We found an amazing document written by the Department Of Energy. This is a 32 page document so we have decided to break it down and turn it into a series so help you understand. There is a lot of information however, there is also a significant savings to be had so we just had to share this information with you. So here is part one of our breakdown of this Department of Energy document on the variable speed pool pump.
According to a 2008 report by the Natural Resources Defense Council (NRDC)1, there are more than 4.5 million in-ground residential pools in the United States, and they consume between $1.1 and $1.6 billion in energy costs per year. Energy use will differ because of variations in swimming season length, energy rates, whether or not (and how) pools are heated, and other environmental factors. However, the NRDC has estimated that, nationwide, residential in-ground swimming pools consume between 9 and 14 billion kilowatt hours (k-Wh) and between 36 and 63 million therms of natural gas each year for pool heating. This results in national CO2 emissions of roughly 10 million tons per year the equivalent of 1.3 million cars and light trucks on the road. In homes with pools, a pool pump can be the second largest energy user and most often is the largest energy user in the home.
Pool pumps provide an important function for in-ground pools by circulating water through the pool’s filtration system. The filtration system keeps the water clean, clear, and sanitary for bathers by screening debris that falls into the pool and also removing algae and microorganisms that can pose potential health threats to swimmers. In addition, pumps may also circulate water through heaters, cleaners (also known as sweeps), water features, or fountains. These single-speed pumps traditionally have a 1- or 2-horsepower motor that will run at least five to six hours per day, if not around the clock, consuming energy.
For a relatively small investment, a variable speed pool pump can reduce pool pump energy use by 50% to 75%. The majority of the savings is derived from a variable speed pump’s ability to reduce the rpm of the motor, thus reducing energy use. A typical 11⁄2-horsepower pool pump draws about 2,000 watts and runs at 3,450 rpm. Reducing the pump speed and flow has a tremendous impact on wattage draw due to the Pump Affinity Law. For example, if you reduce the pump speed from 3,450 rpm to 2,400 rpm (30% reduction in speed) the wattage drops from 2,000 watts to 593 watts (70% reduction in power).
Replacing a single-speed pump with a modern variable speed pump is relatively quick and simple. In order to successfully complete the task, the installer must calculate the number of gallons of water in the pool and calibrate the new pump to circulate water at an appropriate rate. When completed, the variable speed pump will provide the same service as the traditional pump but at a substantial energy savings for the homeowner.
Understanding the importance of a properly functioning pool circulation system
Although the Association of Pool and Spa Professionals (APSP) suggests that the pump be “capable” of turning over the entire volume of water in the pool two times in 24 hours, the actual turnover rate can be slower when conditions permit. Pools that inadequately filtered can incubate dangerous pathogens (disease-causing microorganisms) and pose a health risk for bathers. Algae, bacteria, viruses, and fungi can thrive in a poorly filtered swimming pool, often introduced into pool water by rain, wind- borne debris, bathing suits, or poor quality water used when filling. Chemical disinfectants and chlorination can help to reduce the threat of disease and illness, but, a properly maintained and functioning pool pump and filtration system is critical to keeping the swimming water safe and clean.
Replacing a single-speed pool pump with a variable speed pool pump can create equal or greater potential energy savings than realized by updating an existing home to an ENERGYSTAR® -rated home.
This section will explore the cost and performance benefits associated with replacing a single-speed pool pump with a variable speed pump as well as discuss the physics behind the Pump Affinity Law and other benefits of pool pump replacement not related to energy.
The primary reason that most single-speed pool pumps consume an excessive amount of electricity is that they are typically oversized and
overused in the course of pool operation. A pool pump is called upon to perform multiple water circulation duties during the operation of the pool. While the primary function of the pool pump is to simply circulate water through the filtration system, other tasks can include powering spa jets, backwashing the filter, operating a chlorinator, providing water for the pool sweeper, circulating water through the heater, initiating flow to a solar panel and pumping water to waterfalls and other water features. These occasional tasks require more energy (a greater flow rate) than the circulation of pool water through the filtration system and account for roughly 10% of the pool pump’s operation time. Often, pools have multiple pumps to provide some of the functions listed above.
Single-speed pumps by design can’t change their flow rate so they must be sized to perform the most demanding task. This means that during 90% of the operational time, single-speed pool pumps provide greater circulation than the pool filtration system requires. A standard pool pump is typically 11⁄2 to 2 hp and operates using a single-speed induction motor generating excessive filtration flow rates. This volume of water is achieved by a 3,450 rpm rate that requires between 1,500 and 2,500 watts of electricity depending on the service factor of the motor.
Two-speed pool pumps.
Although not common, installers may encounter a two-speed pool pump during the inspection and replacement process. Two-speed pumps have been available for years and are marketed as an alternative to more expensive variable speed pumps. 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.
