[Equest-users] Modeling Residential Unconditioned Spaces

[Aulbach, John]

Nicolai:

If this is a residential system, then you are modeling this building as
ONE ZONE? Otherwise, the RESYS-2 system doesn't work right, according to
the DOE-2.2 online Help. The building as a single zone may not be seeing
the difference in temperature that actually happens in the real world.

John

-----Original Message-----
From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nicolai
Schlag
Sent: Wednesday, July 30, 2008 10:07 AM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] Modeling Residential Unconditioned Spaces

Hi,

I'm working with a model of a two-story residential building with an
attic being modeled as an unconditioned space in three climates:
Phoenix, San Francisco, and Chicago. I've set up parametric runs varying
the R-values of the exterior walls and the ceiling (attic floor) in
order to determine the optimal values for efficiency's sake, but the
results of the parametric runs don't make much sense. Specifically,
while varying the wall insulation has a notable impact on the heating
and cooling loads, there is only slight variation when the ceiling
insulation is varied (between R20 and R60--would expect a fairly
significant difference). The large savings that one would expect from
such a significant increase in ceiling insulation are not apparent here
in any of the climates. The roof itself is not well insulated
(R2) but is highly reflective.

The problem seems to be rooted in some issue modeling temperature in the
unconditioned zone. Hourly reports show a much narrower range of
temperatures annually in the unconditioned zone (about 20F) than
outdoors (100F)--also somewhat counterintuitive. Somehow, I'd like to
find a way to simulate the larger expected temperature swings in an
attic in order to see the full benefits of increasing ceiling
insulation.

I've made a few attempts to resolve the issue. As per an old post from
the BLDG-SIM list
(http://lists.onebuilding.org/htdig.cgi/bldg-sim-onebuilding.org/2007-Ju
ly/0
05513.html), I tried adjusting the heating and cooling design
temperatures to better reflect the range of outdoor temperatures, but
this had no effect upon household energy consumption.

For curiosity's sake, I also switched the attic to a plenum to see how
this might affect the calculation of loads but got some pretty
nonsensical results in that case as well.

I did also come across another posting
(http://lists.onebuilding.org/htdig.cgi/bldg-sim-onebuilding.org/2005-Se
ptem
ber/002502.html) that suggested integrating glass into the roof deck in
order to allow for the simulation of radiative heat transfer, though
this was in the case of a commercial building. I'm not sure if this is
the solution I'm looking for, but any insight would be appreciated.

Thoughts? Thanks for your help!

Nick Schlag

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