Water to Water Heat Pumps (UNCLASSIFIED)

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The EER of WWHP can vary from 11.8 to 23.3 depending on the water temperature
returning from the well field. Can Trace model this?

We are designing a lot of geo-thermal heat-pumps. If we can't model the
benefit of the well-field accurately, we can't model the energy use.

John Eurek PE, LEED AP

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In TRACE:

The help file (press F1 on any screen in TRACE) and User's Manual are pretty helpful with how to model geothermal heat pumps, I would suggest reading through those first. In terms of modeling the appropriate ground loop temperatures and associated WWHP efficiency, there are a couple of ways of doing it (see help file and User's manual for specifics). Just keep in mind that when you create a new WWHP in the Cooling Equipment library and define the Full Load Energy Rate and the Design Entering Condenser Water Temperature, you need to base them on the worst case entering loop temperatures over the year. TRACE assumes you enter the efficiency at the hottest and coldest entering condenser temperatures for Cooling and Heating efficiency respectively and then uses the Power Consumed and Ambient Modification Unloading Curves to adjust the efficiency for air-side load and change in entering loop temperature.

In eQUEST:

I'm a little rusty on eQUEST, but this is how I remember it. You can enter the ground and well properties for your site and system which will be the basis of entering loop temperature for the equipment as a function of the load on the equipment over the year. eQUEST wants the equipment efficiency at ARI conditions and then you enter the unloading curves (see help/Documentation for more info on this). The concept here is similar to TRACE but from what I remember it is more detailed.

Thanks,

Alex Chapin, E.I.T., LEED AP BD+C

P Please consider the environment before printing this e-mail - Thanks!

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Date: Tue, 22 Feb 2011 10:37:34 -0600

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Subject: [Trace-users] Water to Water Heat Pumps (UNCLASSIFIED)

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Classification: UNCLASSIFIED

Caveats: NONE

The EER of WWHP can vary from 11.8 to 23.3 depending on the water temperature returning from the well field. Can Trace model this?

We are designing a lot of geo-thermal heat-pumps. If we can't model the benefit of the well-field accurately, we can't model the energy use.

John Eurek PE, LEED AP

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I can probably fill in a little on the eQuest side of the coin:

My general understanding is that you should be able to use either Trace
or eQuest to model process efficiency which varies with the ground loop
temperature.

I approached this once in eQuest, and based on that experience and as I
think others have brought up, you're restricted to using a CW loop of
the lake/well type, which means you must define for the program what the
temperature behavior of the GLHX is over the year (as a schedule).

Once the groundwater temps are dealt with, from there you can either use
the default loop-to-loop chiller curves in the eQuest library, or define
your own. The three curves separately define the following:

1. Effects of part load on the EIR (EIR-fPLR)

2. Effects of temperatures on the capacity (CAP-fT)

3. Effects of temperatures on the EIR (EIR-fT)

Unlike centrifugal chillers, finding the manufacturers data necessary to
make your own custom curves in DOE2/eQuest is not a trial by fire - all
the data for the above curves may be found on a single spec sheet
without conversions, depending on who your WWHP manf is... There are
some restrictions regarding pump quantities and behavior of the
"loop-to-loop chiller" system - I'd advise you to carefully review the
DOE2 dictionary entry and diagrams for "Loop-to-Loop Heat-Pump" to get
an sense of how the equipment behaves and how you may need to react
accordingly to match your proposed design.

I'd also refer you to not miss a recent writeup/report posted to
eQuest-users by Dana Troy detailing a strategy/feasibility study to
approach multi-stack heatpumps in eQuest... something I could've used in
the afore-mentioned project.

Best of luck!

~Nicks

NICK CATON, E.I.T.

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