Potting soil ingredient can heat your home

Scientists have discovered that adding a common winter ice melter chemical to vermiculite enables it to store vast amounts of summer heat for months.


Ian Johnston, Science Correspondent
The Independent, Friday 9 September


A mineral used by gardeners for potting plants could be used to heat homes in the winter using the power of the summer sun, scientists have discovered.

When the salt calcium chloride is added to vermiculite, which is normally used to pot plants, it takes on an extraordinary property.

Blow warm air over it — breathing will do — and it dries out. But if you then expose it to cold, damp air, it absorbs the water and releases heat.

Dubbed “magic beans” by researchers at Swansea University, the material can be used to store heat energy for months in this way.

A fridge-freezer-sized box of it could be used to provide effective heating for a domestic house for potentially months during the winter.

A trial is already underway at a building on the Tata steelworks plant at Port Talbot, Wales.

It is used in conjunction with simple solar thermal panels made from a sheet of metal that intensify the heat from the sun.

Professor David Worsley, an engineer at the university, said: “In the summer, we’ve got this massive amount of hot air collected by solar thermal collectors.

“We wanted to make a material you could put heat into and save it for the winter.”

While the material was originally developd at the University of Nottingham by Sean Casey, Professor Worsley and others at Swansea are working out how to incorporate it into buildings.

“You drive hot air over it, it drives all the water off and in the winter all you do is introduce cold damp air. It absorbs the water and releases energy,” he said.