Model: Deep well submersible pumps with VFD control
When a deep well pump runs at full flow while the demand changes, a variable frequency drive can save a lot of power. How it works and when it pays.
| Power | Three-phase submersible motor with variable frequency drive |
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A deep well pump is usually sized for the peak demand. If the demand is lower most of the time, the pump still runs at full speed and the extra water is throttled or wasted. A variable frequency drive (VFD) lets the pump slow down instead.
Pump flow falls in proportion to speed, but power falls with the cube of speed. Running at 80% speed gives about 80% of the flow for roughly half the power. That is where the savings come from.
In ground-source heat pump systems, one well pump often serves two or more heat pump units. The heat pumps spend most of their time at part load, but a fixed-speed well pump keeps running at full flow, and both the power bill and the water bill rise. A common control method uses the temperature of the water returning to the well side: when it is high enough, the drive lowers the frequency and the pump slows; when it falls too low, the drive speeds the pump up again.
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