A volcanic ore is set to move from the garden and into the house, slashing the costs of insulation and in the process helping to cut energy consumption and pollution.
When it comes to finding the least expensive ways to replace fossil fuels, nothing is as cheap as the energy you never use. Dr Harjit Singh of Brunel University, London, points out that 43% of the UK's carbon dioxide emissions come from heating and cooling buildings, primarily homes, making better insulation a very good investment indeed.
The upfront costs of insulation are often a deterrent, no matter what the long-term savings might be. So cheaper insulation matters. In Energy and Buildings, Singh has argued that if perlite replaces fused silica at the core of vacuum insulation panels it will bring down prices for these panels, while easily beating other sorts of insulation for effectiveness.
“In terms of performance vacuum panels are five to eight times more effective a form of insulation than rock wool or solid foam panels,” said Singh, adding that the benefits are even greater when retrofitting insulation to the walls of existing buildings because vacuum panels are thin enough to fit in locations that materials which rely on depth might not. “Perlite-based panels less than 2 centimeters thick perform as well as 100 millimeters of solid foam so the new technique opens up the real possibility of insulating the 2.3 million UK homes with solid walls but from the inside.”
Perlite is a sort of volcanic glass, formed from water-enriched obsidian. When heated to around 900°C (1650°F), the water trapped inside turns to gas and escapes. In the process it causes the perlite to bubble, giving it the nickname “volcanic popcorn”. The expanded material has a density as low as 32kg/m3, as little as 3% of the unheated version or water.
Expanded perlite has such a wide range of uses that we produce almost two million tonnes a year, including as loose-fill insulation. However, Singh thinks that we can do much better than this, having conducted a detailed measurement of the insulating properties of perlite when used as the core in vacuum panels.
Vacuum insulation panels are well established as far more insulating for a given thickness than conventional materials, but also much more expensive to make. Replacing fumed silica with perlite at the panel's core could cut the cost by more than 30%, Singh argues. It also reduces the environmental manufacturing burden. “Perlite is manufactured at less than 1000°C, whereas making fumed silica requires much higher temperatures, up to 3000°C,” Singh says.
In addition to simply substituting the volcanic ore for existing materials, Singh is experimenting with making smaller panels so that if one is damaged the rest will continue to work.
Like any mineral, perlite is a finite resource but it is sufficiently abundant that gardeners using it to prevent soil compaction and brewers relying on perlite filters don't need to stop yet.
Dr Harjit Singh with a vacuum panel and some of the perlite that he thinks should be used at its core. Brunel University.