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<DIV><FONT face=Arial size=2>As you are aware, the program does not fully
address steam loops. Steam loops consist of a myriad of components, many of
which experience large thermal losses, and are prone to failure (such as steam
traps)</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>One way to approximate a steam loop is to
model it as a single hot-water loop, but specifying a steam boiler.
The steam boiler default efficiency is reduced to take into account some of
the losses associated with the de-aerator and other parasitic devices; however
the parasitic losses were not well-researched, and the default efficiency
is simply an semi-educated guess. (I came up with the value after thinking
about it for a total of 5 minutes).</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Steam loops tend to have HUGE annual losses; I
believe that in most cases they exceed the actual annual end-use
load. Throw in a couple of malfunctioning steam traps and they can be
ridiculous. In spite of the fact that DOE-2.2/PowerDOE/eQUEST can model piping
losses, most people neglect them, thinking they are small. They are NOT
small in most cases.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>You should definitely specify the piping UA so
the program can calculate losses. To better account for the UA split between the
hot-water and steam loops, you could model a primary/secondary loop arrangement,
where the primary loop is the "steam" loop, and the secondary loop is the
hot-water loop. To make the pumping energy of the "steam" loop match the
actual pumping energy (condensate, de-aeration, and pressurization),
you can adjust the head loss of the piping, boiler, and valve
modulating flow into the secondary loop.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Hot-water loops can also have very large losses; I
have found that the losses in VAV/hot-water reheat systems
typically exceed the annual reheat load.</FONT></DIV></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=wmclaughlin@dmiinc.com href="mailto:wmclaughlin@dmiinc.com">Wade
McLaughlin</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=Bldg-sim@gard.com
href="mailto:Bldg-sim@gard.com">Bldg-sim@gard.com</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Wednesday, July 31, 2002 10:42
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Bldg-sim] PowerDOE Steam
Loops</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial size=2>In PowerDOE: I have a number of VAV Roof
Top Units with steam heating coils. Zone reheat is handled using hot
water, and the hot water loop is heated with steam from the steam
loop.</FONT><FONT face=Arial size=2> Does anyone have a good suggestion
as to how to model heat exchange between the steam and hot water
loops?</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Thanks,</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=Arial size=2>Wade McLaughlin<BR>DMI<BR>450 Lexington
St.<BR>Newton, MA 02466<BR>p 617-527-1525 x103<BR>f
617-527-6606</FONT></DIV><PRE>
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