Techniques for in Situ Determination of Thermal Resistance of Light Weight Board Insulations

摘要

The most common method for field measurement of building component thermal resistance is the ''averaging'' method, R = sigma delta / sigma q, defined as the ratio of the average temperature over some suitable period of time to the average heat transfer over the same time period. While simple to use, it does have shortcomings: (1) the ratio is unreliable when the average heat transfer is near zero as it often is during the spring and fall seasons, (2) the R-value reported is at best an average over the range of temperatures for the test, and (3) the method does not account for persistent effects related to material heat capacity. Three alternative methods, all of which also use measured temperature distributions and heat fluxes are described. The ''absolute value'' method avoids problem (1), and the ''steady state least squares'' method avoids (1) and (2). The most comprehensive method is PROPOR. PROPOR is based on heat transfer principles and addresses all three of the shortcomings of the averaging method. Experimental data is presented to support these conclusions. (ERA citation 12:039054)