Innovative aquathermal project at Hainer See

Just outside Leipzig lies the Leipziger Neuseenland: a former lignite mining region that was recultivated into an extensive recreational area following the closure of numerous open-cast mines in the early 1990s. On the northern shore of Lake Hain – one of the largest in the region at 600 hectares – a vacation village is now being created that embodies the structural change in the region like no other. The open-cast mining holes that have become lakes are not only being used for flourishing tourism and water sports, but also to supply heat.

The village of Hain, which gave its name to Lake Hain, fell victim to lignite mining in the early 1970s. Now the place that was dredged up is experiencing a rebirth as a vacation village. The “Hafendorf Hain” is one of the first of its kind to use aquathermics to supply heat. Aquathermia is the use of groundwater or near-surface waters to heat or cool buildings – in this case, the ambient heat from Lake Hain. This is fed into a central heat pump system and supplies the entire district with green heat from there. This innovative heat supply is being planned and implemented by Quartiersenergie GmbH, a joint subsidiary of Leipziger Stadtwerken and Tilia GmbH. The trial operation started on March 6, 2024.

The modern vacation village consists of 17 buildings with 34 apartments, plus an administration building, two boat garages and a water sports center. There are also cafés and stores. In total, there is 4,400 m2 of heated floor space, which will benefit from the great potential of aquathermics in the future.

A central boiler house located above the village is the heart of the village’s own 800-metre-long local heating network. From here, the heat is supplied to the 29 house connections via two heat pumps, each with an output of 78 kW. A gas condensing boiler acts as a backup to ensure that the heat supply is guaranteed during peak loads in winter when the lake temperature is too low. In summer, when high temperatures are enjoyed by vacation guests, the system is used to cool the buildings.

Die Lösung bietet Vorteile im Vergleich zu:

Air-to-water heat pumps

• Very low noise emission
• Less visible
• 20% less power consumption

Geothermal energy:

• Lower investment costs
• Higher yield at the site
• No drilling risk
• Less space required
• Easier to maintain

With a power requirement of just 220 watts, Oloid propellers are an energy-saving solution that also benefits the lake’s flora and fauna through increased oxygen input. The research and implementation of this innovative technology is one of five pioneering structural change projects funded by the Federal Ministry for Economic Affairs and Climate Protection.

Aquathermics has been used successfully in countries such as the Netherlands for some time, but interest in the technology is also growing steadily in Germany. Its use – not only at Lake Hain – has many advantages over other supply concepts: compared to a solution using near-surface geothermal energy with borehole probes, the investment costs are comparatively low. Compared to a classic air heat pump solution, there is considerably less noise pollution and better energy efficiency. In general, aquathermics enables a relatively high power density with low space requirements. This also makes the technology interesting for large heat outputs.

The use of aquathermics turns opencast mining lakes into an opportunity for the heat transition. With a youth hostel on Lake Markkleeberg, a second project is already being planned in the structural change region of Central Germany. Further projects and strategic market development could provide an important economic boost for the region as a whole.