[Equest-users] Geothermal Well Field Modeling

[Nick Caton]

Concurring with Demba.

 

Also - if you're looking for an independently developed and free option
- GS2000 has worked well for me in the past.

 

The act of using external software will lead you to resolve your concern
in question #2.  The route I and others have taken is to use something
like GS2000 to size and more importantly determine an annual loop
temperature behavior, accounting for all the variables involved.  Use
that output to create an annual/monthly/weekly temperature schedule in
eQuest and assign it to a GLHX loop.

 

Within eQuest is where you'd define the attached heatpumps and loop pump
properties.

 

~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 Demba
Ndiaye
Sent: Thursday, April 29, 2010 12:23 PM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Geothermal Well Field Modeling

 

eQuest does not pretend to be able to size geothermal well fields. As
the Help says:

 

Important: unlike other HVAC components, the program cannot currently
design a ground loop heat-exchanger system based on the predicted
heating and cooling loads. Except for the design flow, you must input
all necessary design parameters, such as the number and depth of
vertical wells, horizontal trenches, etc. Under-specifying these
parameters can result in extreme temperature swings in the outlet
temperature of the well field. This may cause the WLHP loop to shut down
(if the outlet temperature exceeds CIRCULATION-LOOP:MAX-ALARM-T or
MIN-ALARM-T), or may cause the heat-pump performance curves to
extrapolate to unreasonable values,  yielding results badly in error or
possibly fatal to the simulation. You should always specify an hourly
report for this component and review the predicted outlet temperature
for both winter and summer intervals.

 

The ground loop heat-exchanger model is considered a test capability at
this time (except LAKE/WELL, which is well-tested). We suggest it be
used for production work only with very careful examination of the
results. You should apply careful engineering judgment to be sure all
predictions are reasonable since this feature has not yet been validated
against field measurements.

 

 

Now, one important consideration is the ground temperature change over
time due to the field. eQuest does not necessarily account for that; but
normally sizing programs account for it (I don't know if Gaia does).

 

_____________

Demba NDIAYE

 

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Edward
Allen
Sent: Thursday, April 29, 2010 1:05 PM
To: Dan Russell; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Geothermal Well Field Modeling

 

Dan,

 

I recently (as in this week) had cause to do a deep dive into eQuest's
geothermal modeling capabilities.  Based on your description and my
brief experience I have the following suggestions:

 

1) Is Gaia Geothermal proprietary?  It may have financial incentives to
"suggest" larger well fields than needed.

2) What are the allowable temperature ranges/limits and setpoints for
your ground loops?  I found that  matching these with those of an actual
HP made a difference in whether or not a field of a particular size
would meet the load.  The equest defaults were no where near optimal for
my model.  This is particularly important if your well field becomes
saturated with heat (cold) and the model shuts down the HP to maintain
the ground temperature limits.

 

Edward M. Allen, CEM

Senior Energy Engineer

LONG Energy Solutions

 

 

________________________________

From: equest-users-bounces at lists.onebuilding.org
[equest-users-bounces at lists.onebuilding.org] on behalf of Dan Russell
[danr at engineeringinc.com]

Sent: Thursday, April 29, 2010 10:34 AM

To: equest-users at lists.onebuilding.org

Subject: [Equest-users] Geothermal Well Field Modeling

 

Hi All - I am wondering if anyone has much experience with the
geothermal well field capabilities of eQUEST, in particular with
vertical well fields.  I am concerned about the accuracy of the
calculation methodology for the vertical well fields, primarily due to a
large discrepancy we are getting between the eQUEST results and the
results of a separate geothermal well field software produced by Gaia
Geothermal.  Here are the parameters:

 

Vertical well field

Ground conditions & well field dimensions are identical in both eQUEST
and Gaia simulations.

Equest model has four 4x5 rectangular well fields (80 bore holes total)
with 200 ft bore depth.  Plant report PS-C shows that the fourth well
field has no load, thus using at most 60 of the 200 ft wells.

Gaia software inputs load data from the DOE2 report SS-I for each zone
along with the matching heat pump size (specific to manufacturer)
selected for the project for the zone.  This software uses its knowledge
of the heat pump performance to generate the required well-field size
and depth.  The result is 120 well fields of 250 ft bore depth or 80
well fields of 350 ft bore depth.

 

I would expect some discrepancy between different software, but in this
case the eQUEST simulation is using only about 50% of the required
well-field size calculated by the Gaia software.  The Gaia calculation
is coming out much larger than what the owner and design-build
contractor had planned for.

 

How reliable is the eQUEST simulation on vertical well-fields?

 

I believe the primary difference is that Gaia software uses "real"
manufacturer performance data for heap pump models specified and eQUEST
uses PVVT system with default GSHP performance curves.  Could this
difference really make such huge impact on the results?

 

Thanks in advance for any insight.

 

Dan Russell

[EI Signature]

 

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