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Hi Siliang,<br>
I think you are looking at this the wrong way from reading your
email exchange. I don't understand why you would consider putting
in a high temp high pressure steam boiler with a heat exchanger
between it and the working loop, ie the water loop. Effectiveness
and cost dictate you put in a low temp, low pressure boiler directly
into the water loop. No heat loss to the ground or to the heat
exchanger.<br>
The real reason you don't use that set up is you can't control the
fluid quality on the ground loop side. There is going to be grit
and scaling in the ground loop and it is going to foul your heat
exchanger. The heat exchanger will need to be shut down regularly
for cleaning. You would be exposing, what I assume is your backup
boiler, to the same crud coming out of the ground and would be
taking it off line at the same time for cleaning. It can't serve as
a backup boiler. The water loop is a closed system and you can
control the fluid quality in that loop. The water boiler would be
much less expensive and will provide heat when you have to take the
ground loop heat exchanger off-line for cleaning.<br>
I would also revisit your thinking on the size of the small boiler.
In an ideal world you would take the heat exchanger off line in the
low heating season and have a lower demand on the backup boiler. It
could also allow you to extend the cleaning of the heat exchanger to
a better time, maybe. Real world may require cleaning of the heat
exchanger once in the peak heating season and your water boiler
would be too small. Your low cost heat source will lose a lot of
advantages and efficiency if your water boiler has to do too much
topping up of the heat as the ground water exchanger fouls. Maybe a
second heat exchanger in parallel might be a cheaper way. Be
careful with that idea too. Depending on how much grit there is in
the ground system the other thing you have to deal with is erosion
of your piping system. 2 heat exchangers will do you no good if you
blow out an elbow on the pipe supplying them.<br>
You may be able to model the fouling factor on a time based
schedule. That would still be a guess unless you have data from
other local installations but it could give you useful numbers for
evaluating the economics of the system. eQuest is a tool and gives
idealized results. Your system will run in the real world. The
real skill is in manipulating this tool to deal with all the what
if's and figuring out all the what if's that could apply. There
will be a 1000 perfect days but your reputation is based on the 1
bad day.<br>
I would suggest the smallest size for your water boiler would be to
supply enough heat to maintain the building at say 50F on the
coldest day of the year. The occupants would still not be able to
work but you wouldn't freeze the building. That would be a very bad
day.<br>
Bruce Easterbrook P.Eng.<br>
Abode Engineering <br>
<br>
<div class="moz-cite-prefix">On 8/8/2016 8:58 AM, Siliang Lu via
Equest-users wrote:<br>
</div>
<blockquote
cite="mid:CAGb_anKFzuDOSWGNvY+S-YXwcTAs4+=HKmiPzh8OkpOOb-NvPg@mail.gmail.com"
type="cite">
<div dir="ltr">
<div>
<div>
<div>
<div>
<div>Hi Sharad,<br>
</div>
Thanks for your reply. <br>
My design is ambient geothermal heat pump system. The
water loop temperature ranges between 55-85F and the
ground temperature is not so high as 360-370F. What I am
wondering is that if the boiler setpoint could be much
higher than ground heat exchanger setpoint if the size
of boiler is much smaller than that of GHX? Thanks a
lot!<br>
<br>
</div>
</div>
Have a great day!<br>
<br>
</div>
All the best,<br>
</div>
Siliang<br>
</div>
<div class="gmail_extra"><br clear="all">
<div>
<div class="gmail_signature" data-smartmail="gmail_signature">
<div dir="ltr">Siliang</div>
</div>
</div>
<br>
<div class="gmail_quote">On Mon, Aug 8, 2016 at 5:46 AM, Sharad
Kumar via Equest-users <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org"
target="_blank">equest-users@lists.onebuilding.org</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div dir="ltr">
<div class="gmail_extra">
<div class="gmail_quote">
<div><font color="#073763">Hi Siliang,</font></div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">The Water loop set-point
that you have got as may be 70 °F is the water
temperature that is 21.11 °C.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">It is obvious to take
set-point of the boiler below the Ground source HX
as then it will operate.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">The ground source steam
temperature may shoot up-to 360-370 °F.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">So may be taking steam
boiler or steam plus hybrid boiler that is
electricity and keeping the set-point from 180 to
230 °F can be a take.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><span style="color:rgb(7,55,99)">One can keep the
set-point of the ground water heating loop as more
than 230 °F to 370 °F may be 360 °F.</span><br>
</div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">Then the functioning will
be okay.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><font color="#073763">Generally the boiler
set-point of electrical heater is 180 °F for steam
water to 230 °F which is nearly 82 °C (180 °F ).</font></div>
<div><font color="#0000ff"><b><br>
</b></font></div>
<div><font color="#0000ff"><b>Thanks</b></font><span
style="color:rgb(7,55,99)">,</span><br>
</div>
<div><font color="#073763">Sharad.</font></div>
<div><font color="#073763"><br>
</font></div>
<div><br>
</div>
<div>---------- Forwarded message ----------<br>
</div>
</div>
<div>
<div class="h5">From: Siliang Lu via Equest-users <<a
moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org"
target="_blank">equest-users@lists.onebuildin<wbr>g.org</a>><br>
To: "<a moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org"
target="_blank">equest-users@lists.onebui<wbr>lding.org</a>"
<<a moz-do-not-send="true"
href="mailto:equest-users@lists.onebuilding.org"
target="_blank">equest-users@lists.onebuildin<wbr>g.org</a>><br>
Cc: <br>
Date: Sat, 6 Aug 2016 16:14:27 -0400<br>
Subject: [Equest-users] Boiler temperature for
hybrid geothermal heat pump system<br>
Hi eQuesters,<br>
<br>
I have a problem regarding hybrid geothermal heat
pump system built in a heating dominated building.
From ASHRAE Handbook, it suggests that boiler be
installed separately from geothermal heat exchanger
loop due to high temperature of boiler.<br>
<br>
In addition, one report says that even if there are
some cases that boiler has to be installed into GHX
loop, the setpoint shall be 5-10F lower than GHX
setpoint( e.g. 45F). That is because if the boiler
is installed in the GHX loop, it is likely to dump
heat back into the ground if boiler setpoint is
higher than GHX setpoint.<br>
<br>
However, heat exchange is related to both
temperature and flow rate. With smaller size of
boiler, can we allow to install boiler with higher
setpoint higher than GHX setpoint into the GHX loop?
Thanks!<br>
<br>
All the best,<br>
Siliang<br>
</div>
</div>
</div>
</div>
<br>
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