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<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>A couple of
clarifications and my opinions regarding GSHP in hot
climate.</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>1. "200 well feet
per ton"</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>The "200 well
feet per ton" is not a universal rule for sizing ground heat exchanger (GHX).
According to a veteran of GSHP industry, "200 well feet per ton" was originally
developed based on calculation/experience for single family house at Stillwater,
Oklahoma, which has near-balanced heat rejection and extraction loads and thus
there is no concern of heat built up in long term (in the scale of multi years).
In addition, the undisturbed ground temperature is around 63F. For other
buildings in different locations, GHX has to be sized based on both peak and
cumulative heating and cooling loads, geology information, heat pump
performance, layout of borehole field, and etc. In addition, long-tern heat
built-up needs to be accounted for if unbalanced ground heat rejection and
extraction exists. I'm not sure whether "200 well feet per ton" was used for
sizing GHX of the GSHP systems in Phoenix mentioned in Dan's earlier e-mail. If
it was the case, I will not be surprised about the
failed systems. A simple eQUEST simulation can approve
this.</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>2. Ground (loop)
temperature</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>I agree with
Dan's analysis of heat transfer in the ground and the resulting variation of
fluid temperature in the GHX. Only one addition: due to the fluctuation of the
building loads, the ground may be able to "have some rest" to recover from
the increased/decreased temperature when the loads is reduced from its peak
(i.e. the surrounding ground temperature of a GHX will go down in the summer
night, or during summer break if the building is a school). These factors should
also be accounted for when assessing the feasibility of GSHP and/or sizing the
GHX. </SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008>3. E</SPAN></FONT><FONT color=#0000ff size=2><SPAN
class=464521518-12082008>nergy efficiency of GSHP in hot
climate</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN class=464521518-12082008>While climate
zone 1 may be the extreme for GSHP systems, many GSHP systems have
been working well and energy efficiently in regions with hot summer and
cold winter, such as Oklahoma City and Dallas. For a properly designed GSHP
system, the leaving fluid temperature will rarely exceed 90F, but the daytime
ambient air temperature could be above 90F for couple of months in summer. It
makes the GSHP system more energy efficient than air-cooled chiller when cooling
loads are peaked. To further improving energy efficiency of GSHP system in
cooling mode, following practices are usually taken:</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008> - hybrid GHX with supplemental heat
rejection</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008> - decentralize the borehole field
(to reduce the effect of thermal coupling among boreholes) and the pumping
system (in lieu of variable speed pumping)</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008> - utilize energy recovery
ventilation</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008></SPAN></FONT> </DIV>
<DIV><FONT color=#0000ff size=2><SPAN
class=464521518-12082008>Xiaobing</SPAN></FONT></DIV>
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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B>
bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org]<B>On Behalf Of </B>Dan
Nall<BR><B>Sent:</B> Saturday, August 09, 2008 3:29 PM<BR><B>To:</B>
Edward.A.Decker@jci.com<BR><B>Cc:</B>
bldg-sim@lists.onebuilding.org<BR><B>Subject:</B> Re: [Bldg-sim] GSHP in hot
climate<BR><BR></FONT></DIV>
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<META content="MSHTML 6.00.6000.16674" name=GENERATOR>This is a heat balance
problem. While the sol-air temperature cycle (diurnal or seasonal) may
have little impact some distance below the surface, the annual average surface
temperature will have a big impact. The average temperature underground
reflects the balance of heat transfer between the surface and the very hot
depths. So, the temperature 30 ft. below grade in Alaska is very much
colder than the temperature 30 ft. below the surface in the Arabian
desert. Lateral heat transfer (equi-depth) has little effect unless
there is a local heat source or sink, like a geoexchanger. There is no
magic underground temperature. It is a product of the local heat balance
through a somewhat conductive continuous medium (the ground), between the
surface and the core of the earth. Because the core is so far down, it
has little effect until you get very deep, like miles. Recommended
minimum horizontal spacing between vertical wells is on the order of 30
ft. There is a significant loss of performance when that distance is
reduced to 20 ft.
<P>In the case of a hot climate, think about where the heat goes.
