I let my eQuest model generate U-values (see LV-I report - page 2 of
attached pdf)
The U-values don't seem to make any sense. The LV-I report says a door has
a U-value of 2.080.
I looked up hollow metal insulated doors on the internet and found one that
has a value of 0.16.
Why is there such a difference?
I know how to change u-values in detailed edit mode, but wonder what
experience others have had with determining what U-values should be used.
I used an online calculator to find the u-value for a wall like mine (also
attached).
Having trouble figuring out how to determine/ enter u-value for a roof
assembly that is a trussed attic with insulation above ceiling as well as
others.
I also realize ASHRAE has basic u-values listed, but my leed reviewer
commented saying ASHRAE U-values should be used only if the actual U-values
are unknown. I assume this means if the makeup of a wall or assembly cannot
be determined.
Thanks for your help in advance!
Timothy W. Hill
Hi Tim,
Your LEED reviewer is spot on: refer to Appendix A7/7.1 in 90.1. The "fallback" ASHRAE values provided for various constructions/elements (incl. doors) are there as a means of last resort. If you can determine the correct value, you should use it.
One can only speculate at what inputs you used (or didn't use) to arrive at a given U-value for your doors... sounds like you didn't reference the actual product/specification and should adjust to match as appropriate.
The online tool you found is in a sense already built into eQuest, and as such is probably a more time-efficient way to determine, define, & document construction thermal properties (i.e. in one step). Choose to define your constructions in layers, and you'll find there's a library of materials similar to that online tool.
There can be multiple right answers, but your attic sounds like an unconditioned space of its own, which in turn should be defined with exterior surfaces (walls/roofs), and the spaces immediately below should have interior surfaces to match the insulated ceiling construction.
If you find yourself mostly "stuck" on the specifics/fundamentals of defining the constructions thermally, you might more time-efficiently engage your favorite MEP designer/consultant ;).
Best of luck!
~Nick
[cid:489575314 at 22072009-0ABB]
NICK CATON, P.E.
Tim,
Looks like you just happened to choose an inefficient door from the
library. You selected an uninsulated sgl lyr in your model.
Depending on your choice, the u-values will change. In the model below,
I have selected 3 different doors, for example.
With that said, and as the reviewer commented, I would advise not using
any defaults unless you do not happen to know the door constructions in
your design.