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<p class=MsoNormal>I was interested to see if anyone would share how they model
the exception to G3.1.1 in ASHRAE 90.1-2007 (or 04). This is the part
that says when you have a baseline building with system 5-8, you’re
supposed to model system 3 or 4 for any spaces that “have occupancy or
process loads or schedules that differ significantly from the rest of the
building.” It goes on to say that basically the peak thermal loads
must differ by 10 Btu / h-ft2 or more from the average of the other spaces, or
that schedules must differ by more than 40 full load hours per week, for this
exception to apply.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’ve had reviewers question certain rooms that I’ve
put on separate PSZ-AC systems, and so I’ve sort of defaulted to putting
almost all rooms on the main systems (5-8). However, in looking at
some of my recent models, depending on interior loads and climate, the actual peak
cooling load on a square foot basis varies anywhere from 5-20 btu / h-ft2 range
for offices. So this means there is a big difference between those models
with 5 btu / h-ft2 peak and those with 20. For the models with 5, almost
every space in the building is going to be within +/- 10 btu/h-ft2 of that
average. However, those buildings that average around 20 will have many
rooms that are < 10 btu/h-ft2 peak (ie any internal space whose light + plug
load density is < 3.0 W / sq ft).<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><b><span style='color:red'>To use a simple example as a
question: if your particular office building averaged 20 btuh / h-ft2
peak cooling load, would you model a separate PSZ-AC system for a core bathroom,
whose peak cooling load is only 3 btu/h-ft2?<o:p></o:p></span></b></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>There are lots of rooms where I question whether I should do
a separate PSZ-AC/HP system (storage rooms, stairs, mechanical rooms, lobbies,
etc). I can see where these meet the 10 Btu/h-ft2 delta exception. <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>So does everyone really model a bunch of PSZ-AC systems
based specifically on the average peak thermal loads of the building?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>I’m thinking out loud, but if I had an office building
that averaged on the low side (5 Btu/h-ft2) for cooling peaks, it seems pretty
easy to have a perimeter conference room that exceeded 15 Btu / h-ft2 peak.
Seems like an exhaustive process to confirm this delta for every room in a
model to determine whether it needs its own system…<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Sorry for the long email. Thanks!<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><b><span style='font-family:"Arial","sans-serif";color:teal'>GHT
Limited<br>
</span></b><b><span style='font-family:"Arial","sans-serif"'><ns0:PersonName><span
style='color:black'>James Hansen</span></ns0:PersonName></span></b><b><span
style='color:black'>, PE, LEED AP<o:p></o:p></span></b></p>
<p class=MsoNormal><b><span style='font-size:10.0pt;font-family:"Arial","sans-serif";
color:black'>Senior Associate</span></b><b><span style='color:black'><o:p></o:p></span></b></p>
<p class=MsoNormal><span style='font-size:7.5pt;font-family:"Arial","sans-serif"'><ns0:Street><ns0:address><span
style='color:black'>1010 N. Glebe Rd, Suite 200</span></ns0:address></ns0:Street></span><o:p></o:p></p>
<p class=MsoNormal><span style='font-size:7.5pt;font-family:"Arial","sans-serif"'><ns0:place><ns0:City><span
style='color:black'>Arlington</span></ns0:City><span style='color:black'>, </span><ns0:State><span
style='color:black'>VA</span></ns0:State><span style='color:black'> </span><ns0:PostalCode><span
style='color:black'>22201-4749</span></ns0:PostalCode></ns0:place></span><span
style='color:black'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:7.5pt;font-family:"Arial","sans-serif";
color:black'>703-338-5754 (Cell)</span><span style='color:black'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:7.5pt;font-family:"Arial","sans-serif";
color:black'>703-243-1200 (Office)</span><span style='color:black'><o:p></o:p></span></p>
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color:black'>703-276-1376 (Fax)</span><span style='color:black'><o:p></o:p></span></p>
<p class=MsoNormal><span style='font-family:"Arial","sans-serif";color:teal'><a
href="http://www.ghtltd.com/"><span style='font-size:10.0pt;color:blue'>www.ghtltd.com</span></a><o:p></o:p></span></p>
<p class=MsoNormal><b><span style='color:#31849B'><o:p> </o:p></span></b></p>
<p class=MsoNormal><o:p> </o:p></p>
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