Surface Emissivity

Surface emissivity is a measure of a material’s ability to emit thermal radiation. It is defined as the ratio of radiation emitted by a surface to that emitted by a perfect blackbody at the same temperature. Emissivity values range from 0 (a perfect reflector) to 1 (a perfect emitter).

Most building materials fall within the range of 0.8 to 0.95, meaning they emit most of the thermal radiation they absorb. This property is critical for accurate thermal modelling.

In platforms like EnergyPlus, emissivity can be set for various building components—walls, roofs, floors, and glazing. These values are used to calculate radiative heat transfer between surfaces and their surroundings.

By specifying surface emissivity in Speckel, users can simulate longwave radiation exchange more accurately. This plays a key role in predicting surface temperatures, thermal comfort, and overall energy performance of the building envelope.