Effects of air mass and integration methods on results for optical property measurements of solar cover plate and absorber materials

Abstract

This study was undertaken to compare methods of calculating the transmittance of cover plate materials and the reflectance of absorber materials. The study was limited to evaluation of factors which influence the results with method A of ASTM E 424, Optical data were obtained for both aged and unaged test specimens using an integrating sphere spectrophotometer. The data were integrated using: (1) the weighted and selected ordinate methods in ASTM E 424, Method A, at air mass 2.0, and (2) the selected ordinate method at air mass 1.5 and 1.0. The solar reflectance and solar transmittance values calculated using the various methods are presented in this report along with discussions of the impact of the data in terms of possible revisions to ASTM E 424.

Test methods and standards development for active solar heating and cooling systems

“…• -and accelerated weathering [62,63]; determination of cover plate pr per::*.-69 including stability, warpage, and mechanical response [62]; measurement of optical properties [64]; and determination of procedures for assessing hail impact on the durability of cover plate materials [65] In the first study [62], researchers identified field problems, determined performance requirements for and properties of cover plate materials, and identified degradation factors.…”

“…Most solar collectors, however, are exposed to more hours of radiation that approximates air mass 1.5. As a result, Roberts, Masters, and Clark [64] assessed the effect of varying air mass value upon the transmittance and reflectance values of typical materials. They determined that the three values of air mass studied, 1.0, 1.5, and 2.0, could vary the obtained transmittance values by as much as 4 percent.…”

“…The studies reviewed in section 5.1 [62,63,64,65] formed the technical basis for ASTM Standards E 765-80 [57], E 782-81 [58], E 881-82 [59], and E 822-81 [60], as well as a set of proposed revisions to ASTM E 424-71 [61].…”

Materials research activities at the National Bureau of Standards (1975-1982) pertaining to active solar heating and cooling systems

“…The NBS subsequently conducted a study [5] in which the aforementioned transmittance data were analyzed to determine the influence of air mass and integration technique on Method A of ASTM Standard E424 [4] for measuring solar energy transmittance. As mentioned above.…”

“…In the above mentioned parametric study of cover plates (section 2.1.3) [5], NBS also analyzed laboratory test data on the performance of absorber materials. The purpose of the study was to assess the effect of several variables on an ASTM standard method for measuring the reflectance of absorber materials (Method A of ASTM E424).…”