Facility managers are learning that going ‘green’ can significantly lower operating costs. Pumps and filters are among the items most scrutinized due to the vast amount of energy they consume. To reduce costs, it's important to understand why pumps and filters consume so much energy and what options are available to lower consumption. This article looks at ways an aquatic facility can save energy and money with green options for pumps and filters.
Extracting costs from filtration
The type of filter used (e.g. cartridge, sand or diatomaceous earth [D.E.]) can have a significant impact on energy consumption because each one places different levels of resistance on the circulation system. Resistance is related to energy efficiency because of its impact on water flow. Of the three filter types, cartridge filtration offers the least resistance to flow, which is partially due to the absence of valves. Both sand and D.E. filters require multiport valves to perform routine backwash procedures. These valves create so much resistance to flow that the California Energy Code (Title 24), has banned 1.5-inch multiport valves. As a result, newer backwash valves are designed to lessen flow resistance. On a related note, backwashing consumes water, so using a filter that does not require it will help the facility conserve both water and chemicals.
Although sand and D.E. filters function more effectively as dirt accumulates, a dirty filter can increase the pump’s workload. In fact, the difference between a clean and dirty filter can nearly double the pump’s energy use. If friction loss can be decreased in the facility’s plumbing design and equipment sizing, less horsepower (hp) is required to achieve the desired flow rate. The savings realized when using an oversized cartridge filter to reduce overall system head loss is well documented. Finally, by simply keeping the pool’s filter clean and skimmer basket free of debris, energy savings can be significant.
Circulate savings by selecting the right pump
Proper pump selection (sizing) and optimal flow rates are additional ways an aquatics facility can save energy. Affinity laws indicate the power demanded by a pump is proportional to the cube of the flow rate. For example, if the pump’s flow rate is doubled, then its power demand is increased by a factor of eight. So it is important to utilize the smallest pump that is capable of completely turning over the water in an acceptable amount of time.
When selecting a pump, the facility’s auxiliary features (e.g. spray pads and fountains) also should be considered because it's common for them to use the pool’s main pump. Some building codes, however, require the use of a multispeed pump, or in some cases, a separate pump for each auxiliary pool load. Pumps for aquatic facilities are oversized by design, sometimes more than 20 to 40 percent bigger than needed. This happens because many architects and engineers look at what is required, then upsize to be sure the pump can handle the job.
Speed is a factor
Historically, pool pumps with induction motors, which only operate at one or two speeds, have drawn more energy than is required to circulate pool water. These units must constantly operate at high speed in order to perform the pump’s most demanding jobs (e.g. running a waterfall or pool cleaner). However, it takes far less power to simply keep the pool water filtered — a difference single-speed pumps cannot address.
Where variable-speed pumps (VSPs) differ is in its ability to be programmed to deliver the correct flow rate for each task they perform. This enables an aquatic facility to reduce energy use and increase savings.
They also can be programmed to achieve turnover times of exactly six hours, even if the filter is dirty. This allows motor speed, power and energy to be reduced during times when the filters are clean, instead of sizing the pump to assume worst-case operating conditions.
Some VSPs have built-in, constant-flow software, which maximizes the advantages these pumps have to offer because it will automatically adjust its speed to deliver the required flow rate for each programmed task. For instance, to achieve the maximum laminar height of 7 feet at a distance of 8 feet, a water supply of 10 GPM with 16 feet of head (measured at the laminar) is required to produce a smooth 6 feet of arc water. As the filter accumulates dirt, however, the pump will sense resistance in the circulation system and automatically ramp up its speed to continually provide the proper flow rate the waterfeature requires. With other pump types, the waterfeature will gradually throw a shorter arc of water as the filter gets dirtier.
No matter what type of pump is being used, however, slower pump speeds save energy and dramatically reduce noise levels as well as wear and tear on other pool equipment.
Eliminating sticker shock
Even with the advantages, some facility operators still find the cost of a VSP hard to justify. However, before ruling one out, the price of a new pump should be compared to the expense of doing nothing.
An aquatic facility with a single-speed pump may have operational costs of up to $900 per year. After five years, the facility will have spent $4,500. Comparable costs for a facility with a well-designed circulation system that uses a VSP, however, may be as little as $200 per year and over five years it will cost less than a quarter of the amount the facility would have spent with a single-speed pump. The cost of a VSP can typically be recouped during the second year of use.
With the substantial rebates offered by some local power companies, in conjunction with the savings in operational expenses, some end-users are getting back 50 percent of the pump’s cost in less than a year.