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 either Permanent Magnet Motors (PMM), which use permanent magnets to create a magnetic field between the rotor and the windings. This configuration is similar to the motors used in hybrid cars. Efficiencies are gained by the magnets working to spin the rotor, as opposed to a standard induction motor that requires additional electricity to induce the magnetic field into the rotor. The PMM motor design is much more energy efficient when compared to the standard induction motor, achieving efficiency ratings of 90% while the average single-speed pump will have efficiency ratings between 30% and 70%.
PMM pumps can produce the same gpm flow rate as single-speed induction motors if needed; they simply run much more efficiently. The largest energy savings of installing a PMM pump comes from the ability to program and reduce the flow rate to match the required pumping task. Unlike a single-speed pump that will operate at maximum flow rate even for tasks that require minimum flow rates, the variable speed pump can be slowed down to the optimum level balancing flow rate needs with energy use. In order to fully appreciate how significant these energy savings can be, it is important to understand the physics behind the Pump Affinity Law.
The Pump Affinity Law is a term used to express the relationship between motor speed, flow rates, and energy consumption. While some energy savings come directly from improved motor efficiency, the majority of energy savings gained by replacing a single-speed pump with a
variable speed pump is due to the Pump Affinity Law. This law quantifies that power consumption drops at a nonlinear rate as you reduce pump speed and water flow. When you cut the motor speed in half, the flow rate is also reduced to half, but the power consumption of the pool pump is reduced to 1/8th of the original draw. The following chart demonstrates how the pump speed and flow rates directly impact power usage. Remember, most single-speed pumps have a standard 3,450 rpm speed that cannot be adjusted, even when a flow rate is much less than 66 gpm is required.
The following example illustrates how replacing a single-speed pump with a variable speed pump can create significant energy savings. The average residential swimming pool contains 25,000 gallons of water and has a suggested turnover rate of 24 hours. A single-speed pump drawing 2,000 watts, operating at 3,450 rpms and generating a flow rate of 66 gallons per minute can turn over the entire 25,000 gallons of water in roughly 6.3 hours.
(25,000 gallons / 66 gpm) /60 minutes = 6.3 hours
At this rate the single-speed pump would consume 12,600 watt hours or 12.6 kWh per day, to turn over the pool.
6.3 hours x 2,000 watts = 12,600 watt hours (12.6 kWh)
However, because of the Pump Affinity Law, slower flow rates create greater energy savings. In the field, a variable speed pump set at a flow rate of 22 gpm will draw 116 watts and turn the pool over in 19 hours but only consume 2.2 kWh of electricity.
(25,000 gallons / 22 gpm) /60 minutes = 19 hours
19 hours x 116 watts = 2,200 watt hours (2.2 kWh)
This is a savings of 10.4 kWh per day, or approximately 3,796 kWh per year. The average retail price of electricity to residential customers in California, where there are an estimated 1.1 million in ground pools, is 14.8 cents per kilowatt-hour. Following this example, the homeowner could realize a savings of $561 annually on their electric bill.
Saving energy is a wonderful goal but should not happen at the expense of swimming pool sanitation and water clarity.
Most water clarity problems are caused by improper chemical maintenance, not by debris and silt hovering around indefinitely. Particles large enough to be captured by a filter will sink when the pump is off. This is not to say that the filtration and circulation systems do not impact water clarity; when not run long or fast enough to allow effective chemical feeder/generator operation, they do.. However, it is a common misconception that a slower turnover rate will allow for more contaminants to remain in the pool longer and result in less than ideal water clarity.
When comparing performance issues between single-speed and variable speed pumps, there are no negative performance issues associated with the variable speed pump. When properly calibrated, the variable speed pump can increase flow rates to be equal to or greater than the existing single-speed pump. However, the performance advantages of a variable speed pump go beyond energy savings. 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. The slower circulation rates also put less strain on the filters, plumbing, and other parts of the system, which reduces the chance of leaks, repairs, or premature plumbing component replacement.
Pricing of variable speed pumps remains higher and can be a barrier to adoption during a home retrofit. Although prices may vary, the average cost, with installation, to replace a single-speed pump will range from $400 to $700. A two-speed pump installation will generally range between $700 and $1,000, while installation of a variable speed pump, complete with onboard controller and programmable task manager, can cost between $1,400 and $1,800. In order to offset the additional costs, many utility companies are now providing incentives for installing variable speed pumps. Examples of incentives range from $75 in Nevada to $600 in Florida. The Database of State Incentives for Renewables & Efficiency (DSIRE) has more information on the availability of rebate programs for installing variable speed pool pumps at http://www.dsireusa.org/.
For part 2 of this document be sure to check back next week! If you are ready to start talking to us about retrofitting a variable speed pool pump be sure to contact us today.