Category Archives: Design

Thermoplastic Pipe Expansion

Swimming pool piping is design is notorious for including long straight runs of pipe.  For pools that do include long runs of straight pipe sections, consideration may be given to the use of expansion loops or mechanical expansion joints to accommodate thermal expansion and contraction.  The ASTM Standard 2774 references “Underground Installation of Thermoplastic Pressure Piping”. This ASTM Standard 2774 contains specific information on the topic of expansion in pool piping.  Expansion and contraction of thermoplastic pipe is typically due to temperature changes to either the surrounding pipe embedment materials or changes in the pool water traveling in the pipe system. When temperature changes of the thermoplastic pipe does occur, changes to the piping network in the form of elongation or contraction will occur.  Therefore, in piping networks where there may exist sections of the pipe that are straight and without bends, expansion and contraction of the pipe can cause failures in the system.  Swimming pool piping networks that include PVC pipe used in straight runs nearing 100 LF should take special consideration to the potential expansion and contraction of the pool pipe.  In these instances the design of the pool piping system should have the coefficient of expansion calculated for determination if design accommodations for the expansion and contraction should be included.

In cases where expansion and contraction will be significant, inclusion of an expansion loop or even a mechanical expansion joint can be installed.  A pipe loop is a relatively easy item to include within the piping network.   This pipe loop, or offset, can alleviate the bending stresses that can occur when thermoplastic piping systems experience expansion and contraction.  If expansion joints are required, a detail for the expansion loop may include a specific dimension for the offset lengths.  Mechanical expansion joints work like a piston allowing the pipe to elongate or contract within the pipe run.  The installation of mechanical expansion and contraction joints is critical, particularly cleaning debris (sand, rock, dirt) out of the moving parts.  If small particles come in contact with the mechanical joint mechanism the joints seal can become compromised.

In most instances a linear pipe runs without interruption of bends, joints or pipe size changes is not common.  However, in situations where conditions do allow long pipe runs, your design should pay special attention for need of expansion and contraction loops and mechanical joints.

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Epoxy Grout

Tile, known for its longevity, has proven to be the most durable finish for pool interiors. Selecting the material, size, shape and color of the tile is just one step in the process. Another consideration is the grout selection. Grout can influence tile appearance significantly. If you choose the right grout, it can blend perfectly with the tile color. Or you can choose a contrasting color to highlight the tile. But that also requires an outstanding tile installation. Selecting your grout can be a very important decision as far as aesthetics go. Additionally, there are two different categories of grout; cementitious grout and epoxy grout. Both options are viable solutions for tiled pools, but with certain design parameters, one typically will make a better solution for a specific installation.
Cementitious grout, otherwise known as sanded grout, has been the longtime solution for pools. The cementitious grout can be applied at either indoor or outdoor pool locations, its color does not fade or change and it comes at a lower cost. But this product has also been noted to have a greater likelihood of having issues down the road. There are typically two main causes of failure, with the first being pool water chemistry. The water chemistry often gets exacerbated in spas due to calcium and/or acid issues. The water will begin to leech minerals from the tile grout, which makes the grout will need to be replaced sooner. The other main cause of failure are tile dots. The dots, in Counsilman-Hunsaker specification, have been limited to where they cannot occupy more than one-third of the depth of the tile. The grout is not allowed to occupy the depth or surface area needed to fill the space between tiles. It should be noted that the dots can still be an issue with the epoxy grouts, but it’s not as likely.
Epoxy grout, a product that has become more widely accepted by the aquatics industry as of 2010, is finding its way on more and more pool projects. The epoxy product is known to last longer, but tends to discolor and typically be more expensive. There will usually be a 25%-35% premium, plus additional installation and labor charges. Applications where movement is critical, such as second floors, are ideal installations for epoxy grout. The grout can be used in outdoor pool applications in freeze-thaw environments, however, certain conditions must exist:
• There cannot be a high-water table
• The tile must be porcelain
• The pool should be winterized with water in it (not completely drained)
The exterior application also brings the concern of fading dark colors over time, darkening of light colors over time and in cases where high MVER/high water table exists, the drain rate of the pool water for maintenance becomes just as critical as the fill rate (nothing greater than one-inch per hour).
In project applications where the budget is limited or in the case where minimum trim tile is being installed, the cementitious grout can be considered as a value engineer option.

