Controlling the motor speed in flow applications offers some of the fastest energy saving pay-back times around, and below we show you how.  The Altivar ATV61 drive from Schneider Electric UK is designed specifically to replace the valves and dampers used to control the flow of fluids (mostly air and water but any gasses or liquids) in commercial buildings and industrial processes.

If you’re not sure whether or not they are applicable to your business simply contact us and we will send someone round to your site to make an assessment.  Flow applications include centrifugal fans, pumps and blowers fan systems controlled using valves and dampers.  Similar applications include turbine pumps, agitators, and axial compressors.

Quickly estimating the energy savings available by installing variable speed drives to motors is simple as their power consumption is governed by the cube law.

Cube Law

It’s obvious that reducing the speed of a motor reduces the power consumed by the motor.   As motor speed falls, the reduction in energy required to drive the motor is determined by the cube law.  Simply put, reducing the motor speed by 10% reduces the power required by the motor to 90% x 90% x 90% =72.9% of full speed: a saving of 27.1%.  By the same law, if you reduce the motor speed to 60% then 60% x 60% x 60% = 21.6% or a reduction of 78.4%.

Payback time

Now consider a modern 22 kW IE2 (91.6% efficient) motor running at full load for 10 hours a day 250 days a year.  This will use 22 x 10 x 250/91.6% = 60,000 kW of electricity in a year.  Assume £0.10 per kW that’s a running cost of about £6,000.  From the previous paragraph, by running it at 90% of full speed you save 27.1% of your energy consumption or £1626 a year for as long as the motor runs.  By coincidence, £1626 is about the cost of a 22 kW inverter from 999 Inverters, so you know the payback time too.

This is why almost everyone including the UK Government and the Carbon Trust are incentivising the use of variable speed drives to reduce the carbon emission tax/Climate change levy.  If you don’t believe it ask us and we’ll loan you an inverter to try it for yourself.  If your accountants tell you no capital expenditure, then we’ll lease you one and it will pay for itself from the savings.

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