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UPGRADING SYSTEMS


IS A VFD THE BEST OPTION FOR YOU?


M


aking an upgrade to an irrigation system — especially a significant upgrade — is not a decision


to be made lightly. Numerous factors need to be considered, such as whether the upgrade is appropriate for your system and what the cost versus benefits are.


Variable frequency drives can be used to adjust the speed of alternating current motors. It is becoming more common to see VFDs on new and retrofitted irrigation systems. Using a VDF may be effective in reducing energy costs, among other benefits.


However, VFDs are not appropriate in every situation. In addition to the upfront cost to install a VFD and related items, using a VFD will result in an immediate 3%-8% reduction in overall pumping plant efficiency due to inherent losses within VFDs. The losses are evidenced by heat emitted by the VFD system. In fact, sometimes active VFD system cooling is needed to deal with heat.


 


To avoid unnecessary expenses, it is helpful to first determine if a VFD is appropriate. The scenarios in table 1 help outline various cases where VFDs could be beneficial.





Once it is determined that a VFD is worth considering, it is important to have a sense for potential financial savings. It can be difficult to effectively predict actual energy savings, but it is possible to get a ballpark estimate.


First, there are potential energy-saving items that apply to most pumped irrigation systems. For example, a good irrigation system designer will typically oversize pumps to account for unknowns and other worst-case conditions.


The argument is that there will be client complaints if there is insufficient pressure, but there will be fewer (if any) complaints


Adding a variable frequency drive to your system can provide valuable energy savings.  if this is the best option for you.


By Kyle Feist, MS, PE, CID, CAIS


24 Irrigation TODAY | Fall 2019


irrigationtoday.org


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