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68

Low Temperature Heat Exchanger (LTHX) Margin Vs
Capacity Control Signal

The microprocessor will control the generator
concentrations to maintain the selected Low Temperature
Heat Exchanger (LTHX) service setting setpoint. The Low
Temperature Heat Exchanger (LTHX) margin setpoint is
located in the service settings field startup group menu.
The standard set point is 15°F which is the solution margin
at nominal design conditions. As the evaporator load
decreases and the capacity control signal decreases, the
margin will increase to a maximum of 30°F at minimum
generator flow as illustrated in Figure 18. Between 15% and
minimum solution pump speed, the Low Temperature Heat
Exchanger (LTHX) margin increases to 30°F. The following
chart illustrates this activity. The generator flow is
controlled by changing the Low Temperature Generator
(LTG) pump speed as evaporator load decreases.

Figure 18

Plus 15°F

Service Setting: Low
Temperature Heat
Exchanger (LTHX)
(15°F)

Minimum Flow
(Minimum LTSP
AFD speed)

Capacity flow control signal

Maximum Flow
(Maximum LTSP
AFD speed)

Note:

When the energy input is greater than 90% and if the
margin begins to widen (lack of heat input to concentrator)
the UCP may slowdown the drives in an effort to maintain
Low Temperature Heat Exchanger (LTHX) margin setpoint.

Summary of Contents for HORIZON ABDA

Page 1: ...Controls Single and Two Stage Steam and Two Stage Direct Fired Absorption Chiller With Microprocessor Control Panel Unit Models ABDA ABTF ABSD ABS CTR 3B HORIZON April 2004 ...

Page 2: ... Standard Inc All rights reserved 11 Control System Proportional Integral and Derivative PID Control 69 12 Control System Limits 70 13 Crystallization Sensing Detection and Recovery SDR 71 14 Absorber Entering or Low Condensing Temperature Limit 75 15 Low Chilled Water Temperature Cutout LCWTC Low Refrigerant Temperature Cutout LRTC and Differential to Start and top 76 16 Interstage Pressure Limit...

Page 3: ...basics of the solution cycle how the refrigerant and lithium bromide flows through the chiller An understanding of the absorption cycle is necessary to follow how the lithium bromide cycle is controlled by the Unit Control Panel UCP Sequence of Operation Section 3 The microprocessor has a programmed sequence for machine startup shutdown operating limit and safety shutdown This section describes th...

Page 4: ...ide returning from the high temperature generator by way of the high temperature heat exchanger and float valve The resulting intermediate lithium bromide solution passes through the low temperature heat exchanger to the absorber spray solution pump for distribution over the absorber tubes completing the lithium bromide cycle When the intermediate lithium bromide solution is sprayed onto the absor...

Page 5: ...ely cool area compared to the hot refrigerant vapor is created This cool area draws hot refrigerant vapor 10 Items through the heat exchanger where the vapor condenses transferring heat to the system water 16 to 17 Items within the heat exchanger tubes The condensed liquid refrigerant returns to the high temperature generator It should be noted that there is a trade off during simultaneous heating...

Page 6: ...r Heat Exchanger HXER High Temperature Heat Exchanger HXER Low Tem perature Heat Ex changer HXER High Temperature Generator Pump Low Temperature Generator Evaporator Condenser Purifier Purge Evaporator Spray Pump Low Temperature Generator Pump EDUCTOR Absorber Spray Pump Absorber Refrigerant storage ...

Page 7: ... 346 174 20 346 174 21 Condensate Leaving Machine 210 99 Table 1 ABTF machine cooling cycle See Figure 1 Lithium Bromide Solution or Refrigerant Water Absorber Dilute Solution Entering the Low Temperature Generator LTG Solution Leaving High Temperature Heat Exchanger HTHX and Flow Control Device Mixed Solution Intermediate with Concentrated Entering Leaving Temperature Heat Exchanger LTHX Solution...

Page 8: ...or High Temperature Heat Exchanger HXER Low Temperature Heat Exchanger HXER High Temperature Generator Pump Low Temperature Generator Evaporator Condenser Purifier Purge Evaporator Spray Pump Low Temperature Generator Pump EDUCTOR Absorber Spray Pump Absorber Refrigerant Storage Hot Water Heater ...

Page 9: ...int for example 85 tower 44 leaving chilled water at full load Lithium Bromide Solution or Refrigerant Water Absorber Dilute Solution Entering the Low Temperature Generator LTG Mixed Solution Intermediate with Concentrated Entering Low Temperature Heat Exchanger LTHX Absorber Spray Solution Mixed with absorber dilute Absorber Leaving or Condenser Entering Cooling Water Condenser Leaving Cooling Wa...

