Source: Energy & Management Powernews, 03 August 2022
Some municipal utilities and also companies already use large-scale heat pumps. However, they are not yet common. Examples from southern Germany show the application possibilities.
Large-scale heat pumps are considered a key technology to advance the decarbonization of heat supply. This has worked out a study by the Fraunhofer Institute for Energy Economics and Systems Analysis (IEE). According to the study, large heat pumps are particularly suitable for urban areas. Also the energy efficiency federation AGFW measures potential to the large heat pumps
because they make it possible to integrate environmental and waste heat sources meaningfully and above all efficiently into the heat supply. In addition, they are considered efficient heat generators. However, large-scale heat pump projects are not yet common. "It is therefore very important that reference projects are presented," said Paul Wanning, chairman of the board of the German Heat Pump Association (BWP), during a press tour at the end of June. A number of examples were shown, including projects from Rosenheim and Munich.
Large heat pumps - i.e. systems from around 100 kW upwards - are capable of supplying heating and cooling to building and industrial complexes. But they can also supply city districts and neighborhoods as part of heating networks. In a classic local heating network, the heat generated is raised centrally to the required temperature level by means of a large heat pump. Likewise large heat pumps can use waste heat of existing block-type thermal power stations or draw the warmth from waste water.
A kommunaler supplier, which dared itself now to the topic large heat pump for the urban supply, is the public utilities Rosenheim. In 2021 and 2022, these integrated a total of three large heat pumps into the district heating generation of the waste-to-energy plant (MHKW) in Rosenheim, making use of the temperature of the neighboring Mühlbach stream. Each individual pump provides 1.5 MW of heating capacity. Special equipment from Johnson Controls was installed: two-stage water-to-water heat pumps with screw and reciprocating compressors. The pumps draw water from the stream and thus use its environmental heat. The recovered energy is fed to the district heating network via the MHKW.
Rosenheim installed three large-scale heat pumps
In Rosenheim, the heat pumps are part of a total of three innovative CHP systems. The utility won three awards in iKWK tenders in 2018 and 2019. On June 2, 2022, the first of the three plants went into operation. In iKWK, a combined heat and power plant is combined with a renewable heat source - solar thermal, geothermal or even a heat pump - and an electric heat generator to form a system. A power-to-heat plant, for example, can be considered as an electrical heat generator. All components must feed compellingly into the same heat or cooling net and have a common control and regulation technology.
The public utilities Rosenheim want to increase thereby the security of supply and the renewable portion. Through the flexible use of the plants depending on the market and supply situation, the demand-based heat generation in the future would not only be oriented to the consumer, but also to the load situation of the current power grid.
Bayernwerke has already been using heat pumps for years, for example for its own properties or commercial customers. A special plant was realized in 2022 in the east of Munich. At the former site of Pfanni-Werke, in the new factory quarter, "werkkraft Gmbh", a joint company of Bayernwerk Natur and the real estate company OTEC, has developed, among other things, the energy concept for the quarter, which is still under construction. Already 13 buildings are supplied with energy, heat and cold.
The energy concept includes two natural gas-based combined heat and power plants, each with an output of 850 kW electric and 1,050 kW thermal, two high-temperature heat pumps and an absorption chiller. In addition, a heating network, a cooling network and a dedicated electricity network are being created. The special feature is in the heat pumps: these use the waste heat from the absorption chiller, which runs almost all year round. "The neighborhood is growing and needs more and more energy. We saw the heat gap and thought about how we could cover it by using the possibility of heat recovery here," explains Franz Völkl, managing director of Werkkraft.
Water-to-water heat pumps were installed for this purpose. They contribute medium-load heat up to a maximum of 80 degrees Celsius to the heat supply and also support the cooling supply in summer by taking over peak-load cooling. The system is from Carrier and features another technical trick. The condensers of the two heat pumps are piped together in series. The first raises the temperature from 40 to about 60 degrees Celsius, while the second handles the rest of the temperature difference. The manufacturer Carrier specially developed its own control system for this purpose. In this chosen arrangement, the heat pumps achieve an efficiency of 4, which means that 4 kW of heat are generated from 1 kW of electrical energy.
Munich municipal utility connects heat pumps with cooling network
Another example was also implemented in the Bavarian capital, but by Stadtwerke München (SWM). The municipal utility completed a company housing complex in the heart of Munich near its 2021 headquarters. On just under 8,000 square meters, 114 apartments have been created: from one-room apartments to five-room apartments. There is also a daycare center on the first floor. The heat requirement for hot water and heating is generated by two heat pumps from the manufacturer Viessmann, which are integrated into SWM's Moosach district cooling network.
The Moosach district cooling network has been in place since 2014 and supplies the IT City Hall in Munich (service center and computer center), the Dantebad swimming pool and the Moosach bus depot. The network uses groundwater cooling for this purpose. The new heat pumps extract the energy from the heated return water of the cooling network and are in this way part of a heat recovery system of SWM. In the housing estate in the cellar a low-temperature heat pump with 345 kW as well as a high-temperature heat pump with 285 kW were installed.
In addition one built on the greened flat roof a Photovoltaikanlage with 80 kW, which supplies among other things the pumps largely with river. Stadtwerke München sees heat pumps as an alternative if there is no possibility of connecting the buildings to district heating. SWM has used large-scale heat pumps for the first time for one such property in order to gain experience. Further projects are to follow.
Large-scale heat pumps currently have a high priority in research and development, as shown not only by examples from utilities, but also by projects such as the "Large-scale heat pumps in district heating networks (GWP)" real laboratory. As part of the project, which started in April 2021, the AGFW consortium of five utilities and two research institutes would like to further investigate, among other things, the operation of large heat pumps in district heating networks on real plants. The use of large-scale heat pumps will be tested at power plant sites in Berlin, Stuttgart, Mannheim and Rosenheim. The property partners are planning the plants close to existing heat generator sites and want to integrate the heat generated into the existing district heating systems there.
Author: Heidi Roider
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