Are your VSDs running at maximum efficiency?

Today there are hundreds of thousands of variable speed drives installed in countless applications across the country, saving users many thousands of pounds in energy costs. But are end users getting the most out of their variable speed drives? Are they reaping all of the energy savings that they could be? How many of these VSDs are actually set up to run at their maximum efficiency?

It might be assumed, for example, that having fitted a variable speed drive, you have achieved your energy savings potential – end of story. The drive may certainly be optimising the speed of the motor by matching it to the requirements of the application. In high duty pump and fan applications for example, this will mean taking advantage of the inverse square law of speed to energy consumption to deliver some significant savings in energy use.

However, to really deliver the maximum energy savings, VSDs have to be properly set up at the commissioning stage; this can be as simple as activating one parameter to turn the drive intelligent energy saving mode on.

Where to start looking…

The first area to always look at is nature of the load i.e. is it constant torque or variable torque. The drive can then be adjusted to match its output to the load, thereby maximising the available energy savings. While a drive in constant torque mode will still save energy compared to having no drive on the motor at all, optimum savings will only be achieved in variable torque mode if the connected load is a pump or fan, although it must be stated that some types of pump require the constant torque setting. This needs to be set up when the drive is installed; again this is normally as simple as adjusting one parameter.

Further, many VSDs have specific energy-saving modes, with dedicated algorithms tailoring the profiles of the output to deliver greater optimisation. As an example, Mitsubishi Electric’s FR-F800 – a dedicated product aimed at pump, fan and compressor operations – offers specific energy saving modes that can achieve further energy savings up to 15% compared to standard operating modes. It also provides a number of advanced features specific to the industries relying on fans, pumps and compressors to deliver further improved performance within the application.

Some users may have shied away from enabling such energy saving modes on VSDs, as historically they could make the drive sluggish to respond to changes in the load. However, this is no longer the case, with best of breed products incorporate technologies that will eliminate the problem.

And the survey says…

It is also fair to say that energy optimisation is a constantly moving target. That means ongoing monitoring of energy usage is vital for identifying areas ripe for optimisation. Even more fundamental than that is the need to perform a post installation survey once a VSD has been fitted.

While there is a plethora of energy saving calculation tools that can make the case for fitting the drive in the first place, these tools make a variety of assumptions that may not always be accurate against real world operating conditions. While the tools certainly provide an indication of how much energy can be saved and show estimated payback times, only a detailed post installation survey can highlight real energy savings and show opportunities for further optimisation.

We can see, then, that while variable speed drives offer numerous opportunities to save energy – and are demonstrably doing so in a wide range of industries and applications – spending a little time to set up the technology correctly will deliver so much more.