15.1 SECTION 15 PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES FACILITIES PLANNING AND LAYOUT 15.1 Water-Meter Sizing and Layout for Plant and Building Water Supply 15.1 Pneumatic Water Supply and Storage Systems 15.8 Selecting and Sizing Storage-Tank Hot-Water Heaters 15.11 Sizing Water-Supply Systems for High-Rise Buildings 15.14 PLUMBING-SYSTEM DESIGN 15.23 Determination of Plumbing-System Pipe Sizes 15.23 Design of Roof and Yard Rainwater Drainage Systems 15.29 Sizing Cold- and Hot-Water-Supply Piping 15.32 Sprinkler-System Selection and Design 15.40 Sizing Gas Piping for Heating and Cooking 15.44 Swimming Pool Selection, Sizing, and Servicing 15.48 Selecting and Sizing Building Sewage Ejection Pumps 15.52 Facilities Planning and Layout WATER-METER SIZING AND LAYOUT FOR PLANT AND BUILDING WATER SUPPLY Select a suitable water meter for a building having a maximum fresh water demand of 9000 gal/h (34,110 L /h) for process and domestic use. Choose a suitable storage method for the water and for an emergency reserve for fire protection when there are no local rivers or lakes for water storage. Show how the water-supply piping would be connected to a wet-pipe sprinkler system for fire protection of the building and its occupants. Calculation Procedure: 1. Determine a suitable water-meter size for the installation Refer to a water-meter manufacturer’s data for the capacity rating of a suitable water meter. The American Water Works Association (AWWA) standard for cold water meters of the displacement type is designated AWWA C700-71. It covers displacement meters known as nutating- or oscillating-piston or disk meters, which are practically positive in action. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Source: HANDBOOK OF MECHANICAL ENGINEERING CALCULATIONS 15.2 ENVIRONMENTAL CONTROL FIGURE 1 Pressure loss in displacement-type cold-water meters. The standard establishes maximum output or delivery classifications for each meter size as follows: 5 ⁄ 8 -in—20 gal/min (15.9 mm—1.26 L/s) 3 ⁄ 4 -in—30 gal/min (19 mm—1.89 L/s) 1-in—50 gal/min (25.4 mm—3.1 L/s) 1.5-in—100 gal/min (38.1 mm— 6.3 L/s) 2-in—160 gal/min (50 mm—10.1 L/s) 3-in—300 gal/min (75 mm—18.9 L/s) 4-in—500 gal/min (100 mm—31.5 L/s) 6-in—100 gal/min (150 mm—63 L/s) The standard also establishes the maximum pressure loss corresponding to the stan- dard maximum capacities as follows: 15 lb /in 2 (103 kPa) for the 5 ⁄ 8 -in (15.9-mm), 3 ⁄ 4 -in (19.0-mm) and 1-in (25.4- mm) meter sizes 20 lb /in 2 (138 kPa) for the 1.5-in (38.1-mm), 2-in (50-mm), 3-in (75-mm), 4- in (100-mm), and 6-in (150-mm) meter sizes For estimating pressure loss in displacement-type cold-water meters, Fig. 1 is pro- vided. Pressure loss in meters for flow at less than the maximum rates for any given size of meter can be estimated from Fig. 1. Since the maximum flow through the meter will be 9000 gal/h (34,110 L/h), we can convert this to gal /min by 9000 gal/h /60 min /h ϭ 150 gal/min (568.5 L- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.3 /min). Referring to the listing above, we see that a 2-in (50.8-mm) water meter will handle 160-gal/min (606.4 L/min). Since the required flow for this plant is 150 gal/min, a 2-in meter will be satisfactory. Figure 2a shows how the 2-in water meter would be installed. Normal water- utility practice is to install two identical equal-size water meters with bypass piping and valves to allow cleaning or repair of one meter while the other is still in service. Where a compound meter will be installed, the piping would be laid out as shown in Fig. 2b. 2. Choose the type of storage method for the system served Fig. 3 shows three different arrangements for water storage at above-ground levels. The reservoir in Fig. 3a serves only the plant and domestic water needs. It does not have a provision for emergency water for fire-protection purposes. The constant-head elevated tank in Fig. 3b has an emergency reserve for fire- fighting purposes. Local faire codes usually specify the reserve quantity required. The amount is usually a function of the building size, occupancy level, materials of construction, and other factors. Hence, the designer must consult the local ap- plicable fire-prevention code before choosing the final capacity of the constant-head storage tank. A vertical cylindrical standpipe is shown in Fig. 3c. While storing more water on the same ground area, this type of tank is sometimes thought to be visually less attractive than the elevated tanks in Fig. 3a and 3b. The alternative to the tanks shown in Fig. 3 is an artificial lake, if space is available at the plant site. Such a solution has its own set of requirements: (1) Sufficient land area; (2) Suitable soil characteristics for water retention; (3) Fencing to prevent accidents and vandalism; (4) Approval by the local zoning board for construction of such a facility; (5) Treatment of the water prior to use to make it suitable for process and human use. A final decision on the choice of storage method is usually based on both economic factors and local zoning requirements. 