Reflections On the Insulated Home: the R-value Myth
Dan H. Donnellon
|Published in:||Journal of Green Building, June 2016, n. 3, v. 11|
The R-value is defined as, “a measure of the resistance of an insulating or building material to heat flow, expressed as R-11, R-20, and so on; the higher the number, the greater the resistance to heat flow (Random House, 2016).” The first thermodynamic principle violated by the R-value is the singular use of the word heat flow. Heat flow, or transfer, occurs in three distinct ways; conduction, convection, and radiation. The R-value test will only measure a bulk insulations resistance to conductive heat transfer. This type of heat flow is almost undetectable in the built environment, regardless of climate or season - resulting in the R-value myth. In winter, the stack effect will cause convective flows through the home as warm air under pressure rises and escapes through the top, requiring an equal amount of cold replacement air to infiltrate at the bottom. On hot sunny days, the exterior of the home absorbs long wave ultra violet (UV) rays from the sun and reemits this radiant heat energy into the residence. The thermodynamics of an occupied structure under varying atmospheric conditions is not well understood, leading to major inefficiencies. The goal of this conceptual study is to reveal the shortcomings of current insulation practices at the residential level, conceptualize a series of related issues for future study and develop a preliminary methodological concept for resolutions to the problems identified. Conclusions indicate that further research needs to be dedicated to replacing the R-value rule with a realistic metric that considers the efficiency, health, and safety of the entire building.
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