What is the overall thermal transmittance value (U-factor) and how does it apply to ASTEC?
In numerical terms, the U-factor is the reciprocal value of the total resistance (1/ΣR). The U-factor is only an indication of the conduction rate of heat transfer; it is a quantitative measurement of how well heat conducts through a roof or wall for a given temperature difference. For instance, if the total R-values (ΣR) of a roof’s several components add up to 1.892 (m2 K)/W in the metric system or 10.75 (h ft2 F)/Btu in the U.S. terminology, then the average thermal transmittance (U-factor) is 0.529 in the metric expression and 0.093 in the U.S. language. Although ASTEC has an excellent k-value, this does not translate into a good R- value only because applied ASTEC has very little thickness. Therefore, ASTEC does not have a direct impact on the U-factor per se. However, ASTEC significantly enhances the U-factor value in that it (a) prevents the absorption of 85% of the solar radiation and (b) reduces heat transfer by as much as 70% by lowering the temperature difference across the
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