07 Aug 2021

Integration of Thermal Storage in Existing DH System in the City of Zagreb

The district heating system in Zagreb is the largest in Croatia, with 1,420 MW of thermal power installed that supply 30% of the households in Zagreb.

The upgraded district heating system is owned by TE-TO Zagreb. TE-TO Zagreb operates cogeneration plants, which provide hot water for heating, as well as steam for industrial uses.

In order to increase the efficiency and to lower the costs of the DH system in Zagreb, a buffer storage tank has been installed at the end of 2015. This project presents the first storage tank of such size in Croatia and it already provides significant benefits for the DH utility. With the integrated storage, it was possible to reduce the operating time and fuel consumption of peak-load boilers, and at the same time to increase the operating time of the cogeneration plants. This decreased the annual CO2-emmissions. In addition, due to the installation of the storage system, further invest costs for a new peak-load boiler were avoided.

The project’s motivation was, to achieve multiple benefits with a clear effort in form of invest costs. The implemented measure was intended to prevent the installation of an additional peak-load boiler. Most other benefits were caused by the provided flexibility in heat production. Storages enable to flatten peak-loads (an ideal and quantitative load-profile is illustrated with the graph below) and in the case of cogeneration plants to give flexibility between the production of heat and electricity.

Technical Data of the Installed Heat Storage

• The installed heat storage is classified as a daily, cylindrical thermal storage and nonpressurized water tank.

• Storage volume: 21,500 m3

• Heat storage capacity: 750 MWh

• Minimum charging temperature 98 °C

• Maximum returning water temperature: 58 °C

• Loading capacity: 150 MW

The results of the buffer tank implementation in TE-TO Zagreb showed a number of benefits for the system from both, the technical and the economic side. This project represents a good role model for other large district heating systems in Croatia. Finally, new district heating systems in Croatia already replicated this concept, for example in the small renewable district heating system of Pokupsko.

Information on this page is retrieved from Upgrade DH



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