Energy is one of the few plant costs you can still do something about. You have limited say over the unit price, but you have a lot of say over how much your equipment actually uses. That is why variable speed drives keep coming up in conversations about industrial energy savings, and why they are one of the first things we look at when a customer asks us where their money is going.
The Carbon Trust's motors and drives technology overview guide puts the scale of it plainly: citing the World Energy Council, it reports that electric motors and motor-driven systems account for around 70% of electricity consumption in industry, and close to half of all electricity use globally. If most of your consumption sits in rotating equipment, that is where the opportunity sits too.
A variable speed drive, also called a VSD, inverter or variable frequency drive, sits between your electrical supply and your motor and controls the speed the motor runs at.
An AC induction motor runs at a speed set by the frequency of the supply feeding it. Give it a fixed 50 Hz supply and it runs at one speed, all day, whether the process needs that output or not. A drive rebuilds that supply at a frequency of its choosing, so the motor can run at whatever speed the job actually calls for.
That gives you control over output rather than control over waste. Instead of running a fan flat out and closing a damper to cut the airflow, you slow the fan down and stop generating the airflow you are throwing away in the first place.
Three stages inside one enclosure do that conversion.
For centrifugal loads such as fans, blowers and centrifugal pumps, the relationship between speed and power draw follows the affinity laws. Flow drops in line with speed, but power drops with the cube of speed. Small reductions in speed produce disproportionately large reductions in energy use.
In practical terms, taking 10% off the speed of a centrifugal load can cut its energy consumption by around 27%. Take 20% off and the reduction can reach around 48%, which matches the Carbon Trust's own figure of up to approximately 50% power saving from a 20% speed reduction on variable torque loads. Those are theoretical figures before drive losses and system effects, but they explain why the savings on fan and pump duties are often significant enough to justify the work on their own.
Not every motor is a candidate. The savings depend on the type of load and how the equipment is currently being run.
The quickest indicator on a walk round the plant is a throttled valve, a partly closed damper or a bypass loop running continuously. Every one of those is a sign that the motor is producing more than the process needs.
Energy is usually the reason a VSD gets specified, but it is rarely the only benefit.
A drive is not a component you simply bolt on and walk away from. There are a handful of practical points worth working through first.
We supply, install and support AC and DC drives from manufacturers including ABB, Siemens, Danfoss, Schneider, Vacon and Parker, alongside servo drives, inverters and IP66 rated units for harsher environments. Just as importantly, we work on the motors, pumps, fans and gearboxes those drives are controlling, so the recommendation takes the whole drive train into account rather than the drive in isolation.
Our energy saving service runs in three stages:
We also carry out thermal imaging, vibration analysis and laser alignment on site, which often flags the equipment worth targeting first.
If you have fans running against dampers, pumps running against throttled valves, or a motor list you suspect is costing more than it should, we can look at the numbers with you before anything is bought.
Call the team on 0116 276 4949 or get in touch to arrange an energy audit. Our line is answered 24 hours a day for urgent repairs.
