<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:arial,helvetica,sans-serif;font-size:10pt"><div>I've always interpreted the exceptions you mention as an alternative way in which special spaces MAY be modeled but don't HAVE to be modeled. <br>My experience has been mostly with labs and hospitals which have pressurization requirements and thus typically meet one or more of the criteria for the exception to be used. <br>LEED reviewers and CIRs have generally upheld the optional approach and allowed all the pressurized spaces to be put on the main systems since using individual separate units to model hospital rooms or labs is not in line with what could be done in reality. <br>It may be helpful for you to take a look at the CIRs on the subject as related to application to labs and hospitals. These could be rather enlightening regarding the "spirit" and application of the exception.
<br></div><div style="font-family: arial,helvetica,sans-serif; font-size: 10pt;"><br><div style="font-family: times new roman,new york,times,serif; font-size: 12pt;"><font face="Tahoma" size="2"><hr size="1"><b><span style="font-weight: bold;">From:</span></b> Carol Gardner <cmg750@gmail.com><br><b><span style="font-weight: bold;">To:</span></b> James Hansen <JHANSEN@ghtltd.com><br><b><span style="font-weight: bold;">Cc:</span></b> bldg-sim@lists.onebuilding.org<br><b><span style="font-weight: bold;">Sent:</span></b> Sun, November 7, 2010 11:31:46 PM<br><b><span style="font-weight: bold;">Subject:</span></b> Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them?<br></font><br>
Hi James,<br><br>I must chime in on this. First off, in reality I would more expect to see a transfer grille above the door of the storage room, bathroom, etc., than I would expect each to have their own system. I frequently model them as unconditioned spaces attached to a HVAC system and call it good. Mostly if a room of that type is conditioned, it is fed off the nearest system. Stairs may be separately heated with a unit heater, which I would model in the proposed case, but for the baseline I'd just stick to what makes "engineering" sense following the spirit of the code.<br>
<br>Best,<br><br>Carol<br><br><div class="gmail_quote">On Mon, Nov 1, 2010 at 1:43 PM, James Hansen <span dir="ltr"><<a rel="nofollow" ymailto="mailto:JHANSEN@ghtltd.com" target="_blank" href="mailto:JHANSEN@ghtltd.com">JHANSEN@ghtltd.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">
<div lang="EN-US">
<div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">I see, that makes a little more sense. So if I had a stairwell,
which does not have HIGHER process loads than the average space, and whose
occupancy schedule is basically the same as the rest of the office space, then
I would HAVE to have that stairwell on the base-building System
5-8. I couldn’t have it on its own PSZ-AC. </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Mike, this goes against what you said in your email. This
is sort of why I asked the question…there doesn’t seem to be a
consensus. I model stairwells, elevator shafts, bathrooms, etc as
separate thermal zones in all of my models, and if I read the letter of the
code, it would seem they need to be their own systems, yet the CIR sort of says
that this isn’t the case, and reviewers agree, and don’t like to
see rooms like this on separate systems.</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div style="border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223); padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span style="font-size: 10pt;">From:</span></b><span style="font-size: 10pt;"> Cheney
[mailto:<a rel="nofollow" ymailto="mailto:chenyu73@gmail.com" target="_blank" href="mailto:chenyu73@gmail.com">chenyu73@gmail.com</a>] <br>
<b>Sent:</b> Monday, November 01, 2010 4:35 PM<div><div></div><div class="h5"><br>
<b>To:</b> James Hansen<br>
<b>Cc:</b> <a rel="nofollow" ymailto="mailto:bldg-sim@lists.onebuilding.org" target="_blank" href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them?</div></div></span>
</p></div><div><div></div><div class="h5">
<p class="MsoNormal"> </p>
<div>
<p class="MsoNormal">Hi James, </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">The CIR is dated on 3/23/2007. It clarifies use of
exception to G.3.1.1. to document baseline and achieve greater energy savings
