Saving the heat of summer for a rainy day

4 min reading time

In late September 2016, at the ‘Energy-producing buildings’ symposium, TNO presented the first prototype heat battery. This device had been constructed in the context of the European MERITS research project. The objective of CREATE (a European follow-up project) is a heat battery designed for the home.

“Doesn’t it look great up there, on its throne” says a visibly satisfied Christophe Hoegaerts of TNO. Together with Juliusz Żach, from Poland, he performs an inspection tour of the shipping container, which is situated on a slight rise, right in front of TNO’s MEC Bouwlab (Lab for Materials, Energy and Construction) in Delft. The top of the container is festooned with solar collectors. Inside, there is a small living area with a sink, an under-floor heating system and cooling for hot days. The other half of the container is taken up by Hoegaerts’ and Żach’s pride and joy. The salt-hydrates-based heat battery that was developed and built by the European MERITS consortium.

Storing heat

The battery consists of large containers, filled with salt. The system was built by a Dutch SME company, RTB De Beijer. It works on the basis of salt hydration. The containers store the heat of the summer sun, and use it in the winter to heat homes and for hot running water. The system in the container is the first prototype. The container was only recently shipped to the Netherlands, from Poland. Today, the heat battery is the main topic at the ‘Energy-producing buildings’ symposium, which is being staged by TNO for property developers, architects and installation engineering companies.

Carefully considering every detail

Christophe Hoegaerts and Juliusz Żach have cooperated very closely on this project. Officially seconded from TNO, Mr Hoegaerts worked as the coordinator of the MERITS project. Mr Żach is the head of R&D at the Mostostal Warszawa construction company. Having been in business for no less than 75 years, this company continually rejuvenates itself by investing heavily in R&D. In the context of MERITS, Mostostal Warszawa was responsible for integrating all the components of the heat battery into the container. Juliusz Żach points to the well-insulated pipes that carry hot water from the central boiler to the salt-filled containers. “It just looks like a bundle of tubes, but it actually involves highly precise control technology. This is all so new that there is no experience on which to build, so each and every part involved deep thought and extensive discussions.” “Every one of the participants involved recognized the value of this project, and they were all totally committed”, adds Mr Hoegaerts. Mr Żach points out that “The very fact that you are building a working prototype together is hugely motivating.


Homes that produce energy

Regarding his company’s motive for participating in the MERITS project, Juliusz Żach explains that “Ultimately, the European Union will require all new homes to be energy neutral, or even to produce energy.” All energy neutral or energy positive homes will inevitably involve energy storage, enabling the summer surplus to compensate for shortages in the winter. Mr Żach adds that “We want to act now, to acquire experience in the area of heat storage.” This was also why the other companies in the consortium got involved, to develop expertise and to establish a patent position. The Dutch Energy Agreement states that the built environment must be energy neutral by 2050.

Home demonstration project

Mostostal and TNO are also cooperating in the CREATE project, which is building on some of the MERITS results. “CREATE primarily focuses on industry. While MERITS was a proof of principle project, CREATE represents a step towards a commercial product”, explains Christophe Hoegaerts. The ultimate goal is a house with a built-in heat battery. That step is scheduled for 2018 when, as part of a demonstration project, a heat battery will be built into a house in Warsaw, Poland.

Making it more compact

According to these two gentlemen, there is plenty of work still to be done. In their view, the main issues to be tackled are the cost and service life of the components, the size of the battery itself, the legislation associated with the installation of heat batteries in homes, and the overall reliability of the system. We are now working to make the heat battery four to six times more compact, which would enable it to fit more conveniently into a home. “We are taking a closer look at each and every component. Could the heat exchangers be more efficient? Should the salt be applied differently? According to Mr Hoegaerts, any ‘wasted space’ must be eliminated. The team wants to make the heat battery four to six times more compact than it is right now. Unlike solar panels on the roof, people will actually have to create a space for a heat battery in their homes. This is easiest in the case of new-build properties. In the future, property developers will integrate energy saving measures like this into buildings’ designs. “That won’t happen without future-oriented legislation’’, emphasizes Christophe Hoegaerts.

“The battery’s containers store the heat of the summer sun, and use it in the winter to heat homes and for hot running water”

A cold winter

The development of a compact heat battery is pivotal to the CREATE project, and TNO is keen to work on the first prototype. It has not yet been possible to test the battery under severe winter conditions. Juliusz Żach explains that “Everything was ready in late February, but then Poland experienced its warmest spring for many years.” Mr Hoegaerts adds that “We want to subject the battery to numerous charge-discharge cycles, to clarify a range of issues, such as the service life of its components.” So is he hoping for a cold winter? “Personally, no, but in the interests of the project, yes.”

Would you like to help develop a battery that will make energy neutral homes, or energy positive homes, possible? If so, then please get in touch with us.

contact person
Ir. Christophe Hoegaerts Locatie Leiden - Sch + Page 1 Location: Location Delft - Stieltjesweg
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focus areas
  • Circular Economy & Environment