Green Roofs Emittance And Albedo

When a roof can deliver high solar reflectance or albedo and thermal emittance values it is known as a cool roof.

Green roofs emittance and albedo.

Sustainable roofing glossary albedo. Cool roofs use roofing materials that are highly reflective also called high albedo roofs of the sun s radiant heat. Cool roofs are able to reduce heat gain in buildings due to the high solar reflective index. A vinyl roof can reflect three quarters of the sun s rays usually far more and emit 70 or more percent of the solar radiation absorbed by the building envelope.

Green roofs provide a thermal mass layer which helps reduce the flow of heat into a building. However emittance also matters because the higher the emittance the more readily the roof surface will radiate long wave ir heat to the sky. Albedo or solar reflectance is a measure of a material s ability to reflect sunlight including the visible infrared and ultraviolet wavelengths on a scale of 0 to 1 an albedo of 0 0 indicates that the surface absorbs all solar radiation and an albedo of 1 0 represents total reflectivity. Flat or low pitch roofs in particular need to meet a reflectance value of 0 65 and an emittance value of 0 50.

Cool roofs by chris wark energy editor originally posted march 2 2011. This is due to the nature of the roof itself. They can also reduce the urban heat island effect. A standard white reflectance 0 08 and emittance 0 90 is 100.

Albedo albedo or solar reflectance is a measure of a material s ability to reflect sunlight including the visible infrared and ultraviolet wavelengths on a scale of 0 to 1. A cool roof prevents heat absorption by reflecting the sun s heat and then emitting its radiation back into the atmosphere. They may also have a high thermal emittance value. Emittance is a measure of how much of the absorbed radiant energy is given off into the atmosphere keeping the surface cooler as a result.

The solar reflectance of green roofs varies depending on the plant types generally 0 3 0 5. Although cool roofing is one of the most significant green technologies today it is not a new concept. Peck is the founder and president of green roofs for. Finally keep in mind that the style of your roof will affect the necessary reflectance and emittance values your new roof should meet.

An albedo of 0 0 indicates that the surface absorbs all solar radiation and an albedo of 1 0 represents total reflectivity. An energy calculator for green roofs. By doing this cool roofs allow for a more comfortable and controlled indoor environment. Green roofs may not reflect as much as a cool roof but do have other benefits such as evapotranspiration which cools the plants and the immediate area around the plants aiding in lowering rooftop.

Green roof energy series part 6.