from single-zone systems in <b><u>high</u></b> process load areas. </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">As per G3.1.1. in Appendix G (90.1-2004), my understanding
is to use separate single-zone system for any space has very high occupancy or
process loads or schedules that differ significantly from the rest of the
building. You can understand it in the opposite way that the rooms have
significantly less occupancy or process loads. But I guess the CIR points to
the high process load areas in order to achieve greater energy savings
from single-zone systems. </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">Regards, </p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom: 12pt;">Cheney </p>
</div>
<div>
<p class="MsoNormal">On Mon, Nov 1, 2010 at 12:46 PM, James Hansen <<a rel="nofollow" ymailto="mailto:JHANSEN@ghtltd.com" target="_blank" href="mailto:JHANSEN@ghtltd.com">JHANSEN@ghtltd.com</a>> wrote:</p>
<div>
<div>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">Thanks Cheney, but I’m not sure I
follow your email. I’ve already determined that, for example, a
core bathroom could easily have a peak load that is 10 Btu/hr-ft2 less than the
peak average of the rest of my spaces. Same goes for stairs, storage
rooms, etc. So doesn’t 90.1 REQUIRE that I model these separately?</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);">What CIR are you referencing?</span></p>
<p class="MsoNormal"><span style="font-size: 11pt; color: rgb(31, 73, 125);"> </span></p>
<div style="border-width: 1pt medium medium; border-style: solid none none; border-color: rgb(181, 196, 223); padding: 3pt 0in 0in;">
<p class="MsoNormal"><b><span style="font-size: 10pt;">From:</span></b><span style="font-size: 10pt;"> Cheney
[mailto:<a rel="nofollow" ymailto="mailto:chenyu73@gmail.com" target="_blank" href="mailto:chenyu73@gmail.com">chenyu73@gmail.com</a>] <br>
<b>Sent:</b> Monday, November 01, 2010 12:36 PM<br>
<b>To:</b> James Hansen<br>
<b>Cc:</b> <a rel="nofollow" ymailto="mailto:bldg-sim@lists.onebuilding.org" target="_blank" href="mailto:bldg-sim@lists.onebuilding.org">bldg-sim@lists.onebuilding.org</a><br>
<b>Subject:</b> Re: [Bldg-sim] Exceptions to G3.1.1, and how you model them?</span></p>
</div>
<div>
<div>
<p class="MsoNormal"> </p>
<div>
<p class="MsoNormal">Hi
James, </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">LEED
CIR allows projects to demonstrate substantial energy savings for well-designed
HVAC system serving high process load spaces based on the exception to G3.1.1.
So the premise is "high occupancy or process load" spaces, such
as server rooms, natatoriums, before it comes to the benchmark of 10
btu/h-ft2. Therefore, I guess your storage rooms, stairs, mechanical rooms
should not be modeled separately. </p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">Regards,
</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal">Cheney
</p>
</div>
<div>
<p class="MsoNormal"> </p>
</div>
<div>
<p class="MsoNormal" style="margin-bottom: 12pt;">I guess
your storage rooms, stairs, mechanical rooms, lobbies, etc. should not be
</p>
</div>
<div>
<p class="MsoNormal">On
Mon, Nov 1, 2010 at 5:12 AM, James Hansen <<a rel="nofollow" ymailto="mailto:JHANSEN@ghtltd.com" target="_blank" href="mailto:JHANSEN@ghtltd.com">JHANSEN@ghtltd.com</a>> wrote:</p>
<div>
<div>
<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.</p>
<p class="MsoNormal"> </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).</p>
<p class="MsoNormal"> </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?</span></b></p>
<p class="MsoNormal"> </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. </p>
<p class="MsoNormal"> </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?</p>
<p class="MsoNormal"> </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…</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Sorry
for the long email. Thanks!</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><b><span style="color: teal;">GHT Limited<br>
</span><span style="color: black;">James Hansen, PE, LEED AP</span></b></p>
<p class="MsoNormal"><b><span style="font-size: 10pt; color: black;">Senior Associate</span></b></p>
<p class="MsoNormal"><span style="font-size: 7.5pt; color: black;">1010 N. Glebe Rd, Suite 200</span></p>
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