Heat Recovery Chiller

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Hi Everyone,
I am working on a project where I have a heat recovery chiller that is recovering heat from IT room units in a hospital and then providing heat to VAV reheat systems for other spaces. I am trying to model this in equest and not getting the desired result.

eQuest is not letting me connect to reheat loop. And when I connect it to my steam loop, I see no heating savings whereas I see increased cooling use.
Anyone has any ideas on how to model this properly?

Bikesh Dahal, BEMP

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Bikesh Dahal's picture
Joined: 2016-02-10
Reputation: 0

Heat recovery from chillers is a little tricky in eQUEST. In order to
recover heat, the condenser loop supply temperature must be higher than
the heating loop return temperature. Doing that typically increases the
lift on the chiller increasing the electrical input energy.

You stated you couldn't recover to your reheat loop -- is it a secondary
loop? Unfortunately no primary equipment can be attached to secondary

bfountain's picture
Joined: 2011-09-30
Reputation: 201

Unfortunately it is. So, how is this normally done. Use excel spreadsheet to calculate savings? Or is there a work around to it.

Bikesh Dahal's picture
Joined: 2016-02-10
Reputation: 0

I can think of options but none of them are stellar:

1) make your reheat loop a separate primary loop -- this is good in that
you can model heat recovery more closely. The temperature in this
reheat loop will typically be lower allowing for good pick up from the
chiller condenser. However, you will now have to split your boilers
onto the two loops and create a part load curve for them that you feel
correctly reflects the gas input at varying loads (non-trivial).

2) Artificially drop the temperature of your steam primary loop to get
more heat recovery from the chillers. You will have to watch your pump
flows but, unless you are modelling pipe losses the impact should be
small I think.

bfountain's picture
Joined: 2011-09-30
Reputation: 201

We stopped using the eQUEST heat recovery chiller years ago because it?s not controlled properly. eQUEST exclusively dispatches the heat recovery chiller on cooling demand, and in a hospital the heating or the cooling load may drive the heat recovery chiller. I never checked if v3.65 corrected this.

We use TRNSYS 17 with hourly loads from eQUEST et al as it allows us to be more accurate/flexible on controls, and then submit an exceptional calculation for LEED/compliance.

You can create your own spreadsheet do as it?s a pretty simple heat balance if the chilled and hot water temperatures are constant.

Note, that the capacity and the efficiency of the heat recovery chiller changes with the chilled and hot water temperatures so if you?re resetting temperatures it will make the spreadsheet more complex.

Hope that makes sense.


Fred Betz PhD., LEED AP ?BD+C
Senior Sustainable
Design Consultant

5802 Research Park Blvd. | Madison, WI 53719

P: 608.236.1175 | F: 608.238.2614
fbetz at aeieng.com | www.aeieng.com

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