Thermal emittance
Encyclopedia
Thermal emittance is radiant emittance of heat
. This should not be confused with thermal emissivity
, which is a spectrum-dependent ability of a material to release absorbed heat, although the terms are related. Emittance, M, is given in units of watts per square meter (W/m2), and emissivity, e, is a scale factor, between 0 and 1, used along with temperature
, to calculate emittance for a given material.
For building products, thermal measurements are taken for wavelengths in the infrared
. 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 roofing surface with a high thermal emittance will both absorb heat from the sun and radiate it back into the atmosphere more-readily than one with a low thermal emittance. Exposed reflective metal roof
s usually have a lower thermal emittance than other choices.
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
. This should not be confused with thermal emissivity
Emissivity
The emissivity of a material is the relative ability of its surface to emit energy by radiation. It is the ratio of energy radiated by a particular material to energy radiated by a black body at the same temperature...
, which is a spectrum-dependent ability of a material to release absorbed heat, although the terms are related. Emittance, M, is given in units of watts per square meter (W/m2), and emissivity, e, is a scale factor, between 0 and 1, used along with temperature
Temperature
Temperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
, to calculate emittance for a given material.
For building products, thermal measurements are taken for wavelengths in the infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
. Determining the thermal emittance and solar reflectance of building materials, especially roofing materials, can be very useful for reducing heating and cooling energy costs
Energy accounting
Energy accounting is a system used within industry, where measuring and analyzing the energy consumption of different activities is done to improve energy efficiency.-Energy management:...
in buildings. A roofing surface with a high thermal emittance will both absorb heat from the sun and radiate it back into the atmosphere more-readily than one with a low thermal emittance. Exposed reflective metal roof
Metal roof
A metal roof, often referred to as a tin roof, is a roofing system made from metal pieces or tiles. It is a component of the building envelope.-History:...
s usually have a lower thermal emittance than other choices.