Variable Speed Pumps Explained
If you have a swimming pool then it is an eventuality before you have a variable speed pump. The DOE (Department of Energy) has passed a law that by 2021 all swimming pool filtration pumps will be required to meet efficiency standards in order to be in use. Between the lines, the electrical efficiency requirement is so high that ONLY variable speed pumps will be able to meet this efficiency standard (or highly efficient single speed pumps less than one half horsepower). If you are here reading this article then you might have heard about VS pumps (variable speed pumps) or VFD pumps (variable frequency drive pumps) or you might simply be looking for a way to spend less money on electricity. In any case this page will highlight the main reasons to get a variable speed pump. If you would prefer a longer form article you can also check out this one that includes real world calculations for electricity use for variable speed pumps versus other popular single speed pumps: how a variable speed pump saves you money.
Variable speed pumps have been available for pools for a decade or more now and while it is true that some first generation VS pumps experienced higher than average failure rates, many of these failures can be attributed to improper sizing and installation practices which are rampant within the pool and spa industry. Variable speed pumps are much more powerful than the older generation of 1.5 horsepower super pumps that they are replacing, and much more high tech as well, and failure to follow best practices and minimum standards for installation is much less forgiving than it was in previous decades with simpler pumps (with lower parts and replacement costs).
Why Are Variable Speed Pumps So Much Better?
You can summarize the main advantage of variable speed pumps for pools by first noting that pool pumps are one of, if not the single largest, electrical draw appliance in an average home. If you run your pump all the time or almost all the time then this can equal out to accounting for up to 50% of the entire electrical usage for your home! It would be a big advantage to reduce the electrical costs to run your pump. This is why most people do not run their pump 24 hours a day because the costs associated with doing so are too great.
Turning off your pump for half the day results in a linear drop in electrical usage...half. But turning down a variable speed pump motor RPM by half does not reduce electrical costs by half, it reduces it by eight times! This non-linear drop in electrical consumption, known as the pump affinity laws, are the backbone of why no single speed pool pump will ever be able to compete with a variable speed pump when it comes to energy savings potential. Anyone who says they just turn their pump off for part of the day to save money fundamentally does not understand the science or math behind energy consumption versus electric motor RPM. There are cases and arguments for application specific reasons why you can get away with a suitably sized single speed pump...but this isn't one of them!
Vastly reduced electrical costs - A variable speed pump can run on 1/4 RPM for 64 hours for the same amount of electricity that a similar size single speed pump will use in only a single hour of operation. Water moves more efficiently at low speeds than high speeds, and so the water movement at 1/4 RPM would likely be greater than 1/4 the volume of a single speed pump running for an hour. As an educated estimate, for comparison purposes, a single speed pump might move 4000 gallons per hour, where a similar sized VS pump running at 1/4 speed might move 1500 to 2000 gallons per hour. For a given unit of electrical consumption, this means somewhere around 100,000 to 125,000 gallons of water filtered with a variable speed pump, versus just 4000 gallons for a single speed pump - Yikes!
*Please note that water filtration in a swimming pool is more complicated than simply turning down a variable speed pump to the lowest RPM all day. there are a number of reasons why this is not practical, possible or a good idea in general. For more information about this you should read this article about real world applications for variable speed pump schedules. In short, you can run a VS pump on low most of the time, but you will need some higher flow rates in your schedule as well.
Single speed pumps move too much water - Single speed pumps typically pump more water than a pool needs for filtration. If you were to run a single speed pump for 24 hours it would likely exceed the amount of water that you actually needed to filter by many times over. Yes you could just turn it off part of the day, as many people do, but that is only a linear drop in electrical use, not a logarithmic drop like when using a variable speed pump.
TEFC motors - Totally enclosed fan cooled motors are superior to the older style of electric pool pump motor which has air vents in the bottom for drawing ambient air in and passing it over the heater internal components of the motor. This process is responsible for many pump failures from chlorinated water being drawn into the motor. A totally enclosed motor that uses internal fans for cooling and is impervious to water and dust in the environment is simply superior to a pump that has internals open to environmental factors.
Quiet operation - Single speed pumps are notoriously noisy, especially older ones with failing bearings, and this is largely due to the fact that they operate at such a high RPM. Both the motor and the water flow is so much that it creates vibrations and noises which can be disruptive. Variable speed pumps are much quieter than single speed, RPM for RPM, but when turned down to lower RPM speeds variable speed pumps can become so quiet that you need to touch them just to verify if they are in fact running or not.
Improved filtration - Most pool filters would do a much better job at filtering your water if the water was sent through the filter at a much slower rate of speed. Yes pool filters can usually handle high flow rates, but optimal flow rates are much lower than the rate of flow that single speed pumps typically generate.
More efficient - Variable speed pumps are a much newer technology than single speed pumps, and the design has inherently improved over and above just the speed of the motor. Two pumps of exact size, operating at the same RPM, the single speed pump will use more electricity than a variable speed pump in this apples to apples comparison. Truly VS pumps beat single speed pumps in every possible category except that they cost more to buy.
Another way to look at this would be to consider that variable speed pumps are simply a more versatile tool than single speed pumps. Soon it will be law that older and less efficient single speed pumps will not be able to sold, installed or serviced for pool filtration applications. There is no point in buying a new pump today that will be considered antiquated technology within two years from now where you can not even get parts or service anymore. If you have a pool you should definitely upgrade to a variable speed pump right away. You can find comparison reviews of the most popular models in this article about variable speed pump reviews.
How a variable speed pump saves you money
Variable speed pump reviews
Programming schedule for variable speed pumps
Best variable speed pool pumps
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