Two-Speed versus Variable-Speed Pool Motors
July 2020
In today’s cost-conscious environment, most savvy consumers conduct research before investing in replacement parts or upgrades of pool and spa equipment – or depend on installers they trust to make knowledgeable choices for them. This will undoubtedly prove even more true in the months leading up to the new Department of Energy (DOE) standard governing pool pumps. The DOE’s Energy Conservation Standards for Dedicated-Purpose Pool Pumps takes effect on July 19, 2021 and will apply to both residential and commercial pools that fall within the specified threshold.
Currently, self-priming filtration pumps past a particular horsepower threshold (commonly thought of as 1.15 total motor horsepower and up to 5.0 total motor horsepower), must meet established performance standards. Variable-speed motor powered pumps are the only current technology that will meet the July 2021 DOE Standards.
Many energy advocates hope to include a replacement-motor component to the July 2021 DOE Standards. These advocates maintain that the full potential of energy savings can only be realized by utilizing variable-speed replacement pool pump motors in addition to the July 2021 DOE Standards that mandate variable-speed pumps. Under the July 2021 DOE Standards, pool owners will be able to replace pump motors with any type of pool motor rather than one that meets the new energy efficiency standards. This could result in the continued sales of lower efficiency, non-compliant, pump motor replacements, instead of the more robust variable-speed pumps that will meet the July 2021 DOE Standards.
In light of the upcoming July 2021 DOE Standards and the push for a similar motor component to be added, now is a good time to consider the factors that play into the potential cost-savings presented by two-speed versus variable-speed pool pump motors.
Two-speed pool motors
Under average conditions, the simplest way for a residential pool owner to save electricity is to pump only the volume of water needed each day to turn the pool water over twice. This is considered a generally safe water turnover rate for residential pools. Often pool owners will achieve this by running the pool pump system all day to realize the most significant cost savings.
Some exceptions to this rule are important to note, in particular, the location where the pump system is being used. In California, for instance, since utility costs are more expensive during peak demand hours, many consumers prefer to shut their pool pumps off during those peak hours (typically between 12 pm to 6 pm) and run the system fast in the morning and then late at night.
The July 2021 DOE Standards for pumps and the proposed motor replacement do not allow for two-speed motors to be sold as replacements or to be sold powering pumps. Various energy efficient two-speed motor products are on the market today, which include motor speed controllers, and these products can be very effective for the more cost-conscious purchasers. However, one limitation that comes from using two-speed motors is that they just have a high and low speed. To achieve greater efficiency, it is recommended to run this type of system at low speed as much as possible.
Variable speed motors
Variable speed motors allow for a greater range of flexibility. This type of motor can run at any speed; for example, at 70% speed or at 35% speed, whereas two-speed motors can only run at 100% speed or 50% speed. Variable-speed motors allow for “right-sizing” the pump’s flow rate to optimize any pool’s water turnover and energy savings capabilities. Right-sizing motor performance for each person’s pool helps them to achieve greater levels of energy efficiency and cost savings.
Variable speed motors are generally brushless permanent magnet (BPM) motors that are designed to run ultra-quiet at low speeds and include the time clock functionality with an onboard user interface. This makes it possible for pumps to change speed and maintain peak efficiency as required. These motors generally include the motor, a drive or controller that adjusts motor speed or RPM and a user interface that functions as a very high-end timer to control pumping times.
Pairing a Variable-Speed Pump with a Variable-Speed Motor
One popular choice in today’s residential pool market is to replace the current pool pump with a new variable speed pump. The combination of a new pump along with the variable speed motor makes this option a strong choice for many pool owners – especially in cases where an existing pool pump has aged more than eight years, since that is the industry-accepted maximum lifetime for pump seals.
Residential pool pumps that comply with the July 2021 DOE Standards will include a variable speed motor, the drive or controller, a user interface and a new wet-end or pump assembly. Some utility companies offer rebates with the purchase of variable speed pumps. These rebates, in combination with the energy savings provided by the variable-speed motor, often make these variable-speed pumps a great value for pool owners.
Important factors to keep in mind when considering how to achieve these efficiency gains include:
- Pool size in gallons
- The existing pump’s flow rate
- The current pump’s condition
- The homeowner’s energy cost per kWh
The availability of energy efficiency rebates should also factor into savings calculations. In the case of significant rebates, the variable speed pump alternative may deliver the highest long-term value to a pool owner. One helpful tool when considering the best economical return on investment for the pool owner is our Swimming Pool Energy Calculator: http://www.usmotors.com/poolcalculator.
Bio: Jim Ellis is the Director of Marketing for Nidec Motor Corporation’s Commercial and Industrial Motor Division/US Motors, and his current responsibilities include the management of Nidec’s Leisure Water market customer base. Jim is responsible for strategic marketing, new product development, P&L management and client relationship management with both OEMs and Aftermarket customers. Mr. Ellis has held various positions in marketing for Nidec Motor Corporation and Emerson Motor