E+ 9.3.0: Allow ZoneHVAC:TerminalUnit:VariableRefrigerantFlow to connect to AirLoopHVAC

[jmarrec]

Enhancement Request

Edit: add @eringold details from #4242

From IDD Diffing, it seems that ZoneHVAC:TerminalUnit:VariableRefrigerantFlow gained the ability to be connected to AirLoopHVAC

It would be nice to add this capability to the model API, but this is an enhancement request as the existing behavior should be retained.

EnergyPlus 9.3.0 added the ability to connect a ZoneHVAC:TerminalUnit:VariableRefrigerantFlow to AirloopHVAC and AirLoopHVAC:OutdoorAirSystem:EquipmentList in NREL/EnergyPlus#7605. Request that this be added to OpenStudio.

Detailed Description

The following MCVE in v3.1.0 returns false:

require 'openstudio'
include OpenStudio::Model
m = Model.new
ahu = AirLoopHVAC.new(m)
tu = ZoneHVACTerminalUnitVariableRefrigerantFlow.new(m)
tu.addToNode(ahu.supplyOutletNode)

This needs to be scoped out, but addToNode would have to be overriden. Not sure how that plays out, but it should work. AirLoopHVACUnitarySystem for eg is a ZoneHVACComponent and can be added to a loop.

Possible Implementation

The EnergyPlus implementation allows for a Terminal Unit without a Fan or OutdoorAirMixer. Supply Air Fan is currently a required field:

  A8 ,  \field Supply Air Fan
        \required-field
        \type object-list
        \object-list FansCVandOnOffandVAV
        \object-list FansSystemModel
        \note Supply Air Fan Object Type must be Fan:SystemModel, Fan:OnOff, or Fan:ConstantVolume
        \note if AirConditioner:VariableRefrigerantFlow is used to model VRF outdoor unit
        \note Supply Air Fan Object Type must be Fan:SystemModel or Fan:VariableVolume if
        \note AirConditioner:VariableRefrigerantFlow:FluidTemperatureControl or
        \note AirConditioner:VariableRefrigerantFlow:FluidTemperatureControl:HR
        \note is used to model VRF outdoor unit