Page 10: ... the LTG 64 4 216 102 4 Solution Entering ABS Sump Spray Pump 64 4 129 54 5 ABS Spray Solution Mixed w abs dilute 63 1 121 49 6 LTG Refrigerant Vapor NA 208 98 7 Condensed Refrigerant NA 110 43 8 Evaporator Pump Refrigerant NA 41 5 9 System Chilled Water Entering NA 54 12 10 System Chilled Water Leaving NA 44 7 11 Absorber Cooling Water NA 85 29 12 Absorber Leaving Condenser Entering Cooling Water...

Page 11: ... the start sequence progresses The UCP2 waits up to four minutes and fifteen seconds for proof of chilled water flow after a water pump start command output is enabled Failure to receive chilled water flow confirmation within the allotted time results in a message stating Diagnostics auto This is a MAR auto restart diagnostic where the chiller will start once the chilled water flow switch logic is...

Page 12: ...in AUTO Mode Variable 6 second to 4 minutes 15 seconds Variable 6 seconds to 4 minutes 15 seconds Variable Time Line 1a START AUTO Selected Time Line 2 Events Go to Time Line 3 Next Page Standard Mode Display Ignore Interstage Pressure Sensor Failures until the Solution Leaving Low Temperature Generator LTG is 120 F Command Flame Safeguard to Begin Start Sequence See Note 3 Starting Pre Heating So...

Page 13: ...ed to Cool If There is no need to Cool when Power Returns a Dilution Cycle Will be initiated See Note 1 and 6 See Note 7 Go to Time Line 1a Previous Page Auto Stop Chilled Water Pump Completes Dilution Cycle After Satisfying Load Sequence of Events Panic Stop Stop Stop Auto Chilled Water Pump Off Condenser Water Pump Off Solution Pumps Off Refrigerant Pump Off Absorber Pump Off Energy Input Off Ig...

Page 14: ... heat sequence consists of the energy input command held at a reduced rate 40 until the Lithium Bromide solution concentrations reach 54 Service Tests Manual energy input is allowed during this pre heat sequence Control of Leaving Water Temperature and concentration are overridden Limits and safeties are active Shutdown Dilution Cycle When the chiller cycles OFF a dilution cycle mixes the strong l...

Page 15: ...lay expires When the dilution cycle is complete the machine solution pumps and ventilation fan are stopped The RDV1 which opened when the dilution cycle started remains open until the machine is restarted The CLD displays stop with the completion of the dilution cycle Panic Stop Panic Shutdown Pressing the Stop key twice within 5 Second Interval initiates a machine panic stop NOTE This is not to b...

Page 16: ...r relays transformers starter module and purge module Line voltage is restricted to the right hand side The inner control panel components are illustrated in Figure 4 Modules are stacked in a top bottom or middle configuration Voltages in Panels Voltages present within the unit control panel includes Three phase line voltage power sideonly 115Vac control circuits 24Vac module power supply Low volt...

Page 17: ...s L1 2 3 Main Power Entrance 1TB2 Pump Motor Terminal Block 1TB3 UCP2 Control Panel Mounted Terminal Strip Not Standard 1S1 Line Voltage Fused Disconnect Switch 1K1 Refrigerant Pump Abnormal Relay 1K2 High Temperature Solution Pump Abnormal Relay 1K3 Interstage Vapor High Pressure Cutout Relay 1K11 Refrigerant Pump Contactor 1K12 HT Solution Pump Contactor 1U11 Refrigerant Pump Overload 1U12 HT So...

Page 18: ...icroprocessor control modules within the main unit control panel and burner panel Comm 3 4 IPCB Printer Intf Purge Stepper Class II Wiring Class I Wiring Left Hand Side of Unit Control Panel Right Hand Side of Unit Control Panel Backplane Options Chiller Starter Circuit Burner Remote Mounted Burner Control Panel ABDA only Class II Wiring Class I Wiring Class II Wiring Class I Wiring ...

Page 19: ...eaving Water Temperature control algorithms that control chiller capacity The chiller module manages machine safety operating limits and chilled water temperature by monitoring unit mounted sensors and information from other modules on the interprocessor communications IPC link When machine operating conditions change the chiller module initiates communications to the other panel modules to manage...

