[Equest-users] WS VRF Connected to Campus CHW Return Line

[Matthew S. Garlick]

One more VRF brain teaser folks-

I've been asked to evaluate the performance of a water-source VRF system connected to a campus CHW return line. The idea is that during heating season the campus CHW plant, which operates year round, will see reduced chiller loads from this building's VRF system pulling heat from the return line. During cooling season this would also produce an energy penalty, but we'll do an exceptional calculation later to capture the net effect on the system. Using the water source heat pump work-around to simulate the WS VRF (unless someone has a better idea?), I need to find a way to connect the eQUEST CW loop to a sink with a controllable temperature.

Because a WSHP system type can only connect to a CW loop, I can only add cooling towers, boilers and geo fields to help manage the CW loop temp. Since cooling towers will never be able to produce water temps close to 50F I can't use them for this. Boilers seem to have a low-temp lockout on them and I can't get them to "trim" the CW temps at the level I need them to, and they only operate when there is a call for heating, which reduces their effective season to winter and shoulder months anyway.

What I've landed on is using a ground loop modified to unrealistic levels (ie ground conductivity of 1,000) which produces a relatively consistent leaving CW temp. I've found that with this setup and by modifying the ground temperature I can control the sink temp to a ~5F range over the course of the year, which seems a reasonable approximation of the campus CHW Return line temps.
[cid:image003.png at 01D65482.ED7A8680]

Looking at system efficiencies, which is really the thing I'm after anyway, I am seeing a relatively consistent string of hourly efficiencies for both heating and cooling systems.
[cid:image008.png at 01D65482.ED7A8680]
[cid:image009.png at 01D65482.ED7A8680]

I'm working to get the actual CHWR temps from the campus as well as the performance points for the BOD system at those CW temps, so all of this can be dialed once I have all the information. My question then, is what am I missing? Is there a better way to accomplish what I'm trying to do, understanding that the net effect of this strategy on the CHW plant will be calculated independently later (unless I can somehow approximate it into this model?)

Thank you so much for your brain power and time!


[TBCx]

Matt Garlick, CxA, CEM, BEMP
Commissioning Authority, Energy Engineer | TBCx

E-mail: msg at tbcxinc.com<mailto:msg at tbcxinc.com>
Mobile: 801-907-5654
Direct: 801-401-9492

324 S. State Street, Suite 400
Salt Lake City, UT 84111

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