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The calibrated hot box (ASTM Test for Thermal Performance of Building Assemblies by Means of a Calibrated Hot Box [C 976]) is used to measure thermal performance of wall assemblies under dynamic temperature conditions. ASTM C 976 does not specify procedures for dynamic testing, or analysis and presentation of results. Dynamic testing procedures used by Construction Technology Laboratories (CTL), including instrumentation of test specimens, derivation of dynamic temperature cycles, acquisition of test data, and presentation of results, are described in this paper. Since 1979, CTL has applied dynamic temperature cycles to 25 wall assemblies using the calibrated hot box.
Thermal lag, reduction in amplitude, and the total heat flow ratio are three coefficients used by CTL to describe test specimen behavior under dynamic temperature conditions. These coefficients are derived from comparisons of measured results to values predicted by a steady-state analysis. Thermal lag, reduction in amplitude, and the total heat flow ratio characterize effects of thermal storage capacity. Derivation, usefulness, and limitations of these dynamic heat transmission coefficients are discussed.
Van Geem, MG
Senior Research Engineer, Fire/Thermal Technology Section, Construction Technology Laboratories, a Division of the Portland Cement Association, Skokie, IL
Stock #: JTE11004J