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Control of PTHP and WaterToAirHeatPump

asked 2017-09-14 10:38:39 -0600

updated 2017-09-14 12:57:05 -0600

I have one building with two design options. One applies air source heat pump (simulated as ZoneHVAC:PackagedTerminalHeatPump); the other uses water source heat pump (simulated as ZoneHVAC:WaterToAirHeatPump). Results show WSHP has much more heating than ASHP which seems not reasonable to me. I checked the hourly report and found for ASHP case, heating coil (Coil:Heating:DX:SingleSpeed) did not run at the same time with supplemental electric heating; while in WSHP case, heating coil (Coil:Heating:WaterToAirHeatPump:EquationFit) often run at the same time with supplemental coil. Any control difference between ASHP and WSHP units?

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What does the comparison of outside air rates tell you?

TomB's avatar TomB  ( 2017-09-14 21:37:09 -0600 )edit

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answered 2017-09-14 11:11:57 -0600

The DX heating coil will not operate below the Minimum Outdoor Air Temperature for Compressor Operation while the water-source heating coil will. Check the min OAT for compressor operation and compare to the weather file outdoor temperature.

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@rraustad, thanks for your advice. I checked the control, it does have some influence, but not too much. I use the same building for two cases, but when I checked the heating coil heating rate, WSHP case will have 30-50% more heating rate than ASHP. To my understanding, same building means same load which will bring similar heating rate, is that correct? Why WSHP have much more energy consumption than ASHP? (WSHP even have higher COP)

Yan's avatar Yan  ( 2017-09-14 15:44:50 -0600 )edit

What is the DX heating coil's Minimum OAT for Compressor Operation and what is the weather file outdoor temperature when the DX heating coil does not run and the WSHP heating coil does run?

rraustad's avatar rraustad  ( 2017-09-14 16:35:40 -0600 )edit

@Yan, your correct that the heating loads should be the same. When you add the DX heating coil rate + supplemental heating coil rate and compare that to WSHP heating coil rate + supplemental heating coil rate are these the same? Is WSHP heating coil rate + supplemental heating coil rate still higher than the total heating coil rate from the ASHP?

rraustad's avatar rraustad  ( 2017-09-15 07:52:47 -0600 )edit

@rraustad, the minimum OAT for compressor is 17.6F, and supplemental electric DX heating coil does not run when the DX heating coil runs, this situation happens at most time of the year, anytime of the day, seems not that related with OAT. WSHP supplemental coil, however, run much more than ASHP supplemental coil, usually in early morning

Yan's avatar Yan  ( 2017-09-15 08:30:39 -0600 )edit

@rraustat, yes, when I compare the sum of DX heating coil rate + supplemental coil rate, WSHP higher than ASHP, if the load is the same, what could cause the different heating rates?

Yan's avatar Yan  ( 2017-09-15 08:43:56 -0600 )edit

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Asked: 2017-09-14 10:38:39 -0600

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Last updated: Sep 14 '17