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Air-to-Water Heat Pump PLR performance curve issue

asked 2024-01-30 14:42:54 -0600

vfournier's avatar

updated 2024-01-31 09:35:06 -0600

I have a model using E+ 22.2.0 which consist of one air-to water heat pump for heating and cooling of a small office building in a cold climate. The model uses the HeatPump:PlantLoop:EIR:Heating and HeatPump:PlantLoop:EIR:Cooling object.

When running the model with the CAP_FT factor and the EIR_FT factor, the output COP of the heat pump are the one expected from the performance table. However, I am having an issue when I add the EIR_FPLR factor. I am using a performance table to provide the EIR_FPLR factor with the data provided from an example using the data below. However, when adding such performance table in the model, the COP increases to very high values (9 to 20) especially in cooling mode. From my understanding, this is due to the low PLR operation and thus low EIR_FPLR factor which results in a low electricity consumption from the Heat Pump (Power output = PrefEIR_FTEIR_FPLR). Does anyone have faced similar issues when using the EIR_FPLR for air to water heat pump? Also Is there any recommended performance curve suitable in cold climate for an air-to-water heat pump in E+?

PLR performance Table:

PLR input [0, 0.25, 0.5, 0.75, 1]

HP_EIRFPLR output [0, 0.296357, 0.399506, 0.648768, 1]

Thank you

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answered 2024-01-31 10:55:45 -0600

updated 2024-01-31 11:16:56 -0600

Your EIRfPLR curve looks correct. However, this curve is not properly implemented in code. The EIRfPLR should output a constant 1 (or something far less impactful if you have other data).

HP_EIRFPLR output [1, 1, 1, 1, 1]

The power is calculated as:

this->powerUsage =
    (this->loadSideHeatTransfer / this->referenceCOP) * eirModifierFuncPLR * eirModifierFuncTemp * InputPowerMultiplier * this->cyclingRatio;

where:

loadSideHeatTransfer = availableCapacity * operatingPLR;

InputPowerMultiplier is a defrost term which is 1 when not in defrost

cyclingRatio is the fraction of time the unit cycles below min PLR

So in this equation, the loadSideHeatTransfer already includes the impact of PLR and again applying another PLR factor using the eirModifierFuncPLR curve is double dipping and causing the high COPs. If you were to try to use this EIRfPLR curve with this equation it would be more like:

HP_EIRFPLR output [1.03, 1.02, 1.01, 1, 1] to account for inefficiencies at low PLR (I am guessing on my curve outputs).

See https://github.com/NREL/EnergyPlus/is...

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Asked: 2024-01-30 14:42:54 -0600

Seen: 129 times

Last updated: Feb 07