The Wall Properties Input Screen calculates the overall R and U values for a
sandwich assembly however it doesn't have any way to factor in the "framing
effect" of wall studs which can have a significant effect on average wall
assembly R and U values.
When I queried Carrier, part of Craig's reply was for cooling design loads
and energy modeling, ".U-value is not important, what is important is making
sure the specific heat, density and weight of the composite insulation/stud
layer is correct. Those values are used in the TFM equations not U-value."
Since this isn't as simple as inputting an overall U-Value from ASHRAE, Has
anyone come up with a way to effectively model steel stud framing that would
pass a DOE review?
Thank you,
Michael L. Hardy, PE, F.NSPE
Black Oak Engineering, Inc.
Cell 503.314.5244
Wow, that's kind of alarming to hear. I always assumed the U-value was
more important. I approximate the framing effect by first inputting the
ASHRAE 90.1 assembly for a given wall/roof type, then reduce the R-value
of the insulation (not the other values) until the U-value matches the
value listed in Table A3.3 for the given amount of continuous
insulation. Then I would add in the additional layers of construction
(like brick veneer, block, etc..) that are in the actual design but not
part of the basic ASHRAE tabulated assemblies.
Matt Scott
N.E. Fisher & Associates, Inc.
329 East Second St, 2nd Flr
Boyertown, PA 19512
e: mscott at nefisher.com
p: 610-369-3190
f: 610-369-3194