Water to Air heat pump COP Curves

asked 2023-05-03 15:03:52 -0600

JME
11 ●2

updated 2023-05-04 07:29:09 -0600

Aaron Boranian

14155 ●83 ●24 http://bigladdersoftware.com/

I'm creating a conceptual model for a building utilizing a GSHP and am trying to find load on the ground source heat exchanger and total heating energy from the GSHPs. For the zone and ground source equipment I imported a BCL measure to create the loop and heat pumps. Trying to model the heat pump heating coil with a 4.0 COP but when looking heating coil energy over ground heat exchanger load the model is outputting essential a 2.0 COP for heating. Cooling COP performing much more efficiently than the rated 4.4 COP as well. 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:

Curve:Biquadratic, 
  0.99325699999999995,  !- Coefficient1 Constant
  0.020151200000000001, !- Coefficient2 x
  7.72375e-05, !- Coefficient3 x**2
  -0.031720699999999998, !- Coefficient4 y
  0.00074064900000000002, !- Coefficient5 y**2
  -0.000303875, !- Coefficient6 x*y
  7, !- Minimum Value of x
  27, !- Maximum Value of x
  10, !- Minimum Value of y
  30; !- Maximum Value of y

Thank you

answered 2023-05-04 14:10:18 -0600

Greg Estep
669 ●20 ●6

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.

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Water to Air heat pump COP Curves

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