Radiant Barrier Retrofits to Improve Energy Efficiency of Older Homes in Hot-Humid Climate Zones

PREPARED BY:

The University of Texas at San Antonio's Center for Cultural Sustainability—part of the College of Architecture, Construction and Planning

PRINCIPAL INVESTIGATOR:

Professor William A. Dupont

Co-Principal investigators:

Dr. Hazem Rashed-Ali | Dr. Randall D. Manteufel | Dr. Suat Gunhan

PROJECT SPONSOR:

The National Center for Preservation Technology and Training
National Park Service, U.S. Department of the Interior

GRANT NUMBER:

P14AP00143

Research Purpose

The grant from NPS NCPTT funded a study regarding the energy efficiency and cost-effectiveness of radiant barrier retrofits of historic homes in hot- humid climates.

Project description

This project addresses a national need in preservation technology to educate the public on best practices for energy improvement retrofits to older homes. The research measured the actual energy use impact of one significant retrofit—installation of the radiant barrier—in six case study homes, one story high, historic, and small. The average home size is 1,381 square feet; the median is almost identical at 1,404 square feet. The research project concerns building performance before and after the energy retrofit. The particular retrofit evaluated, a radiant barrier, is relatively inexpensive and straightforward to install within existing homes, thus suggesting high potential value as a retrofit.

Findings and recommendations for next steps

Data collected from the six homes in the study revealed that the radiant barrier was generally effective at reducing the total energy use of the case study homes, normalized for weather, by an average difference of -7.2 percent improvement. The range across the six case studies was rather wide, from a maximum improvement of-25.5% to an actual increase in cost of 4.2%. The median difference, also weather normalized, was -5.9%.

The installation cost of the radiant barrier into each home averaged $1,544; the median cost was significantly lower at $1,228 because there was one outlier in the costs dataset. Based on the median data, and adjusting for the variations in weather over the years of comparison, the simple payback on the installation cost is projected to be 14 years. Compared to the projected payback on other retrofits, this is a good result, but not exceptional. The wide range of results from only six case-study homes must temper consideration of the payback analysis from median data.

The performance variables are many, and the study indicates a wide range of possible results from this one retrofit. Smaller homes appear to be inherently more difficult to show a large percentage of improvement with retrofits because they use less energy overall than bigger homes. Therefore, the smaller the home, the longer the payback one would generally anticipate from a retrofit.

Next steps should include three areas of increased research attention:

1. more homes for analysis to produce more accurate data;
2. more analysis of cost data on the radiant barrier installation because the labor rate has a huge impact on financial efficacy of this retrofit; and
3. exploration ofheating profile and performance in climate zone 2A because the data showed natural gas EUI to be 35% higher than electric EUI. This EUI dataset was unexpected and remains unexplained, given that the cooling load is supposed to be the greater concern in climate zone 2A.

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