Reducing operating expenses with energy-smart equipment

by Sally Bouorm | August 1, 2011 1:02 pm

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By Mike Fowler

Facility managers have learned over the past few years that going ‘green’ can significantly lower an aquatic facility’s operating costs. Pumps and filters are among the items most scrutinized due to the vast amount of energy they consume. To reduce costs associated with water circulation and filtration it is important to understand why pumps and filters consume large amounts of energy and what options are available to lower consumption. This article will look at various 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, as each one places different levels of resistance on the circulation system.

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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 multi-port valves to perform routine backwash procedures. These valves create so much resistance to flow that the California Energy Code (Title 24), The Energy Efficiency Standards for Residential and Nonresidential Buildings, has banned 38-mm (1.5-in.) multi-port valves. As a result, newer backwash valves have been designed to lessen flow resistance. On a related note, backwashing consumes water, so using a filter that does not require this type of maintenance 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 consumption. 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. While the type of filter installed is often a personal preference, the energy 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 leaves and other debris, energy savings can be quite significant.

Circulate savings by selecting the right pump

Proper pump selection (sizing) and optimal flow rates (as mentioned above) are additional ways an aquatic facility can increase energy savings. 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. Therefore, it is important to utilize the smallest pump that is capable of completely turning over the pool water in an acceptable amount of time.

Furthermore, during the pump selection phase, the facility’s auxiliary features (e.g. spray pads, fountains and waterfalls) should also be considered, as it is common for them to use the pool’s main pump. Some building codes, however, require the use of a multi-speed 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 per cent bigger than they need to be,” says Mark Caldwell, president and CEO of Pool Services Corp, a commerical pool service company in Myrtle Beach, S.C. “This happens because many architects and engineers look at what is required, then pick the next size up to be sure the pump can handle the job.”

‘GREEN’ CIRCULATION CHECKLIST

1. Replace pool pump with an energy-efficient unit. 2. Consider a variable speed pump (VSP). VSPs with permanent magnet motors and digital controls can save up to 90 per cent in utility costs compared to one- or two-speed pumps with induction motors. 3. If using an energy-efficient one- or two-speed pump, make sure it is sized to the pool’s requirements. 4. Reduce run time or speed to lower energy use. 5. If using a one-speed pump, reduce filtration run time. In general, water needs to be circulated through the filter once every 24 hours. 6. If using a two-speed or VSP, use the lowest speed to appropriately circulate the water. Reducing speed saves more energy than reducing run time. 7. Run the pool’s filtration system during off-peak hours when electricity demand is lower (generally between 8 p.m. and 10 a.m.). Install a timer or control system to automate hours of operation. 8. Keep intake grates clear of debris. Clogged drains require the pump to work harder. 9. To obtain maximum filtration and energy efficiency, backwash or clean the filter regularly, as required.

Pump selection tips

1. Determine flow rate in litres per minute (lpm) (gallons per minute [GPM]).
2. Calculate total dynamic head (TDH), which is the pressure head difference between the inlet and outlet of the pump, to account for friction loss. Adding 6.1 m (20 ft)/head for a dirty filter is optional. Friction loss is generated by each fitting, valve, filter, heater and chemical feeder that is part of the pool’s circulation system.
3. Refer to the pump’s performance curve to select the preferred unit.
4. Locate the required horsepower of the pump by plotting GPM vs. TDH. (If the plotted point falls between two pump sizes, select the next larger pump size in terms of horsepower.)
5. Do not oversize the pump. Choose the best pump available for the facility’s flow rate requirements (i.e. do not install a 20-hp pump where a 10-hp pump will suffice just because that is all that is available). If the preferred pump does not provide a proper fit, consider a different pump model.
6. Verify the selected filter can handle the system’s flow rate and be sure the minimum backwash flow rates can be achieved.

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 to perform their 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 their ability to be programmed to operate at set speeds to deliver the correct flow rate for each task they perform. This enables an aquatic facility to reduce energy consumption and increase savings.

They can also 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, as it will automatically adjust its speed to deliver the required flow rate for each programmed task. For instance, if an arcing laminar water feature requires 151 lpm (40 gpm) to produce a smooth 1.8-m (6-ft) arc of water, the pump will automatically ramp up its speed when it senses resistance in the circulation system (e.g. as the filter accumulates dirt) to continually provide the proper flow rate. With other pump types, the water feature will gradually throw a shorter arc of water as the filter gets dirtier.

It does not matter what type of pump is being used; slower pump speeds save energy. It also dramatically reduces noise levels, as well as wear and tear on the other pool equipment in the circulation system.

DESIGNING CIRCULATION SYSTEMS WITH EFFICIENCY IN MIND

Swimming pools are often designed without full consideration of the system’s fluid mechanics. For instance, a pool with a large pressure drop or an oversized pump will not operate at peak efficiency. Typically, this will not create any problems for the facility other than the fact it is wasting energy unbeknownst to the facility manager. To ensure the swimming pool operates efficiently, the first place to start is with a properly designed circulation system. Each component in the system (i.e. piping, fittings, valves, filters, heaters, etc.) produces a pressure drop (friction loss), which the pump must overcome. The total pressure drop in the system is commonly referred to as total dynamic head (TDH). The larger the TDH, the greater the amount of power required to achieve a given flow rate. Some of the most common methods used to reduce TDH include: 1. Increasing pipe diameter. 2. Reducing pipe length. 3. Reducing the number of sharp bends and turns in the circulation system (piping). 4. Increasing the size of pool return outlets. 5. Increasing the filter size. 6. Increasing the diameter of backwash (or other) valves when present.Remember, not only will the facility reduce its energy consumption to save costs, it will also likely receive sizeable rebates from local utility companies for using energy-saving technology, thus providing a quicker return on investment (ROI). Be sure to consult the local utility company before embarking on the project.

Eliminating sticker shock

Even with the advantages explained, 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 at all.

For example, an aquatic facility with a 76,000 L (20,000 gal) pool using a single-speed pump may have operational costs of up to $4,700 per year (based on a cost of 20 cents per kilowatt-hour (kWh) and the pump running 24-7). After five years, the facility will have spent $23,500 to operate the pump. Comparable operational costs for a facility with a well-designed circulation system that uses a VSP, however, may be as little as $906 per year. Over the same five-year period, the facility’s costs will be reduced by more than 25 times it would have spent using a single-speed pump. Cost savings will continue to multiply the longer the VSP is used. (Based on the national average. Costs and savings will vary by region).

The initial cost of a VSP can typically be recouped during the second year of operation.

“With the substantial energy-use rebates our local power company offers, in conjunction with the savings in daily operational expenses, our clients are getting back approximately 50 per cent of the pump’s cost in less than a year,” says Caldwell.

 

Mike Fowler is the commercial marketing and sales manager for Pentair Water Commercial Pool and Aquatics in Sanford, N.C. He has been with Pentair since 1992, starting his career in the technical services department at Purex Pool Products. Fowler has held many managerial roles within the company, including marketing, accounting and products. He can be reached via e-mail at mike.fowler@pentair.com[3].

Source URL: https://www.poolspamarketing.com/trade/reducing-operating-expenses-with-energy-smart-equipment/

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