A technical study on the efficiency of new swimming pool pump technology
19 Apr A technical study on the efficiency of new swimming pool pump technology
Motor & Pump Explorations: A Study of Pump Efficiency
from Aqua Magazine
In both 2009 and 2012, the Independent Pool and Spa Service Association (IPSSA) conducted studies of electrical use and overall efficiencies of commonly used pumps and motors, all in an effort to provide its members with unbiased data about pump and motor technology performance in a real-world setting. Here long-time IPSSA member and participant in the study, Robert Nichols, describes the studies and what they mean to service technicians and builders.
When service technicians are faced with replacing pumps and motors, they are charged with recommending the best choice for their clients in terms of product cost and system performance. Unlike builders, they do not have the choice of determining key factors such as plumbing size or the overall efficiency of the circulation system’s layout.
When you couple that challenge with manufacturer information about energy savings claims and pump and motor performance, making the best choice can be surprisingly challenging. Add to that regulations aimed at maximizing efficiency, such as those in California under the state’s Title 20 Appliance Efficiency Regulations and things become potentially even more confusing.
All of that is why IPSSA decided to sponsor two studies, one in 2009 and another in 2012, which examined in detail the performance of commonly used pump/motor technology. The following is a synopsis of those studies and a sampling of what we found.
SETTING THE STAGE
The 2009 study was prompted by our work with the California Energy Commission, which that year was in the process of revising Title 20, which among other things changed the rules for pump/motor replacement. In this first study, IPSSA was attempting to salvage the traditional single-speed ¾ horsepower motors/pumps and prevent them from being prohibited in residential pool systems in favor of two-speed or multi-speed units.
The move was largely the work of Pacific Gas & Electric, the state’s largest utility company, and Pentair, both of whom were pushing for the mandatory change. The arguments coming back at us were based on what many of us in the service industry believed were questionable claims about energy savings to homeowners. We decided to test motor and pump combinations under real-world conditions so we could come up with reliable numbers that, among other things, we hoped we could use in support of maintaining the use of the ¾-hp, single-speed pump, which remains a workhorse in many other states.
Language in CEC Title 20 now in essence states that pumps 1 hp or greater must be replaced with a two-speed or multi-speed motor. IPSSA was fine with that until the requirement was applied to motors based on “full service” rating, which in effect outlaws ¾-hp motors/pumps with a 1.65 service rating.
Right off the bat, here’s where it gets tricky. Full service rating is the sum of the pump’s nameplate rating and service factor (which I discuss in more detail in the sidebar). When applied to the ¾-hp motors, the service factor of a standard or “full rated” motor pushes that motor beyond the 1 hp total horse power (THP) threshold for regulation. What that meant in terms of the Title 20 debate was that when replacing a ¾-hp pump, you had to use either a two-speed or multi-speed pump. At that time, a two-speed required a timer (probably $300 to the homeowner), and with a multi-speed, you’d need a control system that can cost upwards of $800 or more. At IPSSA, we did not want to see our clients incur that expense for a simple pump or motor replacement that provided no benefit for the cost.
We wanted to preserve the ability to replace kind-for-kind with ¾-hp models. Of course, the rationale for the language was to increase energy efficiency. And make no mistake, IPSSA is all in favor of energy efficiency both from an environmental and efficiency standpoint.
The point of our study was to determine whether or not there were, in fact, significant differences in energy efficiency between traditional ¾-hp pumps and two- and multi-speed units. Our goal was to see for ourselves through impartial testing, with completely transparent protocols, whether or not those claims were true. We were not out to necessarily debunk manufacturer claims, but simply put them to the test. Their high return on investment claims were always based on 1.5-hp (THP 2.47) motor, which on any 2-inch plumbing system is inefficient.
One problem we had was comparing apples to apples in the PG&E study. Some data was based on a 12,000-gallon pool, while others were based on a 20,000-gallon pool, often with different total dynamic head operating conditions and turnover rates. That made it extremely difficult to determine if one type of motor/pump combination was, in fact, more efficient than others.
After lengthy discussions, we got everyone with CEC and PG&E to agree on tests based on what we at IPSSA believe is a typical, real-world scenario.
THE 2009 STUDY
The protocol we developed was based on turning over 12,000-gallons on both 2-inch plumbing and 1.5-inch plumbing. We based our findings on running the single-speed units long enough to turn over the water volume, then the two-speed and multi-speed units for two hours at a 1-hp flow rate and then the remainder at the lower speed required to turn over the 12,000 gallons.
The tests were conducted at the International Association of Plumbing and Mechanical Officials (IAPMO) laboratories in Ontario, Calif.
We set up the plumbing configuration with a flow valve at the pump volute to create 50 feet of Total Dynamic Head (TDH). Prior to the study, we surveyed approximately 800 systems in the field and found an average right at the 50-foot level, so were confident that it was a representative number.
Once we set the TDH, we never moved anything that would create a different flow configuration and change the TDH. We compared ½-hp, ¾-hp and 1-hp single-speed, two-speed and multi-speed units using the flow rate of the 1-hp model as the baseline for comparison, on both 2-inch and 1.5 inch plumbing.
The results of the study are laid out in two tables, and I won’t go into every detail here. As one example, we found that the single-speed 1-hp pump required 1789 watts to achieve 79.5 gpm. That, compared to 1424 watts for the multi-speed motor at the same flow rate, leaves a difference of about 350 watts. That is a significant savings, but not nearly as dramatic as some manufacturers claim.
If you run the system fours a day, that comes out to about 1.2 kilowatts savings. depending on your energy rates, that’s a savings about 50 cents per day, or $182.50 per year.
