SWIMMING POOL DESIGN : Water Reticulation System

Swimming Pool means any artificial basin of water modified, improved, constructed, or installed solely for the purpose of public swimming, wading, diving, recreation, or instruction. Swimming pool includes, but is not limited to, a pool serving a community, a subdivision, an apartment complex, a condominium, a club, a camp, a school, an institution, a park, a manufactured home park, a hotel, a motel, a recreational area, or a water park. Swimming pool includes a spa, hot tub, or whirlpool or similar device which (1) is designed for recreational use and not to be drained, cleaned, and refilled after each individual use and (2) may consist of elements, including, but not limited to, hydro jet circulation, hot water, cold water, mineral baths, air induction systems, or any combination thereof. Swimming pool also includes an artificial lake, a pool at a private residence, or a pool operated exclusively for medical treatment, physical therapy, water rescue training, or training of divers.

In this post, we shall take a look at the mechanical services design of a typical swimming pool. Design for the mechanical services for a swimming pool is usually done in the following stages.

a)     Physical pool parameters and design considerations

b)     Piping Layout

c)      Pool Hydraulic Calculations

d)     Pool Equipment Selection

e)     Production of Final Design drawings

The following gives a sample design of water reticulation system for a swimming pool, using the steps outlined above.

Please note that this site is still undergoing construction, and some materials (resources) may not be uploaded at this time. Please feel free to contact me should the need arise for any clarification or further resource requirements.

PHYSICAL POOL PARAMETERS AND DESIGN CONSIDERATIONS

Consider a swimming pool with the following physical parameters. This will vary depending on the architectural design. These parameters are read/taken from the design.

Total Perimeter  =  122.18 m  (Adult = 96.25m     Children   =  25.93 m )

Width                    = 15.425m

Min. Depth           = 9m

Max. Depth           = 1.5m

Total Pool Area   = 541.4 Sq. m.    (Adult = 494 sq m     Children   =  47.4 sq m )

Volume                  = 766.84 cu.m    (Adult =  738.4  cu m             Children  =  28.44 cu m.)

                                =   168,681 gallons

DESIGN CONSIDERATIONS.

Recommended Pool Turnover Periods

o    Leisure Waters 1m to 1.5m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . .1 - 1.5 hours

o    Leisure Pools over 1.5m deep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 - 2.5 hours

o    Conventional Pools up to 25m long with a 1m shallow end . . .   2.5 - 3 hours

o    Competition Pools 50m long and 2m deep . . . . . . . . . . . . . . . . . . 3 - 4.5 hours

o    Diving Pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 6 hours

o    Residential or Private pools . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 - 6 hours

Skimmers

o    The recommended ideal flow rate through a conventional skimmer is usually about 5 cubic metres per hour - about 1,100 imperial gallons per hour. The absolute maximum acceptable flow rate is around 7.5 cubic metres per hour - about 1650 imperial gallons per hour - based on standard swimming pool skimmers .

Water Velocity in Pipework

The velocity of water within a pipe is subjected to physical resistance due to friction and turbulence.

·         The maximum velocity in any suction pipe must not exceed 5 feet per second (1.52 metres per second).

·         The maximum velocity in any pressure pipe must not exceed 9 feet per second (2.74 metres per second).

PIPING LAYOUT

Show the proposed layout for the swimming pool. Take into consideration proper plumbing requirements.

 POOL HYDRAULIC CALCULATIONS.

From the parameters given above, do the following calculations.

Design Flow Rate =    Pool Volume (Gal.)                  =    168681      =  468.56  gpm  

                                  Turnover time (Min. )                                    360)

                                                                                                              = 0.03687  m³ /s

I. Number of Skimmers Required:

Area of Pool

Adult Pool                   =  494 sq m

Children’s Pool           =  47.4 sq m

TOTAL                           =  541.4 sq m     = 5834 sq ft.

From STA-RITE U-3 skimmer recommendation, number of skimmers required for this area of pool is 12

II. Skimmer Flow Rate:

In some pool piping layouts, provision is made for floor return pipes. These are installed on the pool floors as part of the pool water reticulation. In such cases,

Total flow through skimmers  = 0.75 x Design flow rate  

                                =  0.75 x 468.56 gpm

                                = 351.42 gpm   

Therefore flow per skimmer    = Total Skimmer Flow

                                                         No. of Skimmers

                                                    = 351.42  gpm

                                                           12

                                                  = 29.3 gpm  ⁽ Must be at least 25 gpm )

                

III. Number of Inlets Required: (Maximum recommended spacing  = 4.5 m)

No. of inlets used based on 1 inlet per 6 m of perimeter  as recommended        

Therefore number of inlets required is 19.

                                                             

IV. Pipe Size Selection

A. Skimmer Line Size:

Skimmer flow rate                            =  29.3 gpm  = 2.22 x 10^-3 cu m/s

Maximum velocity in suction pipe   = 5 fps = 1.52 m/s

Using the mass flow equation, Q     = AV

Where Q = flow rate,

              A = effective area of pipe,

             V = Velocity of flow

Then   A = Q/V

Therefore for Pipe A, (no. of skimmers served = 3)

Area = 3 x 2.22 x 10^-3 /(1.52)  = 4.38 x 10^-3 sq m.

This gives pipe diameter     D      = 0.0746 m  =  74.6 mm

Pipe size used                                  = 76 mm

Similarly,

Diameter of pipe B =  76 mm

Diameter of Pipe C =  76 mm

Diameter of Pipe D =   67 mm

B. Return Line Size:

Design flow rate  =  0.03687 m³/s              =  132.7 m³/h

No. of inlets                                                    = 19

Using the mass flow equation, Q = AV

For Pipe S_a ,

Area = [((6/19) x 0.03687)] /(2.74)  = 0.00425 sq m.

This gives pipe diameter D = 0.0652 m  =  65mm

Pipe size used = 76 mm

Same was done for pipe S_b         =    76 mm

For Pipe S_c

Area = [((7/19) x 0.03687)] /(2.74)       = 0.0050 sq m.

This gives pipe diameter D = 0.0707 m  =  70.7 mm

Pipe size used                          = 76 mm

C. Main Drain Size:

Select pipe size which gives max. 1.83 m /s  velocity at design flow

rate.

Design flow rate           =  0.03687 cu m/s   

Velocity in drain pipe  = 1.83 m/s 

Using the mass flow equation, Q = AV

For Pipe Ma

Area  = [((0.03687)/2] /(1.83)     = 0.0101 sq m.

This gives pipe diameter D = 0.11313 m  =  113.13 mm

Pipe size used = 110 mm

Same for Pipe Mb

HEAD LOSS CALCULATIONS

Pressure Loss Calculation

Pressure Loss or Head Loss in a pipe can be calculated if the fluid data and the flow rate are known and specific attributes of the pipe are known (such as inner diameter of the pipe, length of the pipe, and roughness of the pipe material).

Head Loss in Pipe Work

The resistance to fluid flow is usually expressed in fluid head. This is the height of a column of fluid which would exert enough pressure on the fluid at the bottom of the column to make the fluid flow within the system.

Fluid head resistance was calculated using the Darcy – Weisbach formula.

h = f (L/D) x (v ²/2g)
f = friction factor (See Moody Friction Factor.)
L = length of pipe work D = inner diameter of pipe work
v = velocity of fluid
g = acceleration due to gravity

Head Loss Through Fittings

The fluid head resistance through various pipe work fittings can be calculated if the ‘K’ factor of the fitting is known. Many manufacturers of pipe work fittings and valves publish ‘K’ factors for their products.

Fluid head loss of these fitting were calculated using:

 h  = ‘K’ x v ² / 2g
‘K’ = manufacturer’s published ‘K’ factor for the fitting
    v = velocity of fluid
    g = acceleration due to gravity

The above formulae was applied to sum the total loss from fittings associated with each pipe work.

Head loss for Return pipe Work  = 13.51 mSkimmer Line Loss = 7.44 m

Floor Drain Line Loss = 5.74

These head loss values were used in the pool equipment selection.

POOL EQUIPMENT SELECTION

Filtration Pump Selection:

There are two main characteristics  considered in determining the correct pump:

• The right type of pump for the application and liquid which in this case is  a centrifugal pump
• The pump performance or characteristic requirements.

A pump's performance is shown in its characteristics performance curve where its capacity (GPM) is plotted against its total developed head (FT), efficiency (%), required input power (BHP), and NPSHr (FT) The pump curve also shows its speed (in RPM) and other information such as pump size and type, impeller size, etc.

The Head refers to the differential head developed by a pump and expressed in feet of liquid:

H = [Pd-Ps] x 2.31 / SG

where:
H = pump head, FT of liquid
Pd = pump discharge pressure, PSIG
Ps = pump suction pressure, PSIG
SG = liquid specific gravity

Following the above, the  filtration pumps can be selected from the manufacturer’s chart  on consideration of the following pump requirements resulting from the friction loss calculations.

Delivery (Return pipe friction)               = 13.51 m

Static delivery head                                    = 1 m

Suction (Skimmer) Pipe friction             = 7.44 m

Static suction head                                      = 1.5 m

Total delivery head                                     = 13.51 + 1 m = 14.51 m

Total suction head                                       = 7.44  - 1.5 m    = 5.94 m

Total Dynamic Head Required, H            = 14.51 + 5.94   =  20.45 m

Flow Required,                               Q            = 132.73 m³/h

Filter Selection:

Filtration Rate

The Filtration Rate is the speed or velocity of the water through the filtration media. The slower the Filtration Rate - the more effective the filtration.

·         Big or heavily used commercial pools will normally use LOW filtration Rates.

·         Schools, hotels, other commercial pools, and heavily used private pools will usually have a MEDIUM filtration rate.

·         HIGH rate filtration is usually only suitable for private home pools,

The Filtration Rate is measured in cubic metres of water per square meter of filter surface area per hour - (m³/m²/hr)

OR gallons per square foot of filter surface area per hour- (gal/ft²/hr)

Filtration Rates for Sand Filters (Metric rates)

·         LOW RATE FILTRATION - Less than 10 m³/m²/hr

·         MEDIUM RATE FILTRATION -11 m³/m²/hr to 30 m³m²/hr

·         HIGH RATE FILTRATION - 31 m³/m²/hr to 50 m³/m²/hr

(NOTE : - Many Sand Filters have a maximum Filtration Rate of 45 m³/m²/hr)

The filter was selected from the manufacturer’s chart on consideration of the above filtration requirements:

Filter area required = Design Flow rate

                                      Filtration Rate

=  ( 0.03687 x 3600 )      = 13.27 m²   (142.84 ft²)

                                                      10

VENTILATION OF THE PLANT (PUMP) ROOM

Adequate air changes are vital for the control of high humidity and excess condensation. The design was made to clear condensation by the introduction of fresh air. This was also used as a means of reducing temperature conditions in the plant room as controlling the room conditions helps the working of the plants.

An exhaust ventilation guide will be used in selecting exhaust fans for the plant room.

CFM required      C  (ft³/min)  =          ROOM    VOLUME  (ft³)                          

                                                            MINUTES PER AIR CHANGE (min.)

                                                        =   15840

                                                                  3

                                                        =  5280  (ft³/min)  

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