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I wish to point out that the methods described below are
approximate, since radiant heat flows are a function of surface
temperature differences (to the fourth power), while conductive heat
flows are a function of air temperatures differences. Believe it or
not, but DOE-2.1E actually has a routine that can backcalculate the
surface temperatures of all interior surfaces, from which it would
be possible conceivably to model the effects of a radiant barrier.
This is part of the work for a project I'm just getting started in
modeling roof and attics. If the procedure proves promising, I'll
probably implement it in DOE-2.1E and then see if there's any
interest to incorporate it into DOE-2.2/eQUEST.<br>
<br>
Joe<br>
<pre class="moz-signature" cols="90">Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
<a class="moz-txt-link-abbreviated" href="mailto:yjhuang@whiteboxtechnologies.com">yjhuang@whiteboxtechnologies.com</a>
<a class="moz-txt-link-abbreviated" href="http://www.whiteboxtechnologies.com">www.whiteboxtechnologies.com</a>
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"
</pre>
<br>
On 4/3/2013 4:25 PM, Aaron Powers wrote:
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<div>Since DOE-2 uses the weight factor method for loads, you
don't have access to the inside emissivity of surfaces directly.
You do have access to the INSIDE-FILM-RES, which is the
combined radiative and convective resistance. Table 12 in the
Volume 2: Dictionary DOE2.2 documentation gives a guide for what
to use based on your material. For example, if your barrier has
an emissivity of 0.05, they suggest you use a film resistance of
1.70. Keep in mind that when the weight factors are calculated
(one time calculation), DOE-2 assumes an emissivity of 0.9 for
all surfaces which you cannot change. This means that your
increased film resistance will have no effect on internal loads
radiating to the wall, only on the energy coming through the
wall via conduction. This should give you a good order of
magnitude estimate, but it will tend to be conservative. As Joe
said, there's probably also a way to equate the effect to a
resistance layer. I believe this is what the wizard does if you
select radiant barrier for a roof.
<div>
<br>
</div>
<div>Aaron<br>
<div><br>
</div>
</div>
</div>
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