Issue overview

In the example file "US+SF+CZ4A+hp+crawlspace+IECC_2006_VRF.idf", when the VRF system capacity is 3000W (AirConditioner:VariableRefrigerantFlow:FluidTemperatureControl field Rated Evaporative Capacity {W}), and the heating coil rated heating capacity is 10023W. A supplemental coil is present and autosized. The zone temperature drops below setpoint when the outdoor is above 0C. As a result, the predicted heating load (output "predicted sensible load to heating setpoint heat transfer rate") is also very large when outdoor temperature is above 0C.

Attempted fixing it by removing the following hardcoded limitation on the fan speed ratio.

     FanSpdRatioMin = min(max(OAMassFlow / Garate, 0.65), 1.0); // ensure that coil flow rate is higher than OA flow rate

This resolved the zone temperature problem, which also resolved the predicted heating load issue. But the fan air mass flow still do not behave as expected

It seems the problem is an instance of the issue #10282, where the supplemental coil is turned off at 0C.

After adding this field explicitly in the idf.

 ZoneHVAC:TerminalUnit:VariableRefrigerantFlow,
    TU1,                     !- Zone Terminal Unit Name
    …    
    Coil:Heating:Electric,   !- Supplemental Heating Coil Object Type
    TU1 Supp Heating Coil,   !- Supplemental Heating Coil Name
    50,                      !- Maximum Supply Air Temperature from Supplemental Heater {C}
    ;                          !- Maximum Outdoor Dry-Bulb Temperature for Supplemental Heater Operation  <-- add this

The problem of zone temperature, predicted heating load, and air mass flow is resolved

Details

Some additional details for this issue (if relevant):

• Platform (Mac 13.5)
• Version of EnergyPlus (23.2)
• Unmethours link or helpdesk ticket number

Checklist

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• Defect file added (list location of defect file here)
• Ticket added to Pivotal for defect (development team task)
• Pull request created (the pull request will have additional tasks related to reviewing changes that fix this defect)