Water Supply Design and Considerations PDF

WATER SUPPLY DESIGN  LECTURE CONTENTS A. Main Parts of a Water Supply System B. Water Distribution System Layout C. Feed Systems D. Hydrostatic force and Pressure E. Water Supply Design Concerns  A. Main Parts of Water Supply System 1. Building Supply The bui...

WATER SUPPLY DESIGN  LECTURE CONTENTS A. Main Parts of a Water Supply System B. Water Distribution System Layout C. Feed Systems D. Hydrostatic force and Pressure E. Water Supply Design Concerns  A. Main Parts of Water Supply System 1. Building Supply The building supply or water service is a large water supply pipe that carries potable water from the district or city water system or other water source to the building. 2. Water Meter A water meter is required by most district water supply systems to measure and record the amount of water used. It may be placed in a meter box located in the ground near the street or inside the building. 3. Building Main The building main is a large pipe that serves as the principal artery of the water supply system. It carries water through the building to the furthest riser. The building main is typically run (located) in a basement, in a ceiling, in a crawl space, or below the concrete floor slab. 4. Riser A riser is a water supply pipe that extends vertically in the building at least one story and carries water to fixture branches. It is typically connected to the building main and runs vertically in the walls or pipe chases. 5. Fixture Branch A fixture branch is a water supply pipe that runs from the riser or main to the fixture being connected. In a water supply system, it is any part of a piping system other than a riser or main pipe. Fixture branch pipes supply the individual plumbing fixtures. A fixture branch is usually run in the floor or in the wall behind the fixtures. 6. Fixture Connection A fixture connection runs from the fixture branch to the fixture, the terminal point of use in a plumbing system. A shut-off valve is typically located in the hot and cold water supply at the fixture connection.  Water Towers - A water tower must be tall enough to deliver adequate pressure to all of the houses and businesses in the area of the tower. Each foot of water height provides 0.433 psi (pounds per square inch) of pressure. Water in a water tower tank must be 100 to 200 ft (30 to 60 m) above the highest plumbing fixture being served. Purpose of Water Towers: 1. To carry a reserve capacity of water. 2. To introduce pressure to the water supply system 3. To equalize supply and demand over periods of high consumption 4. To supply water during equipment failure or maintenance 5. To supply water for firefighting demand  B. Water Distribution System Layout The water service pipe is an underground pipe that is typically called a lateral The water service lateral is connected to a water meter that measures consumption Water meter is typically located in an underground curb box located in the building’s front yard or is located in the building interior, in which case it is connected to a remote readout on the exterior of the building, which allows easy access for meter readings. If pressure available from the water service is too high, a pressure-reducing valve or pressure-reducing arrangement drops the water pressure to an acceptable level  If water softening or treatment is desired in the building, water is passed through a softening or treatment device before the water is distributed to the building chambers are installed as close as possible to the fixture valves or faucet and at the end of long runs of pipe to reduce water hammer.  Rigid Pipe Distribution Configuration In the conventional rigid-pipe distribution configuration, the hot and cold water distribution pipes are installed parallel to one another as they convey hot and cold water to risers and branch pipes Hot and cold pipes should be spaced at least 6 in (150 mm) apart or have insulation placed between them to prevent heat interchange  Parts of a Rigid Pipe Configuration 1. Zone A branch supplying water to two or more fixtures. A zone can supply one or many fixtures on one floor or on a few floors. 2. Groups Fixtures are typically located in clusters called groups. For example, in a commercial building or school, restrooms for men and women are grouped together with fixtures arranged against a common plumbing chase. group arrangement allows several fixtures to be served by the same water main or branch. 3. Plumbing Walls There are times when the width of a wall needs to be increased to allow for pipes running horizontally to pass by drainage pipes (or other pipes) running vertically. These walls of increased thickness are called plumbing walls. 4. Chase - In multistory buildings, risers are pipes that carry water vertically through walls or through enclosures called chases. A chase is a vertical opening through a floor or several floors that is enclosed with walls between floors. A chase can enclose piping only or it can enclose electrical wiring and/or mechanical system ducting and/or pipes that run vertically from floor to floor through the building. 