Although the introduction of the IET 18th Edition Wiring Regulations requires motors with a rated output of 0.75-375kW to meet IE3 efficiency level or IE2 efficiency level and be equipped with a variable speed drive, this isn’t the only reason the use of Variable frequency drives (VFD) should be taken into consideration.
From reducing the running cost to minimising environmental impact, VFD’s are becoming more widely used in applications such as HVAC, elevators, tower cranes, CNC machines and paper making machines. In fact, any process that utilises power hungry products such as electric motors, fans, pumps and compressors.
A VFD can reduce energy consumption as high as 30-40%* for the same work output. For example, fitting a VFD to control a 15 kW pump in continuous use could typically save over £500 in energy costs a year. Other examples of ROI include Nottingham’s Biocity science park, which made a saving of more than £58,000 per year by retrofitting VFD’s to its fans and pumps in several multi-storey buildings used as offices and labs for business start-ups. This achieved a return on investment in less than 3 months. Similarly, a 17 story office complex in London has reduced its energy cost by investing in a £48,000 VFD project which is expected to pay for itself within 18 months.
But how? A VFD has the ability to save the user money through its inherent nature to save energy by controlling the power consumed to only the power that’s needed.
VFD’s can adjust the output speed and torque of an AC motor by varying the voltage and frequency applied to the motor. When your production doesn’t need the motor to run at full speed, you can use a VFD to adjust the motor running speed, so energy can be saved during the process.
In many cases electrical motors are started and run using traditional equipment such as direct-on-line (DOL) motor starters. Not only does this mean that the motor receives a mechanical shock as full power is supplied to it from start up, it also means that the motor is running at full power all the time, whether the load requires it or not and excess power is dissipated as heat.
Adding to this, the saving in maintenance costs and extension of equipment life is achieved by reducing mechanical stress to a motor on start up, using a ramp up process that starts the motor slowly over a set time until optimum speed is obtained.
Want to know how much you could save? Identifying and acting on potential efficiencies in motor control can often mean the difference between profit and loss. Due to many variables when a VFD is working such as the load change, material characteristics, efficiency, process cycle etc, it is not possible to work out the exact energy saving of a VFD without a system survey, which is usually carried out by energy efficiency experts.
However, if your system is more than a few years old it is likely that changing over your current system to utilise VFD’s would improve your profitability and a site survey by an energy efficiency company could reveal a potential boost to your bottom line in a relatively short period of time.
* Based on a typical constant pressure pump being used in a 24/7 water supply system a VFD may save as high as 30-40% of electricity cost.
