Air Cooled Heat Pumps to Provide Hot and Cold Water

asked 2014-12-10 10:04:07 -0600

Annie Marston
4357 ●6 ●32 http://www.resustain.com

updated 2015-01-09 11:40:25 -0600

Neal Kruis

4735 ●10 ●17 http://bigladdersoftware.com/

We have a project which has air cooled heat pumps which provide both hot and cold water to radiant ceiling panels and our AHU coils. I am modelling in EnergyPlus and the only air cooled heat pumps are on the AHU side and not on the plant side, ie they can not supply water to radiant panels (as far as I am aware). The heat pumps on the plant side are all water cooled. We are solving this problem rather inelegantly right now and modelling an air cooled chiller to substitute for the cold water from the heat pumps and a water to water heating heat pump connected to a cooling tower for the hot water supply, in post process we will remove all energy from the cooling tower as well as the pump energy for the cooling tower, I am still considering how we will make the cooling tower act like the outdoor air.

My questions are: 1. Is there a better way to do this in EnergyPlus (ie can we model air to water heat pumps?) 2. How can I make my cooling tower behave like outdoor air, or is there a better condensor object to use that can behave like outdoor air?

As always many thanks for any help I can get, I think we can make it work but it is really messy and I would like something a little more elegant.

Annie

answered 2014-12-10 20:47:10 -0600

MJWitte

9740 ●6 ●10 http://www.gard.com/

updated 2014-12-10 21:03:37 -0600

The standard recommendation for this is to use a heat pump water heater for the heating mode with an air cooled chiller for the cooling mode. If you want to keep your present configuration and control a plant loop to track outdoor air temperature, I can think of three options:

Put district heating and cooling objects on the loop and use SetpointManager:FollowOutdoorAirTemperature and remove the district heating/cooling energy in postprocessing.
Use a large FluidCooler:SingleSpeed along with SetpointManager:FollowOutdoorAirTemperature. This should approach the outdoor dry-bulb temperature if the fluid cooler is large enough, and you can set the power inputs to zero or post-process.
Use PlantComponent:TemperatureSource with a Schedule:File that contains the hourly outdoor dry bulb temperatures.

As a side note, a central plant air-to-water heat pump is on the list of planned development projects for FY15.

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Comments

A central plant air-to-water heat pump will be available starting with EnergyPlus v9.3 (March 2020). See #7489.

MJWitte ( 2019-10-28 09:37:29 -0600 )edit

I am working on a similar project: Radiant floor cooling and heating provided by chilled/hot water generated by air-to-water heat pump. I used WaterHeaterHeatPumpStratifiedtank.idf example file and modified it to incorporate radiant floor and also added air cooled chiller for cooling. The water heater has a water heater tank and a DX coil. The water heater tank has two electric heaters and all the heating load is taken by these heaters and no heating load is passed to the DX coil. If I reduce the size of the electric heaters, the heating load disappears. Many thanks for any help I can get.

jzaidi ( 2019-12-05 10:36:51 -0600 )edit

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