Page 20: ...ther hot water simultaneous heating requirements 1U8 9 10 Optional External Communications Modules IPC Buffer Module Used to communicate to external devices Printer Communications Interface required for printer compatibility The printer interface module provides a pre formatted chiller log to a printer The printer interface can be programmed via the LCLD to print a chiller log on command at the ti...

Page 21: ...e The installation of the transformers must be with the markings all facing the same direction in reference to the current flow through the primary wiring The current transformer outputs are input to the starter module which monitors current Total Motor Current Monitoring Current transformers are used to monitor total unit currents See Table 3 to select CT Rating In many cases more than one select...

Page 22: ...eport Chiller Report Cycle Report Pump or Purge Report Operator Settings Service Settings Service Tests Diagnostics Previous Next Enter Cancel Auto Stop The operator interface or local clear language display LCLD is used to communicate with the chiller The machine operator can select information displayed from group menus that have predetermined information All operator selected and monitored info...

Page 23: ...er communicates with the report and settings menus Functional Keys The Next and Previous keys allow the operator to step through the various menus within a group The report group will sequence around to the top or bottom of that group when the end or beginning is reached respectively The and keys cause the displayed values to increase or decrease respectively If the or key is held down for more th...

Page 24: ... group When there are twenty items in the report no more can be added until one is removed 5 To remove an item from the Custom Report press the key while it is displayed To Change Settings 1 Press the appropriate settings group key 2 Press the Next key at the header display 3 Enter password if required see page 60 4 Use the Next or Previous keys to bring up the item to be changed 5 When the item t...

Page 25: ...port is being displayed from one of the other report menus press the key The custom report group can holdup to 20 entries Attempting to enter more results in the display indicating User Report Full To remove reports from the custom group simply press the key while it is being displayed The custom report sequence starts with the following header display User Defined Report Press Next Previous to Co...

Page 26: ...ing Unit is Running Unit is Running Unit is Running Unit is Running Unit is Running Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Dilution Cycle Transitioning to Stop Panic Shutdown Run Low Cooling Water Temperature Limit Low Absorber or Condenser Temperature Limit Run Evaporator Limit Low Evaporator Refrigerant Temperature ...

Page 27: ...tor Leaving Water Temperature xxx xf c If the source is front panel then Source will not be displayed otherwise Source will be one of the following External Tracer or Reset 5 Chilled Water Reset Source when Enabled Setpoint or Chilled Water Setting Source Setpoint Unless Heat Only Source CWS xxx xf c Settings Source CWS xxx xf c Source will be either Outdoor Air Return Reset or Constant Return Res...

Page 28: ...ature xxx xf c 9 Absorber Entering Concentration xxx x Lithium Bromide Crystallization Margin xxx xf c The Lithium Bromide Crystallization margin is the difference between the mixed lithium bromide solution temperature leaving the low temperature heat exchanger and its theoretical crystallization temperature 10 Solution Temperature Entering Absorber xxx x f c Absorber Spray xxx xf c 11 Solution Te...

Page 29: ...9 Total Motor Phase Currents Amps A xxx Amps B xxx Amps C xxx Amps 10 Option The following will be displayed only if Line Voltage Sensing Option Installed Motor Voltages AB xxx Volts BC xxx Volts CA xxx Volts 11 Chiller Starts and Run Time Starts are incremented and run time is accumulated when the solution pumps start and or run Chiller Starts xxxx Accumulated Run Time xxHours xxMinutesxxSeconds ...

Page 30: ...ge Vapor Temperature xxx x F C Solution Temperature Entering Level Control xxx x F C Mixed Solution Temperature Entering LTHX xxx x F C Solution Temperature Entering Heating xxx x F C Interstage Vapor Pressure xxx x psig kpa Heating Leaving Concentration xxx xx Lithium Bromide LTG Leaving Concentration xxx xx Lithium Bromide Heating Cutout Monitor Temperature xxx x F C Burner Exhaust Temperature x...

Page 31: ...nutes 24 Hours Purge Total Pumpout Time xx xxx x Minutes Purge Total Run Time xx xxx x Hours Service Log Pumpout time xxxx x Minutes Service Log Time Since Reset xxxx Days 30 Day Purge Pumpout Average xxx x Minutes Chiller Average Run time xxx x Hour Day Total Motor Phase Currents RLA A xxxx B xxxx C xxxx Motor Phase Currents Amps A xxxx Amps B xxxx Amps C xxxx Amps Motor Voltages AB xxxx Volts BC...

