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Air-to-water heat pump rating conditions in EnergyPlus

asked 2021-10-08 15:01:35 -0500

updated 2022-03-30 09:55:02 -0500

Keigo's avatar

Hi Energy Modeler Community,

I'm in trouble with HeatPump:PlantLoop:EIR:Cooling and HeatPump:PlantLoop:EIR:Heating objects.

They are not specified neither in I/O reference nor in Engineering reference what are the standard rating conditions to which refers the Capacities and EIR previously entered and consequently what are the the couples of temperatures to which curves are expected to get the unitary value.

With reference to AHRI 551/591 (and to Chiller:Electric:EIR obj, with similar behavior to model central plantn air-cooled chiller that however admit rated conditions to be entered) I can guess:

for cooling mode (HeatPump:PlantLoop:EIR:Cooling obj)

they could refer to:

Conversely for heating mode (HeatPump:PlantLoop:EIR:Heating obj) I'm even more insecure:

they could refer:

  • water leaving: one of 40°C or 50°C or 60°C (if as per AHRI), but eventually which of the three? (no other similar obj in EnergyPlus)
  • air dry-bulb entering: 8°C or -8°C (if as per AHRI), but but eventually which of the two ?

I have the unpleasant feeling that with this object (super-useful in the intentions to cover a plant equipment nowdays widely used at least here in Europe) the modeler can completely misunderstand the performance of the plant equipment itself.

Has anyone already addressed this topic?

Could someone from the development team guide me on what the expected reference conditions are to put rated Capacities and EIR and from which start moving on curves?

Thanks to anybody will spend some time to answer or give an insight.


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I looked at my simulation result (html file): Coil Sizing Summary for Coil:HeatingWater and had the same question. What are "Rating Conditions"? Although it's not for air-to-water heat pump, I/O Reference explains Rated Conditons for DX coil here. EnergyPlus should refer to AHRI standard, but heating mode has several rating conditions such as High-Temperature and Low-Temperature, and I don't know which condition is used.

Keigo's avatar Keigo  ( 2022-03-30 10:44:35 -0500 )edit

I hope I found the correct numbers for the rating conditions for water coils: 82.2 C is the water temp and 16.6 C for air temp (50% RH) for Coil:Heating:Water. 6.67 C water temp and 26.67 C db/19.44 C wb for Coil:Cooling:Water.

rraustad's avatar rraustad  ( 2022-03-30 11:25:24 -0500 )edit

oh I missed your comment and commented on your answer. Understood. Thanks!

Keigo's avatar Keigo  ( 2022-03-30 11:31:26 -0500 )edit

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answered 2022-03-30 11:05:06 -0500

updated 2022-03-30 11:07:40 -0500

I do not see any rating conditions used for sizing these objects. The capacity of this object is calculated based on the delta T inputs in the Sizing:Plant objects. The DesVolFlowRate is the sum of the demand side loads on the plant (e.g., sum of water coil water flow rates). Cp and rho are based on the loop exit temperatures.

tmpLoadVolFlow = PlantSizData(pltLoadSizNum).DesVolFlowRate * this->sizingFactor;
tmpCapacity = Cp * rho * PlantSizData(pltLoadSizNum).DeltaT * tmpLoadVolFlow;

  Chilled Water Loop,      !- Plant or Condenser Loop Name
  cooling,                 !- Loop Type
  7.00,                    !- Design Loop Exit Temperature {C}
  4.00;                    !- Loop Design Temperature Difference {deltaC}

  Hot Water Loop,          !- Plant or Condenser Loop Name
  heating,                 !- Loop Type
  82.,                     !- Design Loop Exit Temperature {C}
  11;                      !- Loop Design Temperature Difference {deltaC}
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HVAC Sizing Summary table shows Coil Total Capacity at Rating Conditions [W] for both COIL:COOLING:WATER and COIL:HEATING:WATER. What are the rating conditions? The values of Coil Total Capacity at Rating Conditions [W] are different from Coil Final Gross Total Capacity [W].

Keigo's avatar Keigo  ( 2022-03-30 11:25:29 -0500 )edit

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Asked: 2021-10-08 15:01:35 -0500

Seen: 104 times

Last updated: Mar 30