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<DIV><SPAN class=265433618-28082009><FONT color=#0000ff size=2 face=Arial>Dear
Ian,</FONT></SPAN></DIV>
<OL>
<LI><SPAN class=265433618-28082009><FONT color=#0000ff size=2
face=Arial>Without looking at the BTS Standard, I suspect the 35 - 80F you
mention below is the delta T between inlet and outlet water. It would be
ridiculous to test a boiler with 35F inlet water.</FONT></SPAN></LI>
<LI><SPAN class=265433618-28082009><FONT color=#0000ff size=2 face=Arial>A
bigger issue, if you are interested in predicting actual operating efficiency
is the "cycling efficiency" of the boiler. In short, an accurately sized
boiler benefits greatly from a) a high turndown in firing rate or b) a buffer
/ storage tank that allows it to operate for long periods even at low
load. <BR>As far as I know, most larger, high water volume boilers
perform reasonably close to the nameplate efficiency when equipped with good
turndown (4:1 or better). <BR> Smaller, low water volume boilers (the
atmospheric type you are thinking about) that cycle Off - High or Off-Low-High
probably need a buffer tank or they'll operate at much lower than nameplate
efficiency during the non-peak periods (i.e., 95% of the heating
season)</FONT></SPAN></LI>
<LI><SPAN class=265433618-28082009><FONT color=#0000ff size=2 face=Arial>A
compounding factor is that all of us engineers routinely oversize boilers
"just to make sure" nobody complains. This oversizing can be 20-50% and
exacerbates the turndown issue.</FONT></SPAN></LI></OL>
<DIV><FONT color=#0000ff size=2 face=Arial><SPAN class=265433618-28082009>Hoping
that's helpful.....</SPAN></FONT></DIV>
<DIV><FONT color=#0000ff size=2 face=Arial></FONT> </DIV>
<DIV class=Section1>
<P style="TEXT-ALIGN: center" class=MsoNormal align=center><B
style="mso-bidi-font-weight: normal"><FONT size=4>The Building Performance
Team<BR></FONT></B><B style="mso-bidi-font-weight: normal">James V. Dirkes II,
P.E., LEED AP<BR></B>1631 Acacia Drive NW<BR>Grand Rapids, MI 49504<BR>616
450 8653<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P></DIV>
<DIV> </DIV><BR>
<BLOCKQUOTE style="MARGIN-RIGHT: 0px" dir=ltr>
<DIV dir=ltr lang=en-us class=OutlookMessageHeader align=left>
<HR tabIndex=-1>
<FONT size=2 face=Tahoma><B>From:</B> bldg-sim-bounces@lists.onebuilding.org
[mailto:bldg-sim-bounces@lists.onebuilding.org] <B>On Behalf Of </B>Doebber,
Ian<BR><B>Sent:</B> Friday, August 28, 2009 2:20 PM<BR><B>To:</B>
bldg-sim@lists.onebuilding.org<BR><B>Subject:</B> [Bldg-sim] Actual Thermal
Efficiency of Boilers<BR></FONT><BR></DIV>
<DIV></DIV>
<DIV class=Section1>
<P class=MsoNormal>ASHRAE 90.1 mandates that a Gas-Fired Boiler ™ 300,000
Btu/hr & ˜ 2,500,000 Btu/hr must have a minimum 75% Thermal Efficiency
(Et) based upon the Test Proceedure Hydronics Institute Boiler Standard.
<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>The Hydronics Institute Boiler Standard official title is
“BTS-2000 Testing Standard : Method to Determine Efficiency of Commercial
Space Heating Boilers” published by The Hydronics Institute Division of
Air-Conditioning, Heating, Refrigeration Institute (AHRI). Can be found
at : <A
href="http://www.ahrinet.org/ARI/util/showdoc.aspx?doc=1198">http://www.ahrinet.org/ARI/util/showdoc.aspx?doc=1198</A>.
<o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>The Testing Standard measures the Thermal Efficiency of the
Boiler at steady state operation, fully loaded maintaining the outlet
temperature at 180œF. Oddly, the inlet water temperature into the Boiler
is between 35œF to 80œF which is much lower than the typical Return Water
Temperature of 150œF in a Building Application. Consequently, these
colder inlet temperatures are most likely overstating the Thermal Efficiency
of the Boiler which is condensing even if the Boiler is a Non-Condensing
Boiler. Based on various Manufacturer’s data, a Boiler operating with an
80œF Return Water Temperature achieves a 10% greater Thermal Efficiency
compared with operating at a standard 150œF Return Water Temperature.
Then operating at a 35œF Return Water Temperature, the Thermal Efficiency
should be boosted even further. <o:p></o:p></P>
<P class=MsoNormal><o:p> </o:p></P>
<P class=MsoNormal>Would it be reasonable to assume that a Standard
Atmospheric Boiler that meets the 75% Tc minimum based on ASHRAE 90.1
according to the BTS-2000 Testing Standard using 80œF Return Water Temperature
would actually operate at 65% Tc in the field operating at 150œF Return Water
Temperature?<o:p></o:p></P>
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