Cooling the VFD Itself

Typical VFD cooling fan configuration

There seems to be no end to the patches, upgrades, and redesigns of Variable Frequency Drives or VFD's that are used to control Variable Speed Pumps. Speaking mainly of small systems for homeowners, it was only a few years ago that some VFD's required being installed with a water line running through the electronics. The water passed through the VFD controller to cool the electronics inside. This design had many obvious problems, so a redesign of the VFD added a fan to cool the electronics. The fan draws in lint, bugs, and other stuff, coating the electronics and causing the VFD to overheat. Another design filters the air intake, which requires routine maintenance to keep the air filter from clogging and destroying the VFD. The most recent design has the fan blowing on a special kind of metal, transfering the cooling into the electronics, without the dirty air actually having to touch the electronics. This keeps the dirty air out of the electronics but, the air intake can still be clogged with debris and overheat the VFD. The maximum ambient temperature allowed for most VFD's is between 104F and 125F degrees. This usually makes indoor installation mandatory, and many times requires air conditioning, that waste even more energy.

Typical cooling fan for VFD clogged after only one year of use

A different manufacturer has put most of the electronics inside the submersible motor. This may be one of the best ways to cool the electronics of a VFD. However, the electronics are now submerged under water, where they cannot be replaced easily, and are also subjected to heat and vibration from the motor itself.

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