Variable Speed Drives save energy in Pumping Applications

When building a new pumping system, “Safety Factors” are often taken into account. These “Safety Factors” take into account future upgrades, wear and tear, breakdowns etc. Often, there are multiple parties involved in commissioning a pumping station, and so the safety factor can grow exponentially.

What does this mean for Pumping Systems?

It means the pumps often deliver much higher flows than is required for the applications. To overcome this, throttling is used to regulate flow in a pumping system. The problem with throttling is the motor is still running at full speed and works even harder as it needs to work against the restriction caused by throttling.

Using Variable Speed Drives in Pumping Systems

Utilising an Electrical variable speed drive is the simplest and most economical way of controlling the pump and matching it to the pump system. A Variable Speed Drive will reduce the speed of the motor, ensuring no more energy than necessary is used to achieve the required flow.

The BPMA state;

“It is estimated that £74 million of savings have already been made by using Variable Speed Drives and High Efficiency motors”.

A worked example with Centrifugal Pumps:

A centrifugal pump running at half speed consumes only one-eighth of the energy compared to one running at full speed. This is because the torque needed to run a pump is the square of the volume. For instance, reducing the pump speed to 80% only requires 64% of the torque (0.8x0.8) (Tµn2). Furthermore, to produce 64% of the torque only requires 51% of the power (0.64x0.8) (Pµn3), as the power requirement is reduced in the same way.

The explanation for this lies in the pressure difference across the impeller. When less pressure is produced, less acceleration of air or fluid across the impeller is required. It is the simultaneous reduction of acceleration and pressure that multiplies the savings.

Resources for calculating energy savings in pumping applications:

Download this Energy Savings Calculator which helps you work out exactly how much you can save by replacing a fixed speed damped or throttled centrifugal load with a variable speed drive controlled solution.

Download this free whitepaper covering Variable Speed Drive - Best Practice Guide.

The guide clearly defines; in simple terms the information required when planning to use an electronic Variable Speed Driven Pumping System. The guide focuses mainly on applications within the Industrial Sector, however the principles used will be applicable to most pumping applications.