Folks:
A quick survey:
Are people using the NRFC standard rating conditions (including standard window unit sizes per http://www.nfrc.org/documents/1997_NFRC100.pdf Table 1 p15) for assembly u-factors for windows in the Proposed Case?
I know the ASHRAE 5.8.2.4 references the NRFC 100 test, but I'm debating whether I should request custom calculations for my project's windows at their actual size, or accept manufacturer's standard literature based on the NRFC 100 rating sizes.
I know I can explicitly define the frame and glazing, which I prefer to do, but sometimes it isn't an option.
Thanks,
Aaron Dahlstrom , PE, LEED(r) AP
Aaron,
It seems like the reviewers are just looking for SOME documentation of how
you established the U-Values for glazing. This is a LEED reviewer comment
from a recent project I was working on. Note that this was a LEED-NC v2.2
job, hence the reference to ASHRAE 90.1-2004:
"Please provide additional information to confirm that the framed assembly
U-value was used for the Proposed Case windows (e.g. showing that the
whole window assembly has been tested by NFRC, or verifying that LBNL
Window5 calculations have been provided for the whole assembly, or
verifying that the frame effects are captured within the energy modeling
software), or revise the model referencing ASHRAE 90.1-2004 Table A8.2 if
needed."
For this particular project, there was no NFRC or Window5 data available,
so we responded by giving them results both for the case where we entered
the center-of-glass U-value and defined the frame effect in eQUEST, and
then also the results for using the terrible default window assembly
U-values from 90.1 Appendix A. It made about a 5% swing in the energy
consumption, so obviously we hope they COG + frame effect results.
Nathan Miller, PE, LEEDRAP
WINDOW5/6 is pretty easy to learn if you understand window systems.
This is the same tool NFRC raters use - you can use it to get whole
window U-factor and SHGC if you're not able to model the glass & frame
explicitly in the whole building simulation tool you're using. Also,
modeling the actual window size in WINDOW is more accurate than assuming
NFRC standard sizes, and is often a significant difference.
It'll take you 15 minutes after you get the hang of it.
http://windows.lbl.gov/software/window/6/index.html
*Aleka Pappas, P.E., LEED AP*