When talking about swim spa energy efficiency, pumps usually take the main stage, but filters also play an important role in conservation.
Resistance
Water encounters resistance as it moves through the skimmer, fittings, pipe, pump, valves, filter, check valves and heater. The sum of these resistances is measured in feet of head, which is the equivalent column of water that would cause the same resistance.
The electrical effect of lowering resistance may depend on the pump. Reducing the head or resistance in a system with a variable flow pump (one that varies the speed to maintain a constant flow) will allow the pump to run at a lower speed, which reduces the electricity consumed.
However, reducing the resistance in a system with a standard induction motor pump will cause the pump to move more water and consume more electricity. With an induction motor, you have to reduce the pump’s runtime to save money and use a flow meter to ensure the water quality isn’t compromised.
In very low head situations, induction motor pumps (which have been traditionally designed for systems that operate in the 40-60 feet of head range) could run at the end of their pump curves (very high flow) and exceed their maximum amperage rating. This is most often seen with water features where the pump incurs little resistance and eventually overheats.
A good practice when installing a single-speed feature pump is to perform an amp check and add resistance via a valve or other method to reduce flow to keep the pump from overheating.
Cartridge filters
Using a constant flow pump is not the only way to improve efficiency with lower resistance. Different kinds of filters add different amounts of resistance to the system, so selection between cartridge, DE and sand plays an important role.
Cartridge filtration offers the least amount of resistance to flow. In the 30 gpm range, a cartridge filter creates about 0.7 to 2 feet of head. At 60 gpm, a cartridge filter sized for that flow capacity creates 2-5 feet of head.
Also, cartridges conserve water and chemicals by not requiring the backwashing of other types of filters. Another advantage of cartridge filters is that they offer more square footage of filtration area. Some have upwards of 400 square feet of media, as compared with DE filters, which max out in the 100-square-foot range, and sand, which offers between 3 and 7 square feet.
A larger area for the water to pass through means it takes less energy to move the water through it.
Also, the resistance to flow increases at a slower rate because it takes more dirt to reach an accumulation level that reduces flow.
DE and sand
Most DE and sand filters add resistance to a system by requiring a backwash valve. However, not all backwash valves are created equal. Multiport valves create much more resistance to flow; in fact, California’s Title 24 has banned 1.5-inch multiport valves from use.
Slide valves, also called push-pull valves, add much less resistance than multiport valves because the water passes through them more directly.
Other kinds of backwash valve styles have been designed to add even less resistance to the system by using larger openings for the water.
However, sand is the preferred method of filtration for many pool service professionals. Sand filters are the quickest and easiest to clean during routine maintenance even though they have to be cleaned more often than large cartridge filters.
Weighing your options
If the most important criteria in your filter selection is the resistance generated by the filter, then it is clear that the best choice is a large cartridge, with a very close second being a DE filter without a multiport valve.
However, it is important to recognize that some customers will prioritize the easy maintenance of sand filtration. And some will want the polished water you get with DE and the ease of maintenance you get with the multiport valve for backwashing.
SpasRealx filter system with filter cartridge and Ozone Purify System and with circulation pumps, it can destroy bacterial and the smell of the chlorine.
