SolarFreezer commissions Saxion to improve clean heating system

It is possible to sustainably heat well-insulated houses or, for example, offices with the SolarFreezer, with solar panels for heat and electricity on the roof and a buffer bag in the crawl space. The technique has already proved itself, the system works and it has already been applied in more than one hundred building projects in the Netherlands. However, SolarFreezer BV still contacted Saxion’s Sustainable Energy Supply department, says researcher Hans Gelten. An earlier study of the system revealed some challenges, which could improve the operation of the buffer bag in particular. The research team will work together with Saxion students from various programmes from 2020 to 2023, and investigate technical solutions to optimise the SolarFreezer.

How does the SolarFreezer work? The system makes efficient use of solar energy throughout the year. Excess heat in warm periods is directed into a large water buffer. This heat is used by the heat pump when the outside temperature drops, together with the heat from the water’s solidification. This supplies the house with energy in the winter. “A relatively large amount of energy is released when the water in the buffer bag solidifies into ice particles when the weather gets colder. This energy plays an important role in driving the heat pump”, explains Hans. “But this formation of ice in the buffer bag also creates a dilemma. The ice also forms around the pipelines in the water bag, which has an insulating effect that we do not want there. On the other hand, you want the ice to form to generate energy. The ice is allowed to float around in the buffer bag, but it cannot sit too tightly around the pipelines. That is the challenge of our research.”

This specific problem prompted Jacques Mathijsen of SolarFreezer BV to seek contact with Saxion. He explains: “We do not have a large development department ourselves. Working together with Saxion is great for both of us: we formulate assignments that are interesting for students, but they also give us opportunities to further develop our product in many cases. We also feel a certain social responsibility to give students the option to further develop themselves through practical research. We notice that their input is refreshing; they have a different perspective than we do as a company.”

Simon Hageman, who is involved in the project as an associate lecturer, agrees with this: “One of our students immediately drew a parallel with the aircraft industry at one of the first meetings, where certain materials can prevent the undesired forming of ice on the wings. We are also researching the effects of a textile coating or running water on the ice formation around the pipes in the buffer bag. This out-of-the-box thinking only strengthens the research.” The students from the Chemistry, Chemical Technology, Fashion & Textile Technologies, Technical Physics and Mechanical Engineering programmes, among others, have already conducted plenty of research into solutions in a short time, through a Smart Solutions project group. “We were able to make perfect use of their creativity, curiosity and brainpower. It could not have worked out any better”, says Simon.

Working together with Saxion is great for both of us: we formulate assignments that are interesting for students, but they also give us opportunities to further develop our product in many cases.

The department will combine all the positive results that the students have obtained after the first research period, says Hans: “We want to combine this fine harvest of thoroughly tested solutions into an integral proposal with which Jacques can further optimise his system. We have already made enormous improvements in only a short time. Working closely together with his company all this time has also been great. The students gave presentations in which they shared their progress with Jacques. It is nice to see how enthusiastic he became as a result. The students, in turn, learned a lot from the research assignments, and these presentations inspired them to learn from each other.”

Is the SolarFreezer the ultimate solution for the energy transition? Simon: “It is one of the solutions, alongside other developments. Not every household has its own roof for solar panels. Not all houses have crawl spaces, and not all houses are well insulated. Nevertheless, this system is a great solution for a large number of homes and offices. The ice melts and solidifies at a temperature of zero degrees. Houses are heated at a low temperature. And if you want to heat your home, a smaller difference in temperature between the energy source and the output temperature increases the energy efficiency. This means that not much is needed to bring the temperature back to a pleasant level in well-insulated houses. These kinds of applications are very suitable for that.”

SolarFreezer BV is thinking about the next steps to further expand the concept, now that the research and the cooperation between Saxion and SolarFreezer have entered a new phase. Jacques: “We are moving towards a development that collects rainwater before it ends up in the sewer. This buffered water, combined with solar energy, can be used to provide heat. The rainwater provides thermal energy, but it can be used for flushing the toilet, watering the garden, or as a supply for the washing machine afterwards. There are many ways in which we can expand or broaden the concept, so being able to work together with Saxion is a great luxury. Especially with such a multidisciplinary team of students and especially when it comes to these kinds of future applications that contribute to the energy transition.”