A pilot project that provides industrial cooling using seasonal subsurface storage will be deployed by the Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (Fraunhofer IEG) and Voltavision at Voltavision’s new battery testing facility in Bochum, Germany.
The MissElly project
The pilot is part of the “MissElly” project, which had a feasibility phase that ran until 2023 and was funded by the state of North Rhine-Westphalia using funds from the European Regional Development Fund (ERDF).The project aims to provide year-round cooling for laboratories and test benches for electrical power engineering using seasonal and short-term cold storage, thus reducing the reliance on conventional refrigeration technology.
“We are designing a geothermal probe cold storage system and operating it so dynamically that it can absorb thermal energy over a wide power range and at speeds that meet demand,” explains project manager Roman Ignacy from Fraunhofer IEG. “The smart control system and flexible system design are probably unique in the world.”
Stationary refrigeration technology accounts for almost 15% of total electricity consumption in Germany. The greatest demand here is for air conditioning, industrial refrigeration systems, and supermarket refrigeration systems. With a share of 95%, cooling is provided almost exclusively by electrically operated air conditioning and refrigeration technologies.
The aim of the project is ultimately to demonstrate a viable path to a significant reduction in energy consumption in the provision of cooling and thus to reduce the emissions of climate-damaging greenhouse gases directly from energy consumption and indirectly through refrigerant leaks by around 50% compared to conventional systems.
Industrial cooling using underground storage
The industrial partner in the project is Voltavision and operates particularly energy-efficient test laboratories, develops test bench equipment and tests battery cells and modules as well as high-voltage batteries for the automotive industry, for example, at its site in Bochum.
During testing, high heat loads can also occur on the test systems for a short time. Cooling this process heat to around 20 °C requires a large part of the company’s energy expenditure. The process heat is released into the surrounding air via a cooling water circuit, chillers and recoolers on the roof. This generally has disadvantages: the system itself is associated with high investment costs when purchasing it, and ongoing operation involves high electricity consumption due to the compression cooling.
“When the outside temperature is low, the cooling water of the systems is already cooled by the ambient cold in the air. This free cooling is not possible on very warm days, so power-intensive compression cooling must be used,” explained Lore Mall, project manager at Voltavision.
“In order to increase the free cooling share to up to 100 percent, knowing that summers are getting hotter, the idea arose to use cold stored in the ground from winter in summer. After the promising feasibility study, we are very pleased to now be implementing the project together with Fraunhofer IEG at our location in the Bochum Technology Quarter.”
The pilot project
The MissEllyDEMO project will be the first to use a field of geothermal probes as storage for an industrial application with a permanent need for process cooling. Between 30 to 40 probes will be laid at intervals of 5 to 10 meters and up to 100 meters deep. A brine will circulate as the operating medium in the closed pipe loops, absorbing the process heat to be dissipated into the subsoil. The smart and predictive operating control will regulate how the probes are connected on a daily basis, for example in parallel, in series or in certain zones, in order to ensure optimal heat transfer during predictive charging and discharging.
The free and otherwise unused cooling capacity of the cooling towers is used to regenerate the cold reservoir. These therefore run not only for a few hours a day during peak load times, but continuously whenever the outside air temperature drops low enough.
In addition, the probe field designed by Fraunhofer IEG can also be “charged” with cold from the night and winter by lowering the temperatures underground, which are usually between 11 °C and 13 °C, to temperatures just above freezing. This means that Voltavision’s test systems always have enough sustainable cold available.
This prototype is intended to show how the dynamics of free, regenerative but volatile environmental cooling can be sensibly integrated into a real economic process. “With our geothermal probe storage facility, we are creating a cooling supply system for industry that meets the high requirements for security of supply and flexibility through the use of a seasonal cold storage facility, the introduction of environmental cooling and the operational optimization of cooling systems in the overall system,” adds Anja Hanßke, Head of the Competence Center Heat Networks 4.0 at Fraunhofer IEG.
The operational experience will also provide the development paths for expansion to other processes and other users. For this purpose, Fraunhofer IEG will create a digital twin of the system which provides scientific monitoring and planning for operational and design optimization.
