Proper pump selection and optimal flow rates are extremely important to ensure proper hydraulics and to get the most efficiency throughout the entire pool or spa. It is also important to avoid ‘dead spots,’ especially in today’s pool designs which often have multiple curves, lazy rivers, inlets, grottos, and vanishing edges. Service professionals can also increase the energy savings for their customers (i.e. aquatic facilities) by using properly sized pumps.

This article focuses on how to choose the right size and speed pump for different applications. With a few tips and rules of thumb, proper pump selection will result in better water flow and reduced energy consumption.

Sizing

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 use the smallest pump that is capable of completely turning over the pool water (i.e. pumping the entire contents of the pool through the filter[s]) in an acceptable amount of time.

Further, 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 on many pools are oversized by design—sometimes more than 20 to 40 percent bigger than they need to be. One reason for this is 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.

Some building codes require the use of a multi-speed pump, or in some cases, a separate pump for each auxiliary pool load.

Pump selection tips

1. Determine flow rate in liters per minute (lpm)/gallons per minute (gpm).
2. Calculate total dynamic head (TDH), the pressure head difference between the inlet and outlet of the pump, to account for friction loss. Adding 6.1 m (20 ft) of head for a dirty filter is optional.
3. Refer to the pump’s performance curve to select the preferred unit.
4. Locate the required horsepower (hp) of the pump by plotting lpm (gpm) versus 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.

Avoiding dead zones

There are two ways to make sure a swimming pool is designed and circulated to eliminate ‘dead zones’—especially with today’s intricate pool designs and elaborate features, as mentioned previously.

First, make sure the plumbing is properly balanced. One of the most important parts of a well-balanced circulated pool is having a hydraulically sound plumbing layout throughout the suction and return sides of the system. Taking larger pipe sizes and then breaking them down to smaller sizes in balanced method around the pool will ensure the entire volume of water in the pool is properly circulated, eliminating any ‘dead spots.’

Secondly, ensure the return lines are placed properly and in the right direction. When bringing water back to the pool after it passes through the filtration system, it is important to make sure the entire volume of water is returned to the pool and distributed as evenly as possible. This is where the importance of balanced plumbing around the pool and properly located returns come into play. If executed properly, it will help to make sure all areas of the pool are circulating water.

One of the most important parts of a well-balanced circulated pool is having a hydraulically sound plumbing layout throughout the suction and return sides of the system.

A technique used by many contractors today is installing the return lines parallel to each other—throughout the installation—which allows water to return to the pool in a circular motion. By using this hydraulics technique, as the water completely circulates around the pool it also passes by the skimmers in a strategic fashion that aids in cleaning the surface, as well as distributing the water.

One suggestion is to cap the end of the return line to increase the hydraulic performance of the lines that are furthest away in the plumbing schematic. This will ensure proper water circulation throughout the entire pool.

In larger pools, it often makes sense to divide the plumbing and pumps into three sections, each with its own pump system. This way, each section of the pool has its own ‘zone’ with a dedicated circulation system. For example, a 6.1- x 12.2-m (20- x 40-ft) pool that includes a grotto with cascading waterfall, a slide (with its own water system) in the deep end, a sundeck with fountain and cuddle cove, and a play area (reverse radius section) in the shallow end, should be divided into three zones.

Starting in the shallow end, the first 3 m (10 ft) should be considered zone one, while the mid-section of the pool (4.5 m [15 ft] plus) should be divided into the second zone. Finally, the deep end area, or last 4.5 m (15 ft), should be considered the third zone. Pumps and plumbing should be sized accordingly for each zone.

Creating zones allows for better circulation in the pool which helps with better surface cleaning as well as better chemical dispersion if the pool is equipped with an automatic feeder. If the pool is not equipped with the proper size circulation pump, the pool water will not turn over the proper number of times to properly sanitize and clean the pool.

Speed

Historically, pumps with induction motors, which operate at only 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 demanding jobs, such as 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.

On the other hand, variable-speed pumps (VSPs) can be programmed to operate at set speeds to deliver the correct flow rate for each task they perform. This allows the pool’s pump to reduce energy consumption and ultimately reduce operating costs. These pumps 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 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, 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.

No matter what type of pump is being used, however, slower pump speeds save energy. Slower speeds also dramatically reduce noise levels and wear and tear on the other pool equipment the water flows through.

This article was written by Mike Fowler and originally appeared on Pool & Spa Marketing [link].