HVAC consultants may be missing benefits of variable-speed drives

Many building services consultants may not be up to date with their HVAC technical specifications for variable-speed drives (VSD) and as a result could be missing out on some critical improvements and enhancements in the technology, claims ABB’s UK HVAC industry manager, Carl Turbitt.

Some eight years after ABB aired its initial concerns about consultants potentially using out-of-date specifications, Turbitt fears that such is the pace of technological change today that there is a high risk that specifications are not updated.
“The problem is compounded by the developments in products associated with VSDs,” says Turbitt. “Take the humble electric motor. Some specifications still assume that motors require a large de-rating when being controlled by a VSD. Also building consultants are confronted with electronically commutated motors, permanent magnet (PM) motors and synchronous reluctance motors (SynRM) – all competing with the traditional induction motor. Yet, each motor type has its pros and cons. Benefits of using a VSD with the SynRM motor, for example, includes harmonic mitigation on the supply, 40 percent lower losses from the motor, easier maintenance compared to PM motors, the ability to achieve specific fan powers and to catch a spinning load as well as ride through a power dip.”
Drive technology is advancing at a rapid rate. In the past 15 years, the size of drives, measured in volume, has decreased by up to 80 percent, while the number of components has come down by some 60 to 70 percent. Thus, drives’ time between failure (MTBF) has increased five-fold. Today the MTBF is better than 1 in 50 years.
However, says Turbitt, there is also a belief that all drives are the same. “This couldn’t be further from the truth. In recent years, the performance of some variable-speed drives has improved dramatically. They offer greater energy efficiency, leading to lower energy bills, reduced maintenance and more flexibility for end users, as well as faster installation and commissioning for contractors. Features such as BACnet interface and the integration of serial communications dedicated to HVAC protocols, is offering greater adaptability and connectivity with automation building networks.”
Other features include highly intuitive user interfaces which guide the user through the set-up, detection of belt breaks and blocking filters and a real-time clock that can change the operation of the control at different times of the day.
Turbitt says that part of the reason consultants may fall behind is that they do not purchase drives and so are not always targeted with the latest information by manufacturers or the specification falls within another department. This is despite consultants being key influencers in the choice of drives with a need to understand the latest developments more than most.

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