Week 5: Water Demand WATER SUPPLY ENGINEERING EAT 237 Fahmi Muhammad Ridwan SCHOOL OF ENVIRONMENTAL ENGINEERING UNIVERSITI MALAYSIA PERLIS 2014
Lecture Outline: Water Use/Consumption Initial & Design Years (or Design Period) Population Projection Per capita Water Demand Water Demand Estimation Fluctuations in Water Demand
DOMESTIC USE Almost 30 - 60% of total water supply is for domestic use In-house use for drinking, cooking, bathing, ablution, sanitation, house cleaning, laundry and car washing Out-of-house use for garden watering, lawn sprinkling and bathing pools In other countries, average water consumption for domestic use is between 100-350 L/person/day In Malaysia, it is generally 225 L/person/day
DOMESTIC USE Factors affecting average water consumption for domestic use: Climate Social status Water quality Cost of water supply Sanitation system Supply system Water pressure
COMMERCIAL USE Includes water consumption in commercial establishments motels, restaurants, offices, hotels, office buildings, shopping centres, service stations, movie houses, airports About 10-20% of total water demand Water demand depends on: Type and area of commercial establishments Number of commercial establishments Number of workers or residents
WATER/PRODUCT (MASS RATIO) INDUSTRIAL USE Generally, large industries develop their own water supply systems Normally, only small industries purchase water at about 25-35% of total water demand Some industrial water demand data: PRODUCT WATER/PRODUCT (MASS RATIO) Cotton, Fur 150-750 Steel, Wood, Pulp, Paper 10-300 Slaughtering and Packaging 15-25 Petroleum production 3-10 Milk, dairy 3-35
INDUSTRIAL USE Industrial water demand may be estimated based on: Type of industries Size of organisation Water quantity and quality Cost of water supply
AGRICULTURAL USE Treated water is also used for crops, livestock, horticulture, greenhouses, dairies and farmsteads In Malaysia, irrigation is predominately for paddy cultivation and to a minor extent for vegetables and cash crops. Agriculture will remain the main user of water in the future, however, its importance will decline with growth in industrial sectors
*3 principal water-using sectors in Malaysia AGRICULTURAL USE *3 principal water-using sectors in Malaysia
AGRICULTURAL USE
PUBLIC USE Water used for public buildings (e.g. city halls, jails, schools) public services (e.g. street watering/washing, public parks irrigation, sewer flushing, fire-fighting) Account for 5-10% of total municipal water demand During dry seasons, sometimes water from public drains is used to reduce demand for treated water supply
LOSSES (UWF) In a water supply system, a certain amount of water is lost or unaccounted for because of: meter and pump slippage leaks in mains faulty meters water evaporation fire-fighting unauthorized water connections In municipal supply system, it is usually about 8-18% of total demand In Malaysia, it is between 17-57%
Total water demand Total water demand can be divided into: Domestic use: 45-55% Industrial and commercial use: 15-20% Public use: 2.5-7.5% Leakage and losses: 15-20% Fire-fighting: < 1%
Initial & Design years A water treatment plant is generally designed and constructed to serve the needs of a community for a number of years in the future Normally designed not > 50 yrs, mostly between 20-30 yrs Initial year the year when the construction is completed and initial operation begins Design year/period the year when the facility is expected to reach its full designed capacity and further expansion may be necessary
Determination of design years Period of design years depends on: Useful life of treatment units (includes wear, tear, development in water treatment technology and process) Convenience of future expansion Anticipated changes in drinking water quality requirement Anticipated changes in raw water quality Growth pattern of the community and the service area Performance of treatment facility during early years when it is oversized Interest rate, cost of present and future construction, and availability of funds
Determination of design years STRUCTURAL COMPONENT CHARACTERISTICS DESIGN YEAR (YEAR) Dam, water conduit, water tunnel and reservoir Complicated and expensive for future expansion 25 – 50 Water treatment works Susceptible for future improvement 10 – 25 Distribution system Life is very long and replacement is expensive Indefinite period Capacity designed is based on maximum anticipated development of the area served
The importance of design years in water supply scheme Avoid water supply scheme design become uneconomic due to large and expensive structures (i.e. pump, treatment units and water mains) have to be replaced within a brief period Avoid from having difficulties to replace distribution system elements which were normally laid below the main streets without adversely affect the surrounding, such as distracting traffic movement Ensure overall cost of water supply scheme development is bearable (avoid overestimation which can burden a relatively small community with the cost of works designed for larger population)
POPULATION ESTIMATION Data of previous and current population can be obtained from population and housing census done by Dept of Statistics Factors affecting population growth? Birth rate Death rate (Mortality) Migration Several methods are used to estimate population growth Arithmetic; Geometric; Incremental Increase; Decreasing Rate of Increase; Graphical Comparison; Ratio and Correlation
