Roof Albedo Definition

Surface albedo is defined as the ratio of radiosity to the irradiance received by a surface.

Roof albedo definition. In los angeles the average roof albedo is about 0 17. 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.

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. Investigators frequently rely on observations of normal albedo to determine. 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. Albedo is usually differentiated into two general types.

Albedo is the fraction of sunlight that is reflected from a surface. Normal albedo and bond albedo. Standard or dark roofs can reach temperatures of 150 f or more in the summer sun. 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.

A perfect reflector would have an albedo of 1 whereas a perfect absorber would have an albedo of 0. The former also called normal reflectance is a measure of a surface s relative brightness when illuminated and observed vertically. A cool roof under the same conditions could stay more than 50 f cooler and save energy and money by using less air conditioning. 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.

A sample cool roof. A high thermal emittance also plays a role particularly in climates that are warm and sunny. Albedo al bee doh is a measure of how much light that hits a surface is reflected without being absorbed. The normal albedo of snow for example is nearly 1 0 whereas that of charcoal is about 0 04.

These values usually are listed in decimals with 0 99 being the best and 0 000 being the worst. 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. It is measured on a scale of 0 to 1 where higher numbers indicate greater reflectance. The words albedo or solar reflectance and emittance are words that relate to energy efficiency in a roof system.

The proportion reflected is not only determined by properties of the surface itself but also by the spectral and angular distribution of so.