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351579-YTS-B-0608Turning on compressors #2 through #4:If the economizer controller is saturated High (i.e. theeconomizer is 100% open while one or more compressors arerunning and the control can no longer maintain the active SATsetpoint requested by the zone control),• Temporarily override SAT setpoint to increase it by 5 °F• When the SAT is within 0.5 °F of this temporary setpoint,turn on the next compressor• Resume SAT control at active setpointNOTE:NOTE:The pre-staging SAT increase must be done “proactively”,by a temporary override of the active SAT setpoint,rather than by allowing the SAT to “drift” up by 5 °Fout of control. The time it would take for the SAT to “drift”up could be fairly long, mostly dependent on the outdoorair temperature change and in the meantime, the zonetemperature may go out of control as the additionalneeded cooling is not being delivered.The standard 5 minute delay before monitoring SATafter a compressor is turned on, or off, and the checkingagainst a stored, predicted SAT temperature drop,applies here also.Turning compressors off:A highest numbered running compressor is turned off when theeconomizer controller is saturated Low.This method of turning compressor off is considered better thanusing the Excessive SAT Control - turning a compressor OFFonly if SAT reaches its specified trip point. If that method wasused and the Excessive SAT Control was not selected, therewould be no means for turning compressors off.NOTE:The compressors also will be turned off in CV systemswith zone thermostat, or zone sensor temperaturecontrol, when the zone temperature control is satisfied.For the case of zone sensor, the compressordestaging is described in section “CV Operation”,paragraph “Control Algorithm for Cooling with the SensorOption, with Economizer”. For the case of zonethermostat, the compressor destaging is described insection “CV Operation”, paragraph “Thermostat Operationfor Cooling with Y1 and Y2 inputs”, subparagraph“Economizer Mode”.Compressor control when exiting Cooling Lockout on OAT:A situation may arise when in Economizer Mode and one ormore compressors are required in addition to full available freecooling in order to maintain the SAT setpoint, but CoolingLockout on OAT prevents the compressors use. This situationmay arise when the SAT setpoint is set very close to, or evenbelow the temperature set for Cooling Lockout on OAT - arelatively unusual case. If the OAT then increases above thelockout setting while the call for several compressors exists, thecompressors will turn on with a delay between compressors.Economizer Loading OptionThis is a programmable option. The user has the ability to turnthis function off. It is automatically disabled if the unit does notuse an economizer. The on/off programming choice is commonto both cooling and heating. The default setting is ON. Thisprogrammable “Economizer Loading” function is used onlyoutside the normal Economizer operation.During the Economizer operation, the “Loading” function isalways used and is an integral part of the Economizer controlalgorithm.Economizer loading option in cooling:In cooling, this function causes changes in mixed airtemperature (as modulated by the economizer dampers) inorder to change SAT and keep it at SAT setpoint when onlycompressor #1 is running. This makes a trade-off betweenenergy and compressor cycling and minimizes cycling ofcompressor #1. The loading is done by the same type of controlalgorithm (PI) as used in the normal Economizer operation.The algorithm will be activated to do this function in followingconditions:• Economizer is “not suitable” (i.e. we are not in a normalEconomizer mode)• The programmable option “Economizer Loading to ControlSAT” is ON• Only compressor #1 is runningThe PI control algorithm in this case has a capability toautomatically change from direct to reverse acting in responseto difference between OAT and RAT. When OAT is less thanRAT, the algorithm is direct acting, for OAT & RAT, the algorithmchanges to reverse acting. This way, the “loading” of the DX coilis correctly done with return, or outdoor air, as appropriate, andthere is no need to activate this “loading” function only at higheroutdoor air temperatures (e.g. OAT > 60 °F).The algorithm controls SAT to its specified setpoint (whenapplicable, e.g. in VAV operation), or, in control modes where noSAT setpoint is specified (such as in Excessive SAT control statein cooling), to a fixed temperature deadband of 50 °F to 55 °F.NOTE:As opposed to the PI algorithm used in economizercontrol, the PI algorithm used here for economizerloading function does not need to utilize the High saturationstate for any additional control functions. Thereforeno complications arise when switching betweendirect and reverse acting modes.Economizer loading option in heating:In heating, this function uses additional outside air (asmodulated by the economizer dampers) in order to decreaseSAT when only the first stage of heating is running and keep theSAT below the programmed “Economizer Loading Setpoint inHeating”. This prevents heating stage from cycling on itsinternal temperature limit safety switch (which is typically setabout 10 °F above the Economizer Loading Setpoint). A need38 Johnson Controls Unitary Products