We published our findings on the IPSSA website, in our newsletter and in Service Industry News, and they remain available for anyone to review. In the briefest summary regarding the ¾-hp question, we found no benefit in terms of energy efficiency when using a two-speed pump/motor over ¾-hp models. Multi-speed motors did show energy savings, as mentioned just above, but according to our study, they do not equal the savings being claimed by manufacturers. Their single advantage is to regulate RPM and flow to achieve additional energy savings.
Across the board we consistently found significant savings between 2-inch plumbing and 1.5-inch plumbing. In fact, we found that on 1.5-inch plumbing you really shouldn’t use anything larger than a ¾-hp pump, and more likely a 1/2-hp pump will serve the purpose.
Despite those findings, the CEC moved forward and approved the California Title 20 language requiring replacement with two-speed or multi-speed pumps/motors.
When we shared our findings with manufacturers, they were somewhat apprehensive to say the least and were, not surprisingly, highly critical of the study. IPSSA’s position was and remains that findings based on our protocol are reliable. That said, it certainly may be that using different protocols would yield different results.
Despite losing the battle over ¾-hp models, we did come away with a valuable resource for our members and anyone else who cares to use the data. We are confident anyone concerned with energy consumption and efficiency, when changing out a pump/motor, can use the tables we’ve developed as a reliable tool to establish reasonable expectations for the system’s performance.
THE 2012 STUDY
A similar challenge came our way in 2012 when the California Utility Commission and other investor-owned energy providers wanted to exclude multi-speed replacement motors from rebate programs. At that time, manufacturers including Emerson and Century had introduced multi-speed motors that could be fitted to standard pump units with what we believed were significant energy efficiency gains.
We approached our friends at the CEC looking for help, saying that these energy-efficient units should be covered under utility rebate programs. They told us they needed numbers, so we set up another study, this time using only 2-inch plumbing with the same 50 TDH and 12,000-gallon turnover volume.
Again, we compared single-speed 1-hp and ¾-hp motors with the multi-speed motors, which we ran at the 1-hp flow rate and then the ¾-hp flow rate. In testing the motors we did two sets of tests, one with 1-hp impellers and then again using 2-hp impellers.
First of all, we found out that when using multi-speed motors, the bigger the impeller and the lower the RPM, the greater the energy savings, which made sense to everyone.
Overall, the multi-speed-drive motors, the primary subject of the study, performed well, but again, not as well as anticipated. For example, the multi-speed units on 1 hp with a flow rate of 80 gpm used approximately 1424 watts, while the multi-speed motor at the 1-hp setting with a 2-hp impeller used 1389. It was a little more efficient, but not dramatically. Again, the ability to adjust RPM to a desired flow is the single advantage to multi-speed pumps.
Note: Although these studies did examine multi-speed systems, which allow up to eight predetermined flow rate settings, neither the 2009 nor 2012 study tested variable-frequency drive technology, which could be defined as those systems that have internal intelligence that sets their own speeds to the most efficient level. The number of variable parameters involved with creating a study like this were extremely complex and based on the relatively few number of VFD sales by our members, so we decided not to test that technology.
We sent the results to the CEC who in turn shared the results with California Public Utilities Commission for their consideration. At this writing the rebate issue has not been resolved. We remain hopeful.
BASIC TAKE AWAY
These studies confirm what many people in our industry have been saying about efficiency for several years now: Smaller pumps, bigger plumbing, less RPM and a bigger impeller work together to maximize efficiency.
For builders, those four factors are available. A service technician obviously cannot dictate the size of the plumbing. So what he or she needs to do is size replacement pumps and motors accordingly.
Looking at the results of these studies, we can conclude that when you’re dealing with 1.5-inch plumbing, you probably shouldn’t use anything larger than ½ hp. The nice thing about ½-hp motors/pumps is that even with service factor they fall under the 1-hp threshold defined by the CEC and are allowable as replacements.
Unfortunately, as stated above, for 2-inch plumbing, you can no longer use ¾-hp full-rated 1.65 service factor technology and must go to the multi-speed units, or two-speed, which are becoming less and less available and these days rarely used.
Click here for more detailed information about the study results.
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For years and years now, people who sell pumps and motors have used the “service factor” as a sales tool. For example, they may claim their pumps have a service factor of 1.75, essentially saying that you get more for your money — the idea being that if you are selling a 1-hp motor/pump combination, with that 1.75 service factor it’s actually a 1-¾-hp “fully rated” pump.
This is why the CEC regulated ¾-hp motors, because with the service factor, i.e. “fully rated,” they exceed 1 hp.
However, the National Electrical Manufacturers Association guidelines recommend service factors of no greater than 1.25. If you exceed that on your electrical load, you need to go up in horsepower or risk damaging the motor. When I first discovered that guideline many years ago, it prompted a question: Why is our industry promoting service factors greater than 1.25?
What I and many other people have discovered, although manufacturers seldom explain it this way, is that what you’re talking about with service factor is the ability to load the motor to a level beyond the motor’s “name-plate rating.”
Here’s another more precise way to look at it. One horsepower equals 746 watts. If you buy a ¾ hp with a 1.65 service factor, you multiply 1.65 by .75, which equals 1.24 (rounded) then multiply 1.24 by 746, which gives a full loading capacity of 923 watts. If you load the ¾ motor with more than 923 Watts you are exceeding the manufacturers specification.
Service factor horsepower has absolutely nothing to do with the impeller size, the output of the pump or energy efficiency; it’s simply a rating that tells you how much you can load the motor before you go up in size in terms of horsepower, nothing more.