Ir Emittance Roof

In general a cool roof is one that has relatively high solar reflectance and high thermal emittance.

Ir emittance roof.

The larger these two values are the cooler the roof will remain in the sun. Cool roofs achieve this by reflecting some of the infrared ir light from the sun. Solar reflectance and thermal emittance are the two key material surface properties that determine a roof s temperature and they each range on a scale from 0 to 1. They can also reduce the urban heat island effect.

Just like reflectance the emittance of the roof is measured on a scale of 0 to 1 with 1 being the highest. However emittance also matters because the higher the emittance the more readily the roof surface will radiate long wave ir heat to the sky. With the exception of a metallic surface most roofing materials can have emittance values above 0 85 85. Applied them to stone coated metal shakes thermal performance of the stone coated metal roofs.

As such it plays an equal if not greater role in defining what s a truly energy efficient roof. The effects of infrared blocking pigments and deck venting on the metal roofing manufacturers and pigment colorant manufacturers selected appropriate irbcps. The term solar reflectance is a measure of the amount of that solar energy that is immediately reflected from the surface. Scientists use a number between 0 and 1 or 0 and 100 to express emittance.

Link between energy savings and emissivity. Emittance on the other hand refers to the roofing material s ability to shed heat rather than retain it. The thermal emittance of a roof or wall component is mainly affected by the characteristics of the layer that is exposed to the solar radiation. Determining the thermal emittance and solar reflectance of building materials especially roofing materials can be very useful for reducing heating and cooling energy costs in buildings.

A low thermal emittance provides improved get content here. In today s market a cool roof is defined by the reflectivity and emissivity requirements set by either title 24 from the california energy commission or by the energy star program. In common construction applications the thermal emittance of a surface is usually higher than 0 8 0 85 except for those layers that are based on metallic components for example aluminum shingles. A cool roof on nonresidential buildings is defined as one with a 3 year aged solar reflectance of at least 0 55 and an infrared emittance of at least 0 75 or minimum sri of 64 in climate zones 2 through 15 for low slopes 2 12 or less.

For building products thermal emittance measurements are taken for wavelengths in the infrared.