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    Single, Dual and Variable Speed Pool Pumps

    June 25, 2012

    There are lots of new options in replacement swimming pool pumps. Buying a swimming pool pump has become more complicated with recent laws requiring new pumps over 1hp to be energy efficient. Specifically, they are calling for dual speed, multi-speed or variable speed pumps.

    Since it was proven that these pumps can save a ton of electricity, energy poor states like Arizona, Texas and California quickly passed laws requiring these energy-sipping pool pumps.

    Many other states are considering mandating the same laws to conserve energy resources. Some cities and states offer rebates through local power companies; offering cash rebates to help convince people to switch to a more energy efficient pump. Check your local power utility website for details on programs in your area.

    Single Speed Pool Pumps: Runs at a single speed, 3450 rpm (revolutions per minute). Imagine if your car ran at 3450 rpm - all the time, and how much gas you would use!

    Dual Speed Pool Pumps: Have a fourth wire coming into the pump, the low speed wire. This allows you to run the pump on low speed for 8-16 hrs per day, and high speed for 4-8 hrs.

    Variable Speed Pool Pumps: Operates at many speeds, programmable and self-optimizing for the highest energy efficiency and greatest energy savings.

    How to Properly Size a Pool Pump: When it comes to pool pumps people always think bigger is always better; that indeed is not true. Pumps of lower horsepower consume much less energy, and one that's too powerful can compromise filtration or even damage small filters, valves or pipes. Your pump should be sized to your pool filter, and most filters will have a specification known as Design Flow Rate and Max Flow Rate. Check your filter owner's manual or the nameplate for this information. Secondly, your pool pump should be sized to the number of gallons in your pool.

    How Many Gallons of Water? For a rectangle pool shape, use the formula L x W x Average Depth of pool x 7.5. An example of this for a 16'x32' pool would be: 16 x 32 x 4.6 (average depth) x 7.5 (gallons of water to a cubic foot) = 17,664 gallons of water in your pool. For round and oval pool shapes, use 5.9 in place of 7.5. L x W x Depth of pool x 5.9.

    After determining the amount of water you have in your pool - divide that amount by the turnover time of 8 hours. Turnover Rate is how long it takes to move all of the water through the filter, and 8 hours is an accepted target for swimming pools. Divide the pool capacity of 17,664 by 8 hours to get 2208 Gallons per Hour. Next, divide this number by 60 to calculate desired 37 Gallons per Minute. Altogether, it looks like this: 17664 / 8 = 2208 / 60 = 37 gpm. We need a pump that produces 37 gallons per minute.

    Now that we know the desired flow rate, we can look at Pump Curves for a particular pump. If not on the webpage, you can usually find it in the back of the owner's manual. It's important to note that not all horsepowers are equal. All pool pumps will produce different flow rates, based on their internal design. If you are considering a single-speed pump, compare pump curves to find the highest flow rate at the lowest horsepower. You may be able to switch pumps, say from a medium-flow 1hp Superpump, to a high-flow 3/4hp Whisperflo and reduce your energy consumption, while keeping the flow rate the same.

    How to Read a Pool Pump Curve: The chart below shows the pump curve for the Hayward Max-Flo II pump. On the vertical axis, we have a measurement of resistance that the pump must overcome. Assume 30 feet of head for the average inground pool, or use 40 if you have a heater. If you have the original pool designs, your pool builder may have calculated the total feet of head in the system for you. If not, it's a rather complicated formula for adding up the varying resistances of every pipe fitting and piece of equipment in your circulation system.

    By way of example, the pink line on the graph, for pump model SP2707X10, shows a flow of 60 gpm, at 40 ft. of head.

    Now that you know what size pump you need for your pool size and pool filter the options are to use a single speed, dual speed or variable speed pool pump. A single speed motor of a lower horsepower will save energy. Dual speed pumps will save you quite a bit of money every year, and you can almost double that amount for variable speed pumps.

    To help determine which pump is best for you, consider how important energy savings are to you. According to the major pool pump manufacturer Pentair, the average cost to run a pump 12 months per year can range from $800- $1000. With operating cost like that it makes most consumers think about switching to a variable speed pump. Another factor is if you are in one of states that have mandated energy efficient pool pumps. Follow the guidelines, or face a visit from the pool pump police !?!

    Check these results for operating a Single Speed, 1.5 hp pump compared to a Dual Speed and Variable Speed pump for 5 months per year. The variable speed pump is typically about 80 to 90% more efficient than a single speed pump. Try It for yourself, just enter your gallons and your zip code.

    Single speed pumps are now more energy efficient than ever, and if you have an older motor, replacing with a single speed pump should save you about 10% on your electrical bill. This is nothing compared to the savings with a dual speed or variable speed pump. As you can see above, the Pentair Calculator shows a savings of $400 per year, by using their Variable Speed pump, the Intelliflo. And that's just for 5 months of use, 14 hours per day!

    One of the most common questions I hear is "Why should I spend more money for a variable speed pump when I can purchase a single speed pump for a lot less money?" Or, "What are the actual energy savings and how long will it take for payback?" Now I just refer them to the Pentair Calculator. It's quite a powerful tool, and a great sales tool for dual speed and variable speed pumps.

    With savings that great, why not take a look at Energy Efficient Pumps? Even if it's not required by your state ... yet.

    Chris Low
    SPP Pool Expert

    Blog Author