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Integrated Heat Pump

asked 2017-06-08 06:32:21 -0500

Fish Lee's avatar

updated 2019-02-02 13:57:27 -0500

I have a system that comprises 4 air-sourced heat pumps for both space heating and cooling. I saw the new integrated heat pump coil system can model a single air-sourced heat pump so it cannot provide both heating and cooling simultaneously.

Is it possible to connect the integrated heat pumps in parallel so that the plant can supply both hot water and chilled water?

Or must I stay with 4 air-cooled chiller + 4 Coil:WaterHeating:AirToWaterHeatPump in order to achieve that?

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answered 2017-06-08 15:57:52 -0500

You are correct, the CoilSystem:IntegratedHeatPump:AirSource object you are referring to cannot provide both space heating and space cooling simultaneously. My solution here is a bit long, so the short answer is:

NO, it is not possible to connect the integrated heat pumps to supply both hot water and chilled water.

Out of the following potential operation modes for the integrated heat pump object, it will only use one at the beginning of each timestep:

  • Space cooling (SC) from a Coil:Cooling:DX:VariableSpeed object
  • Space heating (SH) from a Coil:Heating:DX:VariableSpeed object
  • Dedicated water heating (DHW) from a Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object
  • Combined space cooling and water heating with full condensing (SCWH) from a Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object
  • Combined space cooling and water heating with desuperheating (SCDWH) from a Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object
  • Combined space heating and water heating with desuperheating (SHDWH) from a Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object

I'm having difficulty finding where the Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object is defined in the Input-Output Reference documentation, but it is listed in the Energy+.idd file that specifies the input field data for every EnergyPlus object (see below).

image description

Excerpt from EnergyPlus IDD file for Coil:WaterHeating:AirToWaterHeatPump:VariableSpeed object

This object is meant to be used in combination with a heat pump water heater object, and there are a few EnergyPlus example files that you can reference to see how to implement the integrated heat pump and the variable speed AWHP water coil.

  • ASIHPMixedTank.idf
  • VSHeatPumpWaterHeater.idf
  • VSWaterHeaterHeatPumpStratifiedTank.idf

It seems like you want to create a plant loop where on the supply side, you have two integrated heat pumps in parallel: one to provide space heating and chilled water and another to provide space cooling and hot water. It seems that the first is not possible, because the integrated heat pump system can ONLY use the variable speed DX heating coil, which can ONLY use air streams on the condenser side.

One alternative is to create an AirLoopHVAC:UnitarySystem object that references two Water-to-Air Heat Pump coils: one for heating and one for cooling. That way, the air system can provide space heating from a heating coil that can cool down a water stream. It sounds like you've already thought of a similar setup with chillers to provide any cooling capacity during times when the Water-to-Air heat pump heating coil can't meet the chilled water demand.

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Thanks! It was such a detailed answer.

So basically EnegryPlus cannot model ASHP as a plant equipment but only as a system coil instead? To model the heating, I must have to break down the heating capacity of ASHP into smaller system coils? Or maybe I can use waterheater:heatpump* as the HW plant equipment?

Fish Lee's avatar Fish Lee  ( 2017-06-08 20:48:03 -0500 )edit

Correct, ASHP is technically not plant equipment because the working fluid is air with an internal refrigerant loop. An ASHP uses heat pump coils for heating and cooling an air stream on the load side, then on the condenser side it rejects heat in cooling mode or siphons heat in heating mode from another air stream (usually outdoor air). A WSHP uses similar coils on the load side for air heating and cooling, BUT has a water loop on the condenser side instead. In this case, the water loop can be part of a plant (hot water, chilled water, service hot water, etc.).

Aaron Boranian's avatar Aaron Boranian  ( 2017-06-09 08:37:29 -0500 )edit

@Fish Lee a diagram of the system you are trying to model would be helpful

Aaron Boranian's avatar Aaron Boranian  ( 2017-06-09 08:38:02 -0500 )edit

@Aaron Boranian, IMHO ASHPs are technically plant equipment. They drive the heating/cooling plant loops. I am completing a LEED model submission for a hospital on the West Coast in Canada that has 3 ASHPs serving the heating and cooling loops. The HVAC systems have heating and cooling coils and serve 4-pipe chilled beams. The plant is capable of simultaneous heating and cooling and it also provides the first stage of service hot water heating. A dedicated natural gas boiler tops up the SHW temperature.

Chris Jones's avatar Chris Jones  ( 2017-06-09 12:29:14 -0500 )edit

@Fish Lee and @Chris Jones, if I understand you correctly, you are saying this is an ASHP with air-to-water heat pump coils, meaning that the air stream is the source to heat or cool a plant's water loop. If that is the case, then yes, I agree that it is plant equipment.

I interpreted ASHP to mean the use of outdoor air on the condenser side as a source to heat or cool the product air stream used for space heating and cooling. I didn't realize you were talking about using a totally separate air stream to heat or cool the plant loops. My apologies for any confusion.

Aaron Boranian's avatar Aaron Boranian  ( 2017-06-09 13:23:24 -0500 )edit

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Asked: 2017-06-08 06:32:21 -0500

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Last updated: Jun 08 '17