Roof Albedo Definition

Standard or dark roofs can reach temperatures of 150 f or more in the summer sun.

Roof albedo definition.

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 cool roof under the same conditions could stay more than 50 f cooler and save energy and money by using less air conditioning. 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. 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. The normal albedo of snow for example is nearly 1 0 whereas that of charcoal is about 0 04. Normal albedo and bond albedo. Surface albedo is defined as the ratio of radiosity to the irradiance received by a surface.

The former also called normal reflectance is a measure of a surface s relative brightness when illuminated and observed vertically. A sample cool roof. One of the more recent advancements in the field of green commercial construction are what are known as cool or albedo roofs. These values usually are listed in decimals with 0 99 being the best and 0 000 being the worst.

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

Albedo al bee doh is a measure of how much light that hits a surface is reflected without being absorbed. 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. 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. Albedo in the built environment the term albedo describes the proportion of incident radiation reflected by a system. The words albedo or solar reflectance and emittance are words that relate to energy efficiency in a roof system. A high thermal emittance also plays a role particularly in climates that are warm and sunny.

Albedo is usually differentiated into two general types.