Flagship project for climate protection

The project: Large solar thermal energy system for Radolfzell

A thermal solar system was built for the inhabitants of Radolfzell-Liggeringen that would supply over 150 homes with heat, 20 % of which is generated from solar energy. Solar energy collectors installed on an open area of land at the edge of the village absorb the sun’s rays and heat up the water which flows through the collectors. The stored solar heat flows to the houses via a local heating network and can be used for heating and water heating. To cover the increased level of heating needed during winter, heat is additionally generated from biomass and is available on demand via buffer storage.

The client: Stadtwerke Radolfzell

Stadwerke Radolfzell, the municipal utility of the district town of Radolfzell, is located on Lake Constance in the south of Baden-Württemberg. As a high-performance energy provider, it has a strong ecological focus, supplying around 32,000 customers in Radolfzell with electricity, gas, water, heat and Internet as well as operating the local bus service.

The challenge: Minimal wear and a long service life

A central element in the large solar energy system is the transfer station, which is where heat from the collectors is transferred to the consumers. Distributors and pump groups turn the transfer station into a complete heating station, including control and process control systems.

Solar energy has the unique advantage that the heat output can be calculated for a period of at least 20 years. It must therefore be ensured that the pumps and shut-off valves used offer minimal wear and a long service life.

One particular challenge was the limited space available. In order to work as effectively as possible, the transfer station is designed so that all components, such as heat exchangers, pumps, strainers, calorimeters and sensors,  are housed in a very compact space.

The solution: Perfectly optimised pumps and valves

Austrian solar specialist S.O.L.I.D. was responsible for planning and constructing the system. The experienced company impressed with its high-quality technology and economic efficiency, winning the tender in which four other competitors participated. The transfer station was planned and constructed by Kempten-based company RS Wärme. RS Wärme supplies special distributors for heat generation and refrigeration applications. After weighing up the price/performance ratio, RS Wärme opted for pumps from KSB. As usual, KSB was able offer a high level of availability for services and spare parts.

Working in cooperation, the companies took charge of the planning for the transfer station. KSB was primarily responsible for ensuring that the right pumps were selected for the requirements. Using a 3D CAD system, the needs of Stadtwerke Radolfzell were translated step by step into a practical solution.

When it came to selecting the recirculation pumps in the transfer station, the Etaline type series from KSB was the obvious choice. Both its long service life and size were the ideal fit for the developed concept. Etaline has the dimensions of a large canned motor pump and is equipped with a mechanical seal as well as a low-wear squirrel-cage motor, ensuring the long service life required. Furthermore, every pump is fitted with an impeller that is trimmed exactly to the optimum operating point. This ensures that that no energy is wasted hydraulically.

The Etaline’s hydraulic system is based on the Etanorm type series, the world’s best-selling standardised water pump, which is always the first choice when it comes to combining the advantages of in-line design with ease of service. In addition to recirculation pumps from the Etaline type series, SERIE 2000 dual-plate check valves and BOAX butterfly valves are used in the transfer station. These valves are complemented by the BOA-S strainer.

Integrated into the module are two recirculation pumps on the primary circuit and two recirculation pumps on the secondary circuit. Each pump alone is capable of handling the volume flow of around 31 m³/h. However, to keep the level of wear as low as possible, the pumps are operated in alternation. Thanks to its dual-plate design, the SERIE 2000 dual-plate check valve offers excellent hydraulic properties, and the easy-to-operate plates open stably even with the lowest of approach flow velocities. It was possible to install the valves directly in the piping hence providing a highly space-saving solution. Another advantage was their single-piece cast body design which offers a high degree of mechanical strength and corrosion resistance, making it very robust and maintenance-free.
No special tools were required for installation.

When it came to selecting the shut-off valves upstream and downstream of the pump, the decision was narrowed down to the centred-disc, soft-seated BOAX butterfly valve. The advantage here was the hydraulically optimised valve disc and its very low level of flow resistance. This positively impacts the transfer station’s own energy efficiency.
The valves are complemented by BOA-S strainers, whose screens can be easily replaced and cleaned. 

This carefully selected combination resulted in a reliable system for generating energy from renewable energy sources.

Figures I Data I Facts

System: Large thermal solar system
End customer: Stadtwerke Radolfzell

Project data: 

• 4x Etaline
• 1x Movitec
• BOAX butterfly valves
• BOA-S strainers
• SERIE 2000 dual-plate check valves