central heat pump heating mode power input is constant?
I'm modeling a heat recovery chiller in openstudio v2.8.1 using the centralheatpump object. I noticed that under mode 2 (heating only), the chiller heater heating electric power seems always be constant regardless of the heating output, with a very low COP (e.g. 0.2, 0.3 etc). Compared to the cooling mode (mode 3), the COP is around 1, which seems more reasonable.
And as a result, the annual heating energy is skyrocketing (about 5 times the cooling energy, in San Francisco, where the climate is pretty mild).
Anyone knows what's causing this?
just want to add at I ran the same idf file under energyplus v9.3 and the chiller heater electric power unit 1 decreased from 605,857Btuh reported in the table above to 270,973Btuh (0.44 of 605857), but still constant, and the heating energy dropped to about 1/3. I checked the EquipmentSummary report, the chiller heat size (autosized) was also only about 0.44 of the original file.
But then I tried another file with similar configurations and settings from v9.1 o v9.3, the heating energy only decreased slightly. So I'm not sure what happened.
looks like whenever it's heating mode (mode 2), the part load ratio of the chiller heater becomes 1, and the elec input becomes the full load input, even though the actual heating demand is much less on the HHW loop.