Is Your Pool an Energy Hog?
Replacing your old single-speed swimming pool pump with an efficient variable-speed pump is an energy retrofit measure with a very fast payback
If your home has a swimming pool, your pool pump may use more electricity than any other appliance in your home — as much as three times the electricity used by your refrigerator. Many residential pools in the U.S. have 1.5-horsepower or 2-horsepower pumps that draw 2,000 watts or more. If you’re not paying attention, you may be running your pool pump for 24 hours a day — even though your pool might be perfectly clean with only 6 hours of pump operation per day.
If your pool has one of these older single-speed pumps, installing a new variable-speed pump is one of the most cost-effective energy-saving measures you can take.
You want a variable-speed pump
The main purpose of a pool pump is to circulate water from the swimming pool through a filter. In addition, a pool pump is sometimes used to circulate water through an artificial waterfall or other so-called “features.”
For years, pool installers have specified oversized single-speed pumps — a type of pump that is inexpensive to install but expensive to operate. Many swimming pool pumps perform multiple functions, and installers traditionally sized a pump that was big enough for the most demanding task — for example, circulating pool water through a heater, energizing spot jets, or vacuuming the pool. Most of the time, when the pump is merely circulating water though the filter, it’s oversized.
A two-speed pump or a variable-speed pump does a better job of matching the speed of the pump (and its watt draw) to the task being performed. Compared to a single-speed pump, a two-speed or variable-speed pump can save tremendous amounts of energy. According to one source, compared to a single-speed pump, a two-speed pump can yield 55% energy savings, while a variable-speed pump can yield 83% energy savings.
A useful document prepared by the U.S. Department of Energy, “Measure Guideline: Replacing Single-Speed Pool Pumps with Variable Speed Pumps for Energy Savings,” explains that variable-speed pumps are preferable to two-speed pumps. The document notes, “The two-speed pump uses an induction motor and is basically two motors in one with a standard 3,450 rpm (full-speed) motor and a 1,725 rpm (half-speed) option. Ideally these motors may enable significant energy savings for the homeowner; however, if the half-speed motor is unable to complete the required water circulation task, the larger motor will operate exclusively. Because there is are only two speed choices it is much more difficult to fine-tune the flow rates required for maximum energy savings.”
The most efficient type of swimming pool pump is a variable-speed pump. The document notes, “A variable-speed pool pump will allow the homeowner to achieve the ideal filtration flow rate with the least amount of energy consumption. Variable speed pumps utilize … permanent magnet motors (PMM). … PMM pumps can produce the same gpmGallons per minute. Measure of liquid (usually water) flow. flow rate as single-speed induction motors if needed; they simply run much more efficiently. … Variable speed pumps are noticeably quieter, require less maintenance, last longer, and, through slower water filtration rates, allow for better and more effective filtration of the pool water.”
Reducing pool pump energy consumption
Here’s a list of pool pump energy tips:
- The best pump is a variable-speed pump. Two-speed pumps fall somewhere between variable-speed and single-speed pumps in performance. Single-speed pumps are the worst.
- Choose the smallest possible pump; most residential pools requires a pump that is no larger than 3/4 horsepower.
- All piping connected to the pool pump should be at least 2 inches in diameter. Pipe runs should avoid 90° elbows; instead, use long-sweep 90s or 45s.
- Pool pumps should operate for as few hours a day as possible — ideally 6 hours or fewer. However, it’s better to have a small pump that runs for more hours per day rather than a powerful pump that runs for fewer hours per day.
The Pump Affinity Law
The advantage of a small pump is explained by the Pump Affinity Law, which states that the power consumed by a pump is proportional to the cube of the flow rate. This means, for example, that if a pump’s flow rate is reduced by half, its power draw is reduced to one eighth. If you reduce a pump’s speed from 3,450 rpm to 2,400 rpm — a 30% reduction in speed — the watt draw drops from 2,000 watts to only 593 watts — a 70% reduction in power.
If you reduce the speed of a pump motor by half, you get half the water flow, so you will have to operate the pump for twice as long as you would if you used a pump with a more powerful motor. But since the low-speed motor only draws one-eighth as much power as the high-speed motor, it will only require one-quarter as much energy (in theory; actual savings are somewhat less than theoretical savings) to move the water with a smaller pump.
