Carrier WeatherMaker 48A2020 Controls, Start-up, Operation, Service And Troubleshooting Instructions

75Humidi-MiZer Adaptive Dehumidification SystemUnits with the factory-equipped Humidi-MiZer® option are ca-pable of providing multiple modes of improved dehumidifica-tion as a variation of the normal cooling cycle. The design of theHumidi-MiZer system allows for two humidity control modes ofoperation of the rooftop unit, utilizing a common subcooling/re-heat dehumidification coil located downstream of the standardevaporator coil. This allows the rooftop unit to operate in both aDehumidification (Subcooling) mode and a hot gas ReheatMode for maximum system flexibility. The Humidi-MiZer pack-age is factory installed and will operate whenever there is a de-humidification requirement present. The Humidi-MiZer systemis initiated based on input from a factory installed return air hu-midity sensor to the large rooftop unit controller. Additionally,the unit controller may receive an input from a space humiditysensor, a discrete input from a mechanical humidistat (CEM re-quired), or third-party controller. Dehumidification and reheatcontrol are allowed during Cooling, Vent, and Heating modes inthe occupied period. In Heating mode, Humidi-MiZer will at-tempt to reach the higher heating control point, but if it cannotsatisfy heating demand at full capacity, then Staged Gas supple-mental heating will activate, if installed.SETTING UP THE SYSTEMSettings for Humidi-MiZer system can be found at the localdisplay at ConfigurationDEHU. See Table 69.OPERATIONMode QualificationsAn HVAC: Off, Vent or Cool mode must be in effect to launcha Humidi-MiZer mode. If Staged Gas Heat is available for sup-plemental reheat, then an HVAC Heat mode may also allowHumidi-MiZer to activate. When Humidi-MiZer reaches fullcapacity, if heating demand persists, then Supplemental StagedGas heat will activate.Sensor FailureIf an associated sensor responsible for controlling Humidi-MiZer system fails, dehumidification will not be attempted(RARH).Initiating a Humidi-MiZer Reheat or Dehumidification ModeTo call out a Dehumidification mode in any HVAC mode, oneof the following must be true:• The space is occupied and the humidity is greater than therelative humidity trip point (D.RH.S).• The space is occupied and the discrete humidity input isclosed.Ending a Humidi-MiZer Reheat or Dehumidification ModeWhen either the humidity sensor reading falls below the set-point (Configuration  DEHU  D.RH.S) by an amountsaved in the Relative Humidity Dead Band (Configuration->DEHU->DH.DB, default 5%, range 1 to 30%), or the discreteinput reads "LOW," the Humidi-MiZer mode will end.Relevant OutputsThe Humidi-MiZer 3-way valve (reheat valve) commandedoutput can be found in OutputsCOOLRHV.The Humidi-MiZer Condenser Modulating Valve (CondenserEXV) position output can be found in Outputs  COOL C.EXV. The condenser position will be provided as percent open.The Humidi-MiZer Bypass Modulating Valve (Bypass EXV)position output can be found in OutputsCOOLB.EXV.The bypass position will be provided as percent open.HUMIDI-MIZER MODESDehumidification Mode (Cooling Dehum mode 23)Three modes exist: Cooling Dehum, Venting Dehum, andHeating Dehum. Cooling Dehum was previously subcooling.The Humidi-MiZer coil will reheat to the current normal cool-ing control point if it is greater than the dehumidification coolcontrol point. Venting Dehum is the second reheat mode basedon control type temperature demand.The Dehumidification mode will be engaged to satisfy part-load type conditions when there is a space call for cooling anddehumidification. Although the temperature may have droppedand decreased the sensible load in the space, the outdoor and/orspace humidity levels may have risen. A typical scenario mightbe when the outside air is 85°F and 70 to 80% relative humidi-ty (RH). Desired SHR for equipment in this scenario is typical-ly from 0.4 to 0.7. The Humidi-MiZer unit will initiate Dehu-midification mode when the space temperature and humidityare both above the temperature and humidity setpoints, and at-tempt to meet both setpoint requirements.Once the humidity requirement is met, the unit can continue tooperate in normal cooling mode to meet any remaining sensi-ble capacity load. Alternatively, if the sensible load is met andhumidity levels remain high the unit can switch to Hot Gas Re-heat mode to provide neutral, dehumidified air.Venting Dehum mode (24)This mode is used when dehumidification is required without aneed for cooling, such as when the outside air is at a neutraltemperature but high humidity exists. This situation requiresthe equipment to operate at a low SHR of 0.0 to 0.2. With nocooling requirement and a call for dehumidification, the A Se-ries Humidi-MiZer adaptive dehumidification system will cy-cle on enough compressors to meet the latent load requirement,while simultaneously adjusting refrigerant flow to the Humidi-MiZer coil to reheat the air to the desired neutral air setpoint.The A Series Humidi-MiZer system controls allow the dis-charge air to be reheated to either the return air temperature mi-nus a configurable offset or to a configurable Reheat setpoint(default 70°F). The hot gas reheat mode will be initiated whenonly the humidity is above the humidity setpoint, without a de-mand for cooling.Heating Dehum mode (25)If heating demand occurs along with Dehumidification de-mand, then the Heating Control setpoint HEATCPNT will beset to 85°F. If the unit is equipped with Staged Gas heat andHumidi-MiZer reaches full capacity while heating and dehumdemand persists, then supplemental staged gas heat will add tothe heat created by Humidi-MiZer, in order to meet the higherheating control point.System ControlThe essential difference between the three Dehumidificationmodes is in the supply air setpoint. In Cooling Dehumidificationmode, the supply air setpoint is the temperature required to pro-vide cooling to the space. This temperature is whatever the cool-ing control point would have been in a normal cooling mode. InVenting Dehum mode, the supply air setpoint will be either an off-set subtracted from return air temperature (D.V.RA) or the VentReheat Setpoint (D.V.HT). Both values are configurable. ForHeating dehum the equipment setpoint for reheat will become theHeating control point or go to full heat based on the demand seenfor the control type. For all three Dehumidification modes, the unitcompressor staging will decrease the evaporator discharge tem-perature to the Dehumidify Cool Setpoint (D.C.SP COOL) in or-der to meet the latent load and reheat the air to the required coolingor reheat setpoint. There is a thermistor array called Tempera-tures_AIR.T_CCT connected to the RCB. This thermistor arrayserves as the evaporator discharge temperature (EDT). SeeFig. 17. In Heating Dehum the Humidi-MiZer setpoint will be-come the Heating control setpoint in order to maximize heat fromthe reheat coil.The A Series Humidi-MiZer® system uses refrigerant flow modu-lation valves that provide accurate control of the leaving air tem-perature as the evaporator discharge temperature is decreased to