Water and salt in building walls could provide low-cost heat

Water and salt hidden inside cement walls could be used to provide low-cost heat when needed, researchers have said.

A team at the Polytechnic of Turin and the Italian National Research Centre developed the new material, with cement working as a ‘host matrix’ for salt and enabling thermochemical energy storage.

Heating homes and workplaces is responsible for a third of all energy consumed in Europe, the team said, 75% of which is supplied by fossil fuels. While renewable energy will help reduce emissions, it is not always readily available when needed – there is less solar energy available in the dark and cold winter months, for example.

Low cost storage methods can help overcome this issue, and thermochemical methods could be a promising approach. 

“Try to dissolve a good amount of salt in a glass of water… what you will notice is that the glass heats up with some salts and cools down with others,” said first author Luca Lavagna from Turin. “A similar phenomenon is at the basis of our materials, with the difference that instead of liquid water we use aqueous vapor, without dissolving the salt. The aqueous vapor interacts with the salt and produces heat. Once completely hydrated, it will be possible to revert the salt to the starting state by a simple drying process, that allows us to eliminate the surplus water.”

Zeolites are a promising material candidate for such a system, but they can cost dozens of pounds per kilogram – too expensive for heating buildings. Instead, the team focused on cement as a host matrix, thanks to its low cost and high availability.

The total cost of the materials is very low, and the energy cost is reportedly lower than most materials used already. The team said it shows “extraordinary stability”, even after hundreds of heating/ cooling cycles.

The research was published in Scientific Reports.

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