Quote:
Originally Posted by gtojohn
Inside air film above floor = R-0.68
Inside air film below flooring = R-0.68
Inside air film above EPS (one surface reflective) = R-2.23
Outside air film below EPS = R-0.17
Just trying to make sense of the numbers. Above the floor, is that underlayment, under floor, tar paper? Eps are you calling the polymeric coating and foil the air film? Isn't that in the total R-value called out on the label?
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Air Film is not a thing, it is a phenomenon that results from the tendency of air that is very close to a surface to resist flow. Fluid flow is the primary mechanism of convection, therefore convective thermal loss. A boundary phenomenon that resists heat flow is considered to have an R-value which can be used in calculating total R-value.
this is from
California Energy Commission:
Quote:
AIR FILM -- A layer of still air adjacent to a surface which provides some thermal resistance.
AIR FILM COEFFICIENT -- A measure of the heat transfer through an air film. [See ASHRAE Table 1, ASHRAE Handbook, 1985 Fundamentals]
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If you are still puzzled, you should Google "air film".
-AC