Ground source heat pump/ cooling tower hybrid

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Hi there,
We have a building that is conditioned with water source heat pumps. The
loop is maintained by several ground source wells, and also a closed
loop evaporative cooling tower and a hot water boiler. Does anyone know
how to correctly model this loop? Equest will let you put a boiler and a
cooling tower on a ground loop with the wells, but when you run the
simulation it gives an error that says a boiler cannot be on the loop
with the ground source heat exchanger.

Any advice is appreciated.

Thanks in advance,

Dane Heimerman

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You'll have to calculate the heating portion of your hybrid loop separately
since DOE2 doesn't allow this setup.

The easiest way I can think of would be to export the hourly GHEX report,
find the instances where the ground loop temperature dips below your design
setpoint, take the corresponding heating load served by the GHEX for that
hour and then replace that GHEX energy with boiler energy. Don't forget to
properly account for pumping energy depending on how the loops will operate
as designed.

Notice I said easiest, not the most accurate. It's important to know how
this method will skew your results. In this case, you'll artificially be
cooling your ground loop in the winter months (when the boiler is operating)
and pulling that energy back out in the summer cooling months for free.
This could have a significant impact on the annual average efficiency
(artificially inflating) of the heat pumps.

Anthony Hardman, PE

Anthony Hardman, PE
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