[Bldg-sim] Exterior wall heat transfer in eQuest

Steven Savich ssavich at systemswestengineers.com
Mon Jan 28 12:24:03 PST 2008



Sorry if I wasn't clear.  The concrete has a corrugated exterior finish,
there is no metal layer.  It's a solid (with metal rebar embedded) concrete





From: Graham Carter & Megan Lyall [mailto:hamnmegs at ozemail.com.au] 
Sent: Monday, January 28, 2008 12:22 PM
To: Steven Savich
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Exterior wall heat transfer in eQuest


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 ...




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?






Steven Savich

Systems West Engineers

411 High Street

Eugene, OR  97401-2427

(541) 342-7210

(541) 342-7220 (fax)



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