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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VERTICAL TRANSPORTATION SYSTEMS: HOW TO DO AN ELEVATOR TRAFFIC ANALYSIS

As  architects, developers and building owners race towards adorning the landscape with high-rise commercial and institutional buildings, one of the roles of the mechanical services engineer is to quantify the parameters and criteria which represent quality in the vertical transportation service. At the inception stage of any project the design team establishes design requirements. They establish unique requirements of the building or anticipated occupancy and their influence on the vertical transportation systems (which for this discussion are the elevators).  These requirements are translated into design criteria which combined with the projected population is utilized to conduct an elevator traffic analysis.

Before I proceed further, it is necessary to throw in some definitions of important terms used in elevator traffic analysis.

DEFINITIONS

·        Average lobby time or average lobby waiting time. The average time spent by a passenger between arriving in the lobby and leaving the lobby in a car. This is a key selection criterion.

·        Handling capacity (HC). The maximum number of passengers that can be handled in a time given period—usually 5 minutes, thus the term 5-minute handling capacity. When expressed as a percentage of the building’s population, it is called percent handling capacity (PHC). This is a key selection criterion.

·        Interval (I) or lobby dispatch time. The average time between departures of cars from the lobby.

·        Registration time. Waiting time at an upper floor after a call is registered.

·        Round-trip time (RT). The average time required for a car to make a round trip—starting from the lower terminal and returning to it. The time includes a statistically determined number of upper-floor stops in one direction and, when calculating elevator requirements based on up-peak traffic, an express return trip.

·        Travel time or average trip time (AVTRP).  The average time spent by passengers from the moment they arrive in the lobby to the moment they leave the car at an upper floor. This is a key selection criterion.

Carrying out an elevator traffic analysis will require the following design considerations:

·        Intended usages of the building, height, number of floors, etc.

·        Expected characteristics of “internal traffic” by occupants as follows

o   Domestic floors (less demand on elevator service)

o   Office floors (higher demand on elevator service)

o   Commefrcial floors e.g. shops (high population density and traffic)

o   Restaurants (peak demand at launch and dinning)

·        Level and quality of elevator service required

·        Types of elevator systems to be used : (traction or hydraulic)

o   Passenger elevators

o   Service elevators

o   Fireman’s elevator

o   Dumbwaiter (e.g. for restaurant)

From the above, an assessment of building population and number of persons using the service is estimated. Also the critical traffic period and occupancy loading of the elevator car are assumed.

Depending on the class of service, the basic design criteria for lift performance are:

·        Five minutes handling capacity (HC)

·        Average interval time or waiting time (AWT)

·        Maximum passenger transit time

This analysis can be performed by manual calculations or by computer programs. Also some elevator design sites now have online calculators to help in determining these parameters (e.g. http://www.kone.com/COUNTRIES/EN_MP/TOOLS/Pages/default.aspx ). However they will not show their calculations, just the results.

A typical elevator traffic analysis I did is given below. The building used in this analysis is a four-floor mixed-use building. The ground and first floor are office spaces. The second floor holds 36 nos. single rooms en-suite while the third floor holds a four bedroom family unit.

ANALYSIS TYPE:  UP-PEAK TRAVEL ANALYSIS

·        BUILDING AND POPULATION

No. of floors: 3

Building Population: 296

Floor Name	Height (m)	Floor Level (m)	Description	*Floor Area (sq.m)	Density Sq.m/pers	Gross Population Estimate	Vacancy Factor	Net Population
Pent House	3.15	12.95	Single Family			8	10%	7
2nd Floor	3.15	9.8	Multi Residence			108	10%	97
1st Floor	3.15	6.65	Office	1036	10	104	10%	94
Grd. Floor	3.5	3.5	Office	759	10	76	10%	68
D E S I G N          P O P U L A T I O N								266

*Floor area indicates net lettable area.

·        ELEVATORS

Recommended Control: Schindler ID

ELEVATOR	A	B
Rated Load (kg)	400	400
Weight per person (kg)	80	80
Passenger/Deck gross	5	5
Max. Car Filling	80 %	80 %
Passenger/Deck net	4	4
Maximum speed (m/s)	1.0	1.0
Maximum acceleration (m/s2)	0.5	0.5
Drive Jerk (m/s3)	0.5	0.5
Door width (mm)	900	900
Opening time (s)	1.9	1.9
Closing time (s)	2.6	2.6
Transfer time per person (s)	1.0	1.0
Minimum transfer time (s)	1.0	1.0
Travel height (m)	12.95	12.95

UP-PEAK TRAVEL ANALYSIS

Building characteristics

Type:               Mixed-use (Office on two floors, multi-dwelling on 3^rd floor and Single family dwelling on pent-house)

Tenancy:         Multiple

Floors above terminal floor:            3

Floor Height: 3.15m

Population above terminal floor PATF:      188

Recommended Handling Capacity Factor HCF:     12 %

Recommended Interval:                                           30

Calculating Handling Capacity, HC:

                            HC = PATF x HCF / 100

                             = 188 x 12 / 100

                             = 22.56  (ie 23 persons/5 minutes

Lift Travel Limit, LTL:

                        LTL = Floor Height x Floors above terminal floor

                            = 3.15 x 3

                            = 9.45 m

From HC and LTL, recommended lift speed = 1.6 m/s

The Round Trip Time (RTT) in seconds of a single elevator during up-peak traffic is given by:

RTT = 2Ht_v + (S + 1)t_s + 2N_pt_p

where,

H         is the average highest reversal floor

S_av               is the average number of stops

N_p                is the average number of passengers in the car (assuming an 80% occupancy)

t_v         is the time to transit between two adjacent floors at rated speed (s)

i.e. t_v= df_H / v

where,

df_H       =  average interfloor height (m)

v          =  rated speed (m/s)

t_s          =  time lost at each stop (s)

[ i.e. t_s = t_f (1)+t_o+t_c−t_v = T −t_v ]

where:

tf_H (1) =  single floor flight time (s)

t_o         =  door opening time (s)

t_c         =  door closing time (s)

T          =  performance time (s)

t_p         =  average one away passenger transfer time (s)

RTT = (2 x 3.3 x (3.15/1.6)) + (2+1) x (5.0 + 1.9 + 2.5 – (3.15/1.6) + (2 x 4 x 1.0)

        = 13 + 22.3 + 8

        = 43.3 s

The up-peak interval (UPPINT), in seconds, for the 2 lift cars is given by

UPPINT = RTT/2

              = 43.3 / 2

             = 21.65 s

The up-peak handling capacity (UPPHC) in persons/5 mins is given by

UPPHC = 300 N_pL/RTT where L = No. of lift cars

             = 300 x 4 x 2 / 43.3

              = 55.43

The percentage of the total building population (POP) above the terminal floor that can be served during up-peak is given by:

% POP = (UPPHC / POP) x 100

             = (55.43 / 188) x 100

             = 29.5 %

Average waiting time (AWT) is usually taken as 60 – 70 % of UPPINT

Therefore

AWT = 0.65 x 21.65 s

          = 14 s

RESULTS

Round Trip Time, RTT	43.3 s
Up-peak Interval, UPPINT	21.65 s
Up-peak Handling Capacity, UPPHC	55.43
Percentage Population Handled % POP	29.5 %
Average waiting Time, AWT	14 s

From the Schindler standards and recommendations, 2 nos. 400 kg lifts for this facility has a minimum rating of 5.0

Regulations and Standards:

·        British Standard BS 65655: Part 1 – 11  Lifts and Services Lifts

·        Code of Practice on the design and construction of Lifts and Escalators (EMSD)

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