Tài liệu Handbook of Mechanical Engineering Calculations P15 docx

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 Facilities Planning and

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

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 storagemethod for the water and for an emergency reserve for fire protection when thereare no local rivers or lakes for water storage Show how the water-supply pipingwould be connected to a wet-pipe sprinkler system for fire protection of the buildingand 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 suitablewater meter The American Water Works Association (AWWA) standard for coldwater meters of the displacement type is designated AWWA C700-71 It coversdisplacement meters known as nutating- or oscillating-piston or disk meters, whichare practically positive in action

FIGURE 1 Pressure loss in displacement-type cold-water meters.

The standard establishes maximum output or delivery classifications for eachmeter 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 dard maximum capacities as follows:

stan-15 lb / in2(103 kPa) for the 5⁄8-in (15.9-mm), 3⁄4-in (19.0-mm) and 1-in mm) meter sizes

(25.4-20 lb / in2(138 kPa) for the 1.5-in (38.1-mm), 2-in (50-mm), 3-in (75-mm),

4-in (100-mm), and 6-4-in (150-mm) meter sizes

For estimating pressure loss in displacement-type cold-water meters, Fig 1 is vided Pressure loss in meters for flow at less than the maximum rates for any givensize of meter can be estimated from Fig 1

pro-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⫽150 gal / min (568.5 L

-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 meterwill 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 pipingand 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-headstorage 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 isavailable 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 forconstruction of such a facility; (5) Treatment of the water prior to use to make itsuitable for process and human use A final decision on the choice of storagemethod 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 guishing agent Hence, it is essential that adequate supplies of water be availableand be maintained available for use at all times

extin-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 designedfor 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 therelative pipe capacity for different size pipes

The wet sprinkler system, Fig 4, is connected to the plant water supply whichcan 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 nection includes an alarm test valve, alarm shutoff and check valve, pressure gagesfor water and air, a fire-department connection to allow hookup of a pumper, and

con-an air compressor

Within the building itself, Fig 5, the main riser is hooked into cross mains tosupply each of the floors The wet-pipe sprinkler system accounts for about 75percent 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 forthe 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

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 ifadequate 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 supply contamination caused by backflow and back siphonage from potentialsources of pollution One cause of backflow can be fire-engine pumpers connected

water-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

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.)

TABLE 1 Table for Estimating Demand

Supply systems predominantly for

Water supply fixture units (WSFU)

Demand gal/min L / s

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.7

FIGURE 4 Wet-pipe sprinkler system service piping with typical fittings and devices (Mueller

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 leakageconditions owing to corrosive characteristics of the water and / or to excessive designvelocities 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 neering Corporation, and L C Nelsen—Standard Plumbing Engineering, McGraw-

Engi-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 teria for each type of system

cri-PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.9

FIGURE 6 Pneumatic well-water system for building service (Mueller Engineering Corp.)

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 intermitconsis-tently, 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 theutility, public or private, is sufficient to meet the building demands However, theutility pressure can vary unpredictably As a rule of thumb, the pump must becapable 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 peakwater service demands Hence, a storage tank of sufficient capacity to handle thisdemand is installed, Fig 6, either underground or in the building itself Once thewater 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 supplyneeded 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 deliverwater throughout the building at the desired pressure and in suitable quantities Airpressure in the pressure tank is often set at 25 to 50 lb / in2(173 to 345 kPa) higherthan 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 boosterpump when the water level falls below a predetermined height And when the

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 theneeded water throughout the building, the air compressor starts

As a general rule, the minimum pressure required at ordinary faucets of ing fixtures is 8 lb / in2 (55 kPa) At direct supply-connected flush valves (Flush-ometers), the minimum pressure should be 25 lb / in2 (172 kPa) for blow-out-typewater closets and 15 lb / in2(103 kPa) for other types of fixtures For any type ofplumbing fixture, domestic or process, the minimum pressure provided should bethat recommended by the fixture manufacturer

plumb-In a combined system, Fig 7, there is a check valve in the bypass line aroundthe booster system This check valve is extremely important The valve preventsback 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 watercan only flow to the booster pump Further, the booster pump cannot pull waterbackwards out of the pressurized building water system

In a tall building a rooftop water storage tank can replace the booster systemfor the lower floors where there is sufficient head to operate the fixtures at theneeded pressure In a high-rise building the booster pump raises the water pressuresufficiently to overcome the static and friction pressure of the water-consumingfixtures on the upper floors The booster system can also be designed to pumpwater into the rooftop storage tank for delivery to the lower floors

Related Calculations. Pneumatic water systems find use in a variety of ings: residential, commercial, industrial, etc While they are more expensive than asimple metered system supplied at a suitable pressure and flow rate, pneumaticsystems do ensure adequate water flow in buildings to which they are fitted Wherewater flow is a critical concern, duplicate pumps, compressors, and tanks can befitted

build-PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.11

Data in this procedure come from Mueller Engineering Corporation and L C

Nielsen: Standard Plumbing Engineering Design, McGraw-Hill SI values were

added by the handbook editor

SELECTING AND SIZING STORAGE-TANK

HOT-WATER HEATERS

Size a domestic hot-water storage-tank heater for an office building with publictoilets, pantry sinks, domestic-type dishwashers, and service sinks when the usablestorage volume of the tank is 70 percent of the tank volume and the followingnumbers of fixtures are fitted: 16 lavatories; 6 sinks; 2 dishwashers; 2 service sinks.Use ASHRAE and ASPE information and representative hot-water temperaturesand hot-water demand data in the computation

Calculation Procedure:

