[Bldg-sim] Exterior wall heat transfer in eQuest

[Graham Carter & Megan Lyall]

This is an interesting one.  I gave it some thought a few years back  
when I came across precast concrete blades projecting outside  
(shades), but directly exposed to the outside.  I thought of using  
Therm to estimate the effective U-Value of the wall for winter heat  
loss purposes but didn't take it any further at the time.

The air gap between the corrugated metal and concrete provides a  
relatively significant level of insulation.  If your effective  
exterior surface area is say 1.3 of your projected surface area what  
you would ideally be able to do is raise your external heat transfer  
coefficient by the same or similar factor.  I don't know of a way to  
do this in DOE-2.2 other than modify surface roughness, but you could  
play with the cavity air-gap insulation value to derate the assembly  
but then this value does not vary with wind speed ... .  This would  
approximate only the modified convection effects.

As for solar radiation it should be similar as the corrugation would  
self shade and thus the wall always sees the projected area normal to  
the sun ... .  As for long wave radiative heat transfer you could max  
out the emissivity but this only gives you a 10-15% max increase  
given what the unmodified emissivity likely is.  Could you play with  
sky-view factors (I think you can vary them in 2.2) to increase the  
amount of sky a surface sees to account for the extended surface  
area .... ?

Good luck I would be interested if any of the forum participants have  
come across refereed papers in this area.  In parts of Australia the  
cold bridging created by a concrete blade or an aluminium curtainwall  
fin can be significant.  The latter is disturbingly common on non- 
thermally broken curtainwall suites.  I reckon the benefits of the  
shading could be outweighed by the unaccounted penalties ...

Regards,
Graham
On 29/01/2008, at 4:42 AM, Steven Savich wrote:

> Hello all,
>
>
>
> I’m about to start working on a model for an existing classroom  
> building.  The exterior walls are uninsulated concrete with a  
> “corrugated” exterior surface that would appear to me to greatly  
> increase the effective surface area for winter heat loss/summer  
> heat gain.  Any thoughts about how to approach modeling with this  
> in eQuest?
>
>
>
> Thanks,
>
>
>
> Steven
>
>
>
> Steven Savich
>
> Systems West Engineers
>
> 411 High Street
>
> Eugene, OR  97401-2427
>
> (541) 342-7210
>
> (541) 342-7220 (fax)
>
>
>
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