loop to loop heat pump for preheat coils

3 posts / 0 new
Last post

Hi all,

I am trying to simulate a heat pump which will recover heat from chilled water return pipes to provide preheat for the dedicated outdoor air units in a cooling dominated building. This is my first time trying to model heat recovery with heat pumps, so I appreciate any help with it.

The chilled water system is a district cooling plant which I modeled using a chilled water meter. The heat pump would be in operation only when there is a cooling demand and will be providing heat for LTHW loop which will have preheat coils attached to it. The remaining heating is done via electric resistance heating coils of the air side system which i modeled as a constant volume single zone system.

I am not sure if this the correct way but I am trying to use a loop-to-loop heat pump with default library performance curves; but couldn't figure out which loop types are appropriate for it? This heat pump type seems to require a condensing water loop which is not present in the actual building design, do I still have to create one in the model? Also the regular condensing water loop is not appropirate to be attached to a loop-to-loop heat pump. Does this have to be a lake/well loop?

I am also trying to simulate a similar type of heating for the domestic hot water. In the actual system, service water is preheated to an intermediate temperature via heat pumps that recover heat from the chilled water loop return and the secondary stage heating is done via electric resistance water heaters. Is it possible to model this in Equest?

Thanks in advance,
Alper Erten, PE, LEEDAP

Alper Erten's picture
Joined: 2011-09-30
Reputation: 0


To my knowledge there is no way to do this within eQuest.

What we do is output the hourly loads to a spreadsheet and apply them to heat pumps or heat recovery chillers in TRNSYS.

There is a lot of leg work required to setup a functioning system including controllers, inputting performance maps, etc.

This has worked very well for us in several HP and HRC applications. If this is for a LEED project, it must be documented separately as an exceptional calculation.

Fred Betz PhD., LEED AP

Fred Betz's picture
Joined: 2011-09-30
Reputation: 0


The main problem I see with your approach is that you are essentially
putting the heat pump in series with the district cooling plant. eQuest
currently will not do series chillers. However, if you have the option to
split the plant cooling load so that the heat pump and district plants are
parallel, you should be able to use the loop to loop model.

I have modeled a similar system using canal water instead of return water
from cooling coils. A loop to loop heat pump model assumes that your heat
source goes through one of two heat exchangers instead of going directly
into the chiller.

In your case, the evaporator loop would be a local loop between the heat
exchanger and chiller, while your condenser loop would be the LTHW loop
serving the dedicated outdoor air units. You would also need a ground loop
heat exchanger of the "Lake/Well" type connected to your heat source (CHR)

Since you probably have no heat exchanger, just specify the evaporator loop
with similar conditions to the cooling coil return water.

I have attached a copy of the schematic to help clarify the operation -
Figure 34 most closely resembles your situation.


MaryAnne Mason

Maryanne Mason's picture
Joined: 2011-09-30
Reputation: 0