5. Pipe tunnels - Pipe tunnels may be used on large projects to provide concealed space for the passage of mechanicals at ground level and from building to building. Hangers from the top or side of the tunnel are used to support the pipes. Access may be from either end of the tunnel, or access floors may be provided. 6. Shut off Valve - Readily accessible valves used to close off the water supply to a fixture, appliance, or system are called shut-off valves. - required on the discharge side of the water meter - Valves must be accessible in the dwelling unit they control. Homerun (Manifold) Distribution Configuration A homerun or manifold distribution configuration consists of a plastic or metal plumbing manifold and flexible plastic piping The cold water chamber is supplied from the main water supply line and the hot water chamber is fed from the water heater fewer fittings are required Homerun configurations typically use cross-linked polyethylene (PEX) or composite PEX-AL-PEX piping, which is suitable for cold and hot water use The homerun configuration requires much more pipe than the rigid configuration ,but the plastic pipe used is much less expensive than the metal (copper) pipe used in the rigid-pipe configuration. As a result, the home run configuration is typically cheaper  Homerun configurations equalize pressure, which allows several fixtures to be operated simultaneously without drastic changes in pressure or temperature. A smaller diameter means that hot water arrives at fixtures faster, and less hot water is left standing in pipes after a fixture is operated.  C. Feed Systems 1. Upfeed System - In a conventional up-feed system, water pressure from the water supply main is relied on to drive water flow through the system - Water pressure in building water supply mains typically ranges from 40 to 80 psi (275 to 550 kPa), with 80 psi (550 kPa) considered the upper limit for most systems plumbed with metal pipe and 40 psi the upper limit for plastic pipe - Part of the available pressure is expended in friction losses as the water passes through the meter and the various pipes and fittings; and part of the pressure is expended to overcome gravity, which is the pressure required to push the weight of water upward vertically (up the riser) 2. Pumped Upfeed Distribution System - In tall buildings, water must be supplied through a pumped upfeed distribution system - In a high rise building (e.g., 50 stories), water enters one or more pumps where its pressure is boosted to pressures of 150 to 250 psi (1000 to 1700 kPa) or more. A vertical riser carries this high- pressure water to fixtures at the top of the building - Pressure Reducing Stations are placed at every 10th floors to decrease any excessive pressure before the water enters the fixture 3. Down feed System - In buildings that cannot be adequately serviced to the top floor by an upfeed system, water is pumped to elevated storage tanks in, or on, the building, and the water is fed down into the building by gravity. This gravity system, fed from the upper stories to the lower, is called a downfeed distribution system. Water entering the building flows through pumps that develop sufficient water pressure to drive water to storage tanks serving zones of about 10 floors each. To develop adequate pressure, the storage tanks are placed above the zones that they serve.  D. Hydrostatic Force and Pressure Hydrostatic Pressure Fluid (gas or liquid) molecules tend to seek equilibrium (a stability of forces). When forces acting on a fluid are unequal, molecules in the fluid move in the direction of the resultant forces. Therefore, an elementary property of any fluid at rest (not flowing) is that the force exerted on any molecule within the fluid is the same in all directions. Hydrostatic Force - is a force exerted by the weight of the fluid against the walls of a vessel containing the fluid. Hydrostatic Pressure - the hydrostatic force per unit area, is perpendicular to the interior walls at every point. If the pressure were not perpendicular, an unbalanced force component would exist and the fluid would flow.  D. Hydrostatic Force and Pressure Water Pressure Difference - is the driving force behind fluid flow. Water pressure available at the water service is lost as water flows through the piping of a plumbing system. This pressure loss or pressure drop in a plumbing system is from friction loss as the water moves through the system and pressure loss as water is forced to a higher elevation (e.g., from the basement to an upper story). Residual Water Pressure - is the pressure available at the outlet, just before a fixture. It affects water output of a fixture.  