351579-YTS-B-0608for economizer loading arises in Communicating ZoningSystem applications (“VVT” systems) using supply air bypasswhen heating load in the zones is low and a large amount of hotsupply air is bypassed back into return and mixed airtemperature is very high. Economizer loading may also beneeded when supply air flow across the heat exchanger islower than expected (e.g. wrong setting of fan speed, pluggedair filters). A secondary benefit of economizer loading is animprovement in comfort as the supply air temperature is morestable and cycling of the unit is minimized.The economizer loading option in heating is not implemented inVAV applications as these do not use supply air bypass and (incase of using a zone thermostat) run all heating stages duringheating (economizer loading applies to only the 1 st heating stage).The economizer loading minimizes cycling of heating stage #1and makes a trade-off between energy and the benefitsdescribed above.The Economizer Loading in heating option requires a SATsensor that can sense SAT in heating mode (a sensor placeddownstream of the heating stages). Such a sensor is providedonly as a field-installed accessory, on units equipped withheating stages. The SAT sensor that is factory-installed can beused for cooling mode only. If a field-installed sensor is added, itwill replace the factory-installed one and will then be usable forboth heating and cooling modes.The loading is done by the similar control algorithm as used inthe normal economizer operation. The algorithm is activated todo this function in following conditions:• Heating mode• The programmable option “Economizer Loading to ControlSAT” is ON• Only heating stage #1 is runningThe PI control algorithm in this case has a capability toautomatically change from direct to reverse acting in responseto difference between OAT and RAT. When OAT is less thanRAT the algorithm is direct acting, when OAT is greater thanRAT the algorithm is reverse acting.This way, the “loading” of the heating stage is correctly donewith return, or outdoor air, as appropriate, and there is no needto activate this “loading” function only in some specific range ofoutdoor air temperatures (e.g. OAT > programmed first heatingstage trip point minus 50 °F).NOTE:In this case, the provision for direct vs. reverse actingswitching is not essential feature of the control algorithmand the algorithm could be implemented as direct actingonly in order to simplify implementation and save codespace. The situation when economizer loading in heatingis required while OAT greater than RAT is unlikely and ifit should occur, the difference between OAT and RAT isnegligible in comparison to the SAT control setpoint. TheEconomizer Loading function in heating controls SAT toa fixed temperature deadband of programmed “EconomizerLoading Setpoint in Heating” and 5 °F below thissetpoint (the setpoint is programmable between 100 °F -195 °F, default is 160 °F).In units that use hydronic heat, the Economizer Loading functionmay be enabled in order to be used for cooling (the on/offprogramming choice for this function is common to both coolingand heating). In this case, it is important to ensure that theprogrammed value of the “Economizer Loading Setpoint inHeating” is set higher than the value of “Hydronic Heat First StageSetpoint”. That, in normal conditions, assures that the EconomizerLoading function in heating is effectively disabled and theeconomizer is closed to its minimum position during heating.VAVWhen is the Economizer operation used? If the rooftop unit isequipped with an economizer and free cooling is available thenthe Economizer Operation as specified in this section is used inthe following operation modes:VAV cooling (except the programmed Economizer First StageSetpoint and Economizer Second Stage Setpoint are replacedby the programmed VAV Upper Cooling SAT Setpoint and VAVLower Cooling SAT Setpoint)DEMAND VENTILATIONDemand Ventilation Operation control mode is self-configuringfor the use of an Indoor Air Quality (IAQ) sensor - it willautomatically detect that an IAQ sensor is connected and use itany time the IAQ sensor input indicates an IAQ level of 200ppm, or higher.NOTE:Due to the self-configuration operation, an error due toIAQ sensor failure can be indicated only in case theIAQ sensor fails during normal controller operation. Ifthe IAQ sensor fails, or is removed / disconnected duringa power-off condition (e.g. during servicing of theunit while the control is not powered), the control will,on power up, self configure without the IAQ sensorand no error indication is provided.When the IAQ sensor is detected as available, the control willuse the Demand Ventilation Setpoint to control the IAQ levels inthe building by modulating the Economizer more open.The Demand Ventilation will operate in units equipped with anEconomizer (Economizer option is turned ON) any time thecontrol is in Occupied mode. The Demand Ventilation Operationis applicable in heating, or cooling mode, and will modulate theEconomizer damper more open, if necessary, from itsprogrammed minimum position (in heating, or in cooling wheneconomizer is not "suitable"), or from its modulated positiondetermined as defined in the Economizer Operation section (incooling, when economizer is "suitable").An appropriate control algorithm is used to accomplish thiscontrol. Preferably, this algorithm is a "step-and-wait" type, withthe step size calculated as a function of offset between theDemand Ventilation Setpoint and the current IAQ level, and witha fixed "wait", or sampling time. This algorithm is activatedwhenever the IAQ level exceeds the setpoint and will overridethe economizer position more open, as needed, up to a preJohnson Controls Unitary Products 39
Page 1 and 2: 351579-YTS-B-0608TECHNICAL APPLICAT
Page 3 and 4: 351579-YTS-B-0608THE MILLENNIUM ®
Page 5 and 6: 351579-YTS-B-0608EPROM - This is
Page 7 and 8: 351579-YTS-B-0608ANALOG INPUTS (AI)
Page 9 and 10: 351579-YTS-B-0608Table 3: Simplicit
Page 11 and 12: 351579-YTS-B-0608SIMPLICITY ® PROG
Page 13 and 14: 351579-YTS-B-0608be turned off by t
Page 15 and 16: 351579-YTS-B-0608Once the Unoccupie
Page 17 and 18: 351579-YTS-B-0608Table 5: Settable
Page 19 and 20: 351579-YTS-B-06082. Mechanical cool
Page 21 and 22: 351579-YTS-B-0608determined by the
Page 23 and 24: 351579-YTS-B-0608Pressure Switch -
Page 25 and 26: 351579-YTS-B-0608Table 9: Modulatin
Page 27 and 28: 351579-YTS-B-0608As the ambient tem
Page 29 and 30: 351579-YTS-B-0608mizer damper and u
Page 31 and 32: 351579-YTS-B-0608TYPES OF SPACE SEN
Page 33 and 34: 351579-YTS-B-0608UNOCCUPIED HEATING
Page 35 and 36: 351579-YTS-B-0608Table 12: Holiday
Page 37: 351579-YTS-B-0608The RAH sensor, if
Page 41 and 42: 351579-YTS-B-0608time 60 seconds (N
Page 43 and 44: 351579-YTS-B-0608TROUBLESHOOTING A

analog to digital converter . . . . . . . . . . . . . . . 4 - UPGNet

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