Ground Water/chilled water loop error(s)

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Hello all:

I have a system that is using well water direct to the cooling coils (no heat exchanger to protect the cooling coils) at multiple air handlers in the building. I set it up with the condenser water loop tied to a ground water heat exchanger. This condenser loop then is tied to another heat exchanger on the chilled water loop to the coils. This approach has given me an error on the condenser water loop that it has no design flow. I have been playing with the primary/secondary loop designations, even putting some made up flow values into the loops/pumps etc. but have had no luck. Any ideas?

I would like to eliminate heat exchangers all together and just model the 50? well water directly into the chilled water loop - any advice on how to do this? I already changed the effectiveness of the heat exchanger to 1.0.

Thanks

Travis Miller, PE

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I think you need to create 2 circulation loops: one loop is a lake/well circulation loop and the other is a chilled water loop. Create and attach a ground loop heat exchanger lake/well type to the lake/well loop. Create and attach a chiller heat pump type to the lake/well loop and the chilled water loop. The chiller heat pump type device will have energy coefficients of 1. That should do it.

I have used this system successfully with a 2 pipe circulation loop and I don't see why it wouldn't work with a chilled water loop.

Kathryn Kerns

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Travis - sometimes this error can be addressed by putting a nominal process load on the offending loop - say 0.000001 Mbtu/hr, with a minimal schedule.

There may be a more comprehensive or elegant solution, but this might just get you going.

AD

Aaron Dahlstrom , PE, LEED? AP

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Joined: 2011-09-30
Reputation: 4

Thanks Aaron - I did that and now the error reads:

[Description: C:\Users\tmiller\Desktop\Capture1.PNG]

So I went and gave the chilled water loop the same process load, but that did not fix the problem. Below is a screenshot on how the loops are tied together. Ignore the heat pump loop - that is for a different system in the same building. Any other thoughts would be appreciated. Thanks

[Description: C:\Users\tmiller\Desktop\Capture.PNG]

Travis Miller's picture
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Travis,

If nothing else you can model it as a regular chiller with an open cooling
tower and just use KW/efficiency factors & curves for the various components
so that it equals what you would get from energy used by your well pumps or
what have you. Also, using temperatures that relate to your well water
temperatures for the chilled water temperatures. I did this once, modeling
an existing large office building that was cooled by well water, that varied
from 50 degrees F. in winter to 60 degrees F. in the late summer. Once I
got all the inputs and curves and all set up correctly then it modeled very
closely to what the actual energy use had been from all of our historical
recorded data.

David A. Bastow

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Travis - took a little more time and read the whole thing.

Why not put the offending chiller (and associated circulation pump) on a separate utility meter and just subtract that meter from your total usage as a post-processing exercise?

I'm not sure whether or not eQUEST can explicitly model what you're trying to do.

Aaron Dahlstrom , PE, LEED? AP

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Joined: 2011-09-30
Reputation: 4

I would like to avoid any post-processing exercise(s) - so how about this approach - I created a heat pump as another chiller to serve this chilled water loop tied into the same coils. Now I want to force chiller 1 - the water economizer- to cover the cooling load. I am trying to use the equipment controls/load management options to accomplish this. Never used these functions before - Is this a reasonable approach?

Travis

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