ARITHMETIC PROGRESSION Population is assumed to increase at a constant rate Commonly used for short term estimates (1-5 years) only Can be used for big/old city which is almost fully developed Pn = Pi + nI Pn = number of population in year n Pi = number of current population n = number of year per decade I = average population growth rate per decade
GEOMETRIC PROGRESSION Population is assumed to increase in proportion to the number of population present Based on percentage of population increment between decades Suitable for rapidly developing cities Pn = Pi (1 + i/100)n i = average percentage of population growth per decade
INCREMENTAL INCREASE Pn = Pi + n(I + m) Combination of arithmetic and geometric method m = average increment growth per decade Pn = Pi + n(I + m)
DECREASING RATE OF INCREASE Population is assumed to reach some limiting value or saturation point Suitable for developed cities Pn = Pi 1 + i – k n 100 k = average decreasing rate of increase per decade
Per capita demand Per capita demand Average daily amount of water required per person during a period of 1 year, and including all treated water that is used by residential, commercial, industrial, public service and system losses Estimated by dividing the annual average daily water consumption by total population served Unit liter/capita/day (LPCD) Per capita demand = total water consumption (Q) total population (P) x 365
Category of per capita demand The value of per capita demand is categorised to: City (number of residents > 10 000 people) 230 – 320 L/person/day Small town 180 – 230 L/person/day Rural area 135 – 180 L/person/day
Water Demand Estimation WDn = (Pn x C x F) + Da WDn = total water demand at the end of year n Pn = projected population at the end of year n C = per capita consumption at the end of year n F = service factor at the end of year n Da = additional demand at the end of year n
Water demand estimation Service factor represent percentage of population that will receive water supply service 0.8 service factor means distribution system reaches 80% of population Additional demand includes water demand for industry, institutional etc
Additional Demand Estimation Industrial Demand Water Demand = area of industry x volume of water consumed Heavy industry Normal consumption: 45 000 L/ha/day Water Demand = area of industry x 45 000 Light industry Normal consumption: 22 000 L/ha/day Water Demand = area of industry x 22 000
Fluctuations in water demand Water demand for a city changes within years, months, weeks, days, hours and from one season to another General changes in municipal water demand Changes from dry season (hot days) to rainy season (wet days) Water demand will be reduced Daily changes During weekends and public holidays, water demand for domestic use will be high, while demands for commercial and industrial uses are low Within a day, there are 2 demand peaks morning and evening
Fluctuations in water demand Fluctuations in water demand influence the design of various component in a water supply scheme Generally Monthly fluctuation is used for design of dam and storage tank Daily and hourly fluctuations are used for design of pumping system, service tank, water mains etc
Influence of Fluctuations to Water Flow Estimation Average annual demand are not sufficient for design of water systems due to water demand fluctuations Pumping records or flow measured at pumping station/water source can be used for evaluation of variations in demand In absence of these data, maximum flow rates may be used for estimation Max daily consumption normally ~ 180% of annual average demand
Goodrich Formula (peak flow factor) Based on moderate-sized residential P = 180t -0.1 P = percentage of annual average day demand for period t t = length of the period in days Max daily demand = 180% of annual average Max weekly demand = 148% of annual average Max monthly demand = 128% of annual average Max hourly demand (peak hour rate) = 150% of max daily demand
Max day demand Max day demand amount of water required during the day of maximum consumption on any 24-hour operating day of the year Used to determine maximum or peak flow rate in a water supply system Sensitive to weather conditions Ratio of maximum day demand/average day = 1.6 – 2.2 Typically 1.8 (peak flow factor)
Peak hour demand Peak hour demand amount of water required during maximum consumption hour in a given day Used to analyze peak capacity required of the distribution system, elevated reservoirs, and service pump to be able to deliver water during the peak hour of the day Peak hour demand/max hour demand = 1 – 2 Typically 1.5 (peak flow factor)
Fire demand (Undue demand) Based on moderate-sized residential F = 18C(A)0.5 F = required flow in gal/min (L/min 3.78) C = coefficient related to the type of construction A = total floor area in ft (m2 x 10.76) excluding basement C = 1.5 for wood construction = 1.0 for ordinary construction = 0.8 for noncombustible construction = 0.6 for fire resistive construction
Influence of flow fluctuations to design capacity Flow required during max day demand, QMD demand = Max day demand factor x flow required for annual average daily demand (QAAD demand) Can be used for design of water treatment plant Flow required at peak hour demand, QPH demand = Peak hour demand factor x flow required for max day demand (QMD demand) Can be used for design of water distribution system (pumping, service tank, water mains)
Influence of flow fluctuations to design capacity Flow required based on fire flow Qfire = 3.86P(1-0.01P) Qfire = fire flow, m3/min P = population in 1000 Flow required at peak hour (to design capacity of water distribution system) QMD demand + Qfire @ QPH demand (choose higher flow)