Weighing The Options
Everyone loves the sparkle of crystal-clear pool water. But how do you keep it that way? That’s the job of the filtration system.
Filtration is the mechanical process of removing particles of dirt, organic matter, hair, suntan and body oils, leaves and other debris from the pool water. Many factors influence the selection of a filtration system, such as the anticipated bather load, backwash water-disposal capacities, the perimeter overflow/skimming system, equipment room size and location and the type of sanitizing system.
The following are the most common systems used today, with the advantages and disadvantages of each.
Each system is capable of full manual or automatic operation.
1. High-rate pressure sand filters
In the filtration mode, water enters the top of the filter and is forced by the circulation pump through the filter bed and back to the pool inlets. In the backwashing--or cleaning--mode, the flow of water is reversed so that it enters from the bottom of the filter and discharges through the top. Backwash water is disposed to the sanitary sewer system.
·It’s typically the least expensive filter system.
·Higher filtration rates allow smaller-size filters than other types or sand filters.
·The filter arrangement is flexible. Multiple filters can be grouped, or one large filter can be used. Filters also can be stacked to save floor space.
·Frequent backwashing is required, and a large amount of water is used.
·Depending on the arrangement, more floor space may be required than with other options.
2. Vacuum sand filters
In this mode, water flows by gravity or transfer pump to an open filter tank where it passes through the sand bed and then returns to the pool. The circulation pump is installed on the downstream side of the filter, and pulls the water through.
·The filter tank is installed below the floor slab, which saves space.
·When equipped with an air scour, the amount of water used for backwashing is reduced, which saves ater, chemicals and energy.
·The filter tank provides some capacity for pool surge. (Surge capacity is required to keep the pool from overflowing when swimmers enter.)
·Water quality (clarity or ”polish”) is better than with pressure sand filters.
·The interior of the filter is visible, so the conditions of the sand and inside surface of the tank are easily monitored.
·The backwashing cycle can be observed and controlled more efficiently.
·The system is typically more expensive than high-rate pressure sand filters.
·This system is not a good choice for installation in basements of buildings.
·Frequent backwashing is required.
3. Regenerative pressure diatomaceous earth filters
These filters use diatomaceous earth (DE) as the filter media. DE is a sedimentary deposit of the skeletal remains of diatoms, a group of single-celled marine algae. These remains possess a highly intricate structure, filled with pores and channels, making them ideal for extremely fine-scale filtration processes.
·The filter tank is relatively small, which saves building area.
·This system provides superior water quality.
·The filter cycles are extended, due to the ”bump” mechanism which regenerates the filter media (DE).
·Minimal cleaning of the filter is required, which saves a significant amount of water, chemicals and energy. The system saves significantly on operational costs.
·It’s the most expensive filtration system. However, the expense is partially offset by saving building area ad reduced operating costs.
·DE is considered a carcinogen.
·If DE gets into the sewer system, it settles and will not flow.
·A backwash pit and a separation screen are required.
Alternative filter media such as cellulose and pearlite are available, and can be a good substitute for DE, if these alternatives have been approved for use in your jurisdiction. Both are more environmentally friendly, safer and easier to handle than DE. DE is considered by some to be a superior media when it comes to water quality.
The selection of the filtration system is an important decision, impacting not only upfront costs, but also operational expenses, maintenance and water quality. Thus, the time invested in this decision is time--and money--well-spent.
Douglas J. Holzrichter is a principal and one of the founding partners of PHN Architects in Wheaton, Ill. The award-winning architectural firm specializes in the design of recreational facilities, including indoor and outdoor aquatic centers, recreational centers and golf course clubhouses and learning centers. For more information, visit www.phnarchitects.com.