Thermal Resistance Measurements of Well-Insulated and Superinsulated Residential Walls Using a Calibrated Hot Box

Abstract

Thermal resistance measurements of two highly insulated residential walls are made using a calibrated hot box operated under winter and summer climatic condi tions. The well-insulated wall consists of two insulated wood-frame sections with staggered framing, having a nominal thermal resistance of R-27 F·ft²·h/Btu (4.8 K· m²/W). The superinsulated wall is identical in construction, except for additional in sulation placed between the two wood-frame sections increasing the wall thermal re sistance to a nominal value of R-39 F·ft²·h/Btu (6.9 K·m²/W).

The measured thermal resistance for both walls is examined as a function of mean wall temperature and compared with predictions using the ASHRAE parallel-path method, the ASHRAE isothermal-plane method, and a finite-difference model with temperature-dependent thermal conductivities. Good agreement between measured and predicted values is obtained using both ASHRAE methods and the finite- difference model. At mean wall temperatures above 40°F (4.4°C), the ASHRAE parallel-path method tends to overpredict, while the ASHRAE isothermal-plane method tends to underpredict the overall thermal resistance. The effects of the com pression of glass-fiber blanket insulation and nail penetrations on the overall thermal resistance are investigated.