3. Show how the water supply would be connected to a wet-pipe sprinkler system The most common types of fire-suppression systems rely on water as their extin- guishing agent. Hence, it is essential that adequate supplies of water be available and be maintained available for use at all times. The minimum recommended pipe size for fire protection is 6 in (152.4 mm). Where a pipe network is used for fire protection, a looped grid pattern is designed for the plant or building, or both. It is often cost-effective to use larger pipe sizes in a grid because the installation costs are relatively the same. Table 1 shows the relative pipe capacity for different size pipes. The wet sprinkler system, Fig. 4, is connected to the plant water supply which can include a gravity tank, fire pump, reservoir or pressure tank and /or connection by underground piping to a city water main. As Fig. 4 shows, the sprinkler con- nection includes an alarm test valve, alarm shutoff and check valve, pressure gages for water and air, a fire-department connection to allow hookup of a pumper, and an air compressor. Within the building itself, Fig. 5, the main riser is hooked into cross mains to supply each of the floors. The wet-pipe sprinkler system accounts for about 75 percent of the systems installed. Where freezing might occur in a building a dry- type sprinkler system is used. Related Calculations. Plumbing-system design begins at the water supply for the structure served. The most important objective in sizing the water-supply system is the satisfactory supply of potable water to all fixtures, at all times, and at proper Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.4 ENVIRONMENTAL CONTROL FIGURE 2 (a) Dual water-service meters installed in a pit; (b) Compound water-service meter installed in a pit. (Mueller Engineering Corp.) pressure and flow rate for normal fixture operation. This goal is achieved only if adequate pipe sizes and fixtures are provided. Pipe sizes chosen must be large enough to prevent negative pressures in any part of the system during peak demand. Such pipe sizes avoid the hazard of water- supply contamination caused by backflow and back siphonage from potential sources of pollution. One cause of backflow can be fire-engine pumpers connected to a water main and drawing water out of it in large quantities for fire-fighting use. Pressure in the water main can decrease quickly during such emergency uses, lead- ing to back flow from a building’s internal water system. Hence, sizing of building Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.5 FIGURE 3 (a) Elevated water-storage reservoir. (b) Constant-head elevated water-storage tank having an emergency reserve for fire-fighting use. (c) Vertical standpipe for water storage. (Mueller Engineering Corp.) Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.6 ENVIRONMENTAL CONTROL TABLE 1 Table for Estimating Demand Supply systems predominantly for flush tanks Supply systems predominantly for Flushometer valves Load Load Water supply fixture units (WSFU) Demand gal/min L/s Water supply fixture units (WSFU) Demand gal/min L/s 1 3.0 0.19 2 5.0 0.32 3 6.5 0.41 4 8.0 0.51 5 9.4 0.59 5 15.0 0.95 6 10.7 0.68 6 17.4 1.10 7 11.8 0.74 7 19.8 1.25 8 12.8 0.81 8 22.2 1.40 9 13.7 0.86 9 24.6 1.55 10 14.6 0.92 10 27.0 1.70 12 16.9 1.01 12 28.6 1.80 14 17.0 1.07 14 30.2 1.91 16 18.0 1.14 16 31.8 2.01 18 18.8 1.19 18 33.4 2.11 20 19.6 1.24 20 35.0 2.21 25 21.5 1.36 25 38.0 2.40 30 23.3 1.47 30 42.0 2.65 35 24.9 1.57 35 44.0 2.78 40 26.3 1.66 40 46.0 2.90 45 27.7 1.76 45 48.0 3.03 50 29.1 1.84 50 50.0 3.15 60 32.0 2.02 60 54.0 3.41 70 35.0 2.21 70 58.0 3.66 80 38.0 2.40 80 61.2 3.86 90 41.0 2.59 90 64.3 4.06 100 43.5 2.74 100 67.5 4.26 120 48.0 3.03 120 73.0 4.61 140 52.5 3.31 140 77.0 4.86 160 57.0 3.60 160 81.0 5.11 180 61.0 3.85 180 85.5 5.39 200 65.0 4.10 200 90.0 5.68 250 75.0 4.73 250 101.0 6.37 300 85.0 5.36 300 108.0 6.81 400 105.0 6.62 400 127.0 8.01 500 124.0 7.82 500 143.0 9.02 750 170.0 10.73 750 177.0 11.17 1000 208.0 13.12 1000 208.0 13.12 1250 239.0 15.08 1250 239.0 15.08 1500 269.0 16.97 1500 269.0 16.97 2000 325.0 20.50 2000 325.0 20.50 2500 380.0 23.97 2500 380.0 23.97 3000 433.0 27.32 3000 433.0 27.32 4000 525.0 33.12 4000 525.0 33.12 5000 593.0 37.41 5000 593.0 37.41 Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.7 FIGURE 4 Wet-pipe sprinkler system service piping with typical fittings and devices. (Mueller Engineering Corp.) water supply systems is a matter of vital concern in protecting health and is reg- ulated by codes. Other important objectives in the design of water-supply systems are: (1) to achieve economical sizing of piping and eliminate overdesign; (2) to provide against potential supply failure due to gradual reduction of pipe bore with the passing of time, such as may result from deposits of corrosion or hard-water scale in the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.8 ENVIRONMENTAL CONTROL FIGURE 5 Wet-pipe sprinkler system installation on two floors of a building. (Mueller Engi- neering Corp.) piping; (3) to avoid erosion-corrosion effects and potential pipe failure or leakage conditions owing to corrosive characteristics of the water and/or to excessive design velocities of flow; and (4) to eliminate water-hammer damage and objectional whis- tling noise effects in the piping due to excessive design velocities of flow. Every designer of plumbing systems should familiarize himself/herself with the local plumbing code before starting to design. Then there will be fewer demands for re-design prior to final approval. Data in this procedure come from the National Plumbing Code, Mueller Engi- neering Corporation, and L. C. Nelsen—Standard Plumbing Engineering, McGraw- Hill. SI values were added by the handbook editor. PNEUMATIC WATER SUPPLY AND STORAGE SYSTEMS Design a pneumatic water supply for use with (a) well-water pump, and (b)a municipal water supply augmented by an elevated water tank. Provide design cri- teria for each type of system. