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This paper presents the results of inviting the operators of all guarded and calibrated hot boxes in North America to participate in a round robin, an interlaboratory test program according to ASTM E 691, “Conducting an Interlaboratory Test Program to Determine the Precision of a Test Method”, to establish the precision and bias of the corresponding ASTM standard test methods: ASTM C 236, “Steady-State Thermal Performance of Building Assemblies by Means of a Guarded Hot Box”, and C 976, “Thermal Performance of Building Assemblies by Means of a Calibrated Hot Box”. The data and data analysis are reported from twenty-one laboratories that completed a series of tests on 4-inch thick specimens of cellular polystyrene thermal insulation. The data analysis resulted in two recommended statements of precision and bias.
Ninety-five per cent of the time measurements from two different laboratories on the same specimen would differ by up to +/-7.8% at a mean temperature of 75 F for the guarded hot box, and by up to +/-5.6% for the calibrated hot box. Based on guarded hot plate data for the specimen material, the reference value is 15.9 hr-F-ft sq/Btu. The mean of the thermal resistance reported for guarded hot boxes was 15.77 hr-F-ft sq/Btu, which differs by -1.2% from the reference value. The mean of the thermal resistance reported for calibrated hot boxes was 16.32 hr-F-ft sq/Btu, which differs by +2.6% from the reference value.
bias, hot box, precision, polystyrene, round robin, thermal insulation
Director and Research Professor, Buildings Engineering and Architectural Research Center, New Jersey Institute of Technology, Newark, New Jersey