ASTM Standards for Cool Construction Materials
H. Akbari
We have examined the impacts of using cool surfaces (cool roofs and pavements) on reducing the urban air temperature and hence reducing cooling energy use and smog. At the community scale, increasing the solar reflectance of urban surfaces can effectively and inexpensively limit or reverse an urban heat island. An estimate of the national impact of cool surfaces (combining the cooling effect at the building level and community-wide cooling) is summarized in the Table.
| 1995 | 2015 | ||
| Basecase | Basecase | Savings* | |
| Electricity (TWh) | 440 | 540 | 70 |
| CostÝ (billion $) | 44 | 54 | 7 |
| CO2 (MtC¦) | 110 | 135 | 18 |
Table. Basecase U. S. air-conditioning use and savings potential of cool surfaces. We estimate that 13% of air conditioning can be avoided by the year 2015.
Achieving these potential savings, however, is conditional on receiving the necessary federal support. An important step in initiating an effective program in this area is to work with the American Society for Testing of Materials (ASTM) and the industry to create test procedures, ratings, and labels for cool materials. A subcommittee of ASTM E06, on Cool Construction Materials, was formed as part of a national plan to exploit cool construction technology and materials.
In 1994, a group of industry representatives from the public and private sectors, including several ASTM members, attended two workshops on cool construction materials. The group formed the National Committee for the Planning of the Cool Construction Materials Program. One of the major tasks in this National Plan is to develop performance data and standard procedures for the evaluation of cool construction materials. The subcommittee of E06 was formed as the vehicle to develop standard practices for measuring, rating, and labeling cool construction materials.
The subcommittee has determined that two optical properties (solar reflectance and emissivity) need to be measured in both the laboratory and the field. In response to the lack of standards for field measurements of solar reflectance, the subcommittee has drafted a test method for measuring solar reflectance of the horizontal and low-sloped surfaces. The subcommittee believes that two existing ASTM standards (E 903-Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials Using Integrating Spheres, and E 408-Test Methods for Total Normal Emittance of Surfaces Using Inspection-Meter Techniques) meet the needs for laboratory measurement of these properties.
Another activity of the subcommittee includes developing a Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped Surfaces. It is the objective of this standard to define a Solar Reflectance Index (SRI), which measures the relative steady-state temperature of a surface with respect to standard white (SRI = 100) and standard black (SRI = 0) under standard solar and ambient conditions.
In the coming year, we plan to finalize these standards and develop new ones addressing degradation of solar reflectivity with age and weathering.
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