Energy storage is one of the key issues for a sustainable energy supply. An exciting project is also currently underway at the Münchberg campus of Hof University of Applied Sciences. Here, new types of ice batteries for cooling applications are being researched, which can help to sustainably reduce energy and CO2. They are powered by surplus solar energy. We talked to Tushar Sharma, research associate at the Institute for Water and Energy Management at Hof University of Applied Sciences (iwe) and Richard Genes, managing director of the cooperation partner Genes Kältetechnik GmbH from Hof.
Mr. Sharma, please give a brief explanation: What exactly is an ice store and what do you want to find out and achieve with your research?
The technology itself has been on the market for decades and a lot of research has been done at a fundamental level. This means that the process of ice production in the tank by heat exchangers is known in detail. What is new, however, is that with the concept of an ice battery, we want to market an affordable and energy-efficient alternative to the existing electrochemical batteries that have been used to store surplus solar PV energy. This is of course an interesting approach for companies to avoid energy costs and to improve their own CO2 balance.
My research focuses on maximizing self-consumption of solar PV energy to produce ice in the ice battery. This means that the control system is optimized in such a way that the utilization of the ice battery is maximized in order to meet the cooling requirements of the industry under consideration. So far, we have applied the regulatory strategy to 3 different cases, including a bakery and two breweries. The system was modeled in TRNSYS simulation software and the results showed significant energy and CO2 savings.
How would you describe this technically – there is quite an extensive laboratory test stand in Münchberg?
An ice battery is basically just a water storage tank with heat exchangers immersed in it that can form ice by extracting the latent heat energy of the water. In our laboratory on the Münchberg campus, we have experience with various types of heat exchangers, which differ in their appearance. There are star-shaped, spiral-shaped, snake-shaped, flat plates and recently also as capillary mats. We have also written a detailed software model for flat plate and capillary mat heat exchangers based on the ice battery.
We are able to perform dynamic system simulations and compare the simulation results with the experiments performed in the laboratory test bench. Through dynamic system simulations performed in TRNSYS, it was found that the capillary mat ice battery has better performance in terms of ice mass fraction evolution as well as the amount of latent heat exchanged on an ideal operating day. We have validated the flat plate model with the experiments and are currently conducting experiments with the capillary mat heat exchangers.
At the moment we can operate the entire test stand via remote control with the LabView program. Through this LabView program we are able to monitor, measure and control various sensors and valves. This also allows us to simulate a cooling load profile for any operation. This gives us the ability to test different cooling load profiles, different solar PV data based on different weather data, and adjust the control strategy based on different situations.
Mr. Genes, you have been on board with your company from the very beginning of the project. What prompted you to do this and what do you expect from the project in concrete terms?
I was impressed by the idea of putting solar energy, which has so far been produced superfluously, to good use after all. This energy is used to produce and store cold for an ice store. This has great advantages, because more and more cold is needed, especially in the manufacturing industry. I think if the project is pursued properly, there will be many people interested in the technology. The savings are compelling.
Research is also always based on the principle of try & error: what kind of experiments are currently being carried out?
At the moment, two projects are running on the topic of ice storage: The first project is being carried out on the ice storage test stand in the energy laboratory. On this test bench we are testing two different types of ice batteries based on flat plate and capillary mat heat exchangers. The LabView software allows us to implement a hardware-in-loop simulation in which we can simulate different cooling load profiles and test different control strategies. We do this by controlling the flow of the coolant through valves.
The second project is a cooperation project with the Swiss SPF Institute for Solar Technology in the OST University, Rapperswill in Switzerland. In this project we validate the TRNSYS model with the experiments for an ice storage tank of VIESSMANN (Isocal), which is buried in the ground outside the energy laboratory. For a new set of experiments for this project, we installed new soil temperature and ice fraction sensors to get more accurate results. These should help us understand the dynamics of heat transfer between the soil surrounding the ice storage tank and the water/ice in the tank. Once the icing and melting properties of the Isocal model are validated with the TRNSYS model, full system validation is initiated.
Where could the potential applications of technology lie in the medium and long term, if you think about people’s everyday lives, Mr. Genes?
The use of technology will certainly always be in the manufacturing sector. In the private sector, there could also be medium- and long-term integration into domestic supply, e.g. for air-conditioning of living spaces.
The cost-benefit ratio is also always important for the feasibility of research. What is the situation in this area? Can the technology become suitable for mass use in the foreseeable future?
Both the economic and the energetic performance of the technology were theoretically determined through various case studies in the simulation software Polysun and TRNSYS. Recently, a case study on energy and cost saving analysis was also carried out for the traditional brewery “Meinel Bräu” in Hof. Based on the simulation results, the payback period of the plant was estimated to be about 5 years. After this payback period, significant five-digit amounts can be saved annually in energy costs.
What is the next step and when will the project be completed?
At the moment we are planning a continuation project with a company that can develop a physical control system and implement our concept. We would like to be able to use it in real time with an industrial partner in the foreseeable future. As soon as the project proposal has been elaborated, we will apply for project funding in the Central Innovation Programme for SMEs (ZIM).
Thank you for the interview.