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How to model an air to water heat pump?

asked 2021-12-22 18:12:42 -0600

Tomlai15 gravatar image

updated 2022-01-10 12:03:35 -0600

Hello, I am a beginner in OpenStudio and EnergyPlus. I want to simulate an ASHP (air-water) for space-heating use and DHW use in the OpenStudio/ EnergyPlus, how can I do it?

I am considering the building is a small residential house and zoned with only one room/ thermal zone. Not considering any internal heat gain such as people and elertric equipment, and to maintain the indoor air temperature as 21oC whole year under UK climate data. The hot water from the heat pump is supplied to radiator in the first model and change to floor heating in second model. What schedules should I input and how can I create such HVAC system? I appreciate any help!

5/1/2022 updated: The HVAC system I want to simulate is as followed, serves only a normal UK domestic radiator for providing space heating and hopefully DHW: image description

10/1/2022 updated: The loop for the modelled AWHP system is mentioned as followed: image description

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@Tomlai15 can you update your post to include an image or diagram of the HVAC system that you want to simulate? It sounds like you want to simulate a heat pump water heater that serves radiant floor heating components -- is that correct?

Aaron Boranian gravatar image Aaron Boranian  ( 2022-01-05 10:44:32 -0600 )edit

Hi. Thank you for the advice. I have already updated the post.

Tomlai15 gravatar image Tomlai15  ( 2022-01-05 11:39:54 -0600 )edit

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answered 2022-01-06 12:55:33 -0600

Yes, you can model this in EnergyPlus and most likely the OpenStudio Application. You will need at least 2 plant loops:

  1. [Optional] Heat Pump (AWHP on supply side, storage tank "source side" connections on demand side)

    The AWHP can be modeled with a heating plant loop heat pump using an "AirSource" condenser. This plant loop is optional because you could instead model this as a heat pump water heater (HPWH).

  2. Storage (storage tank "use side" connections on supply side, radiators & DHW tank "source side" connections on demand side)

  3. DHW (DHW tank "use side" connections on supply side, DHW draws on demand side)

You can read more in this post about splitter/mixer pairs in plant loops to have HVAC components in parallel with each other (in your case, the radiators & DHW tank are in parallel between a splitter/mixer pair).

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Thank you very much!!!! I will have a try for it in EnergyPlus. Since when I consulted someone, he said this system (AWHP) can only be built in EnergyPlus but not OpenStudio. And I am going to model it with the WaterHeater:HeatPump:PumpedCondenser object.

One question is that, do I need to include 2 HeatExchanger:FluidToFluid objects for the storage tank as it indirectly heats the radiators and DHW tank? And define the demand side as radiator/DHW, and supply side as the storage tank (Water heater)?

Tomlai15 gravatar image Tomlai15  ( 2022-01-07 16:49:33 -0600 )edit

No HX:FluidtoFluid objects are required. The water will leave the storage tank on the supply side, then be split to flow through the radiator & DHW tank in parallel branches on the demand side. This is an "open" system where the water will be mixing between tanks instead of a "closed" system with WWHXs.

Aaron Boranian gravatar image Aaron Boranian  ( 2022-01-10 10:43:04 -0600 )edit

Thank you for the answers.

As this system is not drawn by me, but aren't there coils in the storage tank link to the radiators and DHW tank for exchanging heat to the water in the radaitors and DHW tank? And I have edited the post to include the loop the author created, that he mentioned to include two HX:FluidtoFluid objects.

Tomlai15 gravatar image Tomlai15  ( 2022-01-10 12:02:34 -0600 )edit

Correct, if you wanted to have this as a "closed loop" with 2 HX:FluidtoFluid components then you will need the plant loops that you added to your post. Note that the HX:FluidtoFluid component needs water flow on both sides of the HX, which isn't technically what's happening. Water inside of the storage and DHW tanks are stagnant, so the HX effectiveness isn't quite the same. This is a small caveat, and the modeled plant loops should still work as intended.

Aaron Boranian gravatar image Aaron Boranian  ( 2022-01-10 12:16:01 -0600 )edit

So would you comment the system in the first image is not a practical system in real life? If not what should it looks like in real life. I am now very confused on the work flow of a real-life AWHP, please point out any mistakes in the following work flow: 1. HP heat the refrigerant by compressor and exchange the heat (in condenser) to water coming from storage tank, refrigerant cools and go back to evaporator again 2. Water go back to the storage tank, extracted from the tank and get distributed to their final heat emitters, or; 3. Water exchange the heat with DHW through coil

Tomlai15 gravatar image Tomlai15  ( 2022-01-10 15:12:20 -0600 )edit
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answered 2021-12-30 01:44:31 -0600

You can refer to this answer.

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Hello, thank you for the answers. I will have a look on it.

But may I ask a very basic and primary question? Is it able to model the ASHP air to water heat pump model in EnergyPlus and its space heating system (water tank as water heater:mixed/stratified, radiators as ZoneHVAC:Baseboard:Convective: water, etc.) in a house with the existing Objects in EnergyPlus?

Because I am still very new to EnergyPlus and OpenStudio, I asked several people. Some say no. Some say yes, both can model the Air to water heat pump for space-heating, some say only EnergyPlus can model it. Thank you.

Tomlai15 gravatar image Tomlai15  ( 2021-12-30 09:46:40 -0600 )edit

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Asked: 2021-12-22 18:12:42 -0600

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Last updated: Jan 10