Fig. 3: Simulation values and measurement results from the 1st and 2nd operating year.
© ZAE Bayern

Fig. 4: Energy balance for the local heating system.
© ZAE Bayern
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High efficiency thanks to low return temperatures

All project participants are very satisfied with the return temperatures achieved of 30 °C. The experience gained shall now be incorporated into further projects organised by Munich’s municipal utility company. “We require the lower return temperatures to increase the degree of utilisation in all sub-systems,” explains the scientific project head, Manfred Reuß from ZAE Bayern. This increases the storage capacity of the heat storage tank, reduces losses in the heating network and increases the system efficiency of the overall system. “It’s important that the local heating and household networks are not hydraulically decoupled. That means that the heat transfer fluid from the local heating network flows directly through the heating systems in the individual homes. Furthermore, there are no domestic hot water storage tanks in the homes. In addition to the low heat losses, the operating energy used, for example, for the circulation pumps can also be saved,” explains Reuß. A pump in the heating centre ensures that the liquid is circulated throughout the entire local heating system. The heat is only transferred to the domestic heating systems in transfer stations located directly in the homes. Here the domestic water is directly heated with freshwater stations. The transfer station contains all the control devices for the space and domestic hot water heating as well as the measurement equipment for calculating the heating costs. Some houses are furnished with a combination of radiators with serially connected underfloor heating, while another part is only equipped with underfloor heating. “This requires diffusion-tight pipes through which the water from the local heating network can flow directly,” according to the scientist. However, not all the developers have used this in their underfloor heating systems: “In order to prevent corrosion in the local heating systems in such cases, we had to install plate heat exchangers in the homes to hydraulically separate the systems,” explains Reuß.


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