At a time when the UK water industry is under immense pressure to cut costs and improve service, this can represent an easy win that, in the right application, not only improves efficiency and reduces energy costs, but also extends pump operating lifetimes.

Consider a pump which is being used to empty a 100,000 litre tank. Using our simplified equation above, if we were to pump at 1,000 litres per hour, it will take 100 hours to empty the whole tank. A 100kW pump running for 100 hours would use 10,000kWh which, at 20 pence per kWh, equates to £2,000 in energy costs.

However, if we use a drive to reduce the speed of the pump motor to 80%, this would provide a pumping rate of 800 litres per hour, and the tank will now take 125 hours to empty. The same 100kW pump will now use only 50kW for 125 hours. This will use 6,250kWh which, at 20p/kWh, equates to an energy cost of £1,250 – a 35% saving. It must be acknowledged that not all applications offer the latitude to make changes such as this but, conversely, not all processes necessarily have to be carried out at specific times and could, for instance, be run at night when demand is lower.

This is just one example of how many small changes, when put together, can add up to big energy savings. Many pump applications in the water industry are installed and then not revisited, sometimes for years. Optimising the control philosophy by small amounts will often make no noticeable difference to the effectiveness or outcome of a process, but when you add them up, can save substantial amounts of energy.