It is being delivered at a continuous, but varying rate over the course of the
year. There is little or no extraction of heat from the ground by the
heat pump. The usual assumption is that closed loop wells need about 200
well feet per ton. In Phoenix, for a residence, you might
expect 2000 full load hours for the year. So, a vastly
simplified calculation would yield that each foot of well has to lose
approximately 17 Btu/hr on average over the year. Some of that heat
will be conducted away and some will (temporarily, until equilibrium is
reached) serve to raise the temperature of the local earth. The
actual thermal mass of the earth is large compared with the heat
conduction coefficient, so that it takes a few years to heat up the ground.
Do the calculation and figure out what the average temperature at the
well has to be to drive that much heat flow, once the system is in
equilibrium, using the concentric pipe insulation formula to calculate the
logarithmic mean heat trtansfer surface area. I think you will be
surprised at how high it is. </P>
<P>David Schaetzle, a former professor at ASU, has some on-hands experience
with this phenomenon, and first brought it to my attention at the Cooling
Frontiers Workshop organized by the late Jeff Cook in 2001. <BR></P>
<BLOCKQUOTE
style="PADDING-LEFT: 5px; MARGIN-LEFT: 0px; BORDER-LEFT: #0000ff 2px solid">-----Original
Message----- <BR>From: Edward.A.Decker@jci.com <BR>Sent: Aug 8, 2008 2:08 PM
<BR>To: Dan Nall <DANNALL@MINDSPRING.COM><BR>Subject: Re: [Bldg-sim] GSHP in
hot climate <BR><BR><BR><FONT face=sans-serif size=2>The sol-air temperature
stops affecting the ground temperature at a distance of 5 meters (roughly).
If you are installing a vertical well, that temperature fluctuation should
not have a significant effect on the performance of the well. I also believe
that the new equilibrium temperature that you are referring too is localized
to within a meter (roughly) of the well. Can't this ground temperature
stabilization can be off-set by increasing the spacing of the vertical
wells?<BR></FONT><FONT size=3></FONT>
<P>
<TABLE>
<TBODY>
<TR>
<TD vAlign=top><FONT face=Arial size=1><B>Edward A. Decker
</B></FONT><BR><FONT face=Arial size=1>Project Development
Engineer</FONT> <BR><FONT face=Arial size=1>Building Efficiency</FONT>
<BR><FONT face=Arial color=blue size=1> </FONT> <BR><FONT
face=Arial color=blue size=1><B>Johnson Controls </B></FONT><BR><FONT
face=Arial size=1>1001 Lower Landing Road</FONT> <BR><FONT face=Arial
size=1>Suite 409</FONT> <BR><FONT face=Arial size=1>Blackwood, NJ
08012</FONT> <BR><FONT face=Arial size=1>Tel : 610-675-9603</FONT>
<BR><FONT face=Arial size=1>Fax : 856-228-6296</FONT> <BR><FONT
face=Arial size=1>Email : </FONT><A
href="mailto:edward.a.decker@jci.com" target=_blank><FONT face=Arial
color=blue size=1><U>edward.a.decker@jci.com</U></FONT></A> <BR><FONT
face=Arial size=1>URL : </FONT><A
href="http://www.johnsoncontrols.com/" target=_blank><FONT face=Arial
color=blue size=1><U>http://www.johnsoncontrols.com</U></FONT></A>
<DIV align=center><BR><FONT size=1> </FONT> <BR><FONT
size=1> </FONT> <BR><FONT size=1> </FONT></DIV><BR><FONT
size=3> </FONT>
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<TD><FONT size=3> </FONT>
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<TD vAlign=top><FONT face=Arial size=1><B> </B></FONT>
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<TD width="40%"><FONT face=sans-serif size=1><B>Dan Nall
<dannall@mindspring.com></B> </FONT>
<P><FONT face=sans-serif size=1>08/08/2008 01:26 PM</FONT>
<TABLE border=1>
<TBODY>
<TR vAlign=top>
<TD bgColor=white>
<DIV align=center><FONT face=sans-serif size=1>Please respond
to<BR>Dan Nall
<dannall@mindspring.com></FONT></DIV></TD></TR></TBODY></TABLE><BR></P>
<TD width="59%">
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<TR vAlign=top>
<TD>
<DIV align=right><FONT face=sans-serif size=1>To</FONT></DIV>
<TD><FONT face=sans-serif size=1>yizhao1@vt.edu,
Edward.A.Decker@jci.com</FONT>
<TR vAlign=top>
<TD>
<DIV align=right><FONT face=sans-serif size=1>cc</FONT></DIV>
<TD><FONT face=sans-serif
size=1>bldg-sim@lists.onebuilding.org</FONT>
<TR vAlign=top>
<TD>
<DIV align=right><FONT face=sans-serif
size=1>Subject</FONT></DIV>
<TD><FONT face=sans-serif size=1>Re: [Bldg-sim] GSHP in hot
climate</FONT></TD></TR></TBODY></TABLE><BR>
<TABLE>
<TBODY>
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<TD>
<TD></TD></TR></TBODY></TABLE><BR></TD></TR></TBODY></TABLE><BR><BR><BR><FONT
size=2><TT>The ground temperature is not a constant if it is subjected to
heat fluxes from a local underground source such as a geoexchanger.
