Field Thermal Performance of Radiant Barriers and IRCC Systems for Attic Retrofits

(This entry contains a paper and a PowerPoint presentation in PDF from the BEST4 Conference.) For over a century, traditional bulk insulation materials like fiberglass and cellulose have been used in attics to prevent heat from escaping or entering American homes. But times are changing and today, builders and homeowners in Southern U.S. locations are discovering that adding attic reflective insulation may offer significant gains in thermal efficiency – often far greater than the same investment in additional layers of conventional bulk insulation. According to the US Information Administration (eia)1, in 2009 in average more than 11% of the US household end-use energy expenditure was for space cooling (air conditioning) while in the US hot humid climate region this space cooling expenditure went up to more than 25%. In order to reduce cooling energy consumption, techniques to limit radiative heat transfer such as Radiant Barriers (RB) and Interior Radiation Control Coatings (IRCC) can be applied to existing residential attics in single family homes or light commercial buildings. RBs incorporate two layers of aluminum foil or aluminized plastic film. Aluminum has a low emissivity, absorbing and emitting a small amount of infrared radiation. The enclosed air space between the two layers reduces conduction across the barrier. IRCC work in a similar manner but is a coating usually sprayed on the back side of the roof deck. There are claims that RB and IRCC are easier to install and very energy efficient in retrofit projects. The goal of this study is to understand these claims with analyzing changes in the annual cooling energy consumption and peak cooling loads by both experimental and numerical approaches. In Austin, Texas, both RB and IRCC were installed in test houses and compared to a baseline house with no modifications. The test houses were instrumented and thermal and energy performances of the attics were monitored for over 6 months. In addition the whole building energy consumption before and after retrofit was compared using EnergyPlus energy consumption simulations.