Why “Smart” Pumps Aren’t Always Smart

• 23 January 2026
• Construction Focus
• 626 Views

Think a “variable speed” pump is a guaranteed money-saver? Think again. A recent analysis has revealed that a common engineering “shortcut” could actually be draining thousands of dollars from utility budgets every year.

Junior engineers often fall for the “Pump Affinity Law”—a simple formula suggesting that if you slow a pump down by 20%, you cut its power use in half. It sounds like a no-brainer for saving energy.

But here’s the catch: Math on a napkin isn’t the same as water in a pipe.  Why “Dumb” Pumps Sometimes Win. Experts warn that simply adding a Variable Frequency Drive (VFD) to a pump can actually lower efficiency.

VFDs are amazing technology, but they aren’t a magic wand. If you don’t use professional modeling software like Bentley’s OpenFlows Water, you’re just guessing. And guessing is expensive.

Using advanced software like Bentley’s OpenFlows Water is a much better option. A standard constant-speed pump actually outperformed the VFD in several scenarios.

Key Findings from the Comparison:

Efficiency: The constant speed pump maintained a steady 69% efficiency, while the VFD pump fluctuated as low as 45% during varied flow periods.

The “Off” Factor: The most cost-effective speed for a pump is “Off.” Constant speed pumps complete their task and shut down, whereas VFDs often keep pumps running at inefficient speeds.

Parasitic Load: VFDs lose energy as heat while “reassembling” electrical sine waves to change frequencies.

In the specific case study analyzed, the constant speed pump saved $4,588 per year in energy costs compared to the VFD, not including the initial price of the drive itself.

Before you upgrade your system, experts recommend running “Time Series” graphs to see how your pumps handle different times of day. Sometimes, the simplest solution is actually the greenest.

• Technology and Engineering
• OpenFlows
• Bentley Systems