I am modeling an existing building right now. The opaque envelope will be maintained (walls and roof) but the entire inside, all HVAC systems, and windows will be replaced. For the model, I will model the HVAC systems as proposed against Appendix G systems. For the windows, do I use the baseline from Table A8.2, or can I use the R-value of the old building windows (which will likely be worse than Table A8.2)? And for the opaque envelope, we do not have an accurate way of measuring the current R-value. Can I just use the values from Table 5.5 for both the baseline and proposed (and therefore assume no savings from the opaque envelope? We are planning on adding some insulation to the opaque walls, but since there's no accurate way of measuring the existing structure, I assume we can't take any savings there. Am I correct? Thanks!
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5868 thumbs up
April 9, 2016 - 6:18 pm
You can use the data for the old windows according to Table G3.1-5 Baseline (f). You must be able to document the performance of those windows. If you can't use the Table A8.2 values.
You don't need to accurately measure the current R-value. It can be derived based on the construction assembly. If you can show that using the Baseline values is a conservative approach it would likely be accepted. Again you don't need to measure the existing structure anymore than you "measure" a new design. You can claim savings for adding insulation to existing walls by estimating the R-value of the assembly before and after.