Pumps are widely used in industrial and municipal applications. A known application for a pump is filling or emptying a reservoir, such as a water tank, by transferring fluid according to requirements set for the pumping process. Such an application can operate on the basis of sensing two surface levels: a high surface level and a low surface level.
For example, in a wastewater storage system, a pump can be started when the high surface level of the reservoir is reached and, correspondingly, the pump can be stopped at the low surface level. Fullness or emptiness of the reservoir can be detected by external low- and high-level sensors installed into the reservoir. Fixed-speed pumps can be used in such applications.
The energy efficiency of such applications can, however, be poor. The fixed-speed pump can be oversized for safety reasons. This can increase the energy consumption of the pumping task unnecessarily. It can be difficult to avoid over-dimensioning when trying to comply with safety requirements for the pumping process. Further, a static head of the pumping process can change during the pumping task. For the above reasons, it can be difficult to achieve minimal energy consumption with a fixed-speed operation of a pumping system.
The energy efficiency can be improved, for example, by optimizing the pumping process and/or the pumping system components. The energy efficiency can also be improved by using an energy-efficient control of the pump operation, for example, by using a variable-speed drive.
U.S. Patent Application Publication No. U.S. 2010/0312400 A1 discloses a method and a system for optimizing energy efficiency of a pump arrangement. In the publication, the energy efficiency of the pumping operation is quantified with the term “energy consumption” representing a required amount of energy (or power) to transfer a unit volume of the fluid (this term is also known as the specific energy consumption, Es, in the literature). The method tries to find a rotational speed at which the resulting energy consumption of a pumping system is minimal. The method and system disclosed utilize a permanent or a temporarily installed flow sensor, which is used to determine the energy consumption characteristics of the pump arrangement.
Flow sensors can, however, be expensive and prone to failure. The method disclosed in the U.S. Patent Application Publication No. U.S. 2010/0312400 A1 also does not take into account the effects of changing process parameters, such as the changing static head during pumping, in the selection of the optimum rotational speed. In practice, a change in the system characteristics can have an effect on the energy consumption characteristics of the pump system and the location of the energy consumption minimum.