Water Basketball Goals

Water basketball can occasionally become an afterthought during the commercial swimming pool design process due to its relatively low startup and maintenance costs. Furthermore, water basketball goals can be accommodated in a variety of places across a typical leisure pool and are hindered by the available water depth more than the available space. Often times, they are placed somewhere in the lap lane area of a pool because the larger amenities such as play structures, current channels, and water slides demand specific water depth and clearance requirements that don’t align with the ideal conditions for water basketball. Counsilman-Hunsaker has recognized a need to consider water basketball during the schematic design phase of a project with the type of water basketball goal specified becoming a function of the pool overflow system (gutter vs. skimmer), the ability to move the goal, and the desire to have an adjustable height goal. Each type of water basketball goal has its advantages and disadvantages that will be further discussed.

 

During initial phases of the design of a swimming pool, a “water basketball nook” should be considered accompanied by an on-looking underwater bench. By designating a confined area of the pool to water basketball, design teams can help mitigate un-desired interactions between calmer portions of the swimming pool and the unavoidable, yet popular, rowdy water basketball game. That being said, the type of water basketball goal to be specified for the pool contractor is determined by the pool overflow system. Water basketball goals have ideal setback distances from edge of the pool to the water basketball goal anchor. For example, SR Smith manufactures a water basketball goal known as the Swim N’ Dunk (S-BASK-ERS) with a setback distance of 18 inches. This smaller setback limits the type of pool that this particular goal can be installed on to skimmer pools. Obviously, the type of overflow system should not be a slave to the type of water basketball goal specified; however, it is important to keep these ideas in mind when discussing potential designs with a facility owner.

Figure 1: SR Smith Swim N’ Dunk Water Basketball Goal

 

Fortunately, SR Smith makes an extended reach model of the water basketball goal previously mentioned that increases the setback distance from the pool edge to 30 inches. The extended reach model could be used on a pool with a gutter perimeter overflow system, but it still lacks adjustability. The Spectrum Adjustable Basketball Hoop allows for the height of the water basketball goal to be raised and lowered. The Spectrum system uses a compression mechanism and two extension arms to do this. The setback distance for this goal is 26 inches and could be specified for a pool with a gutter system. Designers should keep this mechanism in mind when accounting for the surrounding deck space as the lever used to adjust the goal can have a large swing radius. It is important to note that any water basketball goal with an adjustable height should have a safety stopper to prevent the backboard from falling from its highest point. Without this safety implementation, backboards have been known to come crashing down on the coping stone below with some force.

Figure 2: Spectrum Adjustable Basketball Hoop

 

Both of the water basketball goals mentioned thus far have a fixed position. More specifically, they are anchored to the pool deck and, while they can be removed and stored, will more or less be there permanently.  Dunn-Rite, Inc. has a model known as the Splash and Slam that is both movable and has an adjustable height. The base of the water basketball goal is a hollowed polyethylene basin that weighs 500 pounds when filled with water. The water can then be drained to allow pool operators to move the goal. The backboard height can also be adjusted and leveled to compensate for the occasional uneven pool deck. This goal, while it has its advantages, would typically be specified if water basketball was considered as an afterthought during design. It is customizable, but lacks aesthetically and in sturdiness when compared to the fixed position goals.

Figure 3: Dunn Rite Splash and Slam

 

Water basketball goals should be a staple when it comes to leisure pool design because of their sheer popularity and low startup and upkeep cost. Ideally, the goal is placed in an area of the pool far away from where younger children will be playing and adults will be lounging. Different perimeter overflow systems demand different types of goals as fixed goals need to be provided with a deck mounted anchor. If all of these considerations are taken into account during the design phase of a project, water basketball can become the primary feature of a facility. They do bring with them many liability issues, but that is a topic for another discussion.

 

Determining Filter Backwash Rate

Concrete construction is expensive, so it is important to be frugal when designing a new facility. This involves the way the pool is laid out for programming, but it also extends to the mechanical room, which most likely houses a backwash pit. Overestimating the size of the backwash pit means wasted concrete, while underestimating its size can lead to flooding. For this reason, accurately calculating the size of the backwash pit, based on the ideal backwash rate, can help save money. More importantly, once pool construction has been completed, backwashing at the proper flow rate can help conserve filter media, water and operational costs. The backwash rate is measured in gallons per minute per square foot (gpm/sf) and varies from pool to pool.
The Model Aquatic Health Code (MAHC) recommends a backwash rate of at least 15 gpm/sf, which is standard for most pools. The reasoning behind this number more than likely comes from manufacturer recommendations for the backwashing filter rate. For example, Neptune Benson recommends backwashing at a rate 3 gpm/sf higher than the filtration rate. Counsilman-Hunsaker designs for filtration rates between 12 and 12.5 gpm/sf, but this can be increased to 13, or even 13.5, depending on the system. While backwashing at a rate between 15 and 17 gpm/sf is a safe bet, it is not necessarily going to be the most efficient as factors, other than just the filtration rate, can play a role in determining the ideal backwash rate. Additionally, the World Health Organization (WHO) recommends a backwash flow rate of 15-17 gpm/sf.
Per Steve Andrews, the President of Nemato Corporation, a backwash rate should be determined by the filter bed expansion fluidization. Filter bed expansion fluidization can be described as the increase in volume that a bed of particulate experiences when a liquid or gas is forced through it. Andrews explained to Counsilman-Hunsaker that the amount of expansion is a function of filter media density, water temperature and, of course, flow rate. He went on to say that the backwash rate should not be dropped below 12 gpm/sf because it will not be effective. The table below, referenced from the Model Aquatic Health Code Annex, compares the percentage of bed expansion verses the backwash flow rate.

