Variable speed drives show significant energy savings

The study, carried out in cooperation with Tampere University of Technology in Finland, assesses how long a variable speed drive needs to be in operation before it can save the amount of energy - and therefore emissions - used in its manufacture and eventually disposal, compared to a fixed speed system. The 'ecological payback' was calculated for three ABB drives of 0.75, 7.5 and 250kW respectively. The payback times were short in all instances, decreasing with higher power ratings; the 0.75kW drive compensated in 6 days, the 7.5kW drive in 1.1 days, and the 250kW drive in 0.5 days. The company claims an ABB industrial drive will typically provide a total lifetime saving of around 7,500MWh, equivalent to 3,800tons of carbon dioxide. "Investment calculations today are based on financial payback time – companies normally want their money back in two years or less," says Steve Ruddell, ABB's UK energy spokesperson and general manager, drives and motors. "I believe that in five years' time, there will have been a sea change in the way companies look at investment decisions and they will be just as keen to save CO₂ as they are saving money today. Our study shows that using variable speed drives is one of the most cost-effective measures to achieve rapid and radical CO₂ reductions." Variable speed drives are used in industry to control the speed of motor-driven machinery. Two-thirds of the total electricity consumption in industry is used for driving electric motors. Of this, an estimated 20% is wasted in throttling mechanisms that are used to regulate the flow of air and liquids. Using variable speed drives to control motor speed according to demand makes savings of up to 70% in energy consumption possible.