Abstract
Cost of performing hot-box experiments on building envelope assemblies is relatively high. That is why proper estimation of the minimum amount of time necessary to achieve required test accuracy is critical to all hot-box operators. In this paper, two methods are proposed for determining wall specimen time constants, for the hot-box apparatus testing. The requirements published in ASTM C1363-05 “Standard Test Method for the Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus,” concerning determination of the time to reach the steady state of heat flow are discussed. One method requires numerical calculations of the response factors with subsequent determination of time constants. The second method makes use of the approximate relation between the time constant and the product of resistance, capacity, and a structure factor. Both methods may serve for the optimization of the minimum test time during hot-box experiments.