1. Determine the hot-water consumption of the fixtures

ASHRAE publishes hot-water demand per fixture in the ASHRAE Handbook, HVAC Applications Using data from that source, we have the following hot-water con-

sumption: 16 lavatories at 2 gal/h⫽ 32 gal/h; 6 sinks at 10 gal/h ⫽ 60 gal/h; 2dishwashers at 15 gal/h ⫽ 30 gal/h; 2 service sinks at 20 gal/h⫽ 40 gal/h; totalpossible maximum demand⫽32 ⫹60⫹30 ⫹40⫽ 162 gal/h (614 L / h)

2. Find the probable maximum demand on the hot-water heater

ASHRAE publishes demand factors for a variety of hot-water services for apartmenthouses, clubs, gymnasiums, hospitals, hotels, industrial plants, office buildings, pri-vate residences, schools, YMCAs, etc The ASHRAE demand factor for officebuildings is 0.30 Hence, the probable maximum demand on the water heater ⫽

162⫻0.30⫽48.6 gal/h (184 L / h)

3. Compute the storage capacity required for the hot-water heater

ASHRAE also publishes storage capacity factors for hot-water heaters in the erence cited above For office buildings, the published storage capacity factor is2.0 This is the ratio of storage-tank capacity to probable maximum demand perhour Thus, for this heater, storage capacity without considering the usable storagevolume⫽48.6⫻ 2.0⫽97.2 gal (368 L)

ref-Since 70 percent of the tank volume is the usable storage volume, the storagefactor⫽1 / 0.70⫽1.43 Then, storage capacity of the tank⫽97.2⫻1.43⫽138.99gal; say 139 gal (527 L)

Related Calculations. There are a number of ways to generate hot water forcommercial and institutional buildings The most common method is to use a stor-age-tank type water heater, Fig 8 Storage-type hot-water heaters generally areselected when the load profile has peaks that can be met from an adequate volume

of hot water stored in the heater Thus, the heater size and fuel / energy input arenot based on the instantaneous peak load, permitting a more economical equipmentselection

Storage-tank hot-water heaters should be selected and sized based on the specificrequirements for the building Items to be considered in the selection process in-clude: (1) type of facility served; (2) required water volume and peak loads; (3)

FIGURE 8 (a) Storage-tank hot-water heater (b) Gas-fired hot-water heater (Mueller Engineering

Indirect-fired storage hot-water heaters are heated by steam, hot water, or anotherhot fluid via a heat exchanger This heat exchanger may be either within the waterstorage shell or remote from it

Storage-tank hot-water heaters range in size from 2 to several thousand gallons(7.6 L to several thousand liters) capacity The very small units are typically used

in plumbing-code jurisdictions that prohibit the use of instantaneous hot-waterheaters

Typically, the maximum temperature for domestic hot water serving lavatories,showers, and sinks is approximately 120⬚F (49⬚C) at the fixture The maximum

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.13

FIGURE 9 Water heater fitted with thermal expansion tank (Heating / Piping / Air

Conditioning magazine)

desired water temperature from a fixture for personal use can be obtained by ing hot and cold water; mixing faucets are preferred over separate hot- and cold-water faucets Or, thermostatic mixing valves may be installed near the point(s) ofuse For bathing, a temperature-compensated shower valve should be used Thepreferred type is a balanced-pressure model with a high-temperature limit

blend-ASHRAE lists hot-water utilization temperatures for various types and uses ofequipment Facilities requiring a higher water temperature than that required forpersonal use may have a separate hot-water heating system for the higher temper-ature water if there is a significant load Otherwise, a booster heater often is used,

as with a commercial dishwasher The lowest temperature generally used is 75⬚F(24⬚C) for a chemical sanitizing glass washer, while the highest temperature is

195⬚F (91⬚C) in commercial hood or rack-type dishwashers

Hot-water distribution temperatures may be higher than 120⬚F (49⬚C) because

of the concern over Legionella pneumophila (Legionnaries’ Disease) This

bacte-rium, which can cause serious illness when inhaled, can grow in domestic hot-watersystems at temperatures of 115⬚F (46⬚C), or less Bacteria colonies have been found

in system components, such as shower heads, faucet aerators, and in uncirculatedsections of storage-type hot-water heaters

A water temperature of approximately 140⬚F (60⬚C) is recommended to reducethe potential of growth of this bacterium This higher temperature, however, in-creases the possibility of scalding during use of the water Scalding is of particularconcern for small children, the elderly and infirm, patients in health-care facilities,and occupants of nursing homes

All storage-tank hot-water heaters are required to have temperature and pressurerelief valves Separate valves may be used, or a combination temperature / pressure-relief valve may be installed Temperature-relief valves and combinationtemperature / pressure-relief valves must be installed so that the temperature-sensingelement is located in the top 6-in (15.2-cm) of the storage tank

The temperature-relief valve opens when the stored-water temperature exceeds

210⬚F (99⬚C) Its water discharge capacity should equal or exceed the heat inputrating of the heater

A thermal expansion tank, Fig 9, should also be provided in the cold-water lineadjacent to the heater whenever the system thermal expansion is restricted Check

valves, pressure valves, and backflow preventers, when used on the cold-water line

to the heater, restrict expansion of the water when it is heated This results inexcessive pressure buildup and can lead to tank failure ASME construction isrequired on all heaters greater than 200,000 Btu / h (58.6 kW) gas input or 120 gal(455 L) storage Additional data on sizing such hot-water heaters is available in the

ASPE Data Book, published by the American Society of Plumbing Engineers Use

the steps in this procedure to select and size storage-tank hot-water heaters for the

10 types of applications listed in step 2 above, and for