[Equest-users] Geothermal Well Field Modeling

[Anthony Hardman]

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

 



 

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

EI Signature

 

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