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How Growers Can Get the Most Out of Irrigation with Variable Frequency Drive Pumps

By David Wallace, CEO

One reason that the Variable Frequency Drive (VFD) pump in farm irrigation has gained broad adoption is because of the efficiency gains it can bring to an operation.

Another reason is the wide variety of rebates, incentives, and grants provided by power suppliers, state governments, and even Uncle Sam himself in exchange for energy savings. 

But despite their growing use on farms, VFD owners can still miss out on significant benefits. Here’s how growers can get the most out of their VFD irrigation pumps.

Understanding Variable Frequency Drive

Variable Frequency Drive (sometimes called a Variable Speed Drive) is an electrical component that converts incoming constant-frequency electrical power to a different frequency on demand, allowing the component being driven (usually a motor of an irrigation pump) to operate over a wide range of speeds. VFDs come with a wide variety of advantages:

  • Gentle: slow ramp up/down prevents water hammer
  • Efficient: running below max speed reduces energy consumption
  • Versatile: match the specific pressure and flow demands of different irrigation systems on the fly

But those benefits are not without drawbacks:

  • Cost: initial investment in a VFD is substantially higher than a motor starter
  • Complexity: changing settings and programs in VFDs is cumbersome and can damage equipment if done incorrectly

Installing a VFD can be an attractive option in many cases, especially when significant financial incentives are in place. When deciding whether or not to invest in a VFD for a new or existing irrigation well pump, growers should consider the above tradeoffs, and keep in mind the following:

VFDs Match Changing Demands of Irrigation System

The VFD controls the frequency of the electrical output through a process called pulse width modulation, and this produces energy loss in the form of heat. When running at full speed (i.e. maximum frequency), a VFD uses more energy and therefore is less efficient than a simple motor starter, which passes electricity through from the grid to the motor with effectively zero loss.

The efficiency gain from using a VFD comes from the ability to run the irrigation pump at a lower speed in order to match demands of the irrigation system in use. By setting a precise pressure target or speed setting, the grower is able to achieve the optimal conditions for their irrigation system. In contrast, an electric pump with a normal motor starter will always run at 100%, so if it is driving an irrigation system with a small total aperture, the pump will be running at a much higher pressure than the system requires. This wastes electricity, causes unnecessary wear to the pump, and can lead to issues at the end of the system where the sprinklers or drip emitters are located.

In general, reducing drive frequency/speed will decrease power consumption, and even small decreases in pump speed can yield significant reductions in energy use.

Along with VFDs, Mechanical Improvements to Irrigation System Can Also Boost Performance

In many cases, improvements to the mechanical aspects of the irrigation system–rather than the electronics–can yield a higher performance improvement. For example, a worn out impeller can cause a pump to operate well below its optimal efficiency. In many cases, rebuilding the pump with a new impeller could be accomplished for a fraction of the cost of a new VFD upgrade.

VFDs Can Also Adapt to Different Irrigation Systems – But Only If Programmed

For growers who use their VFD to irrigate with different systems (e.g. two different center pivots, or a hose reel and a drip system), the true value of the VFD lies in its ability to adapt to changing irrigation conditions. 

Unfortunately, because VFDs can be difficult to program, many growers do not take advantage of this ability, and instead run their VFDs at the same speed or pressure setpoint in all cases.

That means that many growers with VFDs are leaving money on the table. 

In a future post, I’ll explain how to get more efficiency out of your VFD irrigation pumps. But in the meantime, get in touch with us today if you’d like to explore how FarmHQ can seamlessly integrate with Variable Frequency Drive (VFD) pumps to provide comprehensive control over pump speed.