Control of Heat Recovery Chiller

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Hi All,

Along the same lines as Tony Kriel's post earlier today, I am also
having trouble setting up a heat recovery chiller in eQuest.

Specifically, I am looking for advice on how to control the chiller. I
am using the ELEC-HTREC chiller type. I would like to operate the
chiller when there are simultaneous hot and chilled water loads, up
until the point where either the hot water loop load is satisfied, or
the chiller is operating at maximum capacity. In other words, I do not
want to reject any heat to the condenser water loop, which is required
to be attached to the ELEC-HTREC chiller (in the actual design there is
no CW loop to use!) I only want to operate the heat recovery chiller
only when all heat can be rejected to the hot water loop. Is there a way
to control the chiller operation based on the hot water Loop conditions?

Any ideas on how to do this with the ELEC-HTREC chiller? Is there
another chiller type that can be controlled in this way?

Thanks in advance to anyone who has ideas on this.

Kind regards,

Molly Curtz, P.E.

Molly Curtz's picture
Joined: 2011-09-30
Reputation: 0

I think what you are trying to model is a heat
pump chiller. These machines are pretty cool &
the economics work when you have strong
simultaneous heating and cooling loads
year round, like large hospitals, large universities, etc.

I have worked on two projects that involved
the use of heat pump chillers. We used eQuest
to estimate building loads, but not to model the chiller.

My advice would be to take the 8760 hourly
cooling and heating loop loads from
eQuest to a spreadsheet and finish the
analysis in Excel.

The eQuest program can do a lot, but I'm
pretty sure the eQuest program cannot
model how a heat pump chiller is operated,
at least how they are operated on our

We had the HPC piped into the plant to
be in series with the return chilled water.
In this manner, the HPC would precool the
return chilled water. The control point for the
HPC is actually the hot water side. The HPC
is controlled to maintain leaving hot water
temperature setpoint at 140 to 155 degrees, depending
on summer/winter, hot water reset, etc.
So the HPC is controlled to meet the heating
load, we get whatever cooling we get, and
the main chillers provide the remainder of
the cooling, if required. The HPC was not
piped into a cooling tower loop. In
retrospect we found that a plate and frame heat
exchanger could be a good idea for
when the heating load dropped below the
HPC minimum heating output. This allows
the HPC to be kept online longer when
heating load is dropping, though at some
point it makes sense to shut the HPC down.

Bottom line: These HPC's are very tricky
and I couldn't figure out how to model them
in eQuest, so I did the analysis in Excel.

I hope this is helpful.


James Hess, PE

James Hess's picture
Joined: 2011-09-30
Reputation: 401