Inverter control cuts pumping costs at Coventry swimming pool
Retrofitting inverter control units to three large pumps at Coventry Sports Centre has halved their energy consumption.
The running costs of an installation of three pumps at a swimming pool in Coventry have been halved following the installation of Lenze SMD inverters. The pumps return heated water to the swimming pool at Coventry Sports Centre. As installed, the pumps were sized to cope with the maximum predicted flow, which led to motors normally running at part load. The result was low motor efficiency and a low power factor, which drew extra reactive current. The three pumps are installed in parallel to take water from the boilers and return it to the pool. Each pump has a 5.5 kW 4-pole motor. Working loads depend primarily on outdoor temperature, so that in summer one pump can usually maintain the pool temperature, and the other two are switched off. In colder weather, two or, even, three pumps are needed. The pool is open 24 h a day, seven days a week. The solution devised by Modern Drives & Controls of Leicester and engineers at the sports centre involved the installation of a small panel with three Lenze SMD frequency inverters, each with a potentiometer for manual speed control. Power factor was improved immediately, with the current drawn by each pump falling from 9 A to about 5 A. The pumps were running at about 50% load, resulting in a power factor of less than 0.7. Fitting the inverters brought the power fact back up towards 1. Site engineers can now adjust pump speed according to demand — compared to previously only being able to switch pumps on or off. Reducing motor speed by 10% can reduce power consumption by 27%. Early indications are that reducing pump speeds has cut energy consumption by 17%, and total saving with power factor is over 50%. Payback is expected to be less than six months — and even better results are expected with experience.
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