AHU Applications Application Note - Johnson Controls

1 Issue Date January 31, 2006 2006 Johnson Controls , Inc. Code No. LIT-6375080 Application NOTE AHU Applications Using AHU Applications ..3 Key AHU Applications ..4 Mixed Air Single Path Applications ..5 100% Outside Air Single Path Applications ..18 Mixed Air Dual Path or 100% Outside Air Dual Path Applications ..20 Heat Recovery for 100% Outside Air Applications ..25 Economizer ..27 Heating ..37 Cooling ..42 49 Modes of Fan System ..58 Using an AHU Application in a UNT Controller ..62 Procedure Overview ..64 Detailed Procedures ..65 Creating a Mixed Air Single Path Creating a 100% Outside Air Single Path Creating a Mixed Air Dual Path or 100% Outside Air Dual Path Application ..69 Completing the Heat Recovery for 100% Outside Air Question/Answer Path.

2 70 Completing the Economizer Question/Answer Path ..72 Completing the Minimum Duct Requirements Question/Answer Path ..75 Completing the Vent and Purge Question/Answer Path ..79 AHU Applications Application Note 2 Completing the Preheat Question/Answer Completing the Heating Question/Answer Path ..89 Completing the Cooling Question/Answer Path ..98 Completing the Dehumidification Question/Answer Completing the Humidification Question/Answer Completing the Modes of Operation Question/Answer Completing the Fan System control Question/Answer Troubleshooting ..125 Downloading an AHU Application ..125 Saving an AHU Application File for a UNT Controller ..126 Point Assignments and Parameters ..127 Default Point Assignments ..127 Default Parameters.

3 *131 AHU Applications Application Note 3 Using AHU Applications Introduction The AHU (Air Handling Unit) Application is capable of controlling many different air handlers and control strategies. This Application note introduces AHU Applications and provides procedures for configuring these Applications using the question/answer path. This Application note describes how to: create a mixed air single path Application create a 100% outside air single path Application create a mixed air dual path or 100% outside air dual path Application complete the heat recovery for 100% outside air question/answer path complete the economizer question/answer path complete the minimum duct requirements question/answer path complete the vent and purge question/answer path complete the preheat question/answer path complete the heating question/answer path complete the cooling question/answer path complete the dehumidification question/answer path complete the humidification question/answer path complete the modes of operation question/answer path complete the fan system control question/answer path AHU

4 Applications Application Note 4 Key Concepts AHU Applications The AHU Application is capable of controlling many different air handlers and control strategies (Figure 1). The types of air handling Applications that can be controlled include: Mixed Air Single Path Mixed Air Dual Path 100% Outside Air Single Path 100% Outside Air Dual Path Air Handlers100% Outside Air Dual PathFLWCHT3 NewFileAir HandlersMixed Air Single PathAir HandlersMixed Air Dual PathAir Handlers100% Outside Air Single PathOpenSelect Existing File Name Figure 1: AHU Application Path Each of these Applications are explained in the following topics. Use the Table of Contents at the beginning of this document to locate the Application you are using. Every question is listed for the entire AHU Application , along with explanations for each answer.

5 The AHU controller can be downloaded as a generic point multiplexer. The unused points can be user defined and used with up to 16 sideloops. AHU Applications Application Note 5 Mixed Air Single Path Applications Schematic Figure 2 is a schematic of a mixed air single path Application . Air :Coil arrangement may differ:- Preheat coil may be in the outside air duct before the mixed air Heating coil may be after the cooling coil for dehumidification Heating and/or cooling coil may be after the supply AirTemperaturePreheatTemperaturePreheatC oilHeatingCoilCoolingCoilSupplyFanReturn FanAirflowStatusAirflowStationAirflowSta tionHumidifierReturnDischargeStaticPress ureDischargeAirTemperatureMASPDUCTR eturn Air Temperature andHumidity Figure 2: Mixed Air Single Path Schematic control Strategy The first question in the mixed air single path question/answer path (Figure 50) asks you to select the control strategy.