Backwash Flow Rate (GPM/SF)                              Bed Expansion (%)

12.2                                                                                 4.8

15.8                                                                                 13.0

17.9                                                                                 17.4

19.9                                                                                 21.8

21.5                                                                                25.6

23.9                                                                               31.2
When creating the MAHC, experiments were done in order to determine the ideal backwashing rate of a filtration system. It was found that fluidization, which allows for debris to flow through the filter sand, occurs between 20-23 gpm/sf. As these flow rates coincided with the percentages shown in the chart above, the MAHC recommends a minimum of 20% bed expansion. It is important to note that if the water being used to backwash the system greatly exceeds 68 degrees Fahrenheit, the backwash rate will need to be increased to account for the subsequent change in water viscosity. Counsilman-Hunsaker contacted a representative from Neptune Benson about the language used in the MAHC who confirmed that sizing a filtration system for 35% bed expansion with a target bed expansion of only 20% would allow for adequate backwash and prevent filter media from washing out at the completion of the process.
For a mechanical system that has not been designed to meet such backwashing requirements, there is a trick that can help improve efficiency. The WHO recommends air-scouring sand filters prior to backwashing with water. This is a practice used in the UK and other parts of the world, but hasn’t been commonly practiced in the United States. Air-scouring involves forcing pressurized air through the filtration system, prior to backwash water, in order dislodge debris particles from the filter media. It is considered more efficient than only backwashing using water and could help improve water quality.
Every mechanical system will slightly differ depending on the filter media material, filter media depth and backwash water temperature. However, because the bed expansion is measured as a percentage, the correlating 20-23 gpm/sf backwash rate should become more commonly practiced. In the end, a more efficient backwash cycle means decreased backwash frequency and thus, increased lifespan of the filtration system.

System Bonding for Water Slides

Proper pool bonding is incredibly important when it comes to considering the safety of swimmers. Pools require electricity to power certain components that make the pool function. Things like pumps, lights and heaters cannot operate without electricity. When pools and their necessary components are not properly bonded or grounded, some electricity can make its way into the pool and potentially harm swimmers. This is why Counsilman-Hunsaker ensures our standards are up-to-date and in line with National Electric Code (NEC) requirements.

Bonding involves electrically connecting all exposed metallic items not designed to carry electricity as protection from electric shock. What this essentially means is that bonding keeps electricity separate from swimmers. In an improperly-bonded pool, electrical gradients will seek the easiest path for conductivity. Bonded pools make electric currents flow into a grid that disperses them.

The requirement to bond and ground pools and pool equipment is a safety requirement incorporated into the NEC, specifically article 680. Equipotential bonding is intended to reduce the voltage gradients in the area around the pool by use of a common ground bonding grid in accordance with NEC 680.26.

The pool shell reinforcing steel, including at least three-feet of the perimeter deck, and all metal anchors, inserts, fittings, light niches, and equipment in the pool and within five-feet of the pool’s edge, as well as the mechanical equipment in the filter room, must be bonded together per NEC Article 680 to form an equipotential bonding grid. Further, due to the importance of controlling electrical currents in and around the pool, the bonding system should be taken back and connected to a positive, true and adequate ground. The ground should be tested and certified as a condition of acceptance.

The code does not specify with regards to water slide components that are beyond the five-foot perimeter around the pool. Water slides have a variety of components including the fiberglass flume, support structures, and the start tower. The water slide start tower and support structures are typically metal structures and, despite not being in direct contact with the water, must be bonded. The start tower is easily within reach of those entering the water slide start tub, and leaking water slide joints may provide a direct connection to the water slide support structure.  Thus, there is a need to bond these components with the rest of the pool components. Water slide manufacturers typically show these requirements on their engineered documents.

Ultimately, by properly grounding and bonding your pool components, you make your pool safer for everyone to enjoy. Swimmer safety is a top priority for Counsilman-Hunsaker, which is why we take these NEC requirements very seriously and regularly ensure our designs create a safe environment for everyone.