Construction of a second water supply system

The initial situation

Schongau is a town in Upper Bavaria that forms part of the Weilheim-Schongau district. The majority of the town – in particular the historic old town (Altstadt) – is located on the west bank of the Lech river in the Pfaffenwinkel region. In order to supply the inhabitants, local craft businesses and industry with fresh drinking water, the municipality founded its own company: Stadtwerke Schongau. At the time, the drinking water was supplied mainly via a pipe network in Schwabsoien. Two wells and an elevated tank are also located here. To be able to continue to secure the water supply in the event of faults with the connecting pipes, the elevated tank or the well and to ensure sufficient water reserves (in terms of both quantity and quality), the decision was made to create a “backup”.

“Intelligent” systems technology and control technology make all the difference

In order to guarantee a high level of operational reliability whilst at the same time ensuring that the systems technology operates as efficiently as possible, forward planning that takes into account all eventualities – depending on the initial situation – is required. In this case, installing two pressure boosting systems formed the basis of this. The Hydro MPC 3 CRIE 15-17 system (“small pressure boosting system”), one of these systems, is designed for continuous base load operation. CR series pumps are particularly energy-efficient. Significant changes have been made to their hydraulic system to increase efficiency. The impeller, in particular the impeller blades, have been optimised with laser technology, significantly increasing their efficiency.

Thanks to the modular design, the individual pump components can be combined with each other in a variety of ways, allowing a customised solution to be created for virtually any task. In addition to the aforementioned features, all CR pumps boast sophisticated technology, high-quality materials and low-wear bearings. Another key feature is the unique cartridge mechanical shaft seal, made of highly wear-resistant materials.

Thanks to the cartridge design, the sealing elements can never be incorrectly assembled. The delicate sliding surfaces never come into contact with greasy fingers or dirt. This significantly reduces the chance of failure due to improper installation. The CRIE model is a specification of the CR series. It is a vertical, multistage centrifugal pump with integrated frequency converter. All of its wetted parts are made of stainless steel 1.4301. The suction and discharge ports are opposite each other (inline design). CRIE pumps are equipped with a three-phase, air-cooled permanent magnet synchronous motor (PMSM).

In terms of energy efficiency, the motor is rated IE5 in accordance with IEC60034-30-2. Electronic speed control enables continuous adjustment of the motor speed – and thus pump performance – to meet the current demand.

Key technical data:
Motor power: 7.5 kW
Rated flow: 20.5 m³/h
Rated head: 114.4 m
Max. operating pressure: 16 bar
Number of pumps: 3 x CRIE pumps

The pressure boosting system for base load operation comprises three CRIE pumps. The individual pumps are switched on as needed (alternating pilot pump). In the past, the pumps were activated after reaching a certain load limit following a rather inflexible approach, but this is uncommon nowadays. Instead, the "intelligent" system calculates the optimal economic operation of the individual components. In the event that the first water supply system (pipe network/elevated tank in Schwabsoien) fails or is disrupted, the second pressure boosting system (large pressure boosting system) can be activated. This comprises five CRN 64-3 pumps and can feed water into the pipe network (via the elevated tank) at the maximum extraction rate (Q = 80 l/s) at a head of 110 m. The pumps used for this purpose are identical to those of the “small pressure boosting system” in many respects. However, the CRN pumps are equipped with a three-phase, air-cooled asynchronous motor. An external frequency converter assumes control of the system using the same control system as system 1.

Key technical data:
Motor power: 30 kW
Rated flow: 77 m³/h
Rated head: 76 m
Max. operating pressure: 16 bar
Number of pumps: 5 x CRN pumps

With this systems technology, the “interaction” of the individual components is particularly important. Both pressure boosting systems are customised so that they can carry out specific tasks. This not only increases operational reliability but also ensures energy efficiency, thereby reducing energy costs.