Condenser Water Storage

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Has anyone ever attempted to model condenser water storage using eQuest? The idea is to run the cooling towers at night to take advantage of the low WB temps and then use condenser water directly in a radiant system instead of running the chillers. It looks to me like the only way to model thermal storage is on the chilled water loop.

Please let me know if you have any ideas. Thanks,

Cassie Waddell P.E. LEED AP

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We have modeled in eQUEST an existing large office building that had
chiller/heat pumps with evaporative cooling towers, where we had a hot
water loop with hot thermal storage heated by the heat pump with boiler
back up. The hot water loop was typically like 95 degrees. We also had
a chilled water loop that had cold thermal storage. The separate
cooling tower loop was able to cool the chilled water loop when cooling
tower loop temperatures allowed it. The chilled water loop was
typically like 50 degrees. We had around 250,000 gallons of existing
underground thermal storage tanks on the project. Our building thermal
storage had 4 tanks with the valving capability of us switching from
100% hot thermal storage to 100% chilled water storage and anywhere in
between at 25% levels, at different times of the year.

When we first set out to do this eQUEST model we were not sure from
documentation that eQUEST could model it. Due to the fact that we could
not fail, and delay the project, and lose time having to start over
modeling in another program, we did two concurrent models one with
eQUEST and one with Micro-AXCESS. I did the Micro-AXCESS model and
another gentleman in our firm did the eQUEST model. Micro-AXCESS is a
DOS based hourly climate history based energy modeling program that we
had used for over 17 years, that we had modeled projects of this type in
earlier and we knew it would model it for sure. We compared the output
results of both programs and they were very similar.

In the end both programs, for this particular site showed, that due to
additional losses with the storage tanks,etc., that we used slightly
more energy with the storage tanks than without and for this Northern
USA site the operating costs were higher. This may not be true with a
different climate site location. Also, our site did not have lower
electrical rates at night, that might be a consideration at other
locations.

I have attached some info from the eQUEST item helps on the subject to
take a look at.

David A. Bastow

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