The Evolution of Insulation
Insulation is evolving with progress towards new, thinner materials. So, where have we come from and what does the future look like?
The science behind insulation hasn’t changed. Insulation is there to prevent the transfer of energy in the form of conduction, convection or radiation.
The most basic insulators rely on the principle of blocking the convection mode of heat transfer. This is achieved by creating a matrix of fibres or bubbles such as in mineral fibre or polystyrene (EPS). The voids in this matrix are then filled with a buffer zone of ‘still’ air. Therefore the insulation properties are limited by the conductivity of air plus the conductivity of the matrix.
Thermal conductivity is usually measured as Watts per metre Kelvin (W/m.K), often called lambda (λ). Still air has a thermal conductivity (λ) of ~0.025 W/m.K. Adding in the support matrix (mineral fibres or polystyrene cells), the sum (air plus support matrix) gives typical λ values of 0.030 W/m.K or worse. Aerogels operate on the same principle. By restricting the movement of air molecules in very small spaces, they can improve the insulation performance to around 0.012 W/m.K minimum.
If you replaced the air with something else less conductive, then that would improve the insulating performance still further. Systems like closed cell PIR or closed cell Phenolic replace the air with a different gas (blowing agent). The thermal conductivity of this blowing agent is significantly lower than air and therefore the overall performance is improved, obtaining lambda (λ) values around 0.020 W/m.K minimum.
Replacing the air with a different gas does provide improved performance, but there is still a gas which adds unnecessary conductivity. During the past few years, improvement in performance of these products has been restricted to small incremental steps. This is not due to lack of effort or research but more due to the limit of the physical properties.
To progress any further, we just have to get rid of the air.
Vacuum, or the absence of air, has no thermal conductivity. Only radiation can pass through a vacuum.
A vacuum insulation panel (sometimes called a VIP) is a specially designed panel that utilises the insulation of a vacuum in a board shape. Although such a simple idea, converting it into a product such as Kingspan Insulation’s OPTIM-R is complicated, but it can be done. With this material long term declared values of 0.007 W/m.K can be achieved. This is 3 times better than existing high performing materials and up to 5 times better than insulation materials from the first generation. This is definitely a significant improvement and denotes a radical step change in thermal performance and can clearly be called the next generation of insulation materials.
The www.optim-r.co.uk microsite is a useful resource with further information about the history of vacuums, vacuum insulation, building applications and links to other similar sites.
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