# Radiant barrier in walls

4 posts / 0 new

Hi All,

Does any one have idea about modeling radiant barrier in walls for eQUEST?
What are the specifications those need to be collected from client?

Thank you,
Vamshi.

Offline
Joined: 2012-11-12
Reputation: 0

I don't think eQUEST, or more properly the DOE-2 engine underlying it,
can model radiant barriers, at least not based on first principles,
although it's always possible to equate it as a resistance layer. Are
you really talking about radiant barriers in walls ? I generally think
of radiant barriers as something used in an attic to reduce radiant heat
transfer between different surfaces.

Joe

Joe Huang

Offline
Joined: 2011-09-30
Reputation: 406

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

Offline
Joined: 2011-09-30
Reputation: 0

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

Offline
Joined: 2011-09-30
Reputation: 406