Multivalent Seasonal Geothermal Cold Storage and Supply for Cooling Needs with Permanent Load Demand - MissElly

In Germany, as well as worldwide, the production of process cooling and air conditioning is almost exclusively electrical. While for space heating and lighting the power consumption is decreasing, in Germany it rises up by 0,7 TWh per year in the area of process cooling, thus by about 2 % per year through the construction of new plants and the global warming. However, the energy transition from fossil to renewable energies can only succeed by reducing the absolute power consumption and greenhouse gas emissions. In the field of refrigeration, there are a variety of applications which require continuous cooling due to their requirements. These include, among others, cooling chambers and cold storage, data centers and test stands. All of these buildings have no need for heating, but only a need for refrigeration. If no customer for the dissipated heat from those buildings is found on site, then the entire heat energy must be released to the environment. Mostly the cold is generated by compression refrigeration machines and free coolers. Without a seasonal cold storage, the cold has to be produced at the moment of the needs and the cold production depends directly to the ambient temperature. This leads to the fact that particularly at unfavorable times particularly much cold must be produced and this happens then with a relatively poor efficiency. But in contrast to electrical energy, cold can be stored well and thus generate at times of favorable conditions. Temporary storage over days and also the seasonal storage is possible, whereby the winter of temperate latitudes turns into a location advantage. In this case, the cold does not have to be generated electrically, but is taken directly from the environment during the cold periods of the year. As part of the MissElly project, a demonstration plant will be developed, designed and implemented to provide around 1,2 MW of cold at a temperature of 18 °C. At this location the demonstrator will be implemented to provide cold for a testing stand for power electronics and accumulator cells. Since for this size and at this temperature the sole use of conventional cold storage, such as ice storage, is out of the question. The part of the cold that is needed during the summer period and which is not possible to be generated with the free coolers will be stored in the underground in a borehole heat exchanger field BHE and in an ice storage during the winter period for seasonal cold storage. Also short term periods, like cold weather conditions or cool nights will then be used for regeneration of the cold storage. A large part of the required cold can thus be obtained by conventional free coolers and does not have to be generated by means of a compression refrigeration machine. In the project the innovative entire system consisting of a test stand, compression refrigeration machine, free coolers, geothermal probe field and ice storage will be tested for its performance and the interaction of the different components. Simulations of the overall system form the basis for the demonstration plant. The simulation results will then be validating at the demonstration plant. First basic calculations show, that such a system would significantly reduce the average power consumption and greenhouse gas emissions at around 50 % in comparison to a standard system without cold storage.