High albedo surfaces reflect significantly more solar radiation than low albedo surfaces.
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Reference materials and scientific studies confirm that albedo measures a surface's reflectivity, where a higher albedo indicates greater reflection of solar radiation compared to low albedo surfaces.
In the tropics, the earth surface receives abundant solar radiation annually contributing significantly to building heat gain and, thus, cooling demand. An effective method that can curb the heat gains through opaque surfaces could provide significant energy savings. This study investigates the effectiveness of “high-albedo-high-emittance (or cool) roof” on reducing heat gain through opaque surfaces into buildings. It is hypothesised that building heat gain can be reduced by increasing the albedo of opaque surfaces to reflect off the incident solar radiation. At the same time, by increasing the thermal emittance to emit off the absorbed heat (as infrared radiation) to outdoor. Computational simulations (calibrated using experiments) are conducted to compare the thermal performance of a cool concrete flat roof to that of a green roof and a thermal insulation roof under the tropical climate of Singapore. The cool roof provides higher annual net heat gain reduction of about 81-83% as compared to the green roof (about 60-75%) and the thermal insulation roof (about 68-80%). A novel and general cool roof heat transfer (CRHT) model that is based on the spectral approximation method is proposed. The CRHT model provides very concise and easy-to-use expressions to evaluate the impact of cool coating on roof temperature, ceiling temperature, indoor air temperature and heat flux on single-skin roof (SSR, i.e., solid primary roof with no air-gap between roof layers) and double-skin roof (
Reflective surfaces, or ground-based albedo modification (GBAM), is a solar radiation management method of enhancing Earth's albedo (the ability to reflect the
Reflective surfaces, or ground-based albedo modification (GBAM), is a solar radiation management method of enhancing Earth's albedo (the ability to reflect the visible, infrared, and ultraviolet (UV) wavelengths of the Sun, reducing heat transfer to the surface). The IPCC described GBAM as "whitening roofs, changes in land use management (e.g., no-till farming), change of albedo at a larger scale
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Solar reflectance, also known as albedo, is the ability to reflect sunlight. It is expressed either as a decimal fraction or a percentage. A value of 0 indicates that the surface absorbs all solar radiation, and a value of 1 (or 100%) represents total reflectivity.
Thermal emittance is the ability for a material to radiate thermal energy as heat. It is also expressed either as a decimal fraction between 0 and 1 or a percentage.
Another method of evaluating coolness is the solar reflectance index (SRI), which incorporates both solar reflectance and emittance in a single value. SRI measures the roof's ability to reject solar heat, defined such that a standard black (reflectance 0.05, emittance 0.90) is 0 and a standard white (reflectance 0.80, emittance 0.90) is 100.
A perfect SRI is approximately 122. Such a material would reflect all sunlight (not absorb) and have very high emissivity (emissivity of 1.0). High-reflectivity, low-emissivity roofs maintain a temperature very close to ambient at all times, preventing heat gains in hot climates and minimizing heat loss in cold climates. High emissivity roofs have much higher heat loss in cold climates for the same insulation values.
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