Surface Emissivity

Surface emissivity refers to a property of a material or surface that describes its ability to emit thermal radiation. It represents the ratio of the actual emitted radiation from a surface to the radiation emitted by a perfect blackbody at the same temperature.

Emissivity values range from 0 to 1, where a value of 1 indicates a perfect emitter (blackbody) that emits radiation efficiently. In contrast, a value of 0 indicates a perfect reflector that does not emit radiation. Most building materials have emissivity values between 0 and 1, with typical values falling in the range of 0.8 to 0.95.

EnergyPlus allows users to specify the emissivity of surfaces as input parameters for different building components, such as walls, roofs, floors, and glazing. The surface emissivity is used to calculate the radiative heat exchange between surfaces within the building and with the surrounding environment.

By accurately defining surface emissivity, Speckel can simulate the radiant heat transfer between different surfaces, which is an essential factor in determining buildings' thermal comfort and energy performance. Emissivity values play a crucial role in calculating the net longwave radiation exchange, which influences the building envelope's surface temperatures and energy balances.