I'm using Excel to work out the overall u-value for a wall consisting of several layers. To do this the following formula is used:(adsbygoogle = window.adsbygoogle || []).push({});

[tex]

U = {1 \over {{1 \over {\alpha _{outside} }} + {{t_1 } \over {\lambda _1 }} + ... + {{t_n } \over {\lambda _n }} + {1 \over {\alpha _{inside} }}}}

[/tex]

It is the alpha (thermal conductance, W/m2*K) which turns out to be very difficult to determine. Apparently it is a function of many factors like air speed, density, kinematic viscosity etc. If anyone can assist me in finding a way to determine this value for a variety of circumstances, I'd really appreciate it!

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# Thermal conductance

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