6 The available strategies are: Room control Room control of Cooling, Room Reset of Heating Supply Air Reset from Zone Temperature (Mixed Air) Return Air control Constant Discharge Air Temperature Supply Air Reset from Return Temerature The following provides information on each of the six available strategies. AHU Applications Application Note 6 Room control The Room control strategy uses the zone temperature to directly control each controlled device (Figure 3). As the zone temperature decreases into the heating proportional band, the system commands the preheat (if selected and sequenced) and heating devices in sequence. As the zone temperature increases above the zone cooling setpoint, the system Controls the outdoor air damper (if selected and sequenced) and mechanical cooling device in sequence.

7 As the zone temperature travels through the various proportional bands, the output to the associated controlled device ranges from 0 to 100%. Integration may be added to this control loop to eliminate the inherent offset associated with proportional only control . AHU Applications Application Note - 1 EconomizerCommandReturn SetpointHeating DeadbandHeating Proportional BandPreheat Proportional BandHeating IntegrationEconomizer Proportional BandCooling DeadbandCooling Proportional BandCooling IntegrationReturn Air TemperatureHeating CommandPreheat CommandCooling CommandEconomizer CommandGo ToEconomizerSwitchoverLogicEconomizer 0 SupplyAirflowShutdown 0 HeatingIntegrationTer m0 SupplyAirflowShutdown 0 CoolingIntegrationTer m0 Separate Mixed Air Closed Loop100%0211 Mixed Air SetpointMixed Air Prop Band2 Mixed Air Integration TermMixed Air DeadbandMixed Air TemperatureEconomizer CommandMixed Air Low Limit102112 Mixed Air Low Limit SetpointMixed Air Low Limit Proportional BandMixed Air TemperatureMixed Air Low

8 LimitDeadbandMixed Air Low LimitIntegration TermSupplyAirflowShutdown 0 Mixed AirLow LimitIntegrationTer m0 Single PIReturn control SequencerPHTGHTGECONCLG32141234567567 Mixed AirLow LimitOffsetMinimumPosition**See the section for more Minimum Damper Position Reset from an Air Quality Sensor Needed? Figure 3: Room control AHU Applications Application Note 8 Room control of Cooling, Room Reset of Heating This control strategy uses the zone temperature to reset a discharge air heating setpoint and directly control the cooling device (Figure 4). As the zone temperature increases above the zone cooling setpoint, the system Controls the outdoor air damper (if selected and sequenced) and mechanical cooling device in sequence. As the zone temperature travels through the proportional band, the output to the associated controlled device ranges from 0 to 100%.

9 The controller calculates a discharge heating setpoint based on the input heating reset schedule. The discharge heating low limit establishes a calculated discharge setpoint when the zone temperature first enters the zone heating proportional band. The system adds the discharge heating reset band to this low limit. This value is the number of degrees the discharge setpoint changes as the zone temperature decreases through the zone heating proportional band. The discharge sensor then Controls and sequences the preheat (if selected and sequenced) and heating device as the discharge temperature decreases below the calculated discharge setpoint. Integration may be added to this control loop to eliminate the inherent offset associated with proportional only control .

10 The heating device will remain active when cooling is locked out based on the outside air temperature. This maintains a discharge heating low limit even when the zone temperature is in the cooling proportional band. AHU Applications Application Note 9 SupplyAirflowShutdown 0 HeatingIntegrationTe r m0 SupplyAirflowShutdown 0 CoolingIntegrationTe r CommandHeating SetpointDischarge Htg Prop BandDischarge Htg IntegrationDischarge Preheat Prop BandDischarge SensorEconomizer LogicOccupiedMixed Air LowLimit OffsetOccupied0 - 1 Heating Control100%00 ECONS equencerCLGHTGR esetZone SetpointHeating DeadbandHeating Proportional BandHeating IntegrationDischarge Heating Low LimitDischarge Heating Reset BandEconomizer Proportional BandCooling DeadbandCooling Proportional BandCooling IntegrationZone Temperature0 Heating CommandPreheat CommandMultiplyMaximumSelect14325 67 Discharge Heating SetpointCooling CommandEconomizer CommandSeparate Mixed Air Closed Loop100%0211 Mixed