November 2019

application considering factors such as running speed, efficiency requirements, space and integration with other equipment and systems. Induction motors (IM) - Drives are most commonly paired with an IM for simple and reliable operation in many HVAC applications and in a wide range of environments. This means that spare motors and parts are often readily available. Further simplifying setup, the HVAC drives can be integrated with virtually any type of IM by entering the nameplate motor data only. While energy efficiency of IM is good, at lower power ranges they can struggle to match the extreme efficiency of newer motor technologies. Their asynchronous speed also generates more heat, which can lead to shorter bearing life compared to other motor types. Permanent magnet motors (PM) - PM technology offers users high efficiency across the speed range and customised housing for applications such as fan walls and cooling towers, as well as eliminating the need for mechanical speed reduction equipment. PM achieve very high energy efficiency levels in most applications as their permanent magnets reduce rotor losses. This also brings a compact design, particularly compared to induction motors, with high torque density in a relatively small and light package. However, PM can be more costly to purchase, although this can be mitigated by efficiency savings. They are also more difficult to maintain and repair due to the magnets used. PM require a VSD which adds further to the initial cost, however this can also substantially accelerate the payback time. Synchronous reluctance motors (SynRM) - Combining drive control technology with SynRM gives a motor and a drive package that ensures high energy efficiency, reduces motor temperatures and provides a significant reduction in motor noise. Compared to IM and PM, SynRMs deliver superior efficiency levels up to IE5, using a special cageless rotor which removes traditional rotor losses. It also produces less heat and increases operational lifecycle. As with PM, the SynRM must be used with a drive. There are relatively few downsides to SynRM, and they are particularly well suited to quadratic torque applications like pumps and fans. Electronically commutated motors (ECM) - Rather than traditional configurations which comprise a separate motor and drive, ECMs are an integrated standalone package, which can make them very quick to install, and are often used on HVAC applications. However, ECMs typically have a life span of half of that of a variable speed drive and motor application. This leads to higher total cost of ownership as they are not repairable and will need to be replaced. ECMs also have some other technical drawbacks: they cannot ride through power dip situations, cannot catch a spinning load, have limited speed/power duties, and can generate large amounts of harmonic distortion, particularly at higher frequencies. 36 | Plant & Works Engineering www.pwemag.co.uk November 2019 Energy, the Environment & Water Focus on: HVAC Carl Turbitt