Integrated methodology for evaluation of energy performance of the building enclosures: part 3 — uncertainty in thermal measurements
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abstract
Thermal performance of building enclosure is typically based on laboratory tests performed on dry materials without consideration of air and moisture movement through the assembly. To address the field performance of the assembly, however, one must combine measurements and hygrothermal modeling. Hygrothermal models are necessary to include effects of climate and in particular the effects of moisture movement on thermal performance. Full-scale testing is necessary to relate findings of the models to actual construction details. The first paper in this series (Bomberg and Thorsell, 2008) introduced a test program that starting with benchmarking of the R-value of the tested wall in standard conditions, examined the effects of air flow on its thermal performance. This test program does not use the average R-values of the wall as it is in the ASTM testing, but measures local thermal resistance in selected places and calculates the average R-values. The second paper in this series (Thorsell and Bomberg, 2008) applied this integrated testing and modeling approach to selected wood framed residential walls, identifying the magnitude of air flow effects on steady-state thermal resistance, as well as demonstrating that the thermal performance of the top of the wall differs from that at the bottom. It also showed a systematic and time dependent shift in thermal performance caused by moisture movement. In this, third paper in the series, we present measurements performed on metal frame walls that introduce additional sources of uncertainty in the experimental results. We end with a discussion on the need of improvements to testing procedures for evaluation of energy performance of building enclosures.