Examples of savings
Replacing a typical 1.5-horsepower single-speed pool pump with an efficient variable-speed pump will result in energy savings of 50% to 75%, according to the Department of Energy. Actual savings may be even higher; savings depend in part on how many hours per day you have been running your pool pump.
There are many examples of homeowners who save between $800 and $1,100 a year by installing a new pump; in one case, a pump drawing 1,900 watts was replaced with a variable-speed pump that draws only 150 watts.
How much does a good pump cost?
If you hire a pool contractor to replace an old single-speed pump with a new variable-speed pump (which comes with a controller and programmable timer), expect to pay between $1,400 and $1,800 — significantly more than the cost to install a single-speed pump ($400 to $700) or a two-speed pump ($700 to $1,000). Of course, if you install the pump yourself, the cost will be less.
Although a variable-speed pump is expensive, the payback period for this work can be as short as one or two years. Moreover, many electric utilities and state governments offer rebates to offset some of the cost to install a variable-speed pool pump. These incentives range from $75 to $300 per pump, and are available to at least some customers in Arizona, California, Florida, Massachusetts, New York, Pennsylvania, Rhode Island, Texas, and Vermont. (This is an incomplete list of states with rebate programs; the programs are subject to change.)
For up-to-date information on pool pump rebate programs, visit the Database of State Incentives for Renewables and Efficiency (DSIRE) website.
It should be noted that at least three states — California, Arizona and Florida — have recently passed laws that ban the installation of old-fashioned single-speed pool pumps for residential swimming pools.
A new ANSI standard
Prodded by forward-thinking energy-efficiency advocates in California, Arizona, and Florida, the pool pump industry is (slowly) moving to develop and promote more efficient pumps.
The recent pool pump requirements passed by the Arizona and Florida legislatures both reference a relatively new ANSI standard, ANSI/APSP/ICC-15a, "American National Standard for Residential Swimming Pool and Spa Energy Efficiency."
The ANSI standard is based on California's Title 20 requirements (the California appliance standards) and Title 24 requirements (the California energy code). Pool pumps were first addressed by California Title 20 in 2006, and by California Title 24 in 2012.
How do I know what kind of pump to install?
Here are four pool pump models that are energy-efficient and that have variable-speed motors:
These pumps are listed as examples; the list is not exhaustive. Most electric utilities with rebate programs maintain an online list of approved pool pumps.
The Energy Star program now labels pool pumps
Another source of information on efficient pool pumps is the Energy Star program. To be eligible for an Energy Star label, a pool pump must have a minimum energy factor (EF) of 3.8. (Pool pump EF is the ratio of gallons of flow per hour divided by watt-hours, as measured by the ANSI/HI 1.6-2000 method.)
A list of pool pumps that meet the Energy Star specification has been posted online.
The Energy Star specification for pool pumps allows single-speed pumps to obtain an Energy Star label. So far, no pump manufacturer has been able to develop a single-speed pump that is efficient enough to meet the Energy Star standard, but it is possible that one may be developed in the future. If you are in the market for a variable-speed pump, check the specs before you make your purchase, since an Energy Star label may not be enough to steer you in the right direction.
Should HERS ratings reflect swimming pool energy use?
At this time, HERS ratings ignore energy used for swimming pools. Fortunately, the RESNET Technical Committee is working to amend the way HERS ratings are calculated so that pool energy use is accounted for.
Jeff Farlow is the program manager of energy initiatives at Pentair, a manufacturer of pool pumps. Among pool pump professionals, Farlow is a standout who clearly understands the need for energy-efficient pumps. According to Farlow, “RESNET is developing a HERS-type rating for swimming pool that will be based on ANSI/APSP 15. We’re also talking to BPI [the Building Performance Institute], as well as trying to educate home performance contractors. The Energy Upgrade California program for existing homes now has a component for swimming pools. I’m hearing from home performance contractors who say, ‘Please include swimming pools in any package of energy improvements,’ because a variable-speed pump is a low-cost item compared to other energy upgrades, and it has a payback period as short as one year.”
Martin Holladay’s previous blog: “Climate-Specific Air Conditioners.”
- Ollie Crafoord
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