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<p class=MsoPlainText>eQuest does not pretend to be able to size geothermal well
fields. As the Help says:<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><b><i><span style='color:gray'>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.<o:p></o:p></span></i></b></p>
<p class=MsoPlainText><b><i><span style='color:gray'><o:p> </o:p></span></i></b></p>
<p class=MsoPlainText><b><i><span style='color:gray'>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.<o:p></o:p></span></i></b></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>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).<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>_____________<o:p></o:p></p>
<p class=MsoPlainText>Demba NDIAYE<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>-----Original Message-----<br>
From: equest-users-bounces@lists.onebuilding.org
[mailto:equest-users-bounces@lists.onebuilding.org] On Behalf Of Edward Allen<br>
Sent: Thursday, April 29, 2010 1:05 PM<br>
To: Dan Russell; equest-users@lists.onebuilding.org<br>
Subject: Re: [Equest-users] Geothermal Well Field Modeling<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Dan,<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>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:<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>1) Is Gaia Geothermal proprietary? It may have
financial incentives to "suggest" larger well fields than needed.<o:p></o:p></p>
<p class=MsoPlainText>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.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Edward M. Allen, CEM<o:p></o:p></p>
<p class=MsoPlainText>Senior Energy Engineer<o:p></o:p></p>
<p class=MsoPlainText>LONG Energy Solutions<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>________________________________<o:p></o:p></p>
<p class=MsoPlainText>From: equest-users-bounces@lists.onebuilding.org
[equest-users-bounces@lists.onebuilding.org] on behalf of Dan Russell
[danr@engineeringinc.com]<o:p></o:p></p>
<p class=MsoPlainText>Sent: Thursday, April 29, 2010 10:34 AM<o:p></o:p></p>
<p class=MsoPlainText>To: equest-users@lists.onebuilding.org<o:p></o:p></p>
<p class=MsoPlainText>Subject: [Equest-users] Geothermal Well Field Modeling<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>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:<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Vertical well field<o:p></o:p></p>
<p class=MsoPlainText>Ground conditions & well field dimensions are
identical in both eQUEST and Gaia simulations.<o:p></o:p></p>
<p class=MsoPlainText>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.<o:p></o:p></p>
<p class=MsoPlainText>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.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>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.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>How reliable is the eQUEST simulation on vertical
well-fields?<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>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?<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Thanks in advance for any insight.<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
<p class=MsoPlainText>Dan Russell<o:p></o:p></p>
<p class=MsoPlainText>[EI Signature]<o:p></o:p></p>
<p class=MsoPlainText><o:p> </o:p></p>
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