Roof Albedo Definition

Albedo is the fraction of sunlight that is reflected from a surface.

Roof albedo definition.

Surface albedo is defined as the ratio of radiosity to the irradiance received by a surface. A perfect reflector would have an albedo of 1 whereas a perfect absorber would have an albedo of 0. Most roof manufacturers have total reflectance and thermal emittance values listed for their various roofing colors and finishes. 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. Normal albedo and bond albedo. It is measured on a scale of 0 to 1 where higher numbers indicate greater reflectance. 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. Standard or dark roofs can reach temperatures of 150 f or more in the summer sun. The normal albedo of snow for example is nearly 1 0 whereas that of charcoal is about 0 04. 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.

These values usually are listed in decimals with 0 99 being the best and 0 000 being the worst. 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 proportion reflected is not only determined by properties of the surface itself but also by the spectral and angular distribution of so.

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. In contrast to conventional roofs these kind are specifically designed to reduce internal building temperature by reflecting the sun s uv rays. Investigators frequently rely on observations of normal albedo to determine. Cool roofs can be made of a highly reflective type of paint a sheet covering or highly reflective tiles or shingles.

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. The former also called normal reflectance is a measure of a surface s relative brightness when illuminated and observed vertically. The words albedo or solar reflectance and emittance are words that relate to energy efficiency in a roof system. Albedo is usually differentiated into two general types.

Albedo in the built environment the term albedo describes the proportion of incident radiation reflected by a system.