Question-and-Answer Resource for the Building Energy Modeling Community
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Hi JME, I use the DesignBuilder zone water-to-air heat pump which uses equation fit DX cooling and heating coils. The rated air, water, capacity fields are autosized and the COP comes with a default (7.0 for cooling, 3.167 for heating). These coils only use heating/cooling capacity coefficients and compressor power coefficients. WaterFurnance has rated COP for ground source cooling conditions based on 59F entering water temp, while heating is 50F. This would explain why the cooling performance is better than heating.
You may want to try using the equation fit coils.
I'm wondering if there's something up with the input ratio curve for the heat pumps? Here are the values for the "Energy input ratio as a function of Temperature" Curve:
I don't see any water to air coils that use the Energy input ratio as a function of Temperature" Curve. All I see are these:
Unitary water to air heat pump Coil:Cooling:WaterToAirHeatPump:ParameterEstimation
Coil:Heating:WaterToAirHeatPump:ParameterEstimation
Coil:Cooling:WaterToAirHeatPump:EquationFit
Coil:Heating:WaterToAirHeatPump:EquationFit
Coil:Cooling:WatertoAirHeatPump:VariableSpeedEquationFit
Coil:Heating:WatertoAirHeatPump:VariableSpeedEquationFit
zone water to air heat pump (I think these are the same):
Coil:Cooling:WaterToAirHeatPump:EquationFit
Coil:Heating:WaterToAirHeatPump:EquationFit
Coil:Cooling:WaterToAirHeatPump:VariableSpeedEquationFit
Coil:Heating:WaterToAirHeatPump:VariableSpeedEquationFit
As you know, the COP changes with operating conditions. I would check the entering water temperature during heating (it may be well below 50F). Also, check the water flow rate is adequate. Typical design flow rate is 3 GPM/ton. Also, I don't think you can autosize the plant loop with a ground heat exchanger. the design water flow rates should match in the plant loop and the GHX object.
