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All,<br><br>
I generally agree with Nick's approach. I said the same thing in
the ASHRAE HOF Residential Loads chapter (which I revised in 2005).
For residences, this scheme reconciles with US practice for determining
floor area (a nominal 1000 ft2 house is 1000 ft2 only if you include the
exterior wall thickness) -- that makes it easy to check input.<br><br>
Volume is overstated, as noted, but generally only minimally. I've
also seen procedures for doing blower door leakage tests that recommend
estimating volume from outside dimensions.<br><br>
All in all, then, the outside dimension method is simple to apply
consistently, easy to check, and accurate enough.<br><br>
On the other hand, it does NOT agree with other standards and procedures
that are in use. There is an ASTM standard that defines floor area
(I think) and uses inside dimensions. Also, I think rentable space
is sometimes measured from the window inside surface (which I guess is
the real estate version of split the difference?).<br><br>
As automated data exchange procedures become more ubiquitous, definitions
like this will have to be rigorously standardized so building model
fidelity can be retained as data is passed among applications.
There is an ASHRAE project getting underway related to consistent
extraction of a thermal model from a BIM. That is a step.<br><br>
Chip Barnaby<br><br>
At 01:14 PM 9/11/2009, Nick Caton wrote:<br>
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My practice with all load calculation/energy modeling software has
been:<br>
<br>
All floors/roofs: Top of surface<br>
Exterior glazing/walls: Outermost surface<br>
Interior walls/partitions: Center of construction<br>
<br>
I know this is the advice offered by IES-VE’s support staff, but that
doesn’t mean all modeling engines behave the same. As you may
gather, I’ve always assumed energy modeling and HVAC load calculation
models “subtract out” the thickness of constructions from calculated
space volumes. I don’t know whether this is a “universal standard
practice” between software packages / modeling engines.<br>
<br>
Since I would ultimately much rather slightly oversize than undersize an
HVAC system, I’m of the mindset that the potential for a little extra
surface area / conditioned space would if anything bump my results in a
desired, conservative direction regarding space loads. If absolute
accuracy is your goal, then in lieu of a “universal standard,” I’d
imagine you would have to ask the developers/users of the specific
program you’re using at the moment to determine its true behavior in this
regard.<br>
<br>
~Nick<br>
<br>
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<br>
<b> <br>
NICK CATON, E.I.T.<br>
</b>PROJECT ENGINEER<br>
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<b>From:</b> bldg-sim-bounces@lists.onebuilding.org
[<a href="mailto:bldg-sim-bounces@lists.onebuilding.org" eudora="autourl">
mailto:bldg-sim-bounces@lists.onebuilding.org</a>] <b>On Behalf Of
</b>Ryan Del Balso<br>
<b>Sent:</b> Friday, September 11, 2009 11:50 AM<br>
<b>To:</b> bldg-sim@lists.onebuilding.org<br>
<b>Subject:</b> [Bldg-sim] Where should you choose your wall location
forsimulations, inside, outside or center of wall<br>
<br>
Are there standard practice recommendations for where to place your wall
for a simulation? Knowing every wall has thickness, but the
simulation engines are generally just using no thickness walls with a
calculated U/R value, where should you define your walls for the
simulation? Should they be defined at the exterior face of the
wall, the interior face or the center of the wall. It seems the
exterior face can greatly increase the zone volume, thus incorrectly
determining the energy usage, but the interior face underestimates the
exterior exposure of the wall. The center of wall seems a good
compromise, but is difficult to identify and draw. <br>
<br>
For interior walls/zone delineation the same question applies. From
an energy standpoint is it better to place the zone boundary on the face
of the higher load zone or the lower load zone or split the
difference?<br>
Thanks for any advice or direction to standard practices.<br>
<br>
<br>
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<br>
<br>
<b>Ryan Del Balso<br>
Building Performance Engineer II<br>
ryan@ambient-e.com<br>
130 W. 5th Avenue, Denver, CO 80204 <br>
t 303.278.1532x210 | f 303.278.8533 |<br>
<a href="http://www.ambient-e.com/">ambient-e.com</a><br>
<br>
<br>
<br>
</b> <br>
<br>
<br><br>
<br>
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