AAON Orion VCCX2 Technical Manual

Also see for Orion VCCX2: Technical guide Technical guide Technical guide

Contents

AAON Orion VCCX2 Technical Manual Manual pdf 75 page image

VCCX2 Controller Technical GuideSEQUENCE OF OPERATIONS75When the OAT is below the OAT Compressor Heating Lockout,Compressor Heat is locked out. Auxiliary Heat will then be theprimary heat and can be supplemented with stage(s) of EmergencyHeat (if available). Emergency heat is only available when the OATis below the OAT Compressor Lockout.Heat Pump Standard DefrostOperationIf using the VCCX2 Controller with an installed Defrost CoilTemperature Switch, a Defrost Cycle is available.If the compressor(s) are operating in the Heating Mode and theDefrost Coil Temperature Switch closes, the unit will enter theDefrost Mode, provided the user-adjustable Defrost Interval Timerhas elapsed since the last Defrost Cycle.In the Defrost Cycle, the reversing valve signal is switched to theopposite operation, and the compressors are brought to maximumcapacity. Auxiliary Heat will be used to attempt to maintain theHeating SAT Setpoint. Emergency Heat cannot be used because itis locked out because the Compressors are on.The unit will leave the Defrost Mode after 10 minutes have elapsedor the Defrost Coil Temperature Switch opens.If the unit leaves the compressor heating mode, the Defrost Intervalwill restart once the unit re-enters the compressor heating mode.Heat Pump Adaptive Defrost OperationThe Adaptive Defrost operation adjusts the time interval (AdaptiveDefrost Timer) in between Defrost Mode cycles.As stated above, the unit will leave the Defrost Mode after 10 minuteshave elapsed or the Defrost Coil Temperature Switch opens. If theDefrost Cycle is terminated because the 10 minute timer runs out,this could be an indicator that the unit may need more defrost time.To address this issue, the Adaptive Defrost Timer value will besubtracted from the original Defrost Interval.If the Defrost Cycle is terminated between the 8th and 9th minute, theDefrost Interval will not be changed.If the Defrost Cycle is terminated before the 8 th minute, thiscould be an indicator that the unit may need less defrost time.To address this issue, the Adaptive Defrost Timer value will beinversely proportionally added to the original Defrost Interval as thetermination time moves from 8 minutes to 0 minutes.Adaptive Defrost can be disabled by setting the Adaptive DefrostTimer Setpoint to 0.Water Source Heat Pump OperationCooling Mode will operate in the same manner as described in theCooling section.A reversing valve relay output can be configured to activate with thefirst compressor stage in the Heating Mode or the Cooling Mode ofoperation.In the Heating Mode, Auxiliary Heat can be used with CompressorHeat to achieve the Active Supply Air Heating Setpoint. AuxiliaryHeat can be either modulating or staged forms of heat, or it can bea modulating form of heat followed by staged heat.When Auxiliary Heat comes on in conjunction with a digitalcompressor heat stage, the digital compressor will be locked at100% until the Supply Air Temperature (SAT) rises above the SATHeating Setpoint plus the Heat Staging Window. At that point, theAuxiliary Heat will stage off (after a stage down delay) and the digitalcompressor heat will be allowed to modulate.There is no Dehumidification during Heat Mode of a Water SourceHeat Pump Unit. There is no Defrost Mode on a Water Source HeatPump Unit.The unit can be configured for the percentage of glycol it has. Theoptions are 0%-40% in 5% increments.Electronic Expansion Valve (EXV)OperationIf using EXVs with Bitzer VFD Compressors and the RSMV Module,then a Coil (Suction Line) Temperature Sensor will measure the Coil(Suction Line) Temperature after each Evaporator Coil line for eachcompressor, and this sensor will be connected to an RSMV Module.This temperature will be used in conjunction with the calculatedsaturated refrigerant temperature to calculate the Superheat of eachevaporator coil. The EXV for each coil will then be controlled tomaintain the Superheat Setpoint.Head Pressure ControlThe Refrigerant System Module (RSM) can monitor a Head PressureTransducer and control a Condenser Fan to maintain a Head PressureSetpoint.In the Cooling Mode, the Condenser Signal will modulate to maintainthe Cooling Head Pressure Setpoint.In the Dehumidification Mode, the Condenser Output Signal controlsto the Reheat Head Pressure Setpoint. High Head Pressure conditionsproduce the same effects as in the Cooling Mode.See the appropriate RSM Technical Guide for a more detailedsequence of operation.Heat Pump Standard Defrost, WSHP, EXV & Head Pressure