Frequency inverters optimise the pressure booster station

Hospitals have a tremendous demand for water supply: surgeons wash their hands before an operation, nursing staff wash patients, people take showers and use the sanitary facilities, food is cooked for several hundred people, and each room must be cleaned regularly. Fluctuating water pressure disrupts the tightly scheduled daily hospital routine.

Pressure fluctuations cause enormous costs

In a German hospital, pressure fluctuations between 1 and 1.5 bar at a target pressure of 5.5 bar were a common occurrence. The EBERHARDT Group, the maintenance expert, developed a solution to improve the pressure booster system specifically for this situation. The four pumps already in place continue to be used, and also in other respects no major conversion works were required. Armin Bente, project manager of the EBERHARDT Group explained: “We used a frequency inverter by Mitsubishi Electric for this project. The FR F 740 is designed for the specific demands on the pump management. We realised an energy saving potential of approx. 10% in the optimised system.” The savings in energy are achieved by the functionality of the frequency inverter, which converts fixed voltage and frequency to variable. In doing so, the FR-F 740 provides exactly the kind of performance that is required for the expansion of the currently required pressure. Pressure jumps, which cause excessive water pressure and hence consume too much energy, are thus avoided.

Frequency inverter FR F 740

A special feature of this frequency inverter is a multi-motor function, which enables it to drive up to four motors simultaneously. One of these motors is frequency-controlled while the other motors can be activated or switched off. This technique ensures effective motor management, which is able to respond quickly and flexibly. It is now possible to activate or switch off three of the four pumps when needed, while the fourth motor is driven by reference to the pressure. While in the past the pump capacity of each pump could only be fully activated or switched off, the pressure-related control adjusts to the specific water demand and only supplies the actually required pressure. A pressure sensor is integrated for this purpose. In addition to the constant and even water pressure, it is also possible to respond flexibly to a sharp increase or drop in the demand for water. As a result, the pressure fluctuations of the optimised systems range only between 0.2 and 0.3 bar  - instead of 1 and 1.5 bar - and is hence within a tolerable range. The alternating operation of the four pumps is retained to ensure the life cycle and reliability of the system. Thus the capacity of the FR-F 740 frequency inverter of Mitsubishi Electric was fully used in order to optimise the pressure booster system.