Roof Albedo Definition

The words albedo or solar reflectance and emittance are words that relate to energy efficiency in a roof system.

Roof albedo definition. The former also called normal reflectance is a measure of a surface s relative brightness when illuminated and observed vertically. Normal albedo and bond albedo. Investigators frequently rely on observations of normal albedo to determine. These values usually are listed in decimals with 0 99 being the best and 0 000 being the worst.

Surface albedo is defined as the ratio of radiosity to the irradiance received by a surface. In los angeles the average roof albedo is about 0 17. 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 usually differentiated into two general types.

Cool roofs can be made of a highly reflective type of paint a sheet covering or highly reflective tiles or shingles. Most roof manufacturers have total reflectance and thermal emittance values listed for their various roofing colors and finishes. In contrast to conventional roofs these kind are specifically designed to reduce internal building temperature by reflecting the sun s uv rays. Albedo is the fraction of sunlight that is reflected from a surface.

Standard or dark roofs can reach temperatures of 150 f or more in the summer sun. It is measured on a scale of 0 to 1 where higher numbers indicate greater reflectance. The proportion reflected is not only determined by properties of the surface itself but also by the spectral and angular distribution of so. A sample cool roof.

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 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. Albedo al bee doh is a measure of how much light that hits a surface is reflected without being absorbed.

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. A perfect reflector would have an albedo of 1 whereas a perfect absorber would have an albedo of 0. One of the more recent advancements in the field of green commercial construction are what are known as cool or albedo roofs. Reflective roofs are more energy efficient and cooler inside and out.

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.