A variable speed pump lets you change the motor speed in revolutions per minute (RPM) to “dial in” an optimal speed for your pool. Using a flow meter, you can produce a flow rate to turn over your pool water the desired number of times per day to adequately filter your pool. The advantage of a variable speed pump is that it costs less to run than a single speed pump.
You want to run your pool pump at the slowest speed possible to achieve the required results. Why? The amount of energy required versus the flow rate is not linear. Consider the energy usage from my variable speed pump:
Let’s focus on the middle two speeds. At 1500 RPM the pump consumes 295 watts. At 2350 RPM the pump consumes 947 watts, or 3.2 times the power. However, you do not get 3.2 times the performance out of the pump:
Note that you get about 57 gallons per minute of flow vs. 22 gallons per minute at the two pump speeds, or 2.6 times the flow rate – significantly less than the 3.2 energy difference factor.
I decided that I want to run my pump for 8 hours a day, and looked at how much it would cost to turn my pool water over once per day at various speed settings. My pool volume is 25,000 gallons. For example, at 2,100 RPM pump speed, the pump produces a flow rate of 50 gallons per minute. That means I would need to run the pump at this speed for about 500 minutes at a cost of $16.68 per month to achieve the desired results. How do I know this? Because the pump shows you exactly how much power it is consuming!
This is the real value of the variable speed pump. It quantifies your energy use.
In reality, I run my pump for 12 hours per day. I operate it an an ultra slow speed for about 10 hours and high speed for about two hours so that my automatic vacuum has time to work. The net result is fantastic energy savings!