Drives deliver energy savings

Written by: Justin Cunningham | Published:

The trend toward variable speed drives (VSD) has been exacerbated by the spike in energy prices and a change in attitude toward improved energy efficiency.

"You can change light bulbs or change your electricity supplier, but any significant saving for industrial users is going to come from effectively controlling motors," says Andy Parker-Bates, UK platform marketing manager at Parker SSD Automation, part of the Parker Hannifin Group. "As an industry, we have banged the drum about this for a number of years, but it has been slow going."

VSDs are primarily used to control AC motors and allow motor speed to be varied. The technology might commonly be used for pump and fan applications – for example an extraction system – which has been designed with a worst case scenario in mind. That calculates a certain flow rate requirement and the next size up motor is selected. But this leads to inefficiencies.

"These fans can be as much as 20% oversized," says Parker-Bates. "And they are continuously run at full speed consuming the maximum power. A mechanical device is used to throttle and vary the airflow."

But, a VSD slows the motor itself. And when incorporated with a sensor that constantly monitors flow, the speed of the motor is adjusted to suit the load conditions. "If you reduce the speed of a motor by 20% you actually save 50% of the power to drive it," says Parker-Bates. "So there are big energy savings to be had." In the UK alone, around two thirds of industrial energy consumption comes from motors. The increasing use of VSDs in industry shows significant potential for overall reduction in energy consumption and therefore carbon emissions.

This has been compounded by the Carbon Trust that says the technology can qualify as part of its Enhance Capital Allowance scheme. Additionally, the Carbon Trust is offering interest free loans for energy saving equipment and even has a video on its website to show potential users how to install the devices. "Payback does depend upon application and the system, but typically it is less than 18 months," says Parker-Bates. "We have had customers who have had payback in six to nine months and it is certainly not uncommon to have payback in less than 12 months.

"We have found all the bigger players and industrial end users are switching on to it in a big way. But, the small to medium size companies, that perhaps don't have the expertise in house, can see installation as an issue."

To combat this problem, Parker has developed its 'Fast Pack', an easily installed VSD that comes complete with all the parts and components required to get it working. In the past, drives needed to be sourced with motors, controllers and a host of other components, leaving all but an electrical engineering specialist baffled. However, while the Fast Pack is still a relatively in-depth procedure, "it is so much simpler to fit," says Parker-Bates. "We are seeing more generalist engineers rather than specialists fitting the drives and getting results pretty much instantly."

Parker hopes this will help to encourage small to medium sized companies that do not have the in house expertise of larger companies, overcome installation difficulties that can lead to prolonged downtime on the factory floor.

ABB is also experiencing a trend toward the use of VSDs and has recently completed a study to show how quickly a VSD offsets the energy used in its production. The 'ecological payback' was calculated for three ABB drive sizes of 0.75, 7.5 and 250kW respectively. The payback times decreased with higher power ratings as the energy saving is larger. The 0.75kW drive compensated in 6 days, the 7.5kW drive in 1.1 days, and the 250kW drive in 0.5 days.

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