Skimming the surface: the evolution of perimeter recirculation systems and what it means to your facility.

Leaves, bugs, Band-Aids or even Baby Ruth candy bars in your pool can stir up quite an unfavorable reaction. Removing surface debris and keeping the pool looking its best is a top priority for any aquatic facility operator. However, beauty is only skin deep, and keeping water clean, healthy and recirculating are also key concerns for managing a prosperous facility.

Perimeter recirculation systems or "gutters" are a key factor to keeping your water and pool clean. They are also one of the simplest and most economical ways to give your pool a make-over into a new looking, sleek, technologically advanced pool.

In basic terms, gutters are perimeter troughs that attract surface water away so that debris can be removed and proper circulation of fresh water is established. Over 80% of a pool's dirt and bacteria collect on the surface. This explains why the majority of health department codes establish a 25% bottom versus a 75% surface collection ratio.

Surface water can be collected by plastic skimmers, gutters that rim flow (just like it sounds, the water and debris flow over the rim of the gutter) and gutters that have skimming weirs or surge control assemblies, and plastic skimmers. Over the years several advancements (and a few setbacks) have been made in perimeter recirculation design.

History

Prior to the 1920s, it was common for pools to be constructed with a scum gutter (see Fig. 1). These gutters were just a collection trough for dirty overflow water. As swimmers entered and exited the pool, the water flowed over the rim of the gutter and was considered waste water. The water was piped away to the sewer or another outlet. Typically only 10% or less of a pool's circulation flow could be handled by scum gutters.

[Figure 1 ILLUSTRATION OMITTED]

The next innovation in gutters was made during the late 1920s and early 1930s. Gutters were made larger to handle surge and swallow up waves (see Fig. 2). The overflow water was collected on the suction side of the pump in an attempt to recirculate the water by either a direct plumbing connection or with a balancing tank. Flaws in the initial design of the balancing tanks did not allow for adequate storage of displacement water from the swimmers. Improvements on this design included throttling the main drain water into a collection sump and allowing pool surface overflow to cascade into the pump, which in turn would pump the water back into the pool.

[Figure 2 ILLUSTRATION OMITTED]

During the early 1950s there was a boom in commercial construction of public swimming pools. It was also at this time that the idea of metallic pools was born. The first metal pools and gutter systems were constructed of painted carbon steel. While these pools were very durable (some are still in use today), the high carbon content reacted with the aquatic environment and the pools rusted after a few years. These pools required routine sandblasting. Variations on this metallic theme included galvanized steel pools and systems, and a 50/50 mix of galvanized steel and steel. However, all of these variations had problems with rusting and corrosion.

By the late 1950s surface skimmers (see Fig. 3) were developed for residential and some commercial applications. Today, these are generally not an accepted system for commercial pools over 1,600 square feet according to a 1985 APHA Joint Committee Recommended Swimming Pool Ordinance and Code. If you've ever been in a backyard pool, you know how skimmers work. Skimmers are placed around the pool, one for every 500 to 800 square feet of surface. Collection baskets are installed to collect larger debris from the water.

[Figure 3 ILLUSTRATION OMITTED]

At roughly the same time, commercial designs for gutter systems started to include a surge tank or pit (see Fig. 4). The modern surge tank is roughly a gallon of capacity for every square foot of pool surface area. Utilizing gravity, the water flows freely into the surge tank as usage increases. For this reason, it is very important that the operational water level in the surge tank is below that of the pool.

[Figure 4 ILLUSTRATION OMITTED]

Perimeter recirculation systems remove water from various points around the gutter to be filtered and returned to the pool. Early surge tanks sometimes were not designed to hold all of the surge needed or operators had difficulty striking the right balance between water levels in the pool and the surge tank. Pools built decades ago that are still in use can face problems with a small surge tank during peak usage. The gutters can become flooded and debris does not leave the pool. Older designs also incorporated a large amount of perimeter piping that was made of iron to take the water to and from the pool. Today, a lot of this piping has corroded or broken and experienced leakage. PVC pipe has become the standard replacement for iron piping.

During the 1960s a new type of perimeter system evolved--the stainless steel gutter. Stainless steel did not rust and the design of the gutter eliminated the need for extensive piping because it combined both influent and effluent functions. The gutter itself acted as a channel to carry the water to a collection point where it would be pumped away to the filter and back. At that time the marketplace was small. A section of stainless steel perimeter cost over $1,000. Today, as more manufacturers have entered the market and stainless steel has become the preferred system, that price has dropped 50% to 75%.

Aluminum pools and gutters were also built during the 1960s. The cathodic properties of aluminum in an aquatic environment were not well known at the time. Aluminum has since fallen by the wayside due to electrolytic corrosion.

During the late 1970s another new idea for gutter construction came in the form of PVC. It was thought that PVC gutters would revolutionize the industry and provide a cheaper alternative to concrete or stainless steel gutters. However, the gutters quickly degraded under UV rays, broke at welded seams due to water pressure and were subject to cold cracking. PVC gutters are virtually extinct now.

The next innovation in gutters has been the development of stainless steel gutter systems with surge control assemblies (see Fig. 5). Developed during the late 1970s and early 80s, these assemblies allow for an "in-pool" surge capacity. Static surge is the water that is physically displaced by swimmers' bodies. Dynamic or kinetic surge is the wave that is caused by this motion. On average each swimmer's body displaces two cubic feet or 15 gallons. Most state codes require pools to have a surge capacity of one gallon per square foot of surface area. It is a primary function of a perimeter recirculation system to absorb this surge. A typical system will have a separate surge tank to handle overflow so that the gutters do not overfill and stop working. However, stainless steel systems with "in-pool" surge capabilities eliminate the need for a separate surge tank. These systems have the water level set at just below the lip of the gutter. As the swimmer load increases, the pool itself handles the surge. This also means that when the pool is not in use, its gutter system is not rim flowing. Automatic surge control assemblies solve this situation. The assemblies provide continuous surface skimming at various points around the perimeter.

