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What Is A Variable Speed Pool Pump?

What is a variable speed pool pump?
You would be hard pressed to find a more hot button issue in the pool and spa industry than variable speed pool pumps. There are a lot of terms used to describe these pumps which can lead to some confusion for pool owners who are new to this type of thing. Variable speed pumps, VS pumps, variable flow pumps, variable drive pumps, variable frequency pumps, VFD (variable frequency drive) are all similar things. You might hear these words used interchangeably when in fact there are subtle technical differences between some of these terms. This page you are reading now will help to explain what the differences are with these pumps, as well as the difference between a regular pool pump (single speed pool pump) and a variable speed pool pump.

Before we break down the technical difference between pumps that you need to know, in short is that the Department of Energy has passed a new pool pump efficiency standard that requires a certain efficiency threshold be met. Between the lines, the only pumps that can meet this new standard are highly efficient variable speed pumps. July 2021 is the official start date for when older single speed pool pumps will be banned for use as filtration pumps which means no more service, parts or replacement for these older inefficient pumps. Single speed booster pumps and dedicated waterfall pumps will still be allowed and available for application specific purposes.

What is a variable speed pool pump? - Just like a dimmer switch on a light bulb a variable speed pump is a pump that has the ability to dial up or down speed as needed for various conditions. Just like a light bulb can just be on or off with a regular switch so can a pool pump. That is what pool pumps have looked like for the past 50 years. At best there were two speed pool pumps which were exactly as they sound. These pumps had the same full speed as a regular single speed pump, but also a secondary option for half that RPM speed. All of this sounds simple, and it is, but there is a complex mathematical principle at work here that has significant impact on electrical consumption as you change RPM speeds.

Pool pumps use a huge amount of electricity. More than almost any other appliance in your home. In some houses with larger circulation pumps that run 24/7 the pool pump can account for up to 50% of all of the electrical use in the entire home every month. So there is without a doubt a huge advantage to trying to improve these numbers.

There must be a better way to pump pool water, and there is, and it is extremely effective. So effective that the Department of Energy did a double-take at the report data, probably made a bunch of exaggerated cartoon-like aawhoooga noises, and then immediately created the new law that requires every swimming pool owner in North America to buy an (expensive) new variable speed pool pump and install it for their circulation pump. There might even be some provision that owners of single speed pool pumps must remove the pump and take it to a field and beat it with sticks and rocks and stomps a la the Office Space photocopier scene. That last part might not be true but for sure the aawhoooga noises and new energy conservation laws are both real.

Are variable speed pumps really better? - Pump affinity laws show that when you reduce an electric motor RPM by half, the power consumption reduces by eight times. That is a lot. Here is the kicker, the power drops by eight times, but flow reduces on a linear scale. So imagine full speed 3450 RPM consumes 2250 Watts of power per hour and moves 88 gallons per minute. When you drop to 1750 RPM the power drops to only 375 Watts per hour, but the flow only drops to 42 GPM. Still a lot of flow, but way less power consumption even in this real world operating condition. At 1000 RPM the numbers are 134 Watts and 16 GPM. These are real world numbers from one of my pool pump test lab videos. You can read about it and see for yourself in this article about flow volume from a pool pump. Variable speed pumps are not just more energy efficient than single speed pumps, they are substantially better than the current standards to the extent that it would be negligent to allow the continued wasteful use of energy to the extent that we do.

What do variable speed pool pumps look like? - Pool pumps are often confused with filter tanks by day one pool owners. The pump is the heart of the system. It uses power, a lot of it, to suck water from your pool and then push it through a filter tank and filter media and then on back to the pool. The pump is short, long, and has a wire connected to one end. The other end has a lid that you can see water down through. A pool pump is the total package you are looking at, but this can be broken down into two parts, literally, which are the wet end (with the lid) and the electric motor (with the wire). A single speed pool pump (or a dual speed pool pump) will have a cylindrical electric motor housing which looks the same for almost every brand, make, model and size of pool pumps. A variable speed pool pump has that same cylindrical shape, but it is sealed and sometimes covered in heat sync fins (because VS pumps are TEFC, totally enclosed fan cooled) where a single speed pump does not have fins, but instead holes in the underside where ambient air can draw past the motor to keep it cool. The variable speed drive mounted to the pump is a dead giveaway that you are looking at a variable speed pump, but it should be noted that some VS pumps use remotely mounted controllers which might confuse some pool owners which is why you can check for air vent holes as a backup. If you have air holes this is a single speed pump and not a TEFC variable speed pool pump.

single variable speed pool pump

With a single speed pump there is no interface with which to interact with your pump. At most there is a switch or a breaker that you use to turn it on and off. A variable speed pump has an interface where you control the motor RPM. A variable flow pump is different from a variable speed pump in that they are almost the same, but you control them a little differently. Instead of setting an RPM setting which consumes a specific amount of electricity a variable flow pump will set a specific flow rate and hold that flow rate under changing filter pressure conditions which results in varying electrical consumption but steady flow rate numbers. This would be specifically useful for commercial pool applications where minimum turnover rates are a liability and closely monitored and inspected.

In a residential pool system a variable flow pump seems overkill unless you have a specific aspect of your pool which requires a very specific amount of flow at all times. For everyone else manually dialing the RPM for a variable speed pump is all you need to do to experience substantial electrical savings over what you spend now. For more information you can read this article on variable speed pump schedules to learn about why single speed pumps were always a bad choice and dialing in your turnover rate and flow rate will save you a ton of money with a variable speed pump.

How does a variable speed pump save you money?

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