In which applications do VSDs offer the best efficiency benefits?

Efficiency benefits from installing VSDs to motors


Most motor driven machines benefit from the use of variable speed drives (VSD). In some applications it is from energy savings and in others, improved control of the application.

According to ABB, variable torque loads offer the most energy saving and efficiency benefits. This category includes pumps, fans, and air handling units.


VSDs controlled pump motors transport fluids by ensuring the correct motor speed to maintain a safe pipe pressure. They benefit all types of pumps including HVAC water circulation, boiler feedwater, process cooling, wastewater treatment and clean water applications.

Energy efficiency benefits

In the UK, pumps are responsible for the emission of 2.7 million tons of carbon per annum. They represent the largest single use of motive power in industry and commerce. Since pumps are variable torque, they deliver the largest energy savings when using speed control.

Productivity improvement benefits

VSDs improve system reliability and simplify pipe systems by eliminating the need for control valves and by-pass lines. They also provide soft-start and stop thereby reducing wear and tear on the motors and reducing leaks from pressure surges. All this leads to lower maintenance and life cycle costs and increases plant availability.


There are many types of fans used to move air and gases in commercial applications, for example centrifugal and axial. Whether belt driven, or direct coupled, most benefit from VSD control to save energy, improve processes and reduce maintenance costs.

Energy efficiency benefits

Often, air flow control is via a mechanical damper in the duct work, either before or after the fan. The type of damper is important as different designs affect the fan performance and load. In most cases large energy savings are achievable through VSD control by removing the need for dampers. Where there is no external control, using the drive’s energy optimisation features enables simpler system designs to reduce motor losses and saving energy.

Productivity improvement benefits

Whether belt driven or direct coupled, VSDs can reduce maintenance costs through soft start control of the fan. Significant reductions in belt or gearbox wear and tear improve system reliability and availability. Where large fans ‘windmill’ while out of service, VSDs can catch, slow, and stop them in a controlled manner. This avoids huge stresses when starting direct-online and protects against premature failure of mechanical and electrical components.

Air handling units

Fans in air handling units (AHUs) are often driven by the motor via a pulley system. Designers oversize the motors to cater for the greatest room occupation on hot days and allow for blocked filters. The motors run at full speed and in some systems, control of the air flow is by mechanical dampers.

Energy efficiency benefits

Installing a VSDs on the supply and extract fans allows the AHU to run according to demand, bringing significant energy savings. The fan obeys the affinity laws, so large savings on power are achievable with even small reduction in speed.

Installing a differential pressure switch across the filter will allow alterations of fan speed to provide a constant airflow even when filters become blocked. This allows the motor to run at its most efficient speed.

Productivity improvement benefits

With VSD controlled AHUs, the lifetime of the fans’ drive belts is longer and there is less wear and tear on bearings through soft start/stop. Also, automatic belt monitoring increases intervals between maintenance and gives early warning of breakages. Moreover, slower motor speeds mean lower noise levels and longer intervals between air filter changes (lower speed = less dirt). Finally, configuring the VSD output provides condition monitoring of filters to give an indication of when a filter requires replacement or cleaning.

Contact us for help in selecting the correct VSD for your motor applications.


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