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Condenser water heat recovery

asked 2015-11-05 16:47:56 -0500

Nidhi gravatar image

updated 2016-01-09 13:54:57 -0500

Hi Everyone, I am working on an inpatient hospital project with 24/7 operation and pursuing LEED. The baseline is system 8 as per ASHRAE 90.1-2007. We recently submitted the project for USGBC review and received comment for including the condenser heat recovery for preheating the service hot water in accordance with Table G3.1#11(Baseline)(f) and Section I was wondering if somebody has included this in any project. Also, what’s the best way to model it in eQuest. I am thinking of accounting it by entering the inlet temperature of 85 F (as suggested in ASHRAE 90.1-2007, section at the DHW loop -> Process / DHW loads. I was wondering if there is any other way to account for this. Any help is really appreciated. Thanks,

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answered 2015-11-06 12:25:46 -0500

updated 2018-12-10 19:43:41 -0500

In eQUEST you can model heat recovery from any chiller to a domestic hot water loop. If you open up the "Chiller Properties" window, under the "Basic Specifications" tab, look for Loop Assignments, and click on the drop down menu next to "HtRec". You should be able to select the DHW loop for heat rejection. Following, you may want to set the "Max Heat Recovery" to a ratio of 0.6 under the "Condenser" tab. This sets the keyword "MAX-HTREC" which sets the limit on the amount of heat reclaimed from the chiller on an hourly basis. You will need to make sure that the loop return temperature for the DHW loop is less than 95ºF to allow for heat recovery, but this is usually not a problem for DHW loops with low incoming water temperatures. You may also need to change the design temperature change of the water through the heat recovery heat-exchanger (DOE-2 keyword is HTREC-DT). The default is the LOOP-DESIGN-DT of the attached loop and it needs to be less than 70ºF. I recommend setting this manually, say to 30ºF to bring the temperature of the DHW from 55ºF to 85ºF. Unfortunately, the entry for this setting is greyed out in eQUEST, so you may have to open the .INP file and add the setting manually in a text editor. Alternatively, you could reduce the Loop Design DT for the domestic hot water loop to some number which is lower than 70ºF, making sure that the return temperature is less than 95ºF. So if the Design HW Temp for the DHW loop is 135ºF, you could set the Loop Design DT to 60ºF to get down to 75ºF return water temperature.

Good luck and let me know if you have any further questions.

P.S. You want to make sure you are not modelling recirculation on the loop, as this may lead to high return water temperatures which prevent heat recovery from working.

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answered 2015-11-09 10:46:30 -0500

Nidhi gravatar image

Thank you Daniel. This is very helpful for me.

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Asked: 2015-11-05 16:47:56 -0500

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Last updated: Dec 10 '18