[Equest-users] 2 Pipe Loops

Wed Jan 25 18:50:00 PST 2023

Just to share one more fundamental approach that requires a little extra setup, but offers some unique flexibilities that I’ve had repeat success with:

Considering various limitations/restrictions inherent to DOE2 heat pump chillers, you can also effectively model (real-world) 2-pipe system in the energy model as a 4 pipe system.  You would define the exact same pump/loop properties for both the heating and cooling loops, then just make an effort to schedule each loop in a fashion that will prevent simultaneous operation.

Commonly when emulating  2-pipe systems, a set of snap schedules is an “ideal” control approach which is fine for getting through prescriptive/performance modeling efforts, however out in the real-world I have much more commonly encountered manual (not automated by temperature) heating/cooling season switchover processes.  Those are more accurately modeled with calendar schedules to align with typical/historical changeover dates, and that may be easier than snap schedules ultimately if you need to define a “no heat no cool” period where neither boilers or chillers are operated.

Sorry for digressing!  Back to the modeling approach:  You can alternatively/additionally schedule when heating/cooling is available from the airside systems).  From there it can sometimes be easier to define waterside equipment effectively matching your real-world machine’s cooling & heating performance characteristics, separately.

This can all be a little more work than necessary for a given model/application, so I wouldn’t call it my “Plan A,” but could be a useful strategy to keep in mind and try out sometime if you have the opportunity.

~Nick

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Nick Caton, P.E. (US), BEMP
ニック ケートン, P.E. (US), BEMP
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From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Brian Fountain via Equest-users
Sent: Monday, January 23, 2023 2:06 AM
To: Omer Moltay <omoltay at mimtarch.com>
Cc: Haberl, Jeff via Equest-users <equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] 2 Pipe Loops

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Omer
It seems to me that a loop-to-loop heat pump would better represent the system you are describing.   It can feed hot water and chilled water loops rather than requiring a 2-pipe loop to dictate whether it is in heating or cooling mode.   Further,  it can respond to the higher of the heating or cooling loop loads.
Brian
On Jan 22, 2023, at 9:58 AM, Omer Moltay via Equest-users <equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>> wrote:

Dear All,

I am using two different 2 pipe loops for both HW and CHW produced by a ground coupled heat pump. Each of these loops is only in heating or cooling mode throughout the year. This is necessary as eQuest requires a 2 pipe loop for modeling a chiller heat pump (although the CHW 2 pipe loop might also have been a cooling loop - but the result does not change).

Attached is a simple model that features what I have just described. The simulation run always gives the error that there is zero design flow in the loops, whatever I try (I have tried using secondary loops as well but did not work).

It would help me a lot if anyone could point out what could be wrong with this set-up?

Best,

Ömer Moltay, LEED AP BD+C, ASHRAE BEMP, ASHRAE CPMP
Mimta EcoYapi, LEED Proven Provider
Hekimsuyu Cad. 559. Sk.
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