EnergyPlus is undesirably undersizing autosized heat pump (HVACTemplate)?

asked 2021-11-03 14:54:09 -0600

morgan_energy gravatar image

updated 2021-11-04 09:59:46 -0600

Hello, I'm attempting to simulate ASHP in EnergyPlus with supplemental gas heat (using HVACTemplate:System:UnitaryHeatPump:AirtoAir objects). The simulation is for San Francisco, so one would think the autosizer would have no problem sizing the ASHPs to meet peak load even on the coldest day (typically in the high 30's F / 3-4C). However, in each zone EnergyPlus sizes the ASHP well below the design heating load, with a much higher capacity given to the supplemental coil than the ASHP DX heating coil itself. In my mind, the peak heating load is low enough such that EnergyPlus shouldn't have an issue sizing the ASHP's to meet it, even in the absence of supplemental heat.

What could be causing this? It shouldn't be the minimum outdoor dry-bulb cutoff because the default for that is -8C (18F). Additionally, I'm using a SizingPeriod:WeatherFIleDays object across January and February, so EnergyPlus should be locating the coldest hour of the year and sizing the ASHP appropriately, right? Any help is much appreciated; I'm fairly new to this. Unfortunately I don't have enough points as an UnmetHours user to upload images.

Thanks, Morgan

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