[Equest-users] Geothermal Well Field Modeling

Dan Russell danr at engineeringinc.com
Mon May 3 09:50:49 PDT 2010


Thanks to all for your responses.  As an update, my models are now coming more into line, in fact they are appearing to match very closely with the 20% rule-of-thumb that Anthony has seen in his experience.  The primary contributors to the eQUEST model becoming more accurate were:

1)      The Previous Years of Operation field was set to "0", so I changed it to be "20".

2)      I loaded in some typical ClimateMaster performance curves in lieu of using the default eQUEST curves.

I now have an eQUEST model that is utilizing an 80-bore hole well field with bore lengths approximately 20% shallower than what is being calculated by the Gaia GLD software.

Thanks again for all the input.

Dan Russell
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From: Anthony Hardman [mailto:Anthony at geoenergyservices.com]
Sent: Thursday, April 29, 2010 1:57 PM
To: Dan Russell; equest-users at lists.onebuilding.org
Subject: RE: [Equest-users] Geothermal Well Field Modeling

Dan, not sure if you got all your questions answered?

I typically see about a 20% smaller GHEX with eQUEST when compared to GLD.  I also believe it is the most accurate tool between the two for a couple of reasons.


1)      eQ models the heat transfer on an hourly basis.  GLD does not.  If you look at the Zone Manager, GLD takes the monthly peak and cumulative loads and arbitrarily assigns those loads into one 12 hour block and three 4 hour blocks, and then uses that profile for the entire month.

2)      After talking to Gaia "support," I'm not correct that their equipment libraries interface correctly with GHEX sizing algorithms (and that's probably more than I should say about that).

Some other thoughts:


-          4 subfields will always have more capacity than a single field of equivalent bore length.  So that accounts for some of your error, maybe 10%.


-          You can select "real" manufacturer performance data within the eQuest wizard by clicking the "Select from GSHP Library" command(see screenshot).  Since ClimateMaster developed the add-on, you're limited to their equipment choices of course.  I never use the default performance curves, I simply choose the closest CM unit.



-          Although the totals are the same, I use report SS-D (not SS-l) for these comparisons.



-          Make sure you're setting your "Years of Previous Operation" to 20 so that you account for long term temperature creep.  Just because the GHEX works in year 1 doesn't mean it'll work in year 20.


Anthony Hardman
Building Energy Analyst
LEED AP

Geo-Energy Services
14250 E Easter Pl, STE C
Centennial, CO 80112
303-531-5292 v
303-805-3563 f
720-273-9973 c
www.GeoEnergyServices.com<http://www.geoenergyservices.com>

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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Dan Russell
Sent: Thursday, April 29, 2010 10:35 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
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