ASHRAE 90.1 states that existing buildings shall be modeled as is before renovations. Currently the building has all of the window openings boarded up. I'm thinking that the best scenario would be to model the area of the window openings to be consistent and assign a u-value associated with plywood to the "window" and a SHGC of 0. Has anyone encountered this situation before, if so is this logic correct? Thanks.
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5901 thumbs up
November 30, 2011 - 4:54 pm
I think you need to apply some sense of logic to these situations. As an example, would it be appropriate to model an existing condition as an open hole in the wall even if that was the case?
Assuming that the current opening will be filled with windows I would model windows in the baseline. If this is an old building that had windows, I would likely model single pane windows in the baseline, not plywood. If this was a newer building, say built since the common use of double pane glass, I would use a double pane window. If the building had metal frames, I would use that in the baseline. If wood frames, I would use that.
There are values in Table A8.2 for unlabeled vertical fenestration you could use as a default.
thomas beal
41 thumbs up
November 30, 2011 - 5:02 pm
Based on ASHRAE fundamentals, the u-values are almost identical for 5/8 inch plwood and single pane windows from Table A8.2.
Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5901 thumbs up
November 30, 2011 - 5:32 pm
Sounds right and with a SHGC entered for the windows your baseline will be a more thermodynamically comparable model to the Proposed.