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How to add a WaterToAir Heat Pump

asked 2021-10-12 12:03:44 -0500

MColeman's avatar

updated 2022-02-07 14:24:05 -0500

I'm trying to add the OS objects OS:Coil:Heating:WaterToAirHeatPump:EquationFit and OS:Coil:Cooling:WaterToAirHeatPump:EquationFit to an air loop in my model. While I believe I the object has been added correctly, when I run the model with these coils in them, I get the following error:

* ~~~ * ..Invalid Air Loop Component Type = "COIL:HEATING:WATERTOAIRHEATPUMP:EQUATIONFIT".

Has anyone encountered this problem/ Is there a way to know which object I should be using instead? Thank you for any information you'd be willing to provide me.

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answered 2021-10-15 22:32:43 -0500

mattkoch's avatar

You first must add an OS:ZoneHVAC:WaterToAirHeatPump object to a thermal zone on the Thermal Zones tab. Then you will also need a OS:PlantLoop on the HVAC Systems tab, perhaps with a OS:GroundHeatExchanger:Vertical on the supply side, and also setting that plant loop to have the "Condenser" Loop Type. And don't forget to add a pump and a setpoint manager to the supply side of the OS:PlantLoop as well. Then when you go back to the Thermal Zones tab and click on the OS:ZoneHVAC:WaterToAirHeatPump, the Edit field will pop up on the right. On the top, you will see a gear and then two chain links next to it. Clicking on the first chain link allows you to connect a OS:Coil:Heating:WaterToAirHeatPump:EquationFit to to the OS:PlantLoop via a check box. Clicking on the second chain link allows you to connect a OS:Coil:Cooling:WaterToAirHeatPump:EquationFit to the OS:PlantLoop via a check box. Both coils get added to the same OS:PlantLoop (it's the whole point of a WSHP). When you then go back to the HVAC Systems tab and the OS:PlantLoop, you will see these cooling and heating coils on the demand side of the OS:PlantLoop. So, in essence, you cannot add these coils directly to an air loop or a plant loop, they get added automatically once you add a OS:ZoneHVAC:WaterToAirHeatPump to a thermal zone, and then you must manually link these coils to an OS:PlantLoop.

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To further clarify, you add the OS:ZoneHVAC:WaterToAirHeatPump to a thermal zone by dragging and dropping it from the Library on the right ("under Water to Air HP") into an empty slot in the Zone Equipment column. You have three choices of OS:ZoneHVAC:WaterToAirHeatPump - electric, natural gas or hot water backup. Probably simplest to get you started is electric.

mattkoch's avatar mattkoch  ( 2021-10-15 22:37:22 -0500 )edit

Thank you for the very thorough explanation. This all makes sense to me, and sorry this was my fault for not framing the question clearly, so let me back up and give better context. I am trying to model a DOAS which uses a water-source heat pump. I've been trying to add the coils to the DOAS air loop. I've tried adding the OS:AirLoopHVAC:UnitarySystem object to host these coils, but they come with extra components I don't need (a supplemental heating coil). When I tried to have the object controlled by the load, I notice I have oversizing and an inefficient system. This lead me to my question.

MColeman's avatar MColeman  ( 2021-10-19 11:58:29 -0500 )edit

Also, the since the DOAS is only serving the ventilation requirement, I need to control the coils by a setpoint manager, not the load, so using the OS:AirLoopHVAC:UnitarySystem object hasn't been useful since if I remove anything, it breaks the object and I don't see airflows through the airloop, even though the simulation runs completely. For reference, this post gave me an idea of how to approach it, but so far nothing has worked well. I currently have the objects controlled by the load, and am hard sizing the coils.

MColeman's avatar MColeman  ( 2021-10-19 12:05:14 -0500 )edit

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Asked: 2021-10-12 12:03:44 -0500

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Last updated: Oct 15 '21