Roof Albedo Definition

Cool roofs can be made of a highly reflective type of paint a sheet covering or highly reflective tiles or shingles.

Roof albedo definition.

Albedo is usually differentiated into two general types. A high solar reflectance or albedo is the most important characteristic of a cool roof as it helps to reflect sunlight and heat away from a building reducing roof temperatures. Albedo is the measure of the diffuse reflection of solar radiation out of the total solar radiation and measured on a scale from 0 corresponding to a black body that absorbs all incident radiation to 1 corresponding to a body that reflects all incident radiation. A cool roof under the same conditions could stay more than 50 f cooler and save energy and money by using less air conditioning.

The words albedo or solar reflectance and emittance are words that relate to energy efficiency in a roof system. A sample cool roof. The proportion reflected is not only determined by properties of the surface itself but also by the spectral and angular distribution of so. One of the more recent advancements in the field of green commercial construction are what are known as cool or albedo roofs.

Something that appears white reflects most of the light that hits it and has a high albedo while something that looks dark absorbs most of the light that hits it indicating a low albedo. Investigators frequently rely on observations of normal albedo to determine. Standard or dark roofs can reach temperatures of 150 f or more in the summer sun. These values usually are listed in decimals with 0 99 being the best and 0 000 being the worst.

A high thermal emittance also plays a role particularly in climates that are warm and sunny. It is measured on a scale of 0 to 1 where higher numbers indicate greater reflectance. In los angeles the average roof albedo is about 0 17. Most roof manufacturers have total reflectance and thermal emittance values listed for their various roofing colors and finishes.

A perfect reflector would have an albedo of 1 whereas a perfect absorber would have an albedo of 0. Surface albedo is defined as the ratio of radiosity to the irradiance received by a surface. The normal albedo of snow for example is nearly 1 0 whereas that of charcoal is about 0 04. Albedo in the built environment the term albedo describes the proportion of incident radiation reflected by a system.

In contrast to conventional roofs these kind are specifically designed to reduce internal building temperature by reflecting the sun s uv rays. As one would expect albedo roofs are formulated with special high eminence materials that keep project a high level of thermal energy back into the atmosphere. Reflective roofs are more energy efficient and cooler inside and out. The albedo of several types of roofs reflective surfaces can deliver high solar reflectance the ability to reflect the visible infrared and ultraviolet wavelengths of the sun reducing heat transfer to the surface and high thermal emittance the ability to radiate absorbed or non reflected solar energy.

Normal albedo and bond albedo.