E. Water Supply Design Concerns 1. Water Velocity - Noise, erosion of inner pipe walls and valves, and economy of installation, operation, and maintenance dictate the minimum and maximum water velocity in a plumbing system - If pipe diameters are small, cost is low but noise, erosion (from high velocities), and pumping costs (from high-pressure losses) are high. In contrast, large diameter pipes reduce noise erosion and pumping costs, but result in high installation costs. An intermediate pipe diameter is desirable 2. Cavitation - Cavitation is a physical phenomenon that occurs in a liquid when it experiences a drastic drop in pressure that causes the liquid to vaporize into small vapor bubbles - Vaporization is a problem because the liquid being vaporized expands greatly - Cavitation can caused undesirable vibration that can lead to erosion and leaking 3. Cross – Connection - A cross-connection is an unsatisfactory connection or arrangement of piping that can cause non potable water to enter the potable water system. - A cross-connection can cause used or contaminated water to mix with the water supply. It is an unsanitary and potentially hazardous condition - Most plumbing fixtures are designed to prevent a cross-connection. A gap exists between the faucet and the rim of the bowl in lavatories, sinks, and tubs to create a separation and avert a cross-connection. 4. Backflow - Backflow is a type of cross-connection that occurs when contaminated water or some other liquid or substance unintentionally flows backwards into distribution pipes containing potable water  Backflow Prevention Devices A. Atmospheric Vacuum Breaker (AVB) - the most common type, consists of a body, a check valve-like member (to prevent backflow), and an atmospheric opening. The AVB is not a testable device. B. Pressure Vacuum Breaker (PVB) - is a type of backflow prevention device used to keep non potable (or contaminated) water from entering the water supply C. Double Check Assembly (DCA) or Double Check Valve - is a backflow prevention device assembly that consists of two check valves assembled in series usually with a ball valve or gate valve installed at each end for isolation and testing. 5. Water Hammer - A large pressure develops when fluid moving through a pipe is suddenly stopped. In a plumbing supply system, the sudden closing of a valve will cause fast-flowing water to stop quickly, resulting in a large increase in pressure that is known as water hammer - water hammer produces a force that makes pipes rattle with banging or thumping sounds as they expand and contract from exposure to an increase in water pressure Air Chamber - Air is trapped within the air chamber. The trapped air is compressible, which cushions the pressure surge as the valve is closed and absorbs the hydraulic shock. Water Hammer Arrestor - Water hammer arrestors are patented devices that absorb Hydraulic shock. 6. Thermal Expansion – Material Expansion due to Increase in fluid’s Temperature - In a residence, the upper limit for hot water pipes is usually 125°F (52°C). Cold water piping will be subjected to a much smaller temperature range, usually with a low of 35°F (2°C) and a high of about 80°F (27°C). These ranges will vary, sometimes considerably, on projects and must be checked. Expansion bends - make use of pipe fabricated with U-shaped or circular bends. The increase in the length of pipe from thermal expansion is accommodated by flexing or springing of the bends or loops Expansion Bends 7. Viscosity - As water flows through a pipe, its viscosity (thickness) increases with temperature decrease. Water at 40°F (4°C) is twice as viscous as water at 90°F (32°C) and four times as much at 170°F (77°C). As a result, pumping energy and cost are higher when water temperatures are lower. 8. Volume Change with Temperature Change - Water is the only substance that can exist as a solid, liquid, and gas at ordinary temperatures. Like most substances, water expands when it is heated. 9. Aging - As pipes in a plumbing system are used, their inner walls become increasingly rough - Buildup from calcium deposits (especially in high-temperature hard water) and corrosion (especially in ferrous pipe materials) reduces the inside opening in the pipe, which restricts flow - Over several decades of use, aging galvanized steel and iron pipe can result in a capacity loss of up to 80%. 10. Pipe Insulation - Pipe insulation is applied to the outer walls of piping to reduce heat loss from the pipe or prevent condensation on the outside pipe walls. Foam and covered fiberglass insulation are common pipe insulation materials * In most commercial buildings, heat loss increases the cooling load and the costs of air conditioning. In residential applications in temperate to cold climates, insulating hot water lines is less cost-effective because heat lost from hot water pipes contributes to space heating during the heating season 11. Testing - The water supply system should be tested for leaks before it is covered with finish materials to determine if it is watertight. Tests commonly run on water systems require that it be watertight under a hydrostatic water pressure of 125 psi for a minimum of 1 hr. Any leaks that occur should be repaired with the joint compound originally used. 12. Leaks - Leaks account for about 12.7% of household per capita water use in a typical U.S. home (AWWA). A leak of just one drop per second will waste about 2700 gal (10 200 L) of water a year.  Potential Cause of Leaks A. galvanic (dissimilar metal) corrosion B. changes in water chemistry and chemical water compositions C. the improper addition of chemicals during the water treatment process D. aggressive water, which includes factors such as pH content, presence of chlorides, metal ions, and dissolved gases in the water; E. excessive water velocity in water pipes