A quick win for energy cuts: VSDs

Sensemaking / A quick win for energy cuts: VSDs

Variable speed drives can reduce energy bills by as much as 70%, with a payback of less than 12 months.

23 Nov 2011

Variable speed drives can reduce energy bills by as much as 70%, with a payback of less than 12 months.

Multinational engineering giant ABB is promoting the use of a technology that has existed for more than four decades, in a drive to help organisations reduce their energy consumption. The Swiss-Swedish firm says that employing variable speed drives (VSDs) in industrial pumps, fans and other devices, can reduce energy bills by as much as 70% with a payback of less than 12 months.

Although by no means the only major manufacturer making VSDs, ABB (which developed its first VSD in 1969) has embarked on a mission to encourage their use in the UK after establishing a 50-person Energy Appraisal Team in the country, providing organisations with free assessments to identify applications that can benefit from the installation of VSDs.

ABB points out that around 65% of the total electricity used at industrial sites is consumed by electric motors, so widespread adoption of VSDs would lead to substantial savings over traditional, fixed-speed motors. These have two problems, says independent energy consultant Trevor Floyd. “The first is that they are often overspecified and oversized for the application, so you are constantly wasting energy from normal use,” he says. “The second is that the relationship between the load and the power consumer is curved, rather than linear.” So when you reduce the load, the power consumed isn’t proportionally reduced. This means that a 50% load could consume something like 90% of the power used when the motor is working at its full rate, explains Floyd.

VSDs, on the other hand, can achieve that linear relationship between load and power, so that energy used is directly proportionate to the work being done. Floyd suggests key energy saving applications could include boiler rooms and air handling units. “Pumps and fans are also ideal for VSDs, because the drives are so easy to fit into the supply circuit”, he adds.

The UK’s Carbon Trust has long promoted the use of VSDs in industry. UK businesses can even make use of interest-free loans from the Trust to invest in VSDs, along with other energy saving equipment. In one case study, the Carbon Trust showed that fitting a VSD to just a single boiler forced-draught fan at Dairy Crest Severnside, saved the milk producer £1,840 annually as well as 5.2 tonnes per year in carbon savings.

Brian Horne of the UK’s Energy Saving Trust is similarly positive about VSDs’ potential, describing them as “a major opportunity for saving energy in the industrial sector”. – Jon Mainwaring


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