think of the ground as a large thermal storage medium, with fluxes at
its extreme bottom and top boundaries. At the bottom is the hot core
of the earth. At the top is the fluctating air temperature and radiant
flux at the surface. In general, the average temperature below ground
is going to be approximately the average sol-air temperature of the surface.
The deeper you go, the smaller is the variation over time, and the
more delayed is that variation from what is going on at the surface.
At a few meters below the surface, temperature variation is very
small. Deeper still, the temperature will begin to rise. With a
geoexchanger, however, local heat flux from gthe device can cause
significant variations in temperature. If seasonal flux is not balanced,
over time, the ground local to the geoexchanger will conform to a new
equilibrium temperature, sufficiently variant from the "average"
subterranean temperature to disperse that local heat flux into the
surrounding earth. Given that the thermal conducitivity of "earth" is
not enormous, that temperature differential could be quite
large.<BR><BR>Ground source heatpumps were initially very popular in
Phoneix. Within a year or two, they "heat soaked' the ground surrounding
their wells, and the heat pumps ceased operating. Most of them ahve
been abandoned, or supplemented by evaporative heat rejection
devices.<BR><BR>Think of geoexchangers as annual thermal storage devices,
not as unlimited heat sources or sinks.<BR><BR>-----Original
Message-----<BR>>From: yizhao1@vt.edu<BR>>Sent: Aug 8, 2008 12:45
PM<BR>>To: Edward.A.Decker@jci.com<BR>>Cc:
bldg-sim@lists.onebuilding.org<BR>>Subject: Re: [Bldg-sim] GSHP in hot
climate<BR>><BR>>According to the source we got, the ground
temperature is 85F, although the<BR>>ground temper in a lots of other
locations in the world are about 55F.<BR>><BR>>Do you have some other
source for the ground
temperature?<BR>><BR>>Thanks,<BR>><BR>>Ying<BR>><BR>>Quoting
Edward.A.Decker@jci.com:<BR>><BR>>> For a GSHP, the surface
temperature of the earth should not matter...<BR>>> isn't the
temperature below the surface what makes the GSHP work? A<BR>>>
constant temperature of ~55 deg F.<BR>>><BR>>><BR>>>
Edward A. Decker<BR>>> Project Development Engineer<BR>>>
Building Efficiency<BR>>><BR>>> Johnson Controls<BR>>>
1001 Lower Landing Road<BR>>> Suite 409<BR>>> Blackwood, NJ
08012<BR>>> Tel : 610-675-9603<BR>>> Fax :
856-228-6296<BR>>> Email : edward.a.decker@jci.com<BR>>> URL :
http://www.johnsoncontrols.com<BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>>
yizhao1@vt.edu<BR>>> Sent by:
bldg-sim-bounces@lists.onebuilding.org<BR>>> 08/06/2008 11:50
PM<BR>>><BR>>> To<BR>>>
bldg-sim@onebuilding.org<BR>>> cc<BR>>><BR>>>
Subject<BR>>> [Bldg-sim] GSHP in hot
climate<BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>><BR>>>
Hi-<BR>>><BR>>> We modeled a building with GSHP in a hot climate
(zone 1), so it is almost<BR>>> used<BR>>> for cooling only. The
air-side is PVAVS. water-cooled condenser with GSWL.<BR>>>
The<BR>>> cooling COP input is ~5. However, the system performs almost
the same as<BR>>> ordinary air-cooled
chillers.<BR>>><BR>>> We think the reason may be the high earth
temperature (~85 F is used due<BR>>> to the<BR>>>
local<BR>>> climate).<BR>>><BR>>> GSHP does not appear to
be a solution for hot climate? Any one has some<BR>>>
resource<BR>>> of real data for this?<BR>>><BR>>>
Thanks,<BR>>> Ying<BR>>>
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