[Figure 5 ILLUSTRATION OMITTED]

Circulation is established through a simple, efficient design. The gutter acts essentially as "piping" and the water collected in the gutters goes typically to one or two collector boxes. From there, the water is pumped to the filter, processed and returned back to the pool via jet orifice inlets that inject the water back into the pool at 45 degree angle.

What These Advancements Mean to Your Facility

For older pools in need of renovation, this relatively new method of perimeter recirculation is ideal. Older pools may be operating under several conditions:

* The original piping may be fractured, split and/or leaking.

* The pool may be out of level, and allowing debris to collect in various points around the pool.

* The concrete gutters are literally disintegrating and crumbling.

* Older pools may have gutters that are not designed to meet the state surge capacity code, but they continue operating under a "grandfather clause."

* The facility doesn't have the money or the space to update the pool to current health codes.

Stainless steel perimeter systems offer two important advantages to operators. First, they eliminate the need for any buried perimeter piping and the need for a separate surge control tank. The assemblies are about half the cost of building a surge control tank. Operators don't have to worry about space considerations either. The new gutters can be installed in place of the upper portion of the wall.

Factors to Consider When Evaluating Your Current System

* Health Department Codes

When deciding which perimeter recirculation system is best for your facility, the biggest variable to consider--besides cost--is your state and county health code. These codes can sometimes affect your building or renovation budget more than the cost of materials. Make sure that all designs and improvements meet the codes in your state before you begin construction. A knowledgeable pool consultant can be indispensable in getting renovation or new construction plans up to code.

* Ultimate Use of the Pool

Always consider the long-term use of your facility. Right now you may only have recreational swimmers; however, you may eventually want to attract competitive swimmers. Cost is always the driving factor in any decision. but you should always consider the ultimate users as well. A lower-cost skimmer pool won't work for competitive swimming or heavy usage. Concrete gutters may be an option but if the gutters are not formed level, you will have a serious problem maintaining proper surface skimming, and ongoing maintenance will become a problem.

* Cost

This is most likely the number one consideration for any pool operator. The cost comparisons between stainless steel and concrete really depend on the part of the country in which you operate. In some areas stainless steel may be the same or cheaper than concrete and vice-versa. Regardless of price, you need to choose the system that meets your facility's needs. However, don't go overboard. For instance, the 1996 Olympic competition pool had very large, expensive concrete gutters to swallow up the waves. These gutters were custom designed to reflect a unique style. Since most of us don't have to worry about hosting the Olympics, choose a system that makes sense for your facility. In the case of renovation, ease of installation has been a big reason for the success of stainless steel perimeter systems (see photos).

* Facility Operator's Experience

The bottom line for most facility operators is ease of operation. Stainless steel perimeter recirculation systems are designed with minimal maintenance requirements in mind. This is a big relief for operators who are expected to juggle everything from swimming schedules to chlorine levels.

"The average daily use of our pool is between 1,000 and 1,500. We have competitive swimming here as well as recreational users. We needed a system that could deliver very clean, clear water," said Peter Eddy, aquatics director of the Arundel Swim Center in Annapolis, Maryland. "We have a wonderful system. It is easy maintenance. I like the simplicity of the system. It was quickly installed because of pre-fabricated parts. There also are no underground pipes, which is great if there is a risk of even minor settling."

The Arundel Swim Center is a 50-meter Olympic-size pool that was constructed in 1988 by Olympic Swimming Pool Company in Forestville, Maryland. A stainless steel perimeter recirculation system was installed along with a separate surge tank so that the pool gutter system rim flows.

"In my experience, I think the biggest difference between stainless steel gutters and concrete ones is water level control," said Eddy. "A lot of concrete gutters, especially the older ones aren't set up to handle all of the surge and the result is a lot of waves in the pool."

Bill Bullough, aquatics director for Montgomery County (MD) Recreation Department, has watched how the advancements in perimeter recirculation systems havehad an impact on aquatics over the past 25 years.

"Stainless steel gutters are far superior to skimmer pools. Skimmer pools are higher maintenance," said Bullough.

"They are plastic, so they are subject to breaking. Also, a major factor to worry about with skimmers is broken weirs. If you have broken weirs, the skimmers aren't working properly and the health department generally isn't happy when that happens. However, these pools are a lot cheaper to build."

Bullough says of his experience operating pools with concrete and stainless steel gutters, "Concrete gutters are hand formed and hand leveled. If you got good workmanship then you might get good drainage. Very often though, the pool was not level because the gutters were not level," said Bullough. "With stainless steel gutters, you know what you are getting. They are standard installations with all the components you need in the gutter itself. Now it is rare to see new pools constructed that do not have stainless steel gutters."

"The purest way to set up skimming and recirculation is to have a stainless steel gutter that rim flows with a separate surge tank. However, that is in a perfect world. A lot of facilities don't have the funds or the space to have a separate surge tank," said Bullough. "Surge tank operation and control also requires an understanding of the dynamics involved. Both contractors and operators need to know how everything works. The gutters with the surge control assemblies have simplified renovations for older pools and simplified operations for the pool managers."

Conclusion

Perimeter recirculation systems are basic - they skim the surface and establish fresh water circulation. They are basic until they aren't working properly, and then they are a major problem. When planning new pool construction or renovation, remember to strike a balance between long-term facility needs, budget and health codes. Choosing wisely today will keep problems from surfacing tomorrow.