Modelling air cooled heat recovery chiller in eQUEST

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Hi All,

The building that I am modelling in eQUEST has an air-cooled heat recovery
chiller wherein the rejected heat from air cooled condenser is utilized to
preheat the domestic hot water to the domestic hot water heater.

Is there a workaround in eQUEST for modelling the above system

Thank You

Syed Hussaini, PE, LEED GA

Energy Engineer II

*Partner **Energy*

680 Knox St., Suite 150 |Los Angeles, CA 90502
D: 310-622-8851 | C: 480-512-9739 | F: 310-862-2399 | shussaini at

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Syed Safiuddin Hussaini's picture
Joined: 2016-01-22
Reputation: 0

Hi Syed,

There are inputs for chiller heat recovery in eQUEST. I just tried to model it using your description but it didn't seem to be working. Maybe you'll get some more feedback at equest-users (cc'd).


Bill Bishop's picture
Joined: 2012-02-25
Reputation: 7


Based on the help documentation, "heat will be recovered whenever the return temperature of the loop is less than the maximum allowable condensing temperature of the chiller". This makes heat recovery to DHW loops difficult in eQUEST, because DHW loops are usually once-through (no recirculation, so no return) and even if you model a recirculation pump, the typical design return temperature would be around 120F instead of the low service water temperature of around 50F.

You could try experimenting with the MAX-RECOVER-T and the supply/return temperatures of the DHW loop. I tried dropping the DHW supply temperature but that still didn't seem to make it work.

You could try modeling the DHW as a HW loop with a process load and see if that makes it work.

Best regards,


Bill Bishop's picture
Joined: 2012-02-25
Reputation: 7

Good morning Syed,

What you are describing can be modelled in a reasonably straightforward fashion in eQUEST.

My first observation is you will have to use DOE-2.2 rather than DOE-2.3 in eQUEST. While the heat recovery keywords are implemented in DOE-2.3, it is not recovering heat to the hot water loop in build 7175 (DOE2.3-50h).

Specifying heat recovery on a chiller ? either air cooled or water cooled ? is done by adding the loop that the heat will be recovered to the HTREC-LOOP keyword. You will be prompted for what percentage of the condenser heat is available for heat recovery (i.e. is it desuperheat which might be 25% or condensing heat recovery where almost all the heat is available).

[cid:image002.png at 01D62A95.C292C2A0]

The key input on the chiller is on the Loop Attachments tab:
[cid:image004.png at 01D62A92.6D2D3780]

The MAX-RECOVER-T is the highest temperature that will be recovered. You will likely want to set this to 120?F. If the return water temperature of the heating loop that you are recovering to exceeds this value, you will not recover any heat to the loop. Whether this is an issue with your DHW system will depend on the amount of recirculated water in the loop. With no recirculation the chiller would always recover heat to the DHW loop however I can envision a situation where the recirculation flow is set too high increasing the return water to the DHW heater above the MAX-RECOVER-T preventing heat recovery. If you are not seeing heat recovery from the chiller, you may want to create an hourly report on the loop that heat is being recovered to and look at the loop temperature returning to the plant.

Here is an example .sim where I am attempting to recover heat from an air cooled chiller to a hot water loop set at 180?F. Not surprisingly, no heat recovery.
[cid:image005.png at 01D62A92.E1FB1A50]

By reducing the hot water loop temperature, we now see that heat is being recovered from the chiller and that the boiler load is reduced correspondingly. This is an air cooled chiller example.

[cid:image006.png at 01D62A95.B83E4270]

I hope this helps.




Brian Fountain
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Brian Fountain's picture
Joined: 2019-05-02
Reputation: 0