Page 32: ...ter Setpoint is within 1 7 F of the leaving water temperature cutout setpoint or within 2 7 F of the low refrigerant temperature cutout setpoint the second line of this display will read Limited by Cutout Setpoint to Change 6 Chilled Water Setpoint Source applicable with External Chilled Water Setpoint Only If the Tracer Option is installed the word Default will appear in front of the setpoint sou...

Page 33: ...s to Change Setting 17 Max Reset Displayed when Return or Outdoor Air is selected as the Hot Water reset type Type Max Reset Setpoint xxx x F Press to Change Setting 18 Heat Cool Priority Select Displayed when the Auxiliary Heating Option is installed Heat Cool Priority Status Press to Change Setting Possible values for status are Cooling Only ROM Default Heating Only Cooling Priority Heating Prio...

Page 34: ...ting Default Chilled Water Setpoint Source Source Chilled Water Reset Type type Press to Change Setting Type Reset Ratio xxx Press to Change Setting Type Start Reset Setpoint xxx x F Press to Change Setting Type Maximum Reset Setpoint xxx x F Press to Change Setting Chilled Water Flow Pretest D E Press to Change Setting Front Panel Hot Water Setpoing xxx x F C Press to Change Setting Deftault Hot ...

Page 35: ...he Stop key until the password is entered The password is entered by pressing the Previous and Enter keys at the same time Display and Keypad are Locked Enter Password to Unlock If the keypad is locked and the password is entered the display will return to the Chiller Report and display the current Operating Mode 3 Language xxxxxxxx Press to Change Setting Selections are English Default Francais D...

Page 36: ...ng Password Required to Access Machine Configuration Group Please Enter Password Press Next or Previous Pass Required to Access Field Start up Group Please Enter Password Note Service level password secured press next previous to continue If press enter Display and Keypad Are Locked Enter Password to Unlock PRESS PREVIOUS AND ENTER Upon entering password goes to chiller mode display exits service ...

Page 37: ... selected the CLD displays DISPLAY AND KEYPAD ARE LOCKED ENTER PASSWORD TO UNLOCK No access is permitted to either the Report screens or the Setting Screens when locked With this selection both the STOP and AUTO keys do not function To UNLOCK press the PREVIOUS and ENTER keys at the same time When the keypad lock feature is Disabled the keypad lock display disappears and the non password protected...

Page 38: ...age will be displayed for 2 seconds to indicate that the FPCW setpoint has been increased 10 Softloading Time Setpoint Soft load time control response is the time that the control will use to ramp to a new target set point This setpoint is always active when the machine is started for softload or any chilled water setpoint change The selectable Range of Values is 0 to 100 in increments of 1 The mo...

Page 39: ... See Table 5A for initial settings for items 20 21 22 25 Table 5A Concentration control setpoints Item Conc ABDA ABSD ABTF 20 Prop 150 180 250 Gain 21 Reset 250 350 400 22 Derivative 400 20 300 25 20 20 20 Evaporator Time Constant Generator Time Constant 20 Concentration Control Gain Setpoint The Range of Valves is 0 to 1000 in increments of 1 The module Default is 500 See above Table 5A See also ...

Page 40: ...ext three entries setup the energy input requirements 28 EV Maximum Travel Setpoint This Menu is only displayed on steam or hot water units Range of Values for ABS is 0 to 60 000 Steps in increments of 100 Steps All 90 degree rotational stepper actuators are 16 300 steps Module Default is 16 300 Steps With burners the value will be determined after the burner min and max fire rates are established...

Page 41: ... Auxiliary Heating option installed Factory default setting is 800 Range of Values is 1 to 1000 in increments of 1 36 Hot Water Control Reset This menu is displayed only on Direct Fired units with the Auxiliary Heating option Installed Factory default setting is 200 Range of Values is 1 to 1000 in increments of 1 37 Hot Water Control Derivative This menu is displayed only on Direct Fired units wit...

Page 42: ...to 255 49 Evaporator Pressure Drop High Enter the corresponding pressure drop at the lower flow rate Range of Values is 1 to 255 50 Evaporator Fluid Coefficient This input identifies the proper fluid characteristics Water is 100 This number is found by multiplying the specific gravity times the specific heat times 100 51 Absorber or Condenser Flow Rate High Enter the higher point flow rate Range o...

Page 43: ...u the series of screens shown below are accessed Note that the second line of these screens will indicate whether or not editing of this setpoint is allowed based on chiller operating state 56 Energy Linearization Coefficient Number 0 Energy Coefficient 0 xxx E 1 Press to Change Setting Range of Values is 20000 to 20000 in increments of 1 Default is 0 57 Energy Linearization Coefficient Number 1 E...

