Determining k(T) – two methods for quantifying the temperature dependent apparent thermal conductivity of insulation materials
The apparent thermal conductivity of building insulation materials is commonly measured in accordance with ASTM Standard Test Method C 518 and reported at mean temperature of 75°F. There is, however, a need for temperature dependent thermal conductivity data, k(T), both to perform detailed hourly energy calculations and to guide research into new product development. In many cases, the temperature dependency can be assumed to be linear over a small temperature interval and no further testing or analysis is necessary. However, some insulation products like closed-cell foam insulation exhibit non-linear behavior. ASTM Standard Practice C 1045 introduces an “integral method” for those cases where the temperature dependence exhibits non-linear behavior. This paper explores a new method for measuring the apparent thermal conductivity that determines the limit as the temperature difference approaches zero. The results from the new method and the integral method are compared using data from three laboratories. The paper will compare results for k(T) obtained by the two methods along with a discussion of the uncertainties and limitations.
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Chris Schumacher (POC,Primary Presenter,Author), RDH Building Science Inc., firstname.lastname@example.org;
Andre Desjarlais (Co-Author), Oak Ridge National Laboratory, email@example.com;
David Yarbrough (Co-Presenter,Co-Author), R&D Services, Inc., firstname.lastname@example.org;