CE 3372 Water Systems Design Lecture 008: Demand Estimation

Outline Distribution Systems Estimating Water Demand Network Design Principles Components Fire flow Estimating Water Demand USGS Circular 1200 Plumber Estimate Rural Estimate TCEQ equations

Network Design Principles Water Supply System Includes water supply Treatment Facilities Pumping facilities Transmission lines Local distribution network What is a water supply system?

Water Supply system Distribution network - Consists of items designed to convey potable water at adequate pressures and discharges Pipes Fittings Valves Other appurtenances Why are adequate discharges necessary? To cover the range of flows due to the fluctuation in demand Pressures? Necessary for firefighting, general service to residents, and economic considerations such as leakage and energy losses The pipes/fittings/etc. will be entered into the model. Valves as minor losses.

DESIGN Who? Design parameters and regulations? Personnel within the water company Engineers / Consultants Design parameters and regulations? State board of health Local city/county health departments EPA, AWWA, ANSI

DESIGN REQUIREMENTS Pressure Velocity Age Chlorine concentration Fire Flow This slide was added to the Water Distribution Lecture Engineers have to estimate: amount of water needed for service area + average and maximum daily demand Pressure – will ensure that the beneficiaries will receive water at EVERY house/point considered Velocity – In pipe, determines if the proposed network is too big and expensive to build (low velocities) or too small and too expensive to operate (high velocities) Age – Time water spends in the network meaning the quality deteriorates as the residence time increases Chlorine Concenration – Will ensure the water is drinkable FIRE FLOW REQUIREMENTS! Usually controlling criteria in design of dist piping and storage amount of water req to fight a fire (even if only a few hours) puts a strain on system

Pressure Pressures Must be high enough to.. overcome head losses in the system. But not too high to... prevent damage to fittings and other appurtenances. Pressure Zones – Set pressurized areas (min and max) within the system by storage, boosters, or pressure control valves. Can also be due to varying pipe size and topography May be generated to ensure reliability in meeting fluctuation demands. System pressures are adapted to requirements. Hilly areas – booster pumping Minimum pressures vary state to state Established by the state’s Health Department / other agency Fire Marshall may establish additional requirements. Pressure zones – provide min and max pressures in the zone (could be a set force main) Boosters are pump stations within the distribution network used to maintain a minimum pressure The minimum pressure(20 psi) is a safety requirement to prevent potential back flows from house fixtures, and still have enough energy to push water up three stories. Average for residential 40-60psi

Fire flow Fire Flow Parameters Each municipality establishes own parameters based on local cond. Insurance Services Offices (ISO) - Most used “Guide for Determination of Required Fire Flow” Recommends criteria for Establishing insurance rates Classifying municipality. with reference to their fire defenses and physical cond. Q = required fire flow in gpm C = coefficient related to the type of construction A = total floor area in ft2 (excludes basements) Fire flow tests Before new projects get approved for construction by the fire marshals office. Flow tests are performed to determine fire flow capacity and adequacy of system

Fire flow Fire Flow Parameters City of Houston IDM has specific instructions for locating hydrants and required fire flow to these hydrants Other municipalities will have similar guidelines Fire flow tests Before new projects get approved for construction by the fire marshals office. Flow tests are performed to determine fire flow capacity and adequacy of system

Water supply system Hydraulic Characteristics Service Characteristics Pressures and discharges are a functions of HC Length Size Condition of pipe Service Characteristics Demand as it relates to: Present and projected population Economic base Fire flow Climate Q=VA Pv=nrt Driving in a car in traffic is high pressure Service and hydraulic changes – design must incorporate allowances for changes Changes can be relocating or replacing existing water line, increase pipe sizes, etc.

WATER utility Water utility company Companies exist in two forms …who is responsible for the water quality and operation of the distribution system. Companies exist in two forms public entity that ..“exists for the health, safety, and welfare of the public” privately owned utility that ..provides water for profit

Water supply system Gravity Pump Pump with Storage Dependable Source of supply must be located well above the city High-pressure demand for fire-fighting may require pumper trucks Pump Least Desirable Pressures vary substantially with variations in flow Provides no reserve if power failure Pump with Storage Most common Water supplied at approximately uniform rate Flow in excess of consumption stored in elevated tanks

Pipe System Primary Mains (Arterial Mains) Form basic structure of the system Carry flow from pumping station to elevated storage tanks Carry flow from elevated storage tanks to service areas Laid out in interlocking loops Mains not more than 1 km (3000 ft) apart Valved at intervals of not more than 1.5 km (1 mile) Smaller lines connecting to them are valved

Pipe System Secondary Lines Form smaller loops within the primary main system Run from one primary line to another Spacings of 2 to 4 blocks Provide large amounts of water for fire fighting with out excessive pressure loss

