46 n CLEAN ENERGY July/August 2023 www.drivesncontrols.com Germany mines heat and cold from flooded colliery An industrial park on the site of a former Opel factory in Bochum, Germany, will be the first in the world to be heated and cooled using a novel a combination of geothermal energy, district networks, underground storage and large heat pumps. The 70hectare Mark 51°7 park will use water pumped from different depths in a flooded former coal mine to provide heating and cooling at different times of the year. The scheme is regarded as being one of the most sustainable energy concepts implemented so far in Europe. It has been estimated that it will avoid the emission of approximately 3,200 tonnes of CO2 per year, compared to using compared to using a conventional combination of natural gas heating and electrically-powered cooling. To heat buildings on the site, water at a temperature of 30-35°C will be pumped from an depth of 810 metres in the former Dannenbaum mine and then heated further by heat pumps to around 48°C, before being fed into a district heating network. For cooling, water at a temperature of around 18°C will be pumped to the surface from a shallower 340m-deep location and then cooled to 10°C. In both cases, the water will be retrieved via newly drilled boreholes. It is estimated that the energy from the mine water will satisfy more than 75% of the heating and cooling needs of the connected buildings. Any shortfall will be met by a local heating network and conventional cooling systems. The tailor-made centrifugal pumping system to lift the water to the surface was engineered, built and installed by the artificial lifting specialist, Oil Dynamics. The main challenges were the extremely wide operating range for the pumps and frequent load variations. The energy demand will vary greatly depending on the time of the year, time of day, the weather, the day of the week and other factors. The pump speed is adjusted continuously to achieve flow rates from 30–15 m3/h to satisfy these varying energy requirements. In winter, the system will pump mainly from the deeper, warmer well, while in summer it will use the shallower, colder borehole. During the spring and autumn, the system will vary the way it operates. For example, on a spring day, when it is still cold at night and in the morning, but warm in the afternoon, the system will switch between heating and cooling modes. A pump control system that is gentle on the equipment, while also efficient, is currently being optimised. The heating/cooling network is owned and operated by Stadtwerke Bochum and its district heating subsidiary, FUW. The Fraunhofer Institute for Energy Infrastructures and Geothermal Energy (IEG) was responsible for the hydrogeological simulation of the old colliery, the design of the boreholes, as well as the support and monitoring of the drilling operations. The “fifth generation”heating and cooling network, also known as a “cold district heat network”, is said to be particularly efficient because of the low operating temperature of the circulating fluid. Heat pumps in the individual buildings can draw heat or cold from the network as needed. Network losses in the bidirectional, demand-driven system are said to be low and it will be possible to close energy loops between the connected customers. The concept could be implemented at many abandoned mines around the world. In Germany’s Ruhr region, in particular, old coal mines at several locations contain large reservoirs of water. n A novel system being commissioned at a German industrial park will use water drawn from a flooded coalmine to provide heating and cooling at different times of the year The new Mark 51°7 industrial park in Bochum, Germany, will use energy from mine water to provide it with heating and cooling. One of the centrifugal pumps that will bring water from the flooded mine to the surface
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