FAQ Surface Emissivity.
Surface emissivity is a measure of how efficient a surface is at transmitting radiant heat.
Represented by a dimensionless value between 0 and 1, with 0 representing the lowest emissivity possible and 1 representing an idealised black emitting body, the surface emissivity is one of the variables that influences the surface coefficient of heat transfer.
How is the surface emissivity related to the surface coefficient?
The surface coefficient of heat transfer is a combination of thermal convection and radiant heat from the insulation surface.
The radiative contribution to the surface coefficient is determined largely by the surface emissivity.
Indoors, with little air movement around the insulation likely, the radiative contribution to the surface coefficient dominates. Outdoors the convective contribution becomes far more significant and even big changes in the radiative contribution do not greatly impact on the overall surface coefficient.
What is the surface emissivity of Kaiflex?
As a dark, matt black, rubber Kaiflex generally has a high surface emissivity. Applying a bright “silver” material - such as Kaiflex Protect F-Alu or Kaiflex AluTec - around Kaiflex results in a low emissivity finish.
What are the advantages of a high emissivity surface finish?
Materials with high emissivity surfaces result in higher surface coefficients of heat transfer. This makes materials with high emissivity surfaces far more effective at controlling surface temperatures.
For pipework indoors an insulation material with a high emissivity surface finish will often be able to stop condensation from forming on air-conditioning pipework at less half the thickness that the same material would require if a low emissivity surface finish were applied.
What are the advantages of a low emissivity surface finish?
Materials with low emissivity surfaces are slightly more efficient at preventing energy transfer.
An insulation system with a low emissivity surface finish will normally save 5 - 10% more energy than the same insulation system at the same thickness with a high emissivity surface finish.