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Which is more sustainable: EC fans or VSDs?

01 March, 2023

For AHU applications, particularly in facilities such as data centres, electronically commuted fans are held up as an efficient, sustainable method of powering cooling fans. However, efficiency is not the only factor to consider, as Carl Turbitt, ABB’s UK HVAC drives sales manager, explains.

For AHU (air-handling unit) applications, there are two main choices of fan technology. Electronically commutated (EC) fans consist of a motor and drive package integrated into a single assembly. Their benefits include high efficiency at peak loads, and lower upfront costs. Alternatively, you could opt for a separate motor and VSD. 

EC fans are often promoted as being more efficient, but does this claim stack up? Let’s think about the sustainability angle. Having both a motor and drive in a single assembly may initially seem convenient and a way of cutting costs. However, in practice, EC fans may struggle to dissipate heat as easily as a separate motor and VSD, potentially resulting in more frequent failures. This could lead to overheating and breakdown of the motor insulation and a greater likelihood of premature failures and costly replacements.

If an EC fan fails, it must be replaced entirely, and because they are often made-to-measure, sourcing the correct replacement is not always easy. By contrast, a separate motor and VSD can be installed in the most convenient location, simplifying access for maintenance. 

EC fans can deliver good efficiencies at peak loads, but many installations do not require peak loads for a lot of the time. Data centre cooling systems, for example, are typically designed to be able to handle worst-case scenarios, and will often only operate at part loads. As a result, they are frequently over-specified.

In a typical data centre, loads may vary widely across the day, and only reach anything approaching a peak only once or twice a day – if at all. A VSD and motor configuration will typically deliver greater savings at part-loads, and can also provide much more torque than an EC fan. Cooling systems will therefore need fewer fans to reach required airflows, even at peak loads, resulting in fewer potential points of failure.

Efficiency and sustainability are not necessarily the same thing. EC fans can perform well at peak loads, but if your cooling system rarely requires peak load operation, then a separate motor and VSD might be more cost-effective in the longer term. Furthermore, if you are having to replace your system more frequently due to equipment wear, then what might seem efficient on paper may not be the most cost-effective and sustainable option over the longer term.

 

To learn more about EC fans, VSDs and other competing cooling technologies, there is a downloadable White Paper from ABB: https://drivesncontrols.news/kpfjaz




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