[BLDG-SIM] thermal modeling of air cavity

[Jeff Thornton]

<I'm attempting to model a building that's facade has a ventilated 25mm
air gap between a 100mm brick veneer on the outer side and an EPS/steel
stud construction on the inside. I'm curious exactly how I should account
for the conductance/resistance of the air gap. This will obviously depend
on the inner and outer surface temperatures and the natural convection
currents that results from them, and further to that the outdoor wind
speed; I'm wondering if anyone is aware of any methods that have been
developed to approximate the equivalent thermal properties of an air gap
in such a situation. >

Josh,

We just finished a new first-principles model of exactly that construction
for a client here in Madison.  It's TRNSYS-based and accounts for the
following items (assuming 1-D air flow through the wall cavity):

solar absorbed on the outer surface
convection off the outer surface
long-wave radiation exchange with the sky (outer surface)
conduction through the outer material (brick, terra cotta etc.)
energy storage in the massive outer material
convective/radiative exchange in the air gap (natural and forced convection)
heat transfer through the multi-layer inside wall

I'm not sure what modeling package you're currently using but thought you
might be interested...

Jeff


Jeff Thornton
President - TESS, LLC

2916 Marketplace Drive - Suite 104
Madison WI 53719 USA

Phone: 608-274-2577
Fax: 608-278-1475
E-mail: thornton at tess-inc.com
Web: www.tess-inc.com


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