[Bldg-sim] interior wall with window adjacent to unconditioned area

[Maria Karpman]

James,

 

See ASHRAE 90.1 Figure 5-5, and also definitions for unconditioned and
semi-heated spaces in Section 3.2 (look under Space). According to these
definitions, naturally or mechanically ventilated parking garages are not
considered to be enclosed spaces, so the wall between conditioned space and
garage in your project should be treated as exterior wall.

 

Maria

 

From: bldg-sim-bounces at lists.onebuilding.org
[mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of James Hansen
Sent: Wednesday, April 22, 2009 2:48 PM
To: BLDG-SIM at lists.onebuilding.org
Subject: [Bldg-sim] interior wall with window adjacent to unconditioned area

 

I have a general question about how to model and prove compliance for a
window in an interior wall that separates conditioned space from
unconditioned space.

 

We have a project where there is a conditioned area in the parking level
with a full height storefront window system separating the room from the
unconditioned garage.

 

As far as I know, this "wall" is actually an interior wall per ASHRAE
90.1-2004.  Or rather, it's not defined as an exterior wall (at least
clearly enough).  For certain modeling and compliance programs, you can't
even assign a window to an interior wall.  To further complicate things, the
entire wall is window, meaning there is no actual cavity space for
insulation (which proves difficult for things like Comcheck compliance).

 

Does anyone know how ASHRAE 90.1 views this "wall".  Is it really an
exterior walls?  Are ALL walls that separate conditioned from unconditioned
space considered exterior walls?  If so, this is not properly defined in
ASHRAE.  And if not, there doesn't appear to be anywhere that governs
U-values for windows in INTERIOR walls that separate conditioned from
unconditioned area.  In fact, from what I can tell, ASHRAE advises you to
IGNORE windows in interior walls.  Which is all fine, unless your entire
wall is window.  But at the same time, interior walls appear to require a
maximum U-value of 0.120.  For a window, this is nearly impossible.

 

Can anyone interpret 90.1 for me?  Am I really allowed to ignore windows in
interior walls even if they separate conditioned space from unconditioned
space?  

 

Thanks in advance!

 

GHT Limited
James Hansen, PE, LEED AP

Senior Associate

1010 N. Glebe Rd, Suite 200

Arlington, VA  22201-4749

703-338-5754 (Cell)

703-243-1200 (Office)

703-276-1376 (Fax)

 <http://www.ghtltd.com/> www.ghtltd.com

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