York ZR Series Installation Manual

Also see for ZR SERIES: Technical guide Wiring diagrams Installation manual

Contents

275864-YIM-F-0213Johnson Controls Unitary Products 41room thermostat is set in the "AUTO" position) and drives theeconomizer dampers from fully closed to their minimumposition. If the enthalpy of the outdoor air is below the setpointof the enthalpy controller (previously determined), "Y1"energizes the economizer. The dampers will modulate tomaintain a constant supply air temperature as monitored by thedischarge air sensor. If the outdoor air enthalpy is above thesetpoint, "Y1" energizes compressor #1, condenser fan motor#1, and condenser fan motor #2 (if the ambient temperature isabove 60°F).When the thermostat calls for "second-stage" cooling, the lowvoltage control circuit from "R" to "Y2" is completed. The UCBenergizes the first available compressor If the enthalpy of theoutdoor air is below the setpoint of the enthalpy controller (i.e.first stage has energized the economizer), "Y2" will energizecompressor #1. If the outdoor air is above the setpoint, "Y2" willenergize compressor #2.Once the thermostat has been satisfied, it will de-energize Y1and Y2. If the compressors have satisfied their minimum runtimes, the compressors and condenser fans are de-energized.Otherwise, the unit operates each cooling system until theminimum run times for the compressors have been completed.Upon the final compressor de-energizing, the blower is stoppedfollowing the elapse of the fan off delay for cooling, and theeconomizer damper goes to the closed position. If the unit is incontinues fan operation the economizer damper goes to theminimum position.Economizer With Dual Enthalpy SensorsThe operation with the dual enthalpy sensors is identical to thesingle sensor except that a second enthalpy sensor is mountedin the return air. This return air sensor allows the economizer tochoose between outdoor air and return air, whichever has thelowest enthalpy value, to provide maximum operatingefficiency.Economizer With Power ExhaustA unit equipped with an economizer (single or dual enthalpy)and a power exhaust operates as specified above with oneaddition. The power exhaust motor is energized 45 secondsafter the actuator position exceeds the exhaust fan set pointon the economizer control. When the power exhaust isoperating, the second stage of mechanical cooling will notoperate. As always, the "R" to "G" connection providesminimum position but does not provide power exhaustoperation.Economizer With Optional VAV Or Intelli-comfort II™ControlThe position of the outside air and return air dampers arecontrolled through a 2-10 VDC signal from the VAV or Intelli-Comfort II™ control board. The economizer is enabled only inOccupied or Recovery mode. When the control is not poweredor is in Unoccupied mode, the outside air dampers will beclosed. When the supply fan is powered and there is no Y1 call,or if free-cooling is unavailable, the control opens theeconomizer dampers to the minimum position setting.Free-cooling is available if the outdoor air temperature meetsone of the three criteria discussed below, based upon the unit'sconfiguration.• Dry Bulb: The control refers to input from the Outside AirTemperature sensor and will allow free-cooling when theoutdoor temperature is less than both the First-Stage SATControl setpoint plus 5 °F, and the Economizer OATEnable setpoint.• Single Enthalpy (optional): A field-installed, Outdoor AirHumidity sensor is connected to the control. When themeasured outdoor enthalpy is below the Outside AirEnthalpy setpoint, and the outdoor temperature is lessthan the First-Stage SAT Control setpoint plus 5 °F, free-cooling is available.• Dual Enthalpy (optional): Both the field-installed OutdoorAir Humidity and the Return Air Humidity sensors areconnected to the control. When the measured outdoor airenthalpy is less than the measured return air enthalpy, andthe outdoor temperature is less than the First-Stage SATControl setpoint plus 5 °F, free-cooling is available.If free-cooling is available with a Y1 call, then the controlmodulates the economizer dampers to maintain the First-Stage SAT Control setpoint, plus or minus one degree. If free-cooling is unavailable, then 1st-stage mechanical cooling isinitiated.If at anytime the outdoor air temperature rises above the First-Stage SAT Control setpoint plus 5 °F, while free-cooling isavailable, then a Y1 call will also initiate 1st-stage mechanicalcooling.For a Y2 call, free-cooling is available based upon the criteriadescribed above, except a Second-Stage SAT Control setpointis used in the determination.Once the call for cooling has been satisfied, it will de-energizeany compressors and condenser fans, after the minimumcompressor run times have been satisfied. Otherwise, the unitoperates each cooling system until the minimum run times forthe compressors have been completed.Upon de-energizing the final compressor, the blower willcontinue to run with the economizer damper in its minimumposition if in the Occupied mode; otherwise, the blower will stopfollowing the elapse of the fan-off delay for cooling, and theeconomizer outdoor damper will close.Economizer With Optional VAV Blower With Power ExhaustThe power exhaust motor is energized via the controller'sEXH~ terminal and the ER relay, based on the position of theeconomizer damper parameter settings in the VAV control.Minimum run time is 10 seconds; minimum off time is 60seconds. The outlet pressure of the power exhaust fan forcesthe barometric relief dampers open; gravity closes thedampers when the exhaust fan is off.