OVERVIEW
Solar reflectance of built-up surfaces is receiving increased attention as a result of its impact on summer heating of buildings and metropolitan areas, as well as the resulting implications on energy needs for air conditioning and the electric grid’s peak load. To measure solar reflectance in the laboratory or in the field, a variety of standard test methods are available based on various instruments and procedures. The purpose of this test method is to provide solar reflectance and thermal emittance data which is required to evaluate temperatures and heat flows across surfaces exposed to solar radiation.
Solar reflectance is the ratio of solar energy that falls on a surface to the amount reflected. It is measured on a scale of 0 (not reflective) to 1: (100 percent reflective). Generally, materials that appear light-colored have high solar reflectance and those that appear dark colored have low solar reflectance.
Thermal emittance or emissivity is defined as the ability of a body to release heat. Emissivity is a measurement of a surface’s ability to release/emit absorbed heat and return it to its original temperature. Emissivity is measured on a scale from 0 to 1, with 1 indicating the most effectively emissive substance. In other words, the greater the number, the better at cooling it will be.
When solar reflectance and thermal emittance are combined, the Solar Reflectance Index (SRI) can be determined. The SRI is a measurement of a material’s solar reflectance and emissivity that can be used to predict how hot it will become when solar radiation is directed on it. The lower the SRI, the hotter a material will be in direct sunlight.
DESCRIPTION OF TEST
This test was carried out on metal panels painted with Zenova IP thermal insulation paint at a paint thickness of 0.78mm.
TEST RESULTS
This test concluded that, on average, Zenova IP thermal insulation paint has a very high solar reflectance value of 0.834, a high thermal emittance value of 0.880, and an extremely high SRI (Solar Reflectance Index) of 104.
By comparison, many concretes tested according to ASTM C1549 have a solar reflectance of approximately 0.3 and an SRI of approximately 29, which fail to meet requirements set by LEED (Leadership in Energy and Environmental Design), the most widely used green building rating system in the world.