Pump drive power use can be cut by up to 60%

London – Experts at the German Fraunhofer Institute estimate that the power consumption of most pump systems could potentially be reduced by around 60%.

Pumps for process engineering and building services applications are designed to meet calculated peak demand and provide the pressure needed to ensure that the required flow rates can be maintained. In practice, however, actual consumption is often only a fraction of the rated demand which, in turn, means that only a fraction of the pump output is required.

If the power is not adjusted for low flow operation, the pressure generated shifts along the pump characteristic curve, which increases the energy consumption of the pump drive.

Low flow operation incurs excessively high operating costs because the discharge head and flow rate are inversely proportional to each other and the working energy consumption (kWh/m³) increases as the volume flow rate decreases.

Huge savings can, therefore, be made by reducing the amount of power to what the pump actually requires. Indeed, this potential cannot be underestimated: on industrial and business premises, for example, pumps in a range of different sizes and designs are used in building services and process engineering.

One energy-saving approach involves using special control systems that accurately match pump output to the momentary requirement are instrumental in utilising the savings potential.

Pump manufacturer KSB, for instance, has developed PumpDrive to continuously adjusts pump performance to match varying operating conditions. The motor-mounted control system can be used on all three-phase pump motors from 0.55 to 45 kW regardless of their make. Industrial and business enterprises can thus improve their equipment’s energy efficiency and cut the cost of operating and maintaining pump systems.

KSB lists potential applications as including: Cooling circuits; Transport of process water and chemical liquids; Heat transfer systems; Heating systems in production areas and office buildings; Refrigeration and air-conditioning; and Disposal of waste water

Speed tuning to reduce power consumption

If the pump output is too high, this not only consumes excessive energy and incurs additional energy costs but also results in substantial energy losses, particularly in systems for the transport of warm or chilled water.

The most effective way to reduce the power consumption of pump drives is to implement an output-related speed control system. This was the impetus for pump manufacturer KSB to develop PumpDrive, a continuously variable speed control system that enables operators to precisely match pump performance to actual requirements.

This multi-vendor-capable control module has been designed to ensure that all pump applications in the building can be managed with a single control type and with optimised energy consumption. An important feature of the speed control system is that it can be mounted directly on the pump motor in a separate housing. As the following examples show, output-based speed control not only reduces energy consumption but also prolongs the service life of the pumps.

KSB went on to cite an application for the disposal of waste water, involving a dual-pump sewage lifting unit installed in a collection sump.

The speed control system enables the flow rate to be adjusted in line with the level and amount of waste water. Even a constant inflow of waste water can be discharged continuously without the need to repeatedly start and stop the pumps (the drainage pumps should ideally operate continuously). This not only reduces wear and tear on the pumps but also eliminates surge pressures in the connected discharge lines.

In order to adjust the pump speed, KSB’s control system uses the specified operating point, which is located at the intersection of the pump and piping system characteristic curves.

As the flow rate decreases, PumpDrive registers a rise in pressure, calculates the discharge rate as a function of the target pressure, and reduces the speed accordingly. When consumption starts to increase again, the pump control system responds to the resulting drop in pressure by increasing the pump output.

To manage the different power requirements, the control unit takes into account the friction losses in the piping between the pump and consumer installation as if the differential pressure were being measured directly on the consumer installation itself. This is another effect improving energy efficiency because for each period of low flow operation, the pump only produces the flow pressure required to compensate for the friction losses in the piping towards the consumer installation.

Depending on the application, the energy consumption of the drive can be reduced by up to 60%. In addition, output-based, continuously variable speed control ensures that the pump can be started smoothly and reduces the number of start / stop operations which, in turn, reduces the mechanical loads on the system.

Ready-to-use control system
PumpDrive is installed directly on the motor housing, which means that it can be used in any application and with any make of pump. This also means that energy-efficient pump operation can be achieved without the need for additional, separate measuring and control components. Thanks to PumpDrive, all the pumps installed in a building can now be controlled by means of a standardised control system.

According to the manufacturer, the system is installed and commissioned using the “plug-and-pump” principle.

For example, PumpDrive immediately recognises a connected sensor without the need for additional parameterisation and can, therefore, switch directly to closed-loop control. The control module is available in four different sizes covering power ranges of 0.55 - 3 kW, 4 - 7.5 kW, 11 - 22 kW, and 30 - 45 kW, which means that it can be implemented in almost any application.

The output-based speed control system can also be used in systems comprising more than one pump. A multiple pump configuration in a central cooling water distribution system can, for example, be equipped with a “PumpDrive Advanced” model which then acts as the master. A dual-pump control module is available for the twin pumps typically used in heating and air-conditioning systems.

The control panel on the housing features an easy-to-read backlit display. It outputs continuous readings of the actual speed and allows the user to adjust the speed and other setpoints locally. The housing is also available without a control panel for applications in which manual changes are either not desired or not appropriate. A PI controller, as well as digital and analog inputs and outputs for standard signals, support all the typical pump control modes.

Motor protection functions are also provided as a standard and the system can be integrated in building management systems. If the pump control system is used in building services systems, it can be monitored centrally based on the LON standard. Furthermore, processes can be automated by means of a building management system. PumpDrive can also communicate with Profibus in industrial production processes.

Adjusting the pump output by means of speed control helps reduce the life cycle costs (LCC) of pumps. KSB has developed a life cycle cost comparator that compares conventional pump systems with variants equipped with a variable speed drive, enabling users to quickly and easily determine the profitability of investing in a variable speed system such as PumpDrive. The program displays the results in charts, graphs and tables, allowing the initial investment to be seen in relation to the energy and follow-up costs over the long term.

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