Thermal insulation is the method of preventing heat from escaping an enclosure or from entering the enclosure. In other words, thermal insulation can help keep an enclosed area such as a building warm, or it can keep the inside of a refrigerator cold by slowing down the transfer of heat. Heat is transferred by from one material to another by three routes conduction, convection and radiation.
The effectiveness of insulation depends on the conductivity (k value) and the
Insulation for cold stores and transport is usually measured in terms of W/m2/°C. In the building industry this in known as the “U” value but rather confusingly for ATP it is known at the “K” value. A good K or U value is generally taken to be better than 0.4 W/m2/°C.
Typical insulation materials are mineral wools, expanded polystyrene, isocyanates and polyurethane’s.
PU foams achieve the best insulation though this value depends on the density and are commonly used in containers and trailers.
The denser the PU foam, the physically stronger it is, but the worse its insulation effect.
PU foam needs to be expanded with a blowing agent; historically CFC-11 was used which was extremely effective though the insulation gradually decreased at a rate of around 2-5% each year cause by leaching of blowing agent and ingress of moisture. After CFC-11 was banned by the Montreal protocol an interim-blowing agent was used called HFC-141b, which has similar properties. Currently this chemical is banned in Europe but still used in the developing world. The blowing agent currently used is Europe is cyclopentane though this has had a detrimental effect on the thermal efficiency and the ageing properties.
Because of this ageing, and the requirement to achieve the same values of insulation effect with forever-thinner wall thickness, the search for better insulation materials goes on. Until recently it was thought that the vacuum panels would be the insulation of the future but they appear to have fallen from favour due to issues of longevity. Recently a blanket impregnated with aerogels is showing promise and is said to have twice the insulating effect of PU foams but no structural strength.
CRT has worked on several insulation projects:
- Effect mean wall temperature
- Thermal bridging
- Multi component sandwich panels
- Saturation of panels
- Leaching of blowing agents