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.9 FIGURE 6 Pneumatic well-water system for building service. (Mueller Engineering Corp.) Calculation Procedure: 1. Determine the maximum water flow required for cold-, hot-, and process services Use the procedures given later in this section to determine the flow rate and pressure required for the building served. With a well-pump supply, Fig. 6, the pump should have a capacity to 1.5 times the maximum water flow required. Such a capacity will ensure that the pump does not operate continuously. A booster system such as that shown in Fig. 7 is used when the city or private utility water system pressure is undependable—i.e., the pressure may be consis- tently, or intermittently, lower than that required by various fixtures in the system. The booster pump discharge pressure is set so that it equals, or exceeds, that re- quired by the fixtures or processes in the building. Water quantity supplied by the utility, public or private, is sufficient to meet the building demands. However, the utility pressure can vary unpredictably. As a rule of thumb, the pump must be capable of delivering a pressure at least 25 percent over that required in the plumb- ing supply system. 2. Find the required air compressor discharge pressure for the system Well-water systems generally do not have the capacity to handle a building’s peak water service demands. Hence, a storage tank of sufficient capacity to handle this demand is installed, Fig. 6, either underground or in the building itself. Once the water is in the storage tank, the well pump has served its purpose. A booster pump, Fig. 6, supplies the needed volume and pressure for the building water supply. Since it is undesirable to have the booster pump operate continuously to supply needed water, a pressure tank and air compressor are fitted, Fig. 6. The air com- pressor maintains pressure on the water in the pressure tank sufficient to deliver water throughout the building at the desired pressure and in suitable quantities. Air pressure in the pressure tank is often set at 25 to 50 lb /in 2 (173 to 345 kPa) higher than the pressure needed in the water system. The pressure tank is provided with a pressure relief valve so excessive pressure are avoided. Float switches in the storage and pressure tanks start the well-water or booster pump when the water level falls below a predetermined height. And when the Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.10 ENVIRONMENTAL CONTROL FIGURE 7 Pneumatic water system serving city-water supply. (Mueller Engineering Corp.) hydraulic pressure in the pressure tank falls below a level sufficient to deliver the needed water throughout the building, the air compressor starts. As a general rule, the minimum pressure required at ordinary faucets of plumb- ing fixtures is 8 lb/in 2 (55 kPa). At direct supply-connected flush valves (Flush- ometers), the minimum pressure should be 25 lb/in 2 (172 kPa) for blow-out-type water closets and 15 lb /in 2 (103 kPa) for other types of fixtures. For any type of plumbing fixture, domestic or process, the minimum pressure provided should be that recommended by the fixture manufacturer. In a combined system, Fig. 7, there is a check valve in the bypass line around the booster system. This check valve is extremely important. The valve prevents back pressurization of the city water by the building booster system water which is at a higher pressure than the city water. Under normal operation the city water can only flow to the booster pump. Further, the booster pump cannot pull water backwards out of the pressurized building water system. In a tall building a rooftop water storage tank can replace the booster system for the lower floors where there is sufficient head to operate the fixtures at the needed pressure. In a high-rise building the booster pump raises the water pressure sufficiently to overcome the static and friction pressure of the water-consuming fixtures on the upper floors. The booster system can also be designed to pump water into the rooftop storage tank for delivery to the lower floors. Related Calculations. Pneumatic water systems find use in a variety of build- ings: residential, commercial, industrial, etc. While they are more expensive than a simple metered system supplied at a suitable pressure and flow rate, pneumatic systems do ensure adequate water flow in buildings to which they are fitted. Where water flow is a critical concern, duplicate pumps, compressors, and tanks can be fitted. Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2006 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES