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C E U 2

0 2

PublicSwimming

Pools

Continuing Education from theAmerican Society of Plumbing Engineers

August 2013

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This chapter discusses public indoor and outdoor swim-

ming pool design and the selection of pool plumbing, pipingcomponents, and the equipment required for operation inconformance with the codes of the authority having juris-

diction (AHJ). The goal of any quality pool design shouldbe to maximize the safety of the patrons while providing anenjoyable water-based environment. The design approach

should be to develop a system that provides maximum waterquality, from both a clarity and bacterial safety standpoint.

Potential hazards such as suction or limb entrapment, hairentanglement, or tripping concerns must be examined. Lo-

cal health department codes are designed to ensure that thiscriterion is met, but these codes merely provide minimumstandards. A quality design should go well beyond minimum

requirements.The chapter is organized to assist a designer, possibly

unfamiliar with swimming pool design, in undertakingsuch a project. The first three sections can be used for the

preparation of an initial scope outline of the project’s size,type, and location. The “Pool Operating Systems” section

discusses the key elements that are required for a completecirculation, filtration, water-heating, chemical-control sys-tem. It can be used to make initial decisions on the basic

type of system to consider. The section titled “ComponentEvaluation and Selection” provides guidelines for making

specific equipment selections. It will assist the designer incollecting pertinent data on the various products to assist in

the writing of specifications.

CODES AND STANDARDSIn addition to the plumbing codes, swimming pool construc-

tion and operation are usually governed by state healthdepartment regulations and the requirements of local au-

thorities. Publications of the Association of Pool and SpaProfessionals (APSP) and the National Swimming Pool

Foundation (NSPF) are often-referenced standards. Thecodes usually govern recirculation rates, filtration rates forvarious types of filters, and the spacing of main drains, as well

as maximum velocities (feet per second {meters per second])through main drain grate-free areas. Also of importance

are the locations and types of inlets, spacing and capacity ofgutter drains, and requirements for the use of surge tanks

or skimmers. Heating requirements and feed capacities ofdisinfection systems are other areas requiring review. In addi-tion to the standards noted above, if the pool is to be used for

competitions, the rules and regulations of the International Amateur Swimming Federation (FINA) must be reviewed to

ensure that the pool meets international standards. In theremainder of this chapter, any entity governing the various

aspects of public swimming pools will referred to as the a

thority having jurisdiction.Virginia Graeme Baker Pooland Spa Safety ActIn December 2007, a new federal law was enacted called t Virginia Graeme Baker Pool and Spa Safety Act (VGB). T

federal act set more stringent requirements on main drasizes, velocities, and piping configurations and requires teing protocols to be regulated according to ASME A112.1

(2007): Suction Fittings for Use in Swimming Pools, Wadi Pools, Spas, and Hot Tubs. At a minimum, all existing m

drain cover/grates must be replaced with a compliant covgrate bearing the VGB stamp provided by the manufactu

or be field-certified by a licensed professional engineer atte

ing to its compliance with ASME A112.19.8. In cases whersingle main drain is direct-connected to pump suction, so

form of automatic vacuum release or some form of pipithat provides an air break to prevent suction entrapmen

required. (Refer to ASME A112.19.8 for specific details sumps, piping, and cover/grate requirements.)

The intent of the VGB is twofold: prevent suction entrment and prevent entrapment due to hair entanglement. Tsecond issue (hair entanglement) is the reason why veloc

through main drain grates is an issue. Hair entanglement, cosistently the No. 1 cause of entrapment in pools, is caused

high velocities through main drain grates. When a swimme

hair is drawn through the grate, high velocity can cause itswirl and become tied in a knot on the other side of the graSuction entrapment has nothing to do with veloc

through the grate. Suction entrapment is addressed in VG

by requiring all pools to have multiple main drains spacedleast 3 feet (0.91 m) apart, which makes them “unblockab

in the verbiage of VGB. In instances where there is only omain drain, it must flow by gravity back to a surge tank (i

not be direct-connected to pump suction), be of an “unbloable” size (i.e., larger than 18 x 23 inches [0.46 x 0.58 or with a diagonal dimension greater than 29 inches [0.

m]), or have another means of preventing suction entrament. The most common means of accomplishing this is t

addition of some type of automatic vacuum safety releaSeveral products are on the market, but all manufactur

insist that installation of their device be done by an instalcertified on the proper installation of their product. Howevall manufacturers of these products add the disclaimer “w

not prevent disembowelment” to their product literature ASME A112.19.8 also details tests for finger entrapme

measuring the force needed to pull the cover/grate out of tframe, and resistance to UV degradation, which could ma

Reprinted from Plumbing Engineering Design Handbook, Volume 3. © 2011, American Society of Plumbing Engineers.

Note: In determining your answers to the CE questions, use only the material presented in the corresponding continuing educatio

article. Using information from other materials may result in a wrong answer.

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the cover/grate brittle and cause attachment failure. These

are an important part of the ASME testing because manyof the entrapment accidents that occur are due to detached

cover/grates. However, the primary issue that the designerneeds to be concerned with is the maximum flow rating in

gallons per minute (gpm) (L/sec). VGB also requires main drain cover/grates to be sized for

the maximum flow of the system. The combined maximum

possible flow that the system pumps can produce (which is

usually greater than the design flow) must not exceed themaximum flow rating for the cover/grate intended for instal-lation. In fact, VGB goes one step further. In the instance

where one cover/grate is blocked or partially blocked, the re-maining main drain cover/grates on the system must be sizedto handle the full flow of the system. In other words, where

there are two main drains, each cover/grate must be sizedfor the full flow of the system. With three main drains, each

cover/grate must be sized for 50 percent of the system flow.It is important to note the use of the term “system.” That

is because many pools have water feature pumps that pullfrom the same surge tank as the circulation pumps. Thetotal possible flows of all of those pumps must be added to

determine the full flow of the swimming pool system. The factthat the cover/grates flow by gravity back to the surge tank

might eliminate the first concern of VGB—entrapment—butit has no bearing on the second concern, hair entanglement.

The velocity through the cover/grates is the same when waterflows to the surge tank by gravity as the velocity when the

main drains are direct-connected to pump suction.

The final important requirement of VGB is the ASM

A112.19.8 protocol regarding main drain sump dimensioMany field-fabricated sumps, as well as most previously

stalled fiberglass sumps, do not meet ASME requiremen(see Figure 6-1) and are considered noncompliant. T

reason for these required sump dimensions is somewhcomplicated, but basically it is to ensure even flow across tcover/grate, which is the only way to ensure that velocit

calculated for flow through the free area of the grate a

uniformly less than 1.5 feet per second (fps) (0.46 m/s) atpoints on the face of the cover/grate. Attachment of a necompliant cover/grate to a noncompliant pre-fabricated su

may not create a secure attachment that will meet ASMpull test requirements. The Consumer Product Safety Comission (CPSC) has expressed concern that VGB does

address this attachment issue thoroughly enough sinmost entrapment occurrences have been due to a missi

or displaced cover/grate. A misconception that raises additional concern is the be

of some owners that their system is fully compliant once tstate approves changes to the cover/grates. That is not tcase. Most state codes do not address sump dimensions, a

they also don’t all require multiple cover/grates to be ablehandle full system flow or some percentage of full flow bas

on the number of main drain sumps. Thus, in additionthe state public health code, the design must adhere to t

requirements of VGB.

D D

1.5 min.D

1.5 min.D1.5 min.DD Min. D Min.

D min.

Dmin.

D min.

Field Built Sump

D

D

D min.D min.

1.5 min.D

GENERAL NOTES:(a) = inside diameter of pipe.(b) All dimensions shown are minimums.(c) A broken line ( ) indicates suggested sump configuration.

D

Figure 6-1 Field-fabricated Sump Dimensions

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This method of determining the maximum number

swimmers cannot be applied to all swimming pools. The cial and economic conditions of a particular local commun

must be taken into account when designing a public swiming pool facility. Swimming pool occupancy, or capaci

restrictions are subject to local regulations and vary frone jurisdiction to another. Supervision capability also mlimit pool capacity.

The desirability of accommodating competitive swimm

should be considered when designing a swimming pool. Trequirements for such events are 25- and 50-yard lengfor U.S. competitive meets and 25- and 50-meter lengths

international events. Normal competition pools are dividinto a minimum of six swimming lanes, with each lane hava minimum width of 7 feet (2 m). An additional 3 feet (

m) should be divided equally between the two outside lanto aid in wave quelling. The shallow-end depth should b

minimum of 4.5 feet (1.35 m) for competitive pools and feet (1.1 m) for recreational pools, depending on local cod

The deep-end minimum depth of pools with springboais between 9 and 12 feet (2.7 and 3.7 m) for a 3-foot (1-board and 11.5 and 13 feet (3.5 and 4 m) for a 10-foot (3-

board, depending on local codes. Platform diving is performin specially designed pools, which are outside the scope

this chapter.

Location of the Facility There are no generally accepted rules for choosing t

location of a public swimming pool facility. Only careinvestigation of the available sites and the use of comm

sense will result in a suitable location.First, consideration must be given to the accessibility

the location. A public swimming pool will be used in dirproportion to the local population’s convenience in reachthe facility. Distance is a barrier, and so are stop lights a

railroad tracks. The engineer also must consider the traflow in the area and the relative safety for pedestrians a

bicycle riders of the routes normally taken to and from public swimming pool facility.

Equally important at this stage are the physical propertof the proposed swimming pool site, including its soil qualgroundwater locations, and subsurface obstructions su

as rocks. Attention also must be given to the availabilitywater, gas, sewers, and electricity. If all utilities are not av

able or extensive clearing, grading, or difficult excavationrequired at or near the proposed site, significant additio

expenses may be incurred.The availability of an adequate water supply is essent

The water supply system provides the means to fill the pinitially with water and to make up water lost throuwastewater discharge and evaporation. The preferred sup

source for filling the pool and maintaining adequate volumpotable water. In areas with a limited water supply or wh

the system capabilities are in doubt, consideration shobe given to filtration equipment, which requires minimubackwash water, or an off-peak filling and servicing schedu

Well water is often of good quality and may be used direchowever, the mineral content may be sufficiently high

require treatment. All water should be given a detaichemical analysis in the early planning stages to determ

State Swimming Pool Health CodeRequirementsState health code requirements become an issue whenchanges are made to main drains. Any changes in a pool’s

circulation piping or main drains are considered alterations,and in most states alterations to a pool design require submis-

sion by a Professional Engineer licensed by that state. Manyowners are unwilling to adhere to this requirement because it

adds costs to their attempts to become compliant with VGB.

One of the primary areas of conflict between VGB and statehealth codes is a result of the approach taken by manufactur-

ers to design compliant grates. Most of the designs for gratesthat will prevent suction entrapment result in cover/grates

that are raised anywhere from ½ inch to 2 inches, whichresults in protrusions from the floor of the pool when these

new “compliant” cover/grates are installed. This is not allowedby most state codes because it can present a tripping hazard.However, many states have made, or are making, changes to

their codes to allow main drain protrusions no greater than 2inches above the pool surface.

Important Considerations When investigating what steps to take to comply with theregulations in the Virginia Graeme Baker Pool and Spa

Safety Act, the designer must keep in mind that anythingdone to meet the requirements of the federal act must not

be in conflict with the state code. This does not mean thatthe state code takes precedence; it is merely meant to draw

attention to the fact that there are two AHJs and that satis-fying one set of requirements does not automatically meanfull compliance. Pool compliance inspections will be done by

both the local code authority for adherence to the local codeand by the CPSC for adherence to the requirements of VGB.

PRELIMINARY DESIGN PARAMETERS

Before the plumbing for a swimming pool project can bedesigned, the following information should be obtained: oc-cupant capacity, size of the facility (including pool volume),facility location and configuration, style of pool, times of use,

availability to infants and children (which may necessitate aseparate pool), tournament and racing requirements, toilet

requirements, concession and vending requirements, andbathhouse requirements.

Occupant Capacity and Size of the Facility Assuming that the swimming pool is part of a complex thatincludes other outdoor facilities (such as ball fields, tennis

courts, and basketball courts), following are the generallyaccepted criteria for estimating the number of swimmers:

• The total membership of the facility can be estimated to

be 10 percent of the total population of the communityit serves.

• The maximum attendance on the peak day can be esti-mated to be 68 percent of the total membership.

• Maximum attendance at the public swimming pool facilitycan be estimated to be 40 percent of the projected maxi-mum attendance on the peak day.

• The maximum number of swimmers is approximately33 percent of maximum attendance.

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whether treatment (e.g., softening or pH control) should be

considered. In general, using softened water for filling andmakeup water is not recommended for swimming pools.

Protection of the potable water supply system throughair gaps or backflow prevention equipment is mandatory.

The type required must be determined by checking withthe local AHJ. Some codes may not allow direct connec-tion, even with reduced pressure zone backflow preventers

installed on the freshwater supply.

The rate of water evaporation from the pool should beestimated to determine the average makeup water required.Direct discharge of swimming pool water into the local storm

sewer system or a watercourse without proper treatmentmay not be allowed, since chlorinated water is harmful to theenvironment. The chemistry of the proposed effluent should

be approved by the AHJ.

General Physical CharacterDeciding on the general physical character of a proposedpublic swimming pool facility involves determining suchthings as the type of swimming pool, its style, the intended

use of the pool, its shape and dimensions, indoor versusoutdoor design, bathhouse planning, and the location and

type of equipment. A swimming pool complex with separaterecreation pool, diving well, and wading areas accommodates

all possible uses, including recreation, training, diving, watersports, exercise, therapy, and competitive swimming. Thereis a definite aesthetic trend toward luxury in contemporary

swimming pool design. The use of color, walks, deck areas,and plantings creates a pleasant and interesting personality,

but also substantially increases costs.Before commencing the design, it is important to deter-

mine the style of pools the facility requires and the impactthis will have on the space available for mechanical systems.Many facilities are now being designed with multiple pools

or a multiuse pool. Pool styles can range from leisure poolsto swimming pools with a wave pool component to 25- and

50-meter competition pools with diving facilities.Many leisure pools that allow younger children to play

with interactive water toys and water slides are being de-signed in conjunction with other pool facilities. These poolsusually have water depths that range from 1 to 4 feet (0.3

to 1.22 m) and may have an uneven bottom, depending onthe location of the interactive play toys. The number of toys

and the size of the pool will impact the space requirementsfor pumps and filters.

Wave pools and zero-depth pools have become commoncomponents of public swimming facilities in the last few

years. These designs allow swimmers to experience thesensation of swimming in ocean-like conditions. Many wavepools are designed so that the wave generator can be set to

come on at certain times of the day and/or night or whenrequested by patrons. Both zero-depth and wave pools usu-

ally have a beach component at one end of the pool, whichrequires special consideration to be given to the gutter sys-tems and water pickup at the beachhead, or zero-depth end.

The wave-generation equipment requires additional spacewithin the mechanical room, and this needs to be taken into

consideration when planning a facility with this component.

Competition pools have very specific regulations that g

ern the water quality, clarity, turnover rates, temperatusize, depth, and markings that are permitted within the po

These requirements may be more stringent than the lohealth department requirements and may require more

larger components to be located within the mechanical rooMany alternatives of shape and/or dimension are availa

to the designer. However, public pool configurations m

commonly use straight lines and right angles. Pools of t

nature are much more adaptable to the use of automapool-cleaning equipment. Often, there are good reasons unconventional designs and shapes in private swimmi

pools and, perhaps, in hotel swimming pools where archittural interest (or uniqueness) may be of prime consideratio

The question of indoor versus outdoor swimming pool des

is considered during the preliminary planning of the facilityis well established that, although about 10 percent of the pub

likes to swim outdoors in the summer, less than 1 percentinterested in swimming in the winter, even if indoor facilit

are provided.Therefore, the need for outdoor swimming is address

first. Then, if the budget permits, indoor facilities can

added. An indoor swimming pool facility costs approximatthree to four times more than a comparable outdoor swi

ming pool facility. If the total cost is of little consideratithe same swimming pool facility can be used for both indo

and outdoor swimming. A possible solution to the problem of providing indo

swimming is the cooperative funding, planning, and constrtion of a swimming pool facility adjacent (or connected)a school. This requires the cooperative effort of the sch

board, park district, recreation department, and any othtaxing body. The engineer should plan such a swimming p

facility to have the following:

• An indoor swimming pool of sufficient size to meet t

needs of the school and the local community• An outdoor swimming pool complex planned and co

structed to meet the needs of the local community

• A central shower and toilet area

• Mechanical equipment for water treatment designed

serve both the indoor and the outdoor swimming pooDuring winter, the indoor swimming pool can be us

for the school’s and community’s training and recreationneeds. During summer, both indoor and outdoor swimmipools can be scheduled and used. This arrangement allo

one pool to be out of service for maintenance while tother remains operational. A facility of this type saves

considerable amount of money and provides a swimmipool facility for year-round comprehensive scheduling, w

revenue sufficient to cover the operational and maintenancosts.

Many technical problems are involved in the design

an indoor swimming pool facility. First, there is the obvioproblem of maintaining the proper relationship between

and water temperatures to control condensation and fogginTo be properly balanced, the water temperature should

in the range of 75 to 80°F (23.8 to 26.7°C), and the air teperature in the building should be maintained 3 to 5°F (to 2.6°C) above the water temperature. If this relationsh



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is inverted, the swimmers will become uncomfortable when

they exit the pool, and both fogging and condensation arelikely to occur.

Secondly, there are the additional considerations of acous-tics, ventilation, and air movement. Maintaining maximum

air quality in an indoor pool facility is essential. Evaporationof the pool water and the gassing off of disinfection by-products such as trihalomethanes and chloramines require

careful consideration of relative humidity, the introduction of

large quantities of fresh, outside air, and proper air movementin the space. Refrigeration-loop dehumidification systems,as well as physical heat-transfer systems to allow some pre-

heating of incoming outside air, are frequently employed.The rules for the bathhouse design generally are specified

in great detail by the local governing public health authority.

The preliminary planning of the bathhouse facility must becarried out within the limits of established regulations. Apart

from these rules, however, the designer may exercise imagi-nation with considerable latitude in several areas: achieving

a pleasing and aesthetic architectural balance, providing anadequate floor area for traffic, and providing adequate stor-age and management facilities.

Equipment locations should be established during thepreliminary design phase. It must be decided, for example,

whether equipment is to be located in the bathhouse orin a separate enclosure (keeping in mind that it is usually

desirable to combine all of these facilities under a single en-closure). The filter assembly should be housed in an area with

heat for the off-season and with ample storage space. Thefilter equipment also should be located in the filter room foreasy and efficient operation and maintenance. Consideration

needs to be given to the location of the pumps in relation tothe water levels in the pools. Wherever possible, the pool

pumps should be located below the water level determinedby the gutter system or surge tank so the pumps will have

positive suction. Self-priming pumps are used for a number ofpool applications, but the use of this style of pump is subjectto greater startup problems and maintenance issues.

The construction of a major swimming pool facility withthe filter equipment located outdoors or under drop lids to

save costs is false economy and is not allowed by some codes.This type of installation will cause rapid deterioration of

the pumps, hoses, motors, and other specialized equipmentduring the off-season, as well as make operation during theseason difficult and costly.

Finally, the designer must select the type of filtration andpurification equipment to be used. The most obvious consid-

erations are pool size; available space; the type, location, andavailability of sewer facilities; soil, rock, and groundwater

conditions; and the location, availability, chemistry, and costof the fill water. If the water is plentiful and inexpensive andspace is not a problem, sand filtration may be considered.

Scarce or costly water and limited equipment room floorspace, plus a desire for maximum water clarity during heavy

use, might dictate the use of diatomite filtration. The size ofthe swimming pool facility, as well as the chemistry of the fill

water, will usually determine the type of disinfection equip-ment to be used.

In areas where freezing temperatures are possible a

if the pool is not used year-round, provision must be mafor draining the water lines, exposed drains, and plumbi

fixtures to prevent damage by freezing. Alternatively, areas must be provided with minimum heating equipme

Bathhouses, Toilets, and Showers Adequate dressing and toilet facilities must be provided. Easwimming pool complex must have separate facilities for m

and female bathers, with no interconnections between the

The rooms must be well lighted, drained, and ventilatThey must be constructed of impervious materials, finish

in light colors, and developed and planned so that good sanition can be maintained throughout the building at all tim

The partitions used in dressing rooms, showers, and tlets must be made of durable materials and not subject

water damage. They should be designed with spaces undthe partitions to permit a thorough cleaning of the walls a

floors. If these partitions are subject to vandalism, block waand vandal-proof devices should be considered.

The showers and dressing booths for females should ha

curtains or some other means of providing privacy. This rmay not apply for schools and other institutional facilit

where a swimming pool may only be open to one sex at a tior where supervision is necessary.

Facilities for the physically challenged that meet federal, state, and local regulations for private and pubfacilities also must be provided.

The floors of a bathhouse must be free of joints or opeings, be continuous throughout the area, have a slight textu

to minimize slipping (but also be relatively smooth to ensupositive drainage of all parts of the building), and have an

equate slope toward the drains. An adequate number of flodrains shall be provided. Floor drains should be positionbased on the requirements of the plumbing and buildi

codes, but in no case should the floor slopes be designed less than 0.25 inch per foot (6.35 mm/m) to ensure prop

drainage of all floor areas. An adequate number of 0.75-inch (20-mm) hose bib

must be provided for the washing of the dressing rooms athe bathhouse interior. At least one drinking fountain shoube provided for bathers of each sex in the bathhouse, w

additional drinking fountains provided at the pool.The minimum sanitary plumbing facilities, as manda

by the local plumbing code, should be provided. (A samplea representative code is offered in Table 6-1 as a referenc

These minimum criteria for bathhouse plumbing facilitmust be based on the anticipated maximum attendance.

If the local code does not address swimming pool facilitithe following minimum facilities should be provided:

• Three showerheads for the first 150 male users and o

showerhead for each additional 50 male bathers

• Two showerheads for the first 100 female users and o

showerhead for each 50 additional female bathersTempered water at a temperature of approximately 9

100°F (32.2–37.8°C) should be provided to all showerhea

Water heaters and thermostatic mixing valves should inaccessible to the bathers.

Soap dispensers, providing either liquid or powdered somust be furnished at each lavatory and between each pair

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Facility(example of location and

type)

1. Swimm ing poo ls , w ad ingpools and whirlpools inconjunction with sleeping or d we ll in g u ni ts h av in gplumbing, except for items 2 -5, No open swim lessonspermitted. (i.e. apartments,hotels, motels, condos andmobilehome parks)

CumulativeAreaof Surface Water (in square feet)

< 2000

2000 - 7500

>7500

2.Swimm ing poo ls , w ad ingpools and whirlpools withoutliving units,except for items 3.to 5. Swimming pools,wadingpools, and whirlpools withsleeping or dwelling unitswhere open swim or lessonsare permitted and water attractions where lessons areconducted ( i.e. munic ipalpoolsand campgrounds)

15000

>37500

30

37500

Per departmental approval

aFor water attractions in excess of 37,500 sq. ft., use the following additions:

For each 7,500 sq. ft. or fraction thereof add one sanitary unit - 0.7 male water closets, 1.0 male urinal, 0.85 male lavatories, 1.0 male showers, 0.6 drinking

fountains, 4.0 female water closets, 1.0 female lavatory, and 1.0 female shower

*

For pools in excess of 7,500 sq. ft. and Type 1. above, and for pools in excess of 15,000 sq. ft. and Type 2. above, use the following additions:* For each 4,000 sq. ft. or fraction thereof, add one sanitary unit - 1.0 male water closet, 1.0 male urinal, 1.0 male lavatory, 4.0 male showers, 1.0 drinking fountain,4.0 female water closets, 1.0 female lavatory and 4.0 female showers

For the requirements listed for additional sanitary facilities, each fraction represents an additional fixture

Number of

PublicToilets

PublicUrinals

PublicLavatories

PublicShowers

PublicDrinking

Fountains

F M M F M F M

One unisex 0 One unisex 0 0 1

1

1

1

2

6

8

12

16

20

2

2

4

8

12

12

16

3

4

4

4

10

12

14

1

1

1

1

2

2

3

4

5

1

1

1

2

3

3

1

1

2

2

2

2

3

2

0

0

0

1

2

2

3

4

5

1

1

1

2

3

3

4

2

2

2

2

3

3

4

1

1

1

1

2

2

3

4

5

1

2

2

2

3

3

4

1

2

2

3

4

4

5

1

1

1

1

2

2

3

4

5

1

2

2

2

3

3

4

1

2

2

2

3

3

4

1

1

1

1

2

2

3

4

5

1

3

2

2

3

3

4

2

4

5

5

6

6

7

1

1

1

1

2

2

3

4

5

1

3

2

2

3

3

4

2

4

5

5

6

6

7

1

1

1

1

2

2

3

4

5

1

1

2

2

3

3

4

1

1

1

1

1

1

1

See note below for requirementsa




8

4

1One unisex 0 One unisexOne rinse-off

Shower

One uisex

7500 - 9999

10000 - 14999

15000 -22499

22500 - 29999

30000 - 37500

Table 6-1 Minimum Number of Sanitary Fixtures Required at Public Pools and Water Attractions



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showerheads. The dispensers should be constructed of metal

or plastic; no glass is permitted. Mirrors must be provided overeach lavatory. Toilet paper holders must be furnished at each

water closet combination. As previously stated, vandal-proofdevices should be considered, if applicable.

POOL OPERATING SYSTEMSMost provincial and state regulations now require pool sys-tem components to be certified by an independent testing

agency, such as NSF International. This certification en-sures that all piping and other components meet a national

standard for quality of materials and that public health andsafety issues are addressed. This standard also ensures that

the equipment meets consistent quality controls and buildsa level of confidence in the product.

When considering the broad spectrum of approaches used

for pool design, the designer should attempt to evaluate themajor cost and performance differences between lower-quali-

ty residential or hotel, motel, and health club-type equipmentand higher-end products used on major commercial pool

installations. If the owners have not already made some ofthese assessments on their own, the designer should be pre-

pared to appraise them on the pros and cons of the availablechoices so they can make an informed decision on the valuethey wish to place on the quality of the end product.

If designing a commercial installation for a high school,university, park district, or YMCA, the designer must follow

certain basic board of health requirements beyond the scopeof the plumbing codes that must be met.

Design Parameters

Turnover Rate

The turnover rate (turnovers per day) refers to the time it

takes to move a quantity of water, equal to the total gallons(liters) in the pool and surge vessel, through the filtration

system.Minimum turnover rates for various types of pools are

determined by code. Typically, they fall within the followingranges:

• Swimming pool: Six hours (four turnovers per day)

• Wading pool: Two hours (12 turnovers per day)

• Therapy pool: Four hours (six turnovers per day)

• Hot tub and whirlpool: 30 minutes (48 turnovers per day)Keep in mind that these are minimums. In heavily used

pools, quicker turnovers will help maintain water clarity bymeans of increased filtration and better chemical distribu-tion. Also, pool designs that combine shallow areas, such

as zero-depth pools, with deeper swimming areas require

a turnover rate that combines the characteristics of bothtypes of pool.

A calculation of the flow rate required to move a quantity

of water equal to the gallons (liters) in the shallow area(usually up to 18 inches [0.46 m] in water depth) within two

hours is combined with the flow rate required to achievethe minimum turnover requirements for the deep area ofthe pool (six hours). This combined flow requirement will

result in a greater number of turnovers per day, usually inthe range of six per day (or one turnover every four hours).

One additional point to consider in deciding on a turnov

rate for pools projected to experience heavy usage is the fthat one turnover refers to a volume of water equal to t

total gallons (liters) in the pool system. It has been calculathat it takes more than three turnovers for 95 percent of t

actual molecules of water in the system to pass through tfilter. This is due to the physical characteristics of the poThe only way to remove the dirt load being introduced in

the pool by the users and the environment is through filt

tion or oxidation. No matter how efficient the filter, it caremove what isn’t put through it.

Filter Media Rate

The filter media rate is the rate, measured in gallons pminute (gpm) per square foot (L/min per m2) of filter surfa

area that water is allowed to pass through various typesfilters. These maximum rates are established by NSF/AN

50: Equipment for Swimming Pools, Spas, Hot Tubs, aOther Recreational Water Facilities, as well as local hea

department codes. This rate becomes the determining facin the sizing of the filter area needed for a given minimuturnover rate and the resultant minimum flow rate.

Flow Rate

The flow rate is the rate at which water moves through tfiltration system. It is calculated based on the minimu

turnovers per day. The flow rate has a major bearing on psizing in the distribution system.

Many codes limit velocities in suction piping and retu

piping. In swimming pool parlance, return piping is the pipcarrying filtered water returning to the pool. Some comm

maximums are 5–8 feet per second (fps) (1.52–2.44 m/s)suction piping and 8–10 fps (2.44–3.05 m/s) in return pipi

Required Surge Capacity

The term “surge” describes all water that comes off the t

of the pool, either displaced by the bodies of the swimme

or splashed into the gutters through wind or heavy activiIt must flow to a surge vessel attached to the swimming pcirculation system. Continuous skimming is required evduring times of no activity. The skimming that takes pla

during these quiescent periods is intended to draw marial near the water surface into the gutters and back to t

filtration equipment.The skimming action is essentially accomplished by ma

taining the level of the water in the pool no more than ¼ in(6.35 mm) above the rim of the gutter As the water just bar

breaks over the lip of the gutter, the velocity of the skimmwater increases and creates a pull on the water surfacethe water level is too high, little skimming action occurs

Many years ago, this skimmed water went to waste. Waconservation, as well as the cost of reheating replaceme

water, has resulted in code requirements for the capturethis water. It now must be filtered, chemically treated, a

returned to the pool. Most codes mandate a minimum volurequirement for the vessels that receive and hold this wauntil it can pass through the filter. The volumes are bas

on the estimated water displaced by swimmers plus waaction caused by their activities. A common requireme

is for 0.6–1 gallon (2.27–3.79 L) of surge capacity for easquare foot (m2) of pool surface area. The various means

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achieving this are covered under the “Surge Vessel or Surge

Trench Selection” section of this chapter.Some smaller pools are allowed to use skimmers to re-

turn water from the top of the pool. There are restrictionsto their use, usually based on the size of the pool. Skimmers

are covered in more detail in the “Component Evaluationand Selection” section of this chapter.

Main Drain and Grate VGB states that where one cover/grate is blocked or partially

blocked, the remaining main drain cover/grates must be sizedto handle the full flow of the system. In other words, with

two main drains, each cover/grate must be sized for the fullflow of the system. With three main drains, each cover/grate

must be sized for 50 percent of the full flow of the system. ASME A112.19.8 also details tests for finger entrapment,

measuring the force needed to pull the cover/grate out of theframe, and resistance to UV degradation, which could make

the cover/grates brittle and cause attachment failure. Theseare an important part of the ASME testing because manyof the entrapment accidents that occur are due to detached

cover/grates. However, the primary issue that the designermust be concerned with is the maximum flow rating. VGB

also requires main drain cover/grates to be sized for the maxi-mum flow of the system. The combined maximum possible

flow (which is usually greater than the design flow) that thesystem pumps can produce must not exceed the maximumflow rating for the cover/grate intended to be installed.

To address hair entanglement, VBG requires all existingmain drain grates to be replaced with new cover/grates that

have been tested to ASME 112.19.8. They must bear a stampindicating the maximum flow allowed through the cover/grate

as determined by that ASME testing.Most of the designs for grates that will prevent suction en-

trapment result in cover/grates that are raised, which results

in protrusions from the floor of the pool. This is not allowedby most state codes because it can present a tripping hazard.

However, many states have made, or are making changes totheir codes to allow main drain protrusions no greater than

2 inches (50.8 mm) above the pool surface.In instances where the grates are installed in a wall, the

installation of the anti-suction entrapment cover/grates results

in a protrusion from the wall, which is a separate hazard ad-dressed by most state codes.

No manufacturer is allowed to manufacture or distributea cover/grate that has not met VGB requirements. All cover/

grates or cover/grate and sump systems must bear the VGB-required stamp on the face of the cover/grate. The CPSC is

tasked with inspecting all commercial facilities, and theyhave the authority to shut down and fine facilities that arefound noncompliant.

Main Drain Piping and Location

The typical pool has main drain connections at the deepestpoint of the pool structure. These main drain pipes are con-nected to a formed concrete sump, stainless steel sump, or

prefabricated fiberglass sump covered by a grating.These connections provide a means of drawing water off

the bottom of the pool for filtration purposes. They also usu-ally provide a means of pumping the pool water to waste or

draining the pool via gravity to a remote sump for pumpi

to waste.In some cases, a reverse flow design is allowed. In this ty

of design, all filtered water is returned to the pool throuinlets in the bottom of the pool. All dirty water is skimm

off the top of the pool. In such a design, a main drain is siply used to drain the pool. Not all codes allow such a desi

Due to entrapment concerns, multiple main drain sum

piped hydraulically equal, are usually required. Velocit

through the gratings covering these sumps are usuamandated to not exceed 1–1.5 fps (0.3–0.46 m/s) to reduthe chance of hair entanglement.

The free area of the covering grate typically must beleast four times the area of the connected main drain piCodes also require minimum distances between main dr

sumps, as well as distance requirements from the pool wa

Hydrostatic Relief Valve

In areas where hydrostatic forces are a concern, such asareas with high water tables, protection of the pool stru

ture must be provided. This typically necessitates sufficieunderdrain piping below and around the pool structure

pumped drainage scheme also may be employed.

However, even with proper groundwater removal systein place, a hydrostatic relief valve should be installed in tmain drain sump. This device serves as a spring-loaded wa

stop and relief valve. If the main drain sump is poured cocrete, a 2-inch (50.8-mm) pipe, along with a no-leak flanis situated in the bottom of the pour. The HRV is thread

into the pipe on the pool side of the sump, and a pebble stis threaded onto the backfill side of the concrete. If the p

is drained, the HRV may be the only way to prevent the pfrom being lifted out of the ground (floated like a boat) by

leasing hydrostatic forces into the pool. There have been cawhere large (up to 200,000-gallon [757,082-L]) outdoor pohave popped as much as 24 inches (0.61 m) out of the groun

If the pool is internal to a large building with a large bament area and a substantial drainage system in place, t

use of an HRV may not be a concern. For a diagrammarepresentation of this, see Figure 6-2.

Filtered Water Return Piping

In swimming pool system terminology, return piping ref

to piping returning filtered, chemically treated water backthe swimming pool inlets. The quantity, location, and spac

of these inlets is covered by the plumbing code. If the voluof these inlets cannot be adjusted, care must be taken in t

pipe layout and sizing to ensure equal distribution of chemcal treatment throughout the pool volume.

Basic Piping Schemes

Numerous acceptable piping schemes are available. T

major factors determining which approach to take are desions on the following:

• Where the mechanical equipment room will be locat

(above or below the pool level)

• The type of surge-holding vessel to be used

• Whether to use skimmers instead of a surge vessel the pool is small enough)

Some typical piping layouts are given in Figures 6-3 a6-4. For simplicity’s sake, chemical feed systems and heati



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systems are not shown on these drawings. Those items will

be added to these diagrams in the specific section coveringthose components.

Filtration, Circulation, and Water ChemistryControl Components

Surge Vessels

Surge vessels are basically large holding tanks. They accept

water flowing by gravity from the top of the pool and holdit until the circulation pump can move it through the filter.

To reduce the potential for suction entrapment, the maindrain piping should, ideally, flow by gravity to the surge tank.

Gutters

The water from the top of the pool is usually collected by

a gutter. In the past, these were simply formed out of con-crete with drain connections spaced evenly around the pool.

Though this is still done on occasion, the following types ofgutters are much more the norm.Stainless Steel Gutter This is a dual-function system.It not only collects the skimmed water from the top of thepool, but it also provides the distribution inlets for returning

filtered water. The skimmed water flows into one chamber

of the gutter. Through another chamber, separated from thegutter water by a stainless steel wall or plate welded in placeinternally in the unit, the filtered water is pumped back to

the pool. This pressurized chamber has holes, spaced aroundthe entire perimeter of the pool, that serve as filtered returnwater inlets.

One disadvantage of this system is the fact that the inletsare placed very close to the surface of the pool, and distri-

bution throughout the entire pool volume can be affected.Short-circuiting of filtered water back into the gutter is also

possible. Of additional concern is the potential for internalbreaches between the two flows (gutter water and filteredwater). These may develop over time due to corrosion and/

or expansion and contraction. These breaches are difficult todetect, and they will result in less-than-minimum turnovers

due to short-circuiting of filtered water right back to thefiltration system through the gutter system. To address this

concern, some stainless steel gutter manufacturers weld arectangular stainless steel tube to the face of the rear gutterportion of the assembly, which provides a completely indepen-

dent chamber for the flow of filtered water back to the pool.Surge Gutter Trench This is a formed concrete trench of suf-

ficient width and depth to hold the required surge volume. Itextends around the entire perimeter of the pool and is usually

covered by a grating, which can be as simple as fiberglass barssitting on a formed lip or as substantial as polymer concretecoping stones. The concrete coping stone is even considered

part of the deck, which can be useful when minimum deckwidths might otherwise be hard to accomplish. See Figure 6-5

for details of this approach.

Skimmers

On smaller pools, codes allow the use of skimmers. Theseare devices made of various types of plastics that have a

floating weir (flapper door) that creates a skimming actionat the water surface. They are set in the concrete when it is

poured at one or more locations spaced around the perimeterof the pool or hot tub. Since they are directly connected to

circulation pump suction, they should be piped to an equ

izer fitting that is located well below the pool’s operatilevel (see Figure 6-6). VGB considers this equalizer fittin

suction outlet and requires it to be covered by a compliacover/grate or to be removed or disabled.

Skimmers are not as effective as a continuous gutterskimming debris off the entire surface. That is why they alimited to use on pools with a small surface area. They a

are used when budget concerns dictate.

FiltersThe filter component of a pool system mechanically removdebris from the pool water. Measurable removal efficiency d

ferences exist between the various types. In selecting a filtype, consideration should be given to the following item

• Equipment room floor space and ceiling height

• Availability of backwash replacement water

• Filtration efficacy (turbidity of water leaving the filt

• Water and sewer costs for replacement water

• Ability to handle a possibly large volume of backwa

water

• Cost of heating replacement water

• Ease of operation

• Equipment longevity• Budget requirementsTwo basic media types are used in filters: sand a

diatomaceous earth. Cartridge filters are sometimes uson smaller pools and spas, but they merely use replaceabcartridges, not loose media.

Sand is a granular media (usually #20 or #30 grafilter sand), and a uniformity coefficient is associated w

each grade. The filter manufacturer will indicate the recomended grade of sand, as filtration efficiency is affected

the grade used, with #30 sand having particulate remoefficiencies that are more efficient than #20 sand. Howevmore restrictive sand beds result in higher friction los

through the filter.Diatomaceous earth, known as DE, is considered a d

posable media. It is a fine white powder material made upskeleton-like fossilized diatoms. This powder is mixed w

the water in the filter vessel and deposited in a layer on tfilter element or septum. DE also comes in various gradTypically, for swimming pool use, the product used shou

have permeability in the 3–5 Darcy range. Particulate moval capabilities basically track the permeability range

the 3-Darcy media would be expected to achieve 99 percereduction of 3-micron particles.

The filter area required depends on the media select

and the minimum flow rate requirement for the facility bing designed. The various filter configurations for each

the two primary media types are covered in the “ComponeEvaluation and Selection” section of this chapter.

Circulation Pump

Circulation pump selection must be based on the abilitythe pump to move the required amount of water through tcirculation and filtration system under worst-case conditio

As the filter becomes dirty (loaded), it restricts the flow. piping ages and becomes calcified, it also can substantia

restrict flow.

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For these reasons, many codes mandate that a pump be

selected with a design performance point of the minimumflow required, with an available total dynamic head (TDH)

capability of 70–80 feet. In the absence of such a code require-ment, the designer must assume the expected pressure drop

through a dirty filter, usually 15–20 pounds per square inch(psi) (103.4–137.9 kPa).

In addition to the dirty (loaded) filter, all pipe and fitting

losses on both the suction and discharge sides of the pump,

friction losses through a dirty hair strainer, and lossesthrough a pool heater or heat exchanger must be calculated.The resultant estimated system head requirement dictates

the proper pump selection.

Hair and Lint Strainer

These are devices with removable strainer baskets. They areinstalled upstream of the pump and are required by code.

Their primary purpose is pump protection. Most codes re-quire two strainer baskets, which decreases shutdown times

when cleaning and changing a basket.

Flow Sensor and Display

All systems must include a device to indicate that the

minimum flow rate and resultant turnover rate are beingachieved. Numerous types are available, and their costsversus accuracy and life expectancies vary considerably.

Many codes require gauges to be located properly on the

suction and discharge sides of the circulation pump. Thesegauges, together with a pump curve for that particular pump,

provide the ability to accurately check the performance of thepump and to verify the accuracy of the flow-measuring device.

Flow Control Devices

Consideration must be given to the means that will be used

to control the rate and direction of flow to and from the pool.The circulation pump is selected for a worst-case scenario, so

if it is allowed to run wide open when the filter, hair strainer,

and piping are free and unobstructed, then over-pumping ofthe filter and heater will result.

Manual butterfly valves also are needed as isolation valvesto enable the servicing of system components

without draining the system. Valves must beprovided to isolate the hair strainer to allow

the replacement of a dirty hair strainer basket.Codes also require control of flow from the

pool. Usually, 80 percent of the circulated wateris taken off the top of the pool, and the remain-ing 20 percent is drawn from the bottom of

the pool through the main drain. Some type offloat-operated butterfly valve or manual valve

usually is used to control this.For more accurate control, diaphragm-type

air-operated butterfly valves or piston-operatedbutterfly valves with pilot positioners are used.

The various types are covered in the sectiontitled “Component Evaluation and Selection.”Even if variable-frequency drives (VFDs) are

used to control the rate of flow to the pool, sometype of manual valve should be in place in case

the VFD fails. Manual operation must be ableto be controlled while the VFD is out of service.

Pool Water Heating Systems

The basic types of heating systems are gas-fired water he

ers, steam/hot water heat exchangers, and, infrequentelectric heaters. One possible disadvantage of using heexchangers is that they require year-round operation o

boiler (if the pool is a 12-month operation). The rest of tfacility may not require the use of the boiler, which m

make the case for the use of a supplemental electric heat Venting capabilities, corrosive ambient air, and equipme

space requirements are the primary issues to be given conseration. Many facilities are designed with dehumidificatsystems that use the heat of condensation to heat the p

water or pool space. The various choices are listed in t“Pool Water Heating Systems” section under “Compone

Evaluation and Selection.”

Chemical Control and Feed Systems

Commercial pools must have systems in place that are pable of maintaining the pH and oxidizer/sanitizer levels

the pool water within a code-mandated range. These systecan be as simple as adjustable-rate feed pumps for acid a

chlorine solutions. Some codes require the use of an aumatic water chemistry controller to constantly measure

and sanitizer levels in the pool. These controllers will tuon the associated chemical feed pump or system as neede

Level Control Systems (Surge Tank)

Level control systems can vary from a simple float-operat

main drain valve installed on the main drain pipe after it eters the surge tank to a complex bubbler system (different

pressure controller) controlling an air-operated modulativalve. The decision typically is based on cost versus accuraDiagrams and specific operational characteristics of the

systems are covered in detail later in this chapter.

Fresh Water Makeup

Fresh water makeup can be accomplished by an opera

regularly checking the pool water level and turning on tmanual freshwater fill valve until the pool is filled properMost codes require a skimming action to take place co

Figure 6-2 Formed Concrete Main Drain Sump with Hydrostatic Relief Valv



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stantly, and a good way to ensure this is to provide some

form of automatic fresh water makeup system.From an operational standpoint, since most contaminants

in the pool water are introduced at the top portion of thepool, the top layer of water should pass through the filter the

quickest. Such a water makeup scheme is closely associatedwith the water level control scheme employed. (Informationaldiagrams are provided later in this chapter.)

Specialty Systems

The complexity of pool designs has increased dramatically fromthe days of the simple rectangular lap pool with basic filtration

and chemical feed systems. An seemingly endless variety ofwater play features are now available, as well as supplementalsanitation systems designed to offset the increased demand

created by heavy bather loads.This places an increased responsibility on the shoulders

of the pool designer. The designer must investigate andunderstand the capabilities and special considerations re-

quired of the design when using these products. Some basicinformation can be found in the “Component Evaluation andSelection” section that follows.

COMPONENT EVALUATION ANDSELECTION

Surge Vessels (Surge Tanks)One method used to create a surge-holding capacity is a

buried concrete tank. This type of surge tank is buried some-where between the pool and the equipment room, usually

under the deck, which extends around the perimeter of thepool. It is also frequently located under the equipment roomfloor slab. Water from the perimeter gutter, and ideally the

main drain, is piped to this holding tank. Although the buried tank saves floor space, it complicates

accessibility to key components. Access must be provided for

cleaning or adjustments. Pump strainers and/or level controldevices are often difficult to access. Frequently, draining ofthe surge tank is necessary.

This type of buried concrete structure is considered a

confined space, so the operator will be required to followOccupational Safety and Health Administration (OSHA)

guidelines before working in this area, which should be takeninto consideration before deciding on this approach. Figures

6-3 and 6-4 show how a buried surge tank would be pipedinto the circulation system.

A freestanding vessel is another type of surge tank that

is located in the equipment room. It can be an open or aclosed vessel. Open-tank vessels are still very common in

installations where the equipment room is in a basement orwhere the location prevents venting of a closed tank. The

obvious concern is how to provide protection from floodingif the system shuts down unexpectedly. Properly functioningcheck valves on the piping downstream of the filter, as well

as between the main drain piping and the surge tank (if themain drain isn’t connected to the surge tank), are an absolute

necessity. The open-tank design provides a convenient wayto add fresh water with the required air gap.

The closed and vented tank is a much better option for abasement equipment room. A closed vessel, with flanged con-

nections for the gutter piping, pump suction, and possibly t

main drain piping, is vented through piping extending abothe water level of the pool. Venting is essential, as it allo

incoming water from the gutter and/or main drain to displaair in the tank. It also prevents a possibly damaging vacuu

situation from occurring if isolation valves are inadvertenclosed while the circulation pump is in operation or are lclosed when starting the pump. The vent, if of sufficient si

also provides a means of adding fresh water with the requir

air gap. Figure 6-4 shows such a piping scheme.Surge Gutter TrenchThe surge gutter trench is a continuous concrete trenformed on the exterior of the pool walls around the ent

perimeter of the pool. The trench is sloped to an area clest to the pool equipment room. At that low point, a sing

pipe connection is made to allow the water collected in ttrench to be combined with main drain water at the circu

tion pump suction.The trench is sized to meet or exceed the minimum sur

holding capacity requirement of 1 gallon per square foot (3

L/m2) of pool surface area. The trench typically is covereda fiberglass or Cycolac (a type of ABS plastic commonly us

for pool components) grating. A slightly raised handhold mbe provided at the water’s edge of the covering scheme us

for this trench to provide swimmers with a place to securgrip, if needed.

Another design employs precast polymer concrete cop

stones. This type of pool operates with the pool water sentially at deck level, and the coping stone is considered

extension of the deck. Return piping often is run in this trenaround the perimeter of the pool, which facilitates pipe repa

when needed, without breaking up the concrete deck. Figu6-5 gives a diagrammatic representation of this approach.

Skimmers

Skimmers can be used only on small pools, usually pools lthan 20 feet (6.1 m) in width or less than a certain amouof water.

They don’t effectively skim a very large surface area, athey are directly connected to pump suction. If the poo

operating level isn’t properly maintained and the walevel drops below the opening of the skimmer, the circulati

pump may possibly suck air and be damaged by cavitaticonditions.

To prevent air from reaching pump suction when usi

skimmers, it is important to require the installation of equalizer fitting, located in the wall of the pool a few fe

below the skimmer. An equalizer valve and float are th

installed inside the body of the skimmer. In this way, if tpool level drops, water still will be drawn through the equizer fitting. These items are offered as options with mcommercial skimmers. (See the diagram in Figure 6-6.)

VGB-compliant fitting is required for this equalizer conntion to the pool since it is considered a suction outlet. So

codes may even require the removal or disabling of theequalizer connections to comply with VGB requirements

High-rate Sand FiltersThe high-rate sand filter is currently the most common tyof filter employed on swimming pool systems. High-rate sa


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filters have acceptable particulate removal capa-

bilities, and they are simple to operate.These filters are pressure type, meaning the

filter is installed downstream of the circulationpump, and the pump creates pressure to force

the dirt-laden pool water through the filter. Thewater enters the filter at the top of the mediabed and is forced through the sand to a set of

slotted laterals, which are connected to a col-

lection manifold.The most common media used in high-ratesand filters is #20 or #30 filter sand, with a

specific uniformity coefficient. The #20 sandhas a particle size of 0.018 inches (0.35 mm)to 0.022 inches (0.56 mm) or an effective size

of 0.45 mm and a uniformity coefficient of 1.5maximum. The #30 grade of sand is not as com-

mon as #20. It is finer sand and is sometimesused when higher filtration efficiency is desired.

Not all filters are designed to allow the useof #30 sand, as the underdrain laterals mustbe manufactured with very close tolerances

regarding opening size to disallow the passageof the smaller sand particles back to the pool.

Check the filter manufacturer’s specificationsto ensure that #30 sand can be used.

In general, the flow rate of the water beingfiltered through this type of filter is in the range

of 15–20 gpm per square foot (56.8–75.7 L/min/ m2) of filter surface area. All pool filters mustbe tested by NSF International, given an NSF/

ANSI 50 listing, and bear that label on theirexterior. This listing prescribes the maximum

allowable flow for each listed filter, and manycodes use this listing as their design require-

ment criteria.The backwash rate for any sand filter is based

on research done by the Hydraulic Institute.

It has been determined through testing that aminimum of 15 gpm per square foot (56.8 L/min) of filter area

is required to “fluidize” the sand bed. At less than 15 gpmper square foot (56.8 L/min), the filter bed doesn’t lift up and

allow debris that is deeply embedded in the sand bed to bereleased. If this lower-than-required backwash rate continues,“mud balls” eventually will develop and effectively decrease

the usable filter area.Properly designed high-rate sand filters, using the most

common #20 grade media, can effectively capture particles assmall as 15–20 microns when the filter is clean. As the filter

becomes dirty (“loaded” is a better description), the filtrationefficiency of a sand filter actually increases. The interstitialspaces between the grains of sand media become smaller and

can possibly capture particles as small as 10 microns.

Horizontal High-rate Sand Filters

Horizontal high-rate sand filters may require more equip-

ment room floor space than vertical sand filters, but they lendthemselves to more accurate design possibilities regardingflow during filtration and backwash. Backwash functions are

also more easily automated and are at a lower backwash flow

for each individual tank. Multiple tank arrangements mayused to alleviate concerns about the ability of waste pipi

or transfer pumps to handle large backwash flow ratesthree-tank horizontal system is shown in Figure 6-7.

Vertical High-rate Sand Filters

Depending on the required filter area and the shape of tequipment room, vertical high-rate sand filters sometimcan be a more space-conscious option. An 8-foot (2.44-

diameter vertical filter would have more filter area than t

3-foot-diameter by 6-foot-long (0.91-m-diameter by 1.83-long) horizontal filters with a 6.25-foot by 6-foot (1.91by 1.83-m) footprint. Three horizontal filters, each with

footprint of 9.5 feet by 6 feet (2.9 m by 1.83 m), would required to provide a filter area equivalent to that of t8-foot (2.44-m) diameter vertical filter.

The equipment room floorplan will probably dictate whtype of filter is best suited for the application. However, t

designer also must consider the backwash water remocapabilities. Since the vertical system is forced to backwa

the entire filter area at one time, the backwash flow rate the vertical filter will be three times that of each individu

Figure 6-3 Typical Above-grade Piping Scheme

Figure 6-4 Typical Below-grade Piping Scheme



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and the filter is considered online, or in filtering mode. Fig-ure 6-8 shows the piping configuration for the pre-coat loop.

Contingent on the quality of the media selected, these fil-

ters can achieve a 99 percent reduction of water impurities inthe 3-micron range. The configuration of these filters can alsoplay a major role in their particulate-retention capabilities.

The procedure for cleaning a vacuum DE filter is simplydraining the filter completely, hosing off the filter elements,and flushing the old, or spent, DE completely out of the filter

tank. This can be a laborious, time-consuming task. If thefilter vessel is poorly designed, with a floor that doesn’t have

sufficient slope to the drain, the old DE will be difficult towash over to the drain opening.

Once the filter and elements are sufficiently cleaned,the filter is filled with water. DE is then added by eitherbroadcasting it over the surface of the water or mixing the

required amount of DE in buckets of water and dumping itinto the filter vessel. The pre-coating process is then initiated,

and after approximately three to five minutes, the filter canbe put back online. Typical piping for a vacuum DE filter is

shown in Figure 6-8.

Slurry Feed Systems

When DE is mixed with water it forms a D

water slurry. To extend the time between Dchanges in the filter, additional DE often

added on a continuous basis. For filter medrates above 1.5 gpm per square foot (5.68min/m2), continuous DE slurry feed (som

times called body feed) may be required code. The rate of addition is prescribed

the same code. A dry slurry feeder uses a rotating aug

mounted below a DE holding funnel. As tauger rotates, it carries DE from the funel out to the end of a trough. The dry D

then drops off the end of the trough into twater-filled filter tank and adds an addition

thickness to the coating of DE on the filtelements. These units have digital contr

and adjustments for setting the rate of fein pounds per day.

Wet slurry feeders employ a holding tank filled with wter in which a predetermined amount of DE is mixed. A

agitator pump is required to keep the DE from settling oon the bottom of the holding tank. A feed pump, usuallydiaphragm-type feed pump with a timed auto-flush solen

keeping the check valves clear, is used to draw the slurout of the holding tank and to inject it into the water stre

entering the filter from the pool. Peristaltic pumps also mbe used, and since they don’t require check valves, they mnot require the auto-flush feature.

Pressure Diatomaceous Earth Filters

Pressure DE filters are the most economical regarding equment room floor space. They are of a vertical configuratiwith internal elements that provide a large surface area

filters having such small footprints. Like vacuum DE filtethey provide a high level of filtration efficacy.

Again, in a pressure system, the pump is located upstreof the filter and forces the water requiring cleaning throu

the filter elements. The actual configuration of the elemevaries by manufacturer, but their purpose is to provide a s

face for the DE to coat and to act as a filtering med

Static Cake Diatomaceous Earth Filters

Static cake DE filters receive an initial charge of Dand then are pre-coated in a manner similar to t

process described for vacuum DE filters. They filcontinuously until the DE becomes plugged to a powhere the flow through the filter is dramatically

duced below design operating parameters. Some foof wet slurry feed usually is employed to extend fil

cycles. Due to the required frequency of cleaninthese filters are not usually found on large comm

cial systems.

Regenerative Diatomaceous Earth Filters

Regenerative DE filters are similar to static cafilters in their basic design, but they are far differe

in their performance characteristics. They typicahave a higher initial cost than any other type of fil

Figure 6-5 Deck-level Surge Gutter Trench

Figure 6-6 Skimmer Detail



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system, so care must be taken to ensure that the initial cost

is commensurate with improved performance.To eliminate the need for slurry feed and to greatly re-

duce the frequency of changing DE, regenerative DE filtersemploy an automatic regenerative process in which the

original DE pre-coat is periodically forced (bumped) off thefilter elements. The circulation pump is automatically turnedoff; the filter is automatically bumped; and then the circula-

tion pump is automatically restarted, and a pre-coat cycle is

automatically reinstituted. This procedure essentially clearsfree paths through the DE that is coating the elements andreduces the pressure drop through the media. It allows for

complete use of all the surfaces of the initial DE charge. Aregenerative DE filter, of sufficient size to handle flows up to2,300 gpm (8,706 L/min), is shown in Figure 6-9.

Both static cake and regenerative DE filters are subjectto NSF/ANSI 50 testing requirements. They are NSF listed

by model number regarding the maximum allowable flow.Typically, these flows range between 1.3–1.6 gpm per square

foot (4.92–6.06 L/min/m2) of effective filter surface area. Forparticle retention test results, refer to Figure 6-10.

Filtration efficacy is very dependent on the design and

construction of each specific filter. Flow characteristics re-garding velocity uniformity and uniform turbulence have a

measurable effect on the DE-retention capabilities of eachfilter design. If the equipment choice is based on quality of

filtration, investigation of previously installed operatingsystems of this type should be undertaken.

In general, particulate removal efficacies in a well-

designed filter can be expected to track directly with thepermeability of the DE media used. With the most common

grade of DE used in commercial filters having a permeabilityof 3 Darcy units, at least a 99 percent removal of 3-micron

particles can be expected. Some filters of this type haveproven performance in the 1.5-micron range. In this range,

a 2-log removal of bacteriological contaminants is possible.That is well worth consideration with the current interest inremoving Cryptosporidium bacteria from pool environments.

Again, this should be closely investigated to justify the u

of these systems. As stated, static cake filters require more frequent clea

ing. They also require a pumped backwash to force the Dand dirt out of the weave of the multi-filament fabric of t

filter elements. The filter elements themselves require moval and more thorough cleaning, usually on a yearly baThat is not the case with regenerative DE filters.

The cleaning requirements of a regenerative DE filter va

greatly depending on the load and filter size. In a heavy-uindoor facility, a regenerative DE filter should be rechargevery three to four months. For a heavily used outdoor po

if long filter runs are desired, the filter is sized for a filmedia rate of approximately 1 gpm per square foot (3.79min/m2) of filter area, which usually results in four- to fi

week filter runs. When filters are selected for operation netheir maximum allowable filter media rate, they will probab

require a DE change approximately every two to three weeThe procedure for replacing the DE is quite simple. T

filter is bumped and then drained. No pumped backwashrequired. After one or two additional fills with pool wafor rinsing, the filter is refilled with DE, usually through

specially designed vacuuming system, which eliminates tconcern about airborne DE. The infrequent need for D

changes, along with the fact that these filters don’t requa pumped backwash, can be a major factor in reducing t

water replacement and reheating requirements inherentother systems.

Regenerative Alternative Media Filters

In recent years, some filters listed as regenerative DE filt

under NSF/ANSI 50 have been tested using alternative mdia, and perlite and cellulose have been approved under NS

ANSI 50 as DE substitutes. However, the challenge partilate material (U.S. Silica SCS 106) used in NSF test protois largely incapable of evaluating the particulate reducti

characteristics of any filter aid, including DE productsvarying permeability at or below the 12-micron level. Oth

independent test results indicate that cellulose has filtratiefficacies only slightly better than sand media filters.

A paper presented at the National Swimming Pool Foudation (NSPF) World Aquatic Health Conference in Octob2009 offered findings resulting from careful testing of t

filtration efficacy of perlite compared with DE. When ttwo media were tested at the same permeability (1.5 Darc

same coating thickness (0.125 inch) on the filter elemen(tortuous path), and same filter media rate (1.5 gpm p

square foot), the DE gave a reasonable expectation of a 4-

(99.99 percent) capture of cryptosporidium sized particlcompared with a 2-log (99 percent) capture by perlite. Th

is a sizeable difference when a single diarrheal accident ccontain millions of crypto oocysts. If a million oocysts a

filtered by a DE filter, less than 100 will make it throuThe same million oocysts encountering a perlite-coated fil

have a much better chance of making it through and outthe pool. At a 2-log removal capability, perlite would all

almost 10,000 oocysts to pass through. Since it only takesoocysts to infect a susceptible swimmer, the media choicean important consideration.

Figure 6-7 Horizontal High-rate Sand FiltrationSystem, Multi-tank


AUGUST 2013



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If the choice of a regenerative DE filter is predicated oncrypto-removal capability, some type of performance speci-

fication should be established. The above test results were

arrived at through the use of a “perfect” filter for testing. Actual results in the field will be affected by the design ofthe filter selected, as well as the piping layout in the equip-

ment room.

Circulation Pump SelectionCentrifugal pumps are the type of pump used on swimming

pool circulation systems. They can be of an end-suctionform or a vertical turbine configuration. The most commonend-suction centrifugal pump is the horizontal, either base

mounted or motor mounted. In some instances, an ownermay opt for a horizontal or vertical mounted, inline, split-

case design, but the instances of this are rare.

Horizontal End-suction Centrifugal Pumps A flooded suction centrifugal pump should be used only whenit can be installed below the pool’s operating water level. In

some installations, they are placed on grade, and a checkvalve or foot valve is used, supposedly, to maintain a filled

suction pipe. This configuration is not recommended, as theseinstallations always are operationally problematic. Flooded

suction pumps are not designed to effectively evacuate air.Once the check or foot valve gets jammed by a foreign object,re-priming the pump is almost impossible. Most flooded suc-

tion pumps have a tapped hole in the top of the pump voluteto release air if the pump become air-locked.

Self-priming pumps are designed for installations where

the equipment room is above the pool’s water level. Selectionshould take into account the lift required for the applicationwhen operating at the duty point, as it relates to net positivesuction head required (NPSHR). Self-priming pumps are

effective at passing air during the priming process, but caremust be taken to never operate them dry. A check valve in the

suction piping on the vertical run of pipe as it drops to thesurge tank is helpful during the priming process. If some form

of backflow prevention is in place on the freshwater system,a hose bibb connection on the suction side of the pump also

might be considered to assist in the priming process (if thisis allowed by the local code).

Since swimming pool water has a consta

residual of chlorine, swimming pool pumshould be fabricated of materials that offer

cent life expectancy. These pumps are, accordto most codes, required to operate 24 hours p

day. Pumps with cast iron volutes and implers can be expected to provide many yearsservice. Maintaining proper water balance,

discussed later under “Chemical Control a

Feed Systems,” plays a major role in ensurithis longevity. Proper piping schemes, designto prevent conditions that might lead to cavi

tion, will extend the life of the impeller.For situations in which the pump opera

intermittently, such as when its function is

provide flow to a water feature or as a spa pump, all wetted components of the pump mu

be made of noncorrosive materials. If a cast irpump were used, rust would form during t

quiescent period (primarily overnight). Thwhen the cast iron pump is restarted in the morning, toperator and patrons will be treated to an initial flow

brown, rusty water.Stainless steel pumps are available. These are not tru

noncorrosive; stainless merely means that the material staless frequently than other materials. However, stainless st

pumps will not discharge rusty water after an overnigshutdown period.

Also, many plastic pumps with plastic impellers are us

in the pool industry. Most of these are self-priming pumso they can be used whether the equipment room is abo

or below grade. The stainless steel pumps are a little moheavy duty and seem to hold up better in conditions whe

the equipment room is in a basement below the hot tubwater feature. They are not self-priming pumps, so t

below-grade location is ideal.Many swimming pool codes for filtration and circulat

pumps contain a minimum performance capability requi

ment based on the mandated flow rate needed to attain tminimum turnovers per day. The pump must be able to mo

the resultant minimum required flow at some code-estimatotal dynamic head (TDH). This might be a TDH of 70 f

for a sand filter system or as high as 75–80 feet for a prsure DE filter system.

Basically, the pump must be selected to guarantee tha

can move the required flow through the filter in a worst-cascenario, or when the filter is the dirtiest. Therefore, ev

if the code mandates a minimum pump TDH capability, tdesigner should perform a system head calculation. All p

and fitting losses on the suction and discharge sides of tpump must be included. The additional losses through systcomponents—hair strainer, valves, dirty filter, heater—a

discharge and friction losses through the inlet fittings mube added to the pipe and fitting losses to come to a to

system head requirement. This will verify that the comandated performance requirement is sufficient.

Vertical Turbine

Vertical turbine pumps can save up to 75 percent of flo

space as compared to horizontal end-suction centrifug

Figure 6-8 Vacuum DE Filter in Pre-coat Mode



18/29

pumps. They have smaller footprints mainly due to the loca-

tion of the pump below the floor. However, accommodationsshould be made for pulling these pumps for service. If very

long shaft lengths are necessary, high ceilings and possibly anoverhead I beam may be necessary. These pumps are basically

flooded suction pumps that can be installed above the pool’swater level. The downside to their use is the necessity for ahair strainer screen or basket on the bottom of the pump.

Cleaning during normal use is difficult, so to facilitate this

cleaning, some installations use a screen that slides througha slot in the floor and isolates the section of the surge pitwhere the pump’s suction bell is located.

When a buried concrete surge tank is part of the design,a vertical turbine pump is an obvious choice. These pumpsrequire the operating level in the surge tank to be maintained

at or above the pump’s required minimum submergence.The pressure available at the mouth of the suction bell of

the pump is essential to proper pump operation withoutcavitation. The NPSHR for a particular pump, at the design

operation point, controls the water depth above the suctionbell entry point (minimum submergence), and the resultantdepth-related water pressure at that point must be such that

the net positive suction head available (NPSHA) always ex-ceeds NPSHR. This minimum submergence also guarantees

that the lowest impeller of the pump is always submergedand that it will start pumping when it begins to rotate. This,

in effect, provides the same priming certitude as any floodedsuction pump.

These pumps can be used in a wet-pit installation or theycan be closed suction (direct piped), possibly in a dry pit. Ineither configuration, some protection against large debris

entering the bowl assembly must be provided. The bowl as-semblies can be either semi-open or closed.

Standard materials of construction for clear water ser-vice include cast iron bowls, bronze or cast iron impellers,

and stainless steel shafts. The column shaft connecting thebowl assembly to the discharge head is usually steel, and thedischarge head is cast iron. All components, however, are

available in more corrosion- and abrasion-resistant materials.Pumps can be custom-selected to allow variations in the

slope of the head curve to meet the head and capacity systemrequirements. A pump with a steeper curve will allow for

better control when using a variable-frequency drive (VFD)for flow control.

Placement of the vertical turbine pump (or multiple

turbine pumps) is critical to non-turbulent operating condi-tions. This topic includes too many variables to be effectively

covered in this chapter. As a starting point, the designer canreference Hydraulic Institute Standards for Centrifugal, Rotary, and Reciprocating Pumps, 14th Edition.

Manufacturers of vertical turbine pumps offer variousstrainer basket assemblies for mounting on the suction

bell of the pump. On swimming pool applications wherethe pump is required to operate all day, these strainers will

become fouled quickly, which can present a maintenancenightmare. Often, instead of the factory-provided strainers,

pool designs call for a fabricated, perforated, stainless steelwall or other perforated stainless steel enclosure. If properlydesigned, this can provide much more free area and result

in less frequent cleaning requirements (possibly only at t

end of an outdoor pool season).

Hair and Lint Strainers

Hair and lint st

Documents

ASPE pool.pdf