Ir Emittance Roof

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

Ir emittance roof.

As such it plays an equal if not greater role in defining what s a truly energy efficient roof. 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. Applied them to stone coated metal shakes thermal performance of the stone coated metal roofs. However emittance also matters because the higher the emittance the more readily the roof surface will radiate long wave ir heat to the sky.

A low thermal emittance provides improved get content here. For building products thermal emittance measurements are taken for wavelengths in the infrared. 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. One example is a metal wrench left in the sun which is hot to the touch because it has a low emissivity value.

Cool roofs achieve this by reflecting some of the infrared ir light from the sun. During the daylight hours a roof is constantly subjected to solar energy striking its surface. They can also reduce the urban heat island effect. With the exception of a metallic surface most roofing materials can have emittance values above 0 85 85.

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. Link between energy savings and emissivity. Scientists use a number between 0 and 1 or 0 and 100 to express emittance. The effects of infrared blocking pigments and deck venting on the metal roofing manufacturers and pigment colorant manufacturers selected appropriate irbcps.

The larger these two values are the cooler the roof will remain in the sun. 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. Emittance on the other hand refers to the roofing material s ability to shed heat rather than retain it. 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.

Just like reflectance the emittance of the roof is measured on a scale of 0 to 1 with 1 being the highest.