Page 44: ... anytime straight line control is desired E n e r g y I n p u t Command Signal Linear Figure 10 Butterfly valve coefficients Used on fixed head burners with butterfly valve gas control E n e r g y I n p u t Reference Linear Command Signal Figure 11 Adaptive coefficients As determined by Control System E n e r g y I n p u t Reference Linear Command Signal ...

Page 45: ...ss to change setting 26 Solution pump AFD maximum frequency xx hz Press to change setting 28 EV Maximum Travel Setpoint xx xxx Steps Press to change setting 29 Energy input closed stop xxx Press to change setting 30 Energy input open stop xxx Press to change setting 31 Minimum alternate fuel firing rate xxx Press to change setting 33 Maximum wait for combustion time xx minute Press to change setti...

Page 46: ...ss to Change Setting Machine Must Be Stopped To Change Configuration 1 Machine Configuration Group Heading This header is not suppressed if the headers in the Service Settings menu are not revealed 2 Unit Frequency Possible values of Frequency are 60 Hz module default 50 Hz 3 Unit Types Possible values for type Direct Fired module Default 1 Stage Hot Water 1 Stage Steam 2 Stage Hot Water 2 Stage S...

Page 47: ...input Its use is optional on cooling priority Possible values for statuses are Not Installed Module Default Software and Hardware Sales Order Specified Features 17 Line Voltage Sensing Option Only to be installed if voltage potential transformers and fuses and wiring are present Possible values for statuses are installed or not installed module default 18 Unit Line Voltage The following will be di...

Page 48: ...q 3 Unit type type 4 Nominal unit tons tons 5 Rated load amps xxxx amps 6 Current gain setpoint xx 7 Energy input valve type status 8 Energy input valve size xx inches 9 Adaptive steam control status 10 High pressure cutout setting xx psig 11 Flame safeguard type type 12 Ventilation confirmation status 13 Ventilator contacts status 14 Auxiliary heating option status 15 Four to two pipe conversion ...

Page 49: ...ansition from Running to Stop mode of operation 7 Absorber or Condenser Water Flow Switch Status Flow Switch is open no Flow Or Flow Switch is Closed Flow 8 Water Flow Sensing The following will be displayed if the differential water pressure sensor is installed and selected from the machine configuration menu Absorber or Condenser Differential Pressure xxPsid Press Next Previous to Continue 9 Hot...

Page 50: ...p 18 Auxiliary heating valve Manual auto control Heating units only Auxiliary Heat Valve Control Status Press to Change Setting Values for status are Auto default or manual This setpoint will be return to auto on any transition from running to stop 19 If the Heat Valve control status is Auto the following is displayed Aux Heat Valve Auto Position xxx Limit Mode 19 2 If the heat valve control statu...

Page 51: ... up turn on chilled water Absorber or condenser water flow switch status Flow switch is open or no flow or flow switch is closed or flow Hot Water Pump auto on Press To Change Setting Hot Water Flow Switch Status Flow Switch is xxxxx LTG solution pump control Auto or On Press or to change setting HTG solution pump control Auto or On Press or to Change setting Absorber pump control Auto Off On Pres...

Page 52: ... 1 If there are any diagnostics present the following 3 screens are displayed sequentially when the Next key is pressed The first screen is Diagnostics Report Follows Press Next for More 2 2 The second screen is Press Next to Display Operating Mode At Time of Last Diagnostic 2 3 The third screen will be the chiller operating mode display that was present when the most recent diagnostic occurred 3 ...

Page 53: ...sage clears This start will begin when the reset is complete If dilution cycle was in operation and reset is executed the dilution cycle is aborted and restart will occur 6 Clearing informational warnings IFW If any IFW diagnostics are present the following screen will be displayed Press Enter to Clear all IFW Diagnostics WARNING Resetting Be Aware That If The Chiller Mode Was Auto And There Is A ...

Page 54: ...nostic One Time Display Operating Mode at Last Diagnostic Set of Screens for First Active Diagnostic If More Active Set of Screens for First Historic Diagnostic If More Historic Screen s to Clear Reset Diagnostics Up to 20 Sets Total Up to 20 Sets Total G Diagnostics ...

Page 55: ...tion of electrical components Burner Control Panel BCP Burner Gas Fuel Train GFT or Alternate Fuel Train AFT Pump Starter Panel PSP Purifier Purge Solution Pump Adjustable Frequency Drive 4U1 See View C Burner Control Panel BCP Main UCP2 Control Panel UCP2 Purifier Purge Solution Pump Adjustable Frequency Drive 4U1 Main UCP2 Control Panel UCP2 Vacuum Pump Refrigerant Dump Valve Pump Starter Panel ...

