[Equest-users] eQuest MultiStack HP Chiller/Boiler

[Anthony Hardman]

eQUEST just isn't a good tool for the application you've encountered.  In the past, I've just put the water loops on meters and calculated the multi-stack energy use via post processing.  You'll need to work with the vendor to get enough data points to generate performance curves for the three modes but once you get the data you should be on your way.  FWIW, the simultaneous mode performance curve is relatively "flat" so you can certainly take some simplification liberties there.  In my experience, just doing it in the spreadsheet was less work than trying to force equest to do it.

Anthony Hardman, PE, LEED AP BD+C
Senior Building Performance Analyst, Owner

The Green Engineer | Sustainable Design Consulting
D: 978.341.5459  |  O: 978.369.8978
E: anthony at greenengineer.com<mailto:anthony at greenengineer.com>

From: Daric Adair [mailto:Daric.Adair at hendersonengineers.com]
Sent: Thursday, August 12, 2021 3:07 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] eQuest MultiStack HP Chiller/Boiler

All;
Have a model where a MultiStack Air-Source HP Chiller/Boiler is being considered. This unit is air-source and can operate in cooling only, cooling & heating, or heating only. Hot Water loop will have Electric Boiler as back-up/supplemental. Climate 4A. Air Side is a Multizone VAV with HW / CHW.
Only resource I found online is quite dated,  from Dana Troy in September 2011. However, that write-up was using a ground coupled system for loop imbalance, my potential design will not.

Within eQuest I found the Type: Heat Pump Chiller, but it must be tied to a single Chilled Water or a 2Pipe Loop.  The first work around I tested was to create two loops (Chilled Water and 2Pipe) with double the normal number of chillers and use equipment controls for sequencing. The 2Pipe loop had a High Snap temperature to always keep it in heating mode & act as the Hot Water Loop. The Air-Side allowed Chilled Water loop assignment for cooling, and allowed the 2Pipe Assignment for Heating and Zone Heating. Though, this run resulted in 3000+ unmet hours and the Chilled Water Loop to attempt to operate at 70F. If the Heating source to changed to electric, the unmet hours decrease and the loops control as expected. If I change the Heating Source to a separate dummy/test Hot Water loop, this too allows proper operation. It would appear that when attempting to assign a 2Pipe loop to both Heating and Zone Heating causes the Chilled Water Loop to misbehave(?!). Anyone else experienced this or have other solutions?

In an effort to work around this issue, I swapped the Heat Pump to a Loop-to-Loop Heat Pump Option. This allowed the creation of a Hot Water & Chilled Water loop - but also requires a Lake/Well Loop. Luckily, a Ground Loop Heat exchanger can take a schedule of temperatures. Thus, I extracted the Outside Air temperature to an 8760 schedule and assigned this to the Ground Loop Heat Exchanger. This way the loop is ~to the OA temp, but having doubts that this is legitimate as I am seeing a significant delta in the hourly reports between the Loop Temperatures and the OA Temp for some hours.

Open to ideas. Thanks in advance.


Thanks,
DARIC ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst

HENDERSON ENGINEERS<https://www.hendersonengineers.com/?utm_source=hei&&utm_medium=email&&utm_campaign=hei-shortsignature>
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