FAQ Surface Coefficient of Heat Transfer.
The surface coefficient of heat transfer is a measure of how efficient the surface of insulation is at transferring heat from the insulation into the surrounding air.
Most heat transfer through a solid material takes place by thermal conductance (which is why thermal conductivity is so important when assessing insulation performance!) but, heat transfer from the surface into the surrounding air mostly takes place through a combination of thermal convection and radiant heat.
Why is the surface coefficient important?
The coefficient of heat transfer is one of the most important variables that must be considered when determining the outer surface temperature of insulation. A slight change in the surface coefficient can dramatically alter the outer surface temperature.
Since maintaining a surface temperature above the critical dew-point is the way in which insulation stops condensation from forming on pipework operating at below ambient temperatures, a slight change in the surface coefficient can greatly impact on the thickness of insulation required.
Is it better to have a high surface coefficient or a low surface coefficient?
A high surface coefficient value ensures surface temperatures much nearer to the ambient temperature. This results in greatly reduced thicknesses of insulation for condensation control.
An insulation system with a low surface coefficient will lose slightly less energy but will require a much greater thickness of insulation to prevent condensation.
What is the surface coefficient of Kaiflex?
The surface coefficient of heat transfer is not a fixed value - it varies with the temperature of the air, the temperature of the insulation, the shape of the surface, the surface area, wind speed/air movement and the surface emissivity. ISO 12241 contains a series of equations that can be used to calculate the surface coefficient.
Under normal indoor conditions the surface coefficient of Kaiflex will be in the region of 9 W/(m²·K).
With a bright silver-foil finish applied, and again under normal indoor conditions, the surface coefficient of Kaiflex will be in the region of 5 W/(m²·K).