Why are pool pumps now required to be variable speed?
Friday, August 10, 2018
New or replacement pool pumps of one horsepower or more have been mandated by a Florida State Statute since 2012 to be variable or two speed type. No more single speed pumps are allowed, and the reason is energy efficiency. Being able to adjust the rpm of the pump lower when a high rate of flow is not necessary, and running the pump for a longer period of time to achieve the same total flow of water through the system, decreases energy use drastically. How pump speed affects energy consumption is expressed by the “Pump Affinity Law,” a mathematical calculation used in hydraulic engineering, which expresses the relationship between speed/flow of the water and energy usage. It shows that the relationship is non-linear: energy usage drops much faster that the decrease in pump speed.
The chart below, prepared by the U.S. Department of Energy, as part of a report on the energy-saving characteristics of a variable speed pool pump as compared to single speed, shows how rapidly and disproportionately energy usage decreases with a reduction in flow. The top line shows a flow of a typical one speed pump running at 3,450 rpm and 66 gpm (gallons per minute), which pulls 2,000 watts of electricity.
A variable speed pump running at 1,800 rpm produces half the flow (33 gpm), but uses one-eighth of the electricity (250 watts). So if a typical single speed pump that runs for 6 hours a day is replaced by a variable speed pump running at half the speed for 12 hours a day, the energy consumed is reduced to one-quarter of the original. Huge difference!
Just a reduction in speed of 15% to 3,000 rpm (see line 2 of the chart) drops energy usage rate by over 40%. Even if you are not a tree-hugger trying to save the planet, the energy savings make a variable speed pump a worthwhile investment. In homes with a pool, the pool pump is often the largest electricity-guzzling appliance, and savings of 50% to 75% are typical. Payback of the initial additional cost compared to a single speed pump happens within two years or less.
Also, because a variable speed pump is programmable, when you need more flow for a water feature, cleaner sweep or pool heater, it can be ramped up to fit the demand.
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