Pipe System Small distribution lines Form a grid over the entire service area Supply water to every user and fire hydrants –Connected to primary, secondary, or other small mains at both ends Valved so the system can be shut down for repairs Size may be dictated by fire flow except in residential areas with very large lots

Water SUPPLY system Water source (Main Supply) Treatment Facility Lake River Aquifer Treatment Facility Treats and disinfects water Meet water quality standards Potable water Transmission Lines Convey water from source – treatment facility facility – network Pumping Facilities Provide energy to move water Intermediate Storage Facilities Stabilize line pressures Reserve for peak demand periods Provide storage for fire flow req. Distribution Lines Convey water from storage – service areas Looped(grid) and Branched Layouts Appurtenances Fire Hydrants. Valves, auxiliary pumps, fittings Water Source – Larger may have multiple sources Lakes and Res located in outlying areas – less pollution + hope of larger runoff from catchments Rivers – water’s extracted upstream of civilization Min supply volume of water source MUST serve present AND projected demand Int Storage Facilities In times of high demand, pressure in the network is decreased Low demand, pressure is increased Water volume fluctuates from 40-70% daily (discounting fire flow storage) Distribution Lines Service areas include residential/commericial/industrial areas Appurt Valves allow system to isolate small service areas when repairs are needed

Water Use Systems Spatial and temporal distribution in support of human habitation Water supply/treatment/distribution Waste water collection/treatment/discharge Capacity is based on POPULATION served hydraulic dominated designs We briefly went over water use systems

Water Use AND DEMAND Water Use Water Demand Consumptive Municipal Agricultural Industrial Mining Non-consumptive Hydropower Transportation Recreation Water Demand Quantity that consumers use per unit of time Ex: Mgpd Depends on population, climate, industry and economic factors Water demand is what you have to estimate as an engineer include FUTURE development

Water DEMAND Residential Commercial Industrial Single-family, multi-family (apartments) Water for drinking, landscape, swimming, fires, street cleaning, etc. Usually two demand peaks (morning and evening) Commercial Motels, hotels, offices, shopping centers Usually less peak demand and less varied than residential Industrial Chemical plants, food processing plants, mines Water for fabrication, cooling, petroleum refining, etc. Water use depends on type of industr. Also the 3 main developments

Assigning Demand Assign demand using network models (links and nodes) Network models contain nodes that represent a multitude of actual connections. While conceptually possible to model to every single connection, it is discouraged because Model is hard to maintain Small errors may go unnoticed The operation of any single connection is not well known.

Network Types Branch No circulation Has terminals and dead-ends Water in dead-ends is stagnant Disinfection residual Corrosion

Network Types Grid/Loop Furnishes supply from more than one direction Water circulates Disinfection is more effective. Water “age” in system is younger (fresher). In case of water main break, fewer people are inconvenienced It’s cost that prohibits

Network Types Loop vs. Branch during network failure Every link in a branch system is a single point of failure that isolates all downstream nodes. Not with loop, only main supply line is failed

Estimating Flow Rate Demand estimation is used to determine how much water a system is likely to use (for sizing reservoirs and tanks Flow rate estimation (a plumber’s perspective) is used to determine how much capacity a system should be able to provide

USGS Circular 1200 Contains maps and tables by location Useful gross estimate tool

USGS Circular 1200 Contains maps and tables by location Useful gross estimate tool

Plumber Estimate How Much Water Can You Actually Get? Inside home How Much Water Can You Actually Get? Flow Rates are measured in gallons per minute (gpm). For our purposes, we will talk about the amount of water that you can get through a pipe at a velocity of 8 feet per second (a standard velocity used to engineer a plumbing system). Plumbing diameter will limit the flow rate you can get – the larger the pipe, the more water you can get. A home with 1″ plumbing can use substantially more water than a home with 3/4″ plumbing. Meter to house

Plumber Estimate 1. Think about the maximum number of fixtures and appliances you might operate at the same time. 2. Look at the chart to see how many gallons per minute each device requires. 3. Add up the flow rates for all the devices you selected. You just figured out the PEAK FLOW RATE that you need. Now, think about your continual water use, or water use that may run for more than 10 minutes. Add up the fixtures again, and you just calculated your SERVICE FLOW RATE.

Rural Estimate http://extension.psu.edu/natural-resources/water/drinking-water/best-practices/water-system-planning-estimating-water-use

TCEQ Tool(s)

Using the estimate Estimate need per connection to size the system; Run a hydraulic model at these values to size pipes Estimate demand to evaluate how the system is likely to perform in terms of pressure zones and such Run a hydraulic model at these values to check pressures – no fire flow Run a hydraulic model with fire flow to check minimum pressures

Readings Several readings on server will be useful:

Next Time Introduction to EPANET How to install on PC How to install on MAC (Experimental – Unsupported) 4-Examples (of increasing complexity)