When ordering dessert at a restaurant, is a plain piece of apple pie enough, or is the whipped cream on top an important added bonus? Are the substantial energy and cost savings that come with installing a Variable Frequency Drive (VFD) enough, or is there whipped cream on top – the whipped cream, of course, being the non-energy benefits that add even more value to that VFD installation?
Depending on the application, using a VFD can deliver one or more of the following whipped cream benefits:
- Less motor and belt wear
- Fewer start-stop cycles
- Less noise
- More accurate capacity control than throttling devices like dampers and control valves
- Soft start capability
- Lower cooling loads when the motor is in an air-conditioned space
VFDs can be used to continuously adjust supply of fresh air and exhaust to minimize ventilation and fan energy requirements. It may also reduce wear on the fan belts, bearings, and motors and increase filter life. Controlling building pressure can make door operation easier and may even increase occupant comfort!
Pumps are another example where a VFD offers energy and non-energy benefits. Many pumps are used in ‘tank-filling’ applications, such as a pump that might be used to fill an elevated reservoir. This is commonly done with a single-speed pump where the pump is cycled on and off to maintain tank levels within a desired range. Installing a VFD for this type of application will result in modest energy and demand kW savings when compared to cases where capacity would otherwise be controlled by cycling. However, the non-energy benefits may be as important as the energy savings. The VFD will provide tighter control of the target level and replacing the start-stop controls will reduce the number of motor start/stop cycles. The VFD will also provide soft starting (and stopping) that may eliminate water hammer in systems that are susceptible to it.
When deciding whether a VFD is worth the investment, don’t forget to account for the non-energy benefits as well. If the energy savings (and energy efficiency program rebates that go with them) aren’t enough incentive to install a VFD, maybe the non-energy benefits should also be considered. If the conditions are right, there might be whipped cream on the pie and maybe even some nutmeg.