VRF vs PTHP System
Hello,
I'm trying to compare the energy use between a VRF system and a PTHP system in EnergyPlus. Both systems have a DOAS to supply outdoor air (efficiencies of the DOAS are the same, OA rates are the same), and all other parameters are the same. The VRF and PTHP system have the same rated efficiencies: cooling COP 3.3, heating COP 3.5. Capacities and supply air flow are being autosized. Both systems' fan mode is cycling. Other parameters are using the default values in OpenStudio.
I'm getting higher energy use in the VRF model, and I'm not sure what the reason is to that... any insight would be greatly appreciated.
Thanks Tina
Comments
Might be good to see end use breakdown to see where that increase is coming from. Another first step if you haven't done it is to look at the warnings in the eplusout.err for anything suspicious.
Thanks David, I looked in the error file and one warning I'm getting for the VRF is:
Warning ** AirConditioner:VariableRefrigerantFlow "VRF SYSTEM" -- Exceeded VRF Heat Recovery min/max outdoor temperature limit error. VRF Heat Pump Min/Max Outdoor Temperature in Heat Recovery Mode Limits have been exceeded and VRF heat recovery is disabled.
I've tried expanding the range of the min/max outdoor temperature for the heat recovery mode but I'm still getting this error.
I'm having an increase of energy mainly in heating, a little bit in cooling and some in fan energy.