This new device can make it cheaper to heat your home

Heat pumps are becoming increasingly common in private homes. But storing the heat they produce has not been possible – until now. 

“Think of it as a thermal battery, which stores the heat from the heat pump and can be used later. In practice, this means that people get more energy out of the stored heat. It becomes easier and more comfortable to use, and the energy is also used in a smarter way,” says Galina Simonsen, a researcher at SINTEF.

Simonsen is a member of the team that has developed the new thermal batteries.

“The batteries have high efficiency, and they charge and deliver heat quickly, making it easier to meet the demand. Like when several people are taking showers one after the other, or you need hot water early on a cold morning,” she says.

The solution benefits your wallet too, because excess heat can be stored when electricity is cheap and used later when you need more.

Heat pumps extract energy from the environment – air, soil, or water – and transport the heat into our homes.

But in homes and other buildings, heat demand changes depending on how the building is used, the time of day, and outdoor temperature and weather. 

The research team has worked to meet these fluctuations in a smarter way.

“A heat pump that runs constantly is expensive, energy-consuming, and can lead to overloading the power grid. With the new batteries, heat pumps combine storage and smart distribution of heat,” says Simonsen.

First out with a solution for private homes

Although thermal energy storage already exists, the team is among the first to develop a solution that is efficient enough to be appealing for private homes.

The secret lies in a combination of technical solutions and materials called salt hydrates.

“Unlike the salt we sprinkle on food, salt hydrates lock water into their structure and behave in a unique way when exposed to heat,” says Simonsen.

Substances that can undergo this physical transformation, from melting to solidification, belong to a broader group of materials known as phase change materials (PCMs).

“Think of thermal batteries as sponges: When they’re heated to a certain temperature, they undergo a change from solid to liquid and can store heat. When they are cooled, they return to solid form and release heat again,” says Simonsen.

She explains that they can store much more thermal energy than water, and they retain heat longer, even if the temperature does not change that much.

In other words: More heat and more stable temperatures.

Takes up less space than traditional hot water tanks

Salt hydrates unlock new options for smart heating because they allow heat to be produced when energy demand is low and used later. 

“Salt hydrates aren’t toxic, they’re not flammable, and they're also relatively inexpensive. This makes them a safe and good choice for use in private homes," says Simonsen.

She also adds that heat storage with salt hydrates takes up less space than a traditional hot water tank – up to four times less.

Uses recycled aluminium

SINTEF’s role in the project has been to improve the efficiency – in other words, how the heat is stored and released in the batteries.

“Specifically, we have designed and tested a type of heat sink that improves heat transfer in the thermal batteries,” says Simonsen.

The cooling fins are thin metal structures made from recycled aluminium, which conducts heat very well. This helps the heat spread quickly and evenly through the salt hydrate.

“Aluminium is a light material, has good thermal conductivity, and is easy to form. The use of recycled aluminium also reduces the environmental footprint and costs, and helps to promote a more circular use of materials," says Simonsen.

At the same time, recycled aluminium can be challenging because it may contain impurities that make it more prone to corrosion.

“Corrosion is particularly critical because salt hydrates are tough on aluminium, especially when impurities are present. Without protection, the cooling fins can degrade over time, reducing performance and shortening the lifespan of the entire system,” the researcher explains.

To address this, the researchers used a coating called plasma electrolytic oxidation (PEO), which forms a thin ceramic layer on the surface of the aluminium.

“This coating is similar to what's used on non-stick pans and provides a very durable and corrosion-resistant barrier,” says Simonsen.

About the research

Researchers at SINTEF and the Swiss company COWA Thermal Solutions are collaborating on the solution.

This content is paid for and presented by SINTEF

This content is created by SINTEF's communication staff, who use this platform to communicate science and share results from research with the public. SINTEF is one of more than 80 owners of ScienceNorway.no. Read more here.

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