Abstract
With the implementation of the Energy Star Roof Products Program by the U.S. Environmental Protection Agency and the U.S. Department of Energy, techniques are especially needed that yield in situ measurements of the average solar reflectance of roof surfaces without damage to them. This paper presents results of limited field surveys with two types of instruments that permit such measurements. Solar reflectances on a scale from 0 to 1 were obtained by the established laboratory technique for five samples covering the range exhibited by low-slope roofs and coating systems for them. Based on these results, the average bias for one instrument, a portable solar spectrum reflectometer using a built-in light source, was +0.003. The maximum bias for the five samples was ±0.02. Scatter of readings over a roof area with this instrument depends upon characteristics of the specific surface. Scatter can be as little as ±0.001 but is typically more than ±0.02. The other instrument uses a pyranometer and is operated by recording the responses when the pyranometer faces the sun and when it is inverted facing the surface of interest. The reflectance is the ratio of the response when inverted to the response facing the sun. For a variety of roof surfaces, the average of readings with both instruments agreed within 95%confidence intervals of ±0.02 to ±0.06, calculated as ±tċs.d., where t is the t-statistic for the number of measurements and s.d. is the measurement standard deviation.
Similar content being viewed by others
REFERENCES
K. E. Wilkes, T. W. Petrie, J. A. Atchley, and P. W. Childs, Proceedings, 2000 ACEEE Summer Study on Energy Efficiency in Buildings (American Council for an Energy Efficient Economy, Washington, DC, 2000), pp. 3.361–3.372.
T. W. Petrie and P. W. Childs, Report ORNL/CON-439/V2 (Oak Ridge National Laboratory, Oak Ridge, TN, 1998).
P. Berdahl and S. E. Bretz, Energy Build. 25:149 (1997).
R. S. Schmeltz, Roof Products Memorandum of Understanding, Version 1.0 (U.S. EPA, Washington, DC, Oct. 13, 1998).
The Solar Spectrum Reflectometer, TN 79-16; Solar Spectrum Reflectometer Updates and Design Modifications, TN 82-1; Solar Spectrum Reflectometer Design Modifications Revision #4, TN 83-1; Solar Spectrum Reflectometer Version 5.0, TN 86-1 (Devices and Services Co., Dallas, TX, 1979, 1982, 1983, 1986).
E. R. G. Eckert and R. M. Drake, Jr., Heat and Mass Transfer (McGraw–Hill, New York, 1959), Chap. 13.
M. D. Rubin, LBNL Internal memorandum to P. H. Berdahl: Reflectance of 5 roofing materials (Lawrence Berkeley National Laboratory, Berkeley, CA, Dec. 4, 1997).
Designation E903-96, Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres (ASTM, West Conshohocken, PA, 1996).
Designation E1918-97, Standard Test Method for Measuring Solar Reflectance of Horizontal and Low-Sloped Surfaces in the Field (ASTM, West Conshohocken, PA, 1997).
P. G. Lapujade, Report FSEC-RR-28-94 (Florida Solar Energy Center, Cape Canaveral, 1994).
Roof Surface Albedometer Instruction Manual, Revision 3.0 (Davis Energy Group, Inc., Davis, CA, Apr. 10, 1999).
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Petrie, T.W., Desjarlais, A.O., Robertson, R.H. et al. Comparison of Techniques for In Situ Nondamaging Measurement of Solar Reflectances of Low-Slope Roof Membranes. International Journal of Thermophysics 22, 1613–1628 (2001). https://doi.org/10.1023/A:1012821827012
Issue Date:
DOI: https://doi.org/10.1023/A:1012821827012