[Equest-users] Ground-loop HX Error

[Nick Caton]

Colleen,

 

If you're in the boat of not having the borefield built or designed yet
to reference from, you can get a good estimation of a system that would
work for your site by investing some time into learning and using the
free program GS2000 - check out my other posting I made this afternoon
"RE: [Equest-users] Hybrid GSHP."

 

That said, eQuest can still trip up even if you've entered all
properties of your well field accurately in the wizards.   Here are some
tips assuming you've done that:

*         Recognize to start that no GLHX should be operating at -31F.
You can go below freezing (using antifreeze!!!), but start with a design
temperature range in mind that meets both the minimum/maximum
recommended by your heatpump manufacturer (it's in their spec sheets).
Even better - figure out what COP / EER values you want your system to
operate at in the winter/summer respectively, and use those same spec
sheets to read off what minimum/maximum temperatures make sense to be
sure you're in that range or better.

*         Once you know what range is desired, you can try to assess
what, entered or defaulted incorrectly, is causing such an extreme
temperature outside of your target temperature range.  Some things may
include:

o   A loop head that doesn't make sense

o   A pump whose GPM has been defined (or auto-sized) to something way
too low (or zero), causing the fluid in the field to move slowly and get
so cold

o   Mistakenly entered GLHX borefield/ground properties can certainly
have a great effect - perhaps you meant for your bores to be 400ft deep
but accidentally entered 40?  Give these properties a once-over to be
sure nothing's amiss.

o   Double check the operating parameters of any associated equipment to
be sure everything is running that should be at the time your extreme
case happens... maybe eQuest is appropriately set to auto-size all of
your terminal heatpumps correctly, but for some reason they aren't
running when they should be putting heat into the loop?

o   Make sure everything that should be is assigned to the loop

o   Is there any intended source of auxiliary electric/gas heat at the
units that isn't firing up, causing your GLHX to shoulder 100% of the
heating demand?

 

Hassan is correct in that the GLHX (well field) itself will not be
auto-sized by eQuest - in other words it won't know that your 5 x 10
vertical well borefield of 25' spacing and 300' depth really needs to be
5 x 20 and have a depth of 500'.  To be fair, eQuest does I believe have
the capacity auto-size some elements like circ-pump size based on your
GLHX inputs.  

 

eQuest has a capacity to model thermal behavior of GLHX's for certain
kinds of systems, to a limited degree of control over the GLHX
parameters.  From an accuracy/flexibility standpoint however, I think
you're better off picking up something like GS2000 to design, model and
re-design a GLHX, then export it's thermal behavior (in the form of
monthly temperature averages) into eQuest by means of creating a custom
temperature schedule for a well-type loop, to which your heatpumps and
other associated equipment would be attached and accounted for.  GS2000
itself is not without design limitations ("free" always has a cost), but
once you understand it you'll also feel like designing GLHX's with
eQuest is like hammering nails with a screwdriver (frustrating, time
consuming, ultimately painful)!

 

Best wishes,

 

~Nick

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

Check out our new web-site @ www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Zareh,
Hassan
Sent: Wednesday, October 07, 2009 2:28 PM
To: Colleen Nelson; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Ground-loop HX Error

 

Colleen,

eQuest doesn't auto size the GSHX. You should define the specification
of the borefield.

 

Hassan

 

________________________________

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Colleen
Nelson
Sent: Wednesday, October 07, 2009 3:16 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Ground-loop HX Error

 

I receive the following error message when attempting to run simulation:

 

                Ground-loop HX:  GLHX (VertWell-CM) is undersized for
the load and is producing an extreme temperature of -31F.

 

I allowed eQUEST to auto-size the GSHP equipment.

 

Any help is appreciated.

 

 

Colleen Nelson, LEED-AP

Mechanical Engineering

Michaud Cooley Erickson

612.673.6995

 

 

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