Requirement Summary
This measure can be claimed if the solar reflectivity (albedo) of the external wall finish is greater than the local base case as set out in the Key Assumptions for the Base Case in the Design section. EDGE will calculate any improvement beyond the base case.
Intention
Specifying a reflective finish for the walls can reduce the cooling load in air-conditioned spaces and improve thermal comfort in non-mechanically cooled spaces. Due to the reduction in surface temperature, the service life of the finish can also be improved and the impact on the urban heat island effect can be reduced.
Approach/Methodologies
EDGE uses the solar reflectivity of the wall finish as the indicator of best practice. This is the part of the total incident solar radiation that is reflected back from a surface. Unlike Visible Solar Reflectance, it includes the full solar spectrum, but does not include the effect of emittance which is reflected in a metric such as Solar Reflectance Index (SRI).
The solar reflectivity for specific wall finishes can be acquired from the product manufacturer. It is often indicated in the product data-sheet or laboratory test results published on manufacturers’ websites.
Table 19 provides an indication of the ranges for different materials but is meant only as a guide. Manufacturers’ published values must be used in the EDGE assessment. If manufacturer data is not available, the EDGE reference values may be used as an exception.
Table 19: Solar reflectivity of typical wall finishes
Potential Technologies/Strategies
The key consideration of the material used on the façade is its color and potential solar reflectivity.
Relationship to Other Measures
The impact that the solar reflectivity of the walls has upon the energy consumption in a building is dependent on the insulation levels, as well as the approach used to cool the building and the efficiency of any cooling systems.
The solar reflectivity of the wall finish has a decreased effect on the internal heat gains as the insulation levels are increased. Super-insulated buildings may not benefit significantly from wall finishes with a high solar reflectivity. Higher solar reflectivity values will have no effect on the energy consumption in passively cooled buildings, but may have an impact on the EDGE rating due to occupant comfort.
As the efficiency of the cooling systems increases, the solar reflectivity will have a decreasing impact on reducing the energy consumption.
A highly reflective surface might cause glare and should be taken into consideration by the design team.
Assumptions
The base case for solar reflectivity may vary in different countries. The base case assumption can be seen in the Design tab under Advanced Settings: Key Assumptions for the Base Case. The typical default value is 30%. The improved case has a default value of 70% which can be adjusted by the user. The actual solar reflectance / reflectivity provided by the manufacturer must be provided for certification.
Compliance Guidance
At both the design and post-construction stage it is important to ensure that the value obtained for the wall material/finish is the solar reflectivity of the finish rather than an alternative indicator of performance. Other values that may be provided by a manufacturer include the solar reflectance index (SRI), visible solar reflectance, the emittance or gloss units, which are not the same as solar reflectivity.
| Design Stage | Post-Construction Stage |
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At the design stage, the following must be used to demonstrate compliance:
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At the post-construction stage, the following must be used to demonstrate compliance:
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