Abstract
This study analyzed the convergence of the in-situ thermal resistance (R-value) and thermal transmittance (U-value) obtained by the average method using criteria of ISO 9869-1 and ASTM C1155-95. Onsite measurement was conducted for an northwest-facing opaque exterior wall of a 30-year-old apartment house over a period of three weeks during winter. The in-situ R-value and U-value obtained at the end of the test are 51.1% smaller and 113.0% larger than the theoretical values calculated according to the ISO 6946. These results show that identifying the in-situ thermal performance of exterior walls is important for building energy efficiency. When using criteria of ASTM C1155-95, the minimum measurement duration was 3 days, but the results of this period showed a deviation of approximately 10% from the values at the end of the test. On the other hand, the convergence conditions of ISO 9869-1 were satisfied continually from 17 days after the start of measurement. Therefore, the findings show that the convergence criteria of ASTM C1155-95 can reduce the test duration but it is possible to derive the results with lower confidence level, whereas the convergence criteria of ISO 9869-1 increases the test duration but can produce a more reliable results.
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