High-Temperature Heat Pumps for Urban District Heating

The Qwark³ project in Berlin demonstrates how industrial high-temperature heat pumps can convert waste heat from district cooling into usable district heating. The system targets dense urban environments where space constraints and high supply temperatures are critical technical factors.

Sector coupling in a dense urban energy system
Since the late 1990s, the district cooling network around Potsdamer Platz has supplied offices, residential buildings, hotels, and cultural institutions with locally generated cooling. With an installed cooling capacity of 45 MW operating year-round, the system produces a large and continuous stream of low-grade waste heat. Historically, this heat was released to the environment via cooling towers.

In 2018, BEW initiated the Qwark³ (Quartiers-Wärme-Kraft-Kälte-Kopplung) project together with Siemens Energy to integrate an industrial high-temperature heat pump into the existing cooling center. The objective was to feed recovered heat into Berlin’s district heating network and reduce fossil fuel dependence through sector coupling between cooling, heating, and electricity.

Compact heat transfer as an enabling technology
A major engineering constraint was the limited space available in the existing plant. Conventional shell-and-tube heat exchangers were excluded due to their size and weight. Instead, compact plate heat exchangers supplied by Alfa Laval were selected as core components of the heat pump.

Compared with shell-and-tube designs, the plate heat exchangers occupy roughly one-third of the installation volume while delivering the required heat transfer capacity. Their compactness also reduces structural loads and simplifies installation within the confined plant layout.

For the evaporation stage, a semi-welded plate heat exchanger allows a small temperature approach between the heat source and the refrigerant, supporting a higher coefficient of performance (COP). For condensation and subcooling, multiple brazed plate heat exchangers rated up to 28 bar are used, providing reliable operation at elevated temperatures without gaskets.

Safety, efficiency, and operating parameters
The compact heat exchanger design reduces the refrigerant charge by approximately 80% compared with alternative technologies. This is particularly relevant for the refrigerant R1233zd(E), which is non-flammable and non-toxic but still subject to cost and handling considerations. Lower refrigerant volumes translate into reduced procurement costs and simplified operation.

The high-temperature heat pump delivers a maximum thermal output of 9 MW and supplies around 55 GWh of heat annually. Supply temperatures range from 85°C to 117°C, meeting district heating requirements without additional boosting. All electrical energy required for compression is sourced from renewable electricity.

Measurable impacts on emissions and resources
Since commissioning in 2024, the system has fed recovered heat directly into the district heating network, providing domestic hot water for approximately 30,000 households in summer and space heating for around 3,000 apartments in winter. By capturing heat that would otherwise be dissipated, the project reduces waste heat losses by an estimated 36 GWh per year.

This translates into annual savings of roughly 6,500 tonnes of CO₂ emissions. In addition, reduced reliance on cooling towers lowers freshwater consumption by about 120,000 cubic meters per year. The project illustrates how a digital supply chain of energy flows—linking cooling, heating, and renewable electricity can improve overall system efficiency at the district scale.

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