|Pump Affinity Law|
|Operating the pump at half speed:
• reduces the flow rate to approximately half;
• slower moving water reduces the amount of resistance in the hydraulic system (total dynamic head [TDH]) in feet by one-quarter;
• uses approximately one-eighth the power (approximately); and
• uses one-quarter the energy (75 per cent savings) at the same turnover (twice the run time). Greater savings are possible if operated at less than half speed.
As noted earlier, VSPs are the fastest growing segment within the pool product market. With more choices than ever before, consumers are finding the multiple-speed pump that best serves their needs.
VSPs were first introduced almost a decade ago. Since then, most pool manufacturers have launched full model lines. While the majority of pool pumps on the market today remain single speed, multiple-speed pumps are catching up quickly.
What is holding the industry back?
While the trend is going strong, there is still some resistance to VSPs. Pool owners are often slower to upgrade their equipment to more energy saving technologies than they are in other areas of their lives (e.g. smartphones and TVs), perhaps because they do not regularly interface directly with their equipment.
Another reason why many pool owners are not looking for the greenest, most advanced equipment technology can be attributed to a simple matter of habit. Single-speed pumps have been tried-and-true for more than 40 years, this alone has made it difficult to convince people to switch to newer technology. Further, the upfront cost of converting to a VSP may also deter some pool owners. Prior to having the hard data to show consumers the realized energy and cost savings, which would offset the expense of a VSP, many were simply unwilling to spend the money. Energy savings were largely masked in the past as most could not answer the pool owner’s question about how much their pump costs them. But this is all changing.
Now, there is documented data showing the significant savings a pool owner can realize by switching to a VSP.
According to the U.S. Department of Energy, the following example illustrates how replacing a single-speed pump with a VSP can create significant energy savings. The average residential swimming pool contains 94635 L (25000 gal) of water and has a suggested turnover rate of 24 hours. A single-speed pump drawing 2,000 watts, operating at 3450 r.p.m. and generating a flow rate of 250 litres per minute (lpm) (66 gallons per minute [gpm]) can turn over the entire volume of water in roughly 6.3 hours.
(94635 L [25000 gal] / 250 lpm [66 gpm] / 60 minutes per hour = 6.3 hours)
At this rate the single-speed pump would consume 12,600 watt hours (12.6 kWh) per day to turn over the pool.
(6.3 hours x 2000 watts = 12600 watt hours [12.6 kWh])
However, because of the pump affinity law, slower flow rates create greater energy savings. In the field, a VSP set at 1150 r.p.m. would generate a flow rate of 83 lpm (22 gpm) and draw approximately 116 watts. This would turn the pool over in 19 hours but only consume 2.2 kWh of electricity.
(94635 L [25000 gal] / 83 lpm [22 gpm] / 60 minutes per hour = 19 hours)
(19 hours x 116 watts = 2200 watt hours (2.2 kWh)
This math cannot be argued. While there may have been some reluctance to make the conversion in the past, the phrase popularized by Star Trek comes to mind: “Resistance is futile.”
VSPs: From trend to necessity
Going green is so much more than a trend or, worse, a fad. The movement to make pools more energy-efficient will potentially save consumers millions of dollars in energy costs. It is also a huge boon to the trade as it represents millions in technology upgrades in Canada and the United States. This is a tremendous (even daunting) opportunity for the entire pool and spa industry.
It is not an overstatement to say the greatest potential for pool owners to save on operating costs is to switch their single-speed pump to a two or, better yet, VSP. In making the switch, consumers can not only save money, but also do their part to help the planet.
Scott Petty is the global product manager for pumps and above-ground equipment for Hayward Pool Products. Previously, he managed Hayward’s test facilities and agency compliance activities. Over the course of 10 years in the pool industry, Petty has cultivated an expertise in energy efficiency and hydraulics. He has a bachelor of science in mechanical engineering from North Carolina State University and a MBA from Wake Forest University. He can be reached via e-mail at firstname.lastname@example.org.