66 67 67 67 68 68 68 69 69 69 70 70 0 3 5 8 10 12 14 16 18 19 21 23 24 26 27 28 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 45 46 47 47 48 48 49 50 50 51 52 53 54 55 56 57 58 58 59 60 60 61 62 62 63 63 64 64 65 65 65 66 66 67 67 67 68 68 1 4 6 8 10 12 14 16 17 19 20...

Page 504: ...tion 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 406 Control 403 Dual Duct Pressure Independent 410 411 Dual Duct 410 Induction VAV 406 Parallel Fan 408 Pressure Independent Constant Volume 411 Dual Duct 410 Pressure Dependent 403 Series Fan 408 Single Duct VAV 404 Throttl...

Page 505: ...ilding pressure balance 270 Butterfly Valve 437 Butterfly valve 435 C capacity index 433 Capacity Relay 80 Celsius Fahrenheit Conversion Tables 478 Central Cooling Plants 304 Central plant 297 Centrifugal Chiller Control Application 305 Single 304 Centrifugal Chiller Control With Absorption Chiller 315 Centrifugal Chillers Control Application 309 Multiple Dissimilar Control 315 Multiple Similar Co...

Page 506: ...oop 15 Control methods 16 Control Modes Electronic 128 Control modes 17 Control Point 59 120 Control point 5 Control Systems Electronic 120 Controlled medium 5 Controlled Variable 59 Controlled variable 5 15 26 Controller 5 33 98 Configuration 135 DDC Configuration 135 Microprocessor Based 133 Microprocessor based 134 Programming 142 System Level 136 146 Zone level 136 145 Electric Classification ...

Page 507: ...istics 463 Types Fire 456 Low Leakage 454 Multiple section 457 Parallel and opposed Blade 454 Round 454 Smoke 456 Damper Control 105 Dampers 76 Data File Programming 143 Data Penetration 196 DDC 6 Deadband 6 297 Definitions Chiller Boiler And Distribution System Control Ap 297 Degree Days 472 Dehumidification 12 Dehumidification and Reheat 52 Dehumidification control processes 243 Dehumidifier Air...

Page 508: ...al Conductors 484 Electrical Data 482 Electrical Distribution Systems 482 Single Phase System 482 Three Phase Delta System 483 Three Phase Four Wire Wye System 483 Three Phase Three Wire Wye System 483 Electronic Indicating Devices 129 Output Control 128 Output Devices 128 Power Supply 129 System Application 130 Transducer 129 Electronic Control 120 Electronic control 6 Electronic Control Systems ...

Page 509: ... 168 Graphic Penetration 196 H Hand Off Auto Start Stop Circuit 115 Hardware Configuration 187 Head pressure 297 Heat anticipation 18 Heat Exchanger 384 Heat Exchanger Substation 384 Heat pump 11 Heat Pumps 425 Operation 425 Heat Recovery System 325 Heat Surface Factor 384 Heat Transfer Station 384 Heating 9 Heating Anticipation 102 Heating coil 10 Heating control processes 223 Heating Data 473 He...

Page 510: ...78 Low Pressure Steam Distribution Systems 372 Low Voltage 99 Low Limit Controller 102 103 111 Low Pressure Selector Relay 79 M Main Line 60 Main Sensor 121 Management Level Processor 185 188 Manipulated 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 475 Mi...

Page 511: ... Electronic 129 Preheat control processes 228 Sensing elements 31 Pressure Controller 71 Pressure Conversion Multipliers 475 Pressure drop 434 critical 434 Pressure Independent Constant Volume ATU Dual Duct 411 VAV ATU Dual Duct 410 Pressure Reducing Stations District Heating 386 Pressure Reducing Valve Station 68 371 Pressure Reducing Valves 69 Pressure Sensor Electronic 127 Pressure sensors 277 ...

Page 512: ...neumatic Transducer 83 Hesitation 82 High Pressure Selector 79 Load Analyzer 79 Lockout 78 Low Pressure Selector 79 Pneumatic Electric 82 Positive Positioning 80 Ratio 81 Reversing 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 Water 363 Supply Air Temperature 226 Supply ai...

Page 513: ...Codes and standards 174 General 173 Layout of system 174 Purging 178 Stairwell pressurization control 180 Zone pressurization control 179 Snap Acting Relay 78 Software Application 133 137 Building Management 142 Direct Digital Control 137 Operating 133 137 Solenoid Brake 97 100 101 Solenoid Valve 128 Specific Volume 39 Spring Range 74 Stack effect 271 Starters 114 Static head 298 Steam Heating Dev...

Page 514: ...ipliers 481 Total and static pressure sensors 279 Total Heat 39 Tower Free Cooling Dual Chillers 327 Toxicity 153 Transducer 33 Electronic 121 125 128 129 Electronic to Pneumatic 129 Transformer 99 Transmission 9 Transmitter Electronic 121 125 127 Turndown 433 Twisted Copper Pair 189 Two Pipe Steam Systems 372 Two Position Control 105 Electric 107 Two position control 7 17 Two Pressure Reducing Va...

Page 515: ...Air Volume ATU 403 405 406 Variable speed pumping VSP 298 Variable Vacuum Return Systems 373 Velocity Conversion Multipliers 479 Velocity Pressure 490 Velocity Sensor Controller 73 Ventilation 10 13 Ventilation control processes 209 Volatile organic compound 153 Voltage Conversion 487 Volume Conversion Multipliers 477 W Warmup control 286 Water Valves Sizing 441 Weather Data 472 Weight Mass Conver...

Page 516: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL GENERAL ENGINEERING DATA 506 Notes ...

Page 517: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL GENERAL ENGINEERING DATA 507 Notes ...

Page 518: ...ENGINEERING MANUAL OF AUTOMATIC CONTROL GENERAL ENGINEERING DATA 508 ...

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