A topic of much conversation in the industry lately
has been energy efficiency in swimming pool systems.
The focus of these conversations is usually the pump, but
filters play an important role as well. Before we can discuss why
filter selection affects energy consumption, it’s important
to understand the role of resistance in the system.
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
Consider that 1 psi = 2.31 feet of head. If a filter gauge reads
23 psi, then it can be calculated that 23 X 2.31 = 53.13 feet of
head. This means that the resistance to push water through the
filter and back to the pool is equivalent to a pump raising a
column of water up 53.13 feet, regardless of the size of the
The effect of lowering resistance may depend on the pump.
Reducing the head or resistance in a system with a constant 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
However, reducing the resistance in a system with a standard
induction motor pump will cause the pump to move more water, and it
will 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.
Also, in low head systems, induction motor pumps (which have
been traditionally designed for systems that operate in the 40- to
60 feet of head range) could run at the end of their pump curves
over their maximum amperage rating.
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 filter 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
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.
However, cartridges don’t guarantee the most energy
efficient equipment pad. Anyone who has ever cleaned a filter knows
that when the pleats are packed tight in the cartridge, they often
will stick together, and some pleats will have dirt on them and
appear to be filtering while other pleats are completely clean.
DE and sand
Most DE and all sand filters add resistance to a system by
requiring backwashing, typically by using a valve. However, not all
backwash valves are created equal. Multiport valves create much
resistance to flow; in fact, Title 24 has banned 1.5-inch multiport
valves. Slide valves, also called push-pull valves, add 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.
The reliance of some Diatomaceous Earth (DE) filters on backwash
valves to occasionally remove used DE from the grids is one reason
DE filters are not always the most energy efficient. Of course, DE
is a great filter media when it comes to fine particle removal, but
it takes more pressure to move water through the DE than other
In terms of resistance, a DE filter without a multiport valve
creates around 1.5 to 2 feet of head at 30 gpm; add about 3 feet
for a 2-inch multiport and about 7 feet of head for a 1.5-inch
valve. At 60 gpm, a DE filter creates about 5-6 feet of head, plus
about 12.5 feet for a 2-inch multiport valve, and 18 feet for a
Some builders choose to install DE filters without multiport
valves to reduce resistance, which requires that the DE filter be
taken apart to remove the used DE. These filters may present a good
alternative for customers who want the polish of DE with the energy
efficiency and maintenance ease of cartridge.
Of the three filter designs, sand adds the most resistance to
the system. Most residential applications include a multiport
valve, and moving that water down through those particles of sand
requires a great deal of pressure.
For the sake of comparison, a large residential sand filter (3.4
sq. ft. of filtration area) without a multiport valve creates
around 3- to 4 feet of head at 30 gpm and add about 3 feet with a
2-inch multiport valve. At 60 gpm, the same sand filter adds about
11 feet of head, plus 12.5 feet for the 2-inch multiport valve. See
the table on page 30 for how the three filter types compare on this
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.
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.
As with any equipment choice, the important thing about filter
selection is to understand the pros and cons of each option and
give your customers the best advice possible.