By John Guthrie, UK Energy Efficiency Manager – ABB Limited
In theory, undertaking an energy assessment of motor-driven applications should be straightforward. Identify the inefficient pump, fan or compressor, for example. Then by switching control to a variable speed drive (VSD) you can determine the energy, money and carbon saved, along with a payback.
In this presentation, John Guthrie identifies three aspects of an energy assessment, which, if overlooked, can result in increased costs. These relate to the way energy consumption is calculated, the way the cube law is interpreted and wider considerations surrounding the actual installation.
For instance, when calculating how much energy a motor will use, what is often overlooked in that the actual load on the motor is less than its rating because of design oversizing, throttling and head.
The net result is that not only is the existing energy usage overstated but so are the potential savings that can be achieved.
Also when installing a variable speed drive it is important to consider the “big picture”: is there sufficient physical space around the application to install the drive or is a special room or cabinet needed? Is a long cable needed between a motor and a VSD, and if so is it correctly sized and designed for EMC performance?
While the VSD itself will substantially lower your energy bill, it is important to avoid the pitfalls if surprise costs are to be avoided.