[Equest-users] Radiant barrier in walls

Joe Huang yjhuang at whiteboxtechnologies.com
Wed Apr 3 16:51:46 PDT 2013


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.

Joe

Joe Huang
White Box Technologies, Inc.
346 Rheem Blvd., Suite 108D
Moraga CA 94556
yjhuang at whiteboxtechnologies.com
www.whiteboxtechnologies.com
(o) (925)388-0265
(c) (510)928-2683
"building energy simulations at your fingertips"


On 4/3/2013 4:25 PM, Aaron Powers wrote:
> 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.
>
> Aaron
>
>
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