Page 56: ... of the absorption fluid cycle see table 7 Front View Direct Fired Absorption Unit Low Temperature Generator Optional Hot Water Heater High Temperature Generator Pump Direct Fired Generator HTG Absorber Spray Pump LTSP Low Temperature Solution Pump Evaporator Spray Pump Refrigerant Storage Evaporator Absorber Condenser ...

Page 57: ... TBD 12 Diff Tower Water Pressure NA Monitor TBD 13 Interstage Vapor Pressure Transducer 14 9 0 PSIG Circuit 15 200 320 Concentration Calc Circuit Design 300 HTG 16 Solution Temperature Entering Level Control 120 200 Calc Mixed Circuit Before Level Control Design 190 Concentration 17 120 200 Calc Mixed Circuit Design 190 Concentration 18 Solution Temperature Entering Absorber 80 180 Control T Marg...

Page 58: ...actory mounted and wired External controls are connected with field wiring and are controlled by the chiller or used by the chiller system Figure 14 Machine sensor locations Other Sensors on Next Page Detail A A Rear View Left Hand End Left Hand View ...

Page 59: ...59 Figure 14 Machine Sensor Locations Continued Front View Left Hand End Right Hand End Right Hand View To Control Panel Detail B B ...

Page 60: ...e Entering LTHX 4RT3 3 Condenser Leaving Water Temperature 4RT9 15 Solution Temperature Entering Absorber 4RT15 4 Absorber Leaving Water Temperature 4RT8 16 Solution Temperature Leaving Absorber 4RT14 5 Absorber Entering Water Temperature 4RT10 17 Solution Temperature Entering LTG 4RT16 6 Solution Temperature Leaving LTG 4RT18 18 Solution Temperature at Absorber Sprays 4RT13 7 Saturated Evaporator...

Page 61: ...wer Water Pressure NA Monitor control option 11 Interstage Vapor Pressure Transducer 14 9 0 PSIG Circuit Limit 12 200 320 Concentration Calc Circuit Design 300 HTG 13 Solution Temperature Entering Level Control 120 200 Calc Mixed Circuit Before Level Control Design 190 Concentration 14 120 200 Calc Mixed Circuit Design 190 Concentration 15 Solution Temperature Entering Absorber 80 180 Control T Ma...

Page 62: ...essure Differential 11 N A 12 N A 13 Soln Concentration LiBr Derived Value 14 N A 15 N A 16 N A 17 Solution Temperature Entering Absorber 18 Solution Temperature Leaving Absorber 19 Solution Temperature Entering LTG 20 Solution Temperature at Absorber Sprays 21 Crystallization Detection Temperature 22 N A 23 N A 24 Generator Entering Hot Water Temperature Hot Water Only 25 Steam Condensate Tempera...

Page 63: ...The resulting refrigerant spray temperature produces the desired leaving chilled water temperature setpoint 2 Concentration Control The concentration control adjusts the energy input for optimum solution efficiency The strong solution concentration is typically maintained at 15 degrees F from the theoretical crystallization point This is called the low temperature heat exchanger LTHX temperature m...

Page 64: ...Concentration Control provides a margin of safety from the cycle to the Lithium Bromide Crystallization Line Cycle Management Refrigerant Temperature F Lithium Bromide Crystallization Line Loss of Refrigerant Interstage Pressure Limit Generator Temperature Limit Solution Temperature F Management Functions Low Refrigerant Temperature Limit Control Freeze Protection High Generator Solution Temperatu...

Page 65: ...e changes in the machine cycle Any change in solution flow is matched by a corresponding change in heat input The net result is to minimize disturbances to concentration control The unit control maintains leaving water temperature setpoint by varying the refrigerant vapor pressure in the evaporator The leaving water temperature is third in the hierarchy of control after safety functions first and ...

Page 66: ...n control A stable control band is a result of a properly tuned control Gains The control band is affected by Proportional Integral Derivative PID gain settings Factory settings accommodate most applications Gain adjustments are accessible to allow a qualified individual to adjust unit performance for a given installation Only qualified personnel should attempt gain adjustments Figure 17 Leaving W...

Page 67: ...mperature Heat Exchanger Margin LTHX Margin The LTHX margin is typically set at 15 degrees F Above 15 load the strong solution leaving the low temperature heat exchanger will be maintained 15 degrees from theoretical crystallization point The control system determines if the margin is less than greater than or equal to the LTHX setpoint and adjusts the energy input to maintain the LTHX margin thro...

