Low Energy House - What is Aerogel Insulation?
Aerogel is a low density solid state material derived from gel in which the liquid component of the gel has been replaced with gas. The result is an extremely low density solid with several remarkable properties, most notably its effectiveness as thermal insulation
Aerogel is an almost transparent, very lightweight, material that is produced from silica (silicon dioxide) and up to 99.8 per cent air. It is the world’s lightest solid, weighing as little as a third that of air, and exhibiting superb insulating properties. Although aerogel appears to be very light in weight, it has a very high compressive strength. It has been calculated that a block of aerogel that is approx half a kilogram in weight, could support a load of half a tonne.
Production of Aerogel Insulation
Aerogel insulation starts as a silica dioxide gel, similar in texture to gelatine (jelly). Liquid is removed from it without collapsing the gel and the material undergoes super critical drying; where the liquid within the gel is removed leaving only the linked silica network. Aerogel insulation does not collapse but retains its original size and shape.
Extra High Thermal Performance of Aerogel Insulation
Aerogel insulation is very porous with typically 95.7 per cent up to 99.8 per cent air space. Its pore size is 20 nanometres which is very small and less than the mean free path of nitrogen and oxygen in the air. This prevents the air particles moving and colliding with each other which would normally give rise to gas phase heat conduction. Aerogel insulation is extremely good thermal insulation because it considerably reduces the three methods of heat transfer: convection, conduction and radiation. The aerogel insulation with the most effectiveness as an insulator is silica aerogel with carbon added to it.
- Silica aerogel is a good convective inhibitor because air cannot circulate throughout its structure
- Silica aerogel is an especially good conductive insulator because silica is a poor conductor of heat
- Carbon aerogel is a good radiative insulator because carbon absorbs infrared radiation that transfers heat
First developed in 1931, Aerogel is composed of over 90 per cent air, making it a highly effective insulator with the lowest thermal conductivity of any solid. Because of its unique properties, aerogel is now being developed for use in the building industry.
Use of Aerogel Insulation in Glazing Units
With a very low percentage of solid material, heat conduction is much reduced.
When used to fully fill a cavity in glazing units, aerogel granules prevent the movement of air, thus reducing the heat transfer by convection currents. In these circumstances heat transfer can only occur across the glazing unit by radiation.
Light transmission through aerogel is approx 80 per cent per 10mm thickness, providing diffuse light and eliminating the transmission of ultra violet rays. Because it contains such a high percentage of air, it appears semi-transparent. This causes the material to appear smoky blue against dark backgrounds and yellowish against bright backgrounds.
Double and triple wall glass or polycarbonate panels can be filled with aerogel that will provide a high level of insulation and still permit the transmission of light.
Uses of Aerogel Insulation Commercially Available
- Thin strips of aerogel can be applied between wall framing and internal or external sheathing of timber stud and metal stud walls to prevent heat loss through the stud timber or metal material
- Aerogel blanket with high thermal efficiency good compression strength and thin profile make it attractive as an underfloor insulating layer ideal where height is limited.
Aerogel Insulation in Space
Aerogel insulation was used on the Sojourner Mars rover in 1997, when external temperatures dropped as low as minus 67 degrees C, but a temperature of 21 degrees C was maintained inside the rover
The Future of Aerogel
It is predicted that, in the next few years, aerogel will become a common household material. Although its commercial development is limited at present, potentially there are hundreds of products that could be manufactured using aerogel technology.
Thermal Conductivity of Aerogel Insulation
The thermal conductivity of aerogel silica is typically 0.018 W/m K at 10 degrees C.
In the UK, when comparing the thermal values of insulating materials, it is important to remember that the best performing material is the one with the lowest thermal conductivity value
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