Page 68: ...m of 30 F at minimum generator flow as illustrated in Figure 18 Between 15 and minimum solution pump speed the Low Temperature Heat Exchanger LTHX margin increases to 30 F The following chart illustrates this activity The generator flow is controlled by changing the Low Temperature Generator LTG pump speed as evaporator load decreases Figure 18 Plus 15 F Service Setting Low Temperature Heat Exchan...

Page 69: ...g water temperature control and concentration control 1 Leaving Water Temperature Input 2 Conc Input Control System Leaving Water Temperature PID Conc PID Limit Control AFD Control Energy Control An input from Leaving Water Temperature or Conc control must first pass through PID control and second limit control before reaching the output device The microprocessor first performs the PID functions o...

Page 70: ...ng a shut off condition The microprocessor will shutdown the chiller if a condition is reached that could cause damage to the machine When the limit or safety takes over the priority control the clear language display will indicate the active limit mode A limit mode does not necessarily mean that a problem exists In many cases this limit is a normal function such as soft load during startup During...

Page 71: ...operating conditions may cause salt crystals to precipitate out of the solution Continued operation with this condition can restrict solution flow through the heat exchanger resulting in a chiller failure that may be difficult to correct The SDR control system detects this condition and takes corrective control action first to correct the condition and second to maintain limited machine operation ...

Page 72: ...n OFF The display indicates 3 min Pump Off SDR timer 3 minutes elapses 4 System will restart normal chiller operation unless the system has been commanded to Stop or there are pending diagnostics Total time elapsed is 11 minutes If a Stop has been commanded or there is an active MMR or MAR diagnostic the unit will enter a Dilution Cycle The active Low Temperature Heat Exchanger LTHX Margin is incr...

Page 73: ... indicates where the SDR temperature has been reduced to the recovery temperature SDR sensor temperature is below the low temperature solution temperature 3 F required for operation Operation will be restored after the 11 minute recovery cycle is complete Figure 23 An indication that the CDR was Successful Crystallization Detection and Recovery CDR Trip Recovery Temperature LTG Solution 3 Degree T...

Page 74: ...t is the actual target that the control is proceeding towards At the end of the soft load time setting the filtered and setting values will be equal On startup the filtered setpoint will be equal to the current leaving water temperature Soft load will slope the filtered setpoint towards the active setpoint over the softload time period The Active setpoint will be reached at the end of the filtered...

Page 75: ...new ABS temperature When the saturated condensing temperatures drops below 90 F 100 F ABSD there is a potential capacity flow boundary limit imposed on solution capacity flow control AFD signal and an energy input adjustment See Figure 25 Reference the left column for the maximum Flow that will be allowed at a saturated condensing temperature Only when the desired control system capacity flow sign...

Page 76: ...ing water temperature Leaving Water Temperature setpoint allowed is 39 8 F with 38 F LCWTC Figure 26 illustrates a pictorial relationship 15 Chilled and Refrigerant Temperature Cutouts Limit and Differential to Start or Stop Lowest setable leaving water temperature in this example is 39 8 F because low chilled water temperature cutout 38 F plus 1 7 equals 39 7 and setpoint must be greater than thi...

Page 77: ...approaches the cutout setpoint This is accomplished by limiting loading holding or unloading in sequence to prevent the refrigerant temperature from reaching the cutout setpoint If the limiting action is successful the chiller will stay in limit until the refrigerant water temperature recovers If the limiting actions do not prevent a continued decline in refrigerant temperature the low temperature...

Page 78: ...t that the supply water temperature drops before the chiller shuts down The differential to stop setpoint is adjustable on the LCD from 1 to 10 F 0 5 to 5 55 C Both are integrated functions to avoid nuisance start or stops on momentary fluctuations in temperature Both setpoints move with respect to the active chilled water setpoint Differential to stop must be set above low leaving water temperatu...

Page 79: ...d water setpoint and the leaving water temperature Figure 29 Three examples of setpoint changes with and without the filter feature Each of the differential control functions is softened with an integration of time and temperature difference from the chilled water setpoint Setpoint Changes Without Filter feature Chilled Water Setpoint change greater than differential to stop Would cause the unit t...

Page 80: ... leaving water temperature setpoints LWT STPT 40 F 41 F 42 F 43 F 44 F 45 F 46 F 47 F 48 F 49 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 10 F 1 1 4 F 1 2 4 F 1 3 4 F 1 4 4 F 1 5 4 F 1 6 4 F 1 7 4 F 1 8 4 F 1 9 4 F 1 10 F LCWTC 38 F 38 F 38 F 38 F 38 F 38 F 38 F 38 F 38 F 38 F LRTC 36 F 36 F 36 F 36 F 36 F 36 F 36 F 36 F 36 F 36 F Differential to Start Differential to Start ...

Page 81: ...that limits loading as the Interstage Vapor Pressure approaches the UCP2 high pressure cutout setpoint See the illustration below for an understanding of the allowed loading verses interstage pressures Low Interstage Pressure Limit To avoid sensor diagnostic at startup the diagnostic is not enabled until the Solution Temperature Leaving the LTG is above 120 Degree F At this point the microprocesso...

Page 82: ...ture increase will hold at 325 to 330 F and unload at 330 to 335 F and shut down the machine above 335 F Operation at or above solution temperatures above 335 F will cause rapid solution inhibitor depletion and potential operational problems The resulting machine shutdown causes a manual reset MMR diagnostic The high limit must be cleared and problem corrected before a restart is attempted The con...

Page 83: ...the burner module The flat jacketed cable connects the HTC sensor to the high temperature generator cutout switch High Exhaust Gas Temperature Limit This limit function reduces the burner fire rate or turns off the burner lowering the overall generator temperature when the temperature zone is violated Figure 33 illustrates the associated temperatures Several events could potentially cause a high e...

Page 84: ...dule Figure 34 is located in a small enclosure along side of the burner control panel The sensor is located in the exhaust gas temperature probe along with the limit temperature sensor The HTC trips if the sensed stack temperature exceeds 425 F for more that 6 continuous seconds The HTC device normally closed contacts NC open removing the burner flame safeguard start command and the normally open ...

Page 85: ... Power Side of Machine Control Panel HTC Input 120 vac Optical Burner Module Located in the Burner Control Panel HTC Reset Relay Burner Start Rel ay HTC Stack Temperature Burner Safety String HTC Flame Safeguard FSG A B A and B represent the FSG pins that must be tied to allow burner start and run ...

Page 86: ...ic equation for steam flow is solved for valve position If steam pressure fluctuates the energy valve is repositioned to maintain the desired energy input therefore the energy valve mechanical position likely will not always be the same for a given energy input auto command Energy valve position is indicated as the last item in cycle report For a given valve opening position there is greater steam...

Page 87: ... above and below the limit value where no loading is allowed If the limit value is reached and exceeded beyond the dead band the limit algorithm will cause the unit to unload at a rate that is proportional to the amount of error that is sensed The loading and unloading proportional rate is 3 F The limit value for a single stage unit is fixed at 270 F and the limit value for a two stage absorber is...

Page 88: ...rface of the purge evaporator When the refrigerant vapor touches the surface of the purge evaporator it condenses into a liquid leaving a partial vacuum behind More condenser refrigerant vapor migrates to fill this vacuum As the refrigerant condenses into a liquid any non condensables present in the chiller are left behind to fill more and more of the space in the tank The liquid refrigerant retur...

Page 89: ...om 1 to 250 minutes It is used to generate a diagnostic when the actual 24 hour rate exceeds this value The default setpoint is 200 minutes Explanation Pumpout activity is indicative of the amount of air leaking into the chiller refrigerant system The operator wants to know when the air leakage rate changes Through this set point he can indicate the expected leakage rate and can set a criteria upo...

Page 90: ...urge pumpout compressor The purge pumpout compressor pumps the air out of the primary purge tank and into the chiller vent line Tank Valve Relay This relay is used to control the tank valve The tank valve controls the flow of purge tank exhaust from the primary purge tank to the pumpout pump Alarm Relay This relay will be energized in the presence of latching purge diagnostics It will be de energi...

Page 91: ...ime expires Service Pumpout The service pumpout status is intended to aid the serviceman in accomplishing certain mechanical repairs Service Pumpout mode initiates the pumpout sequence regardless of the chiller running state OR the refrigerant suction temperature The outputs should have the following states Diagnostic Alarm This status is active whenever the purge has an active latching diagnostic...

Page 92: ...ns should perform the installation and servicing of equipment referred to in this publication Literature Order Number File Number Supersedes Stocking Location Trane A business of American Standard Companies www trane com For more information contact your local sales office or e mail us at comfort trane com ABS CTR 3B SL RF ABS ABS CTR 3B 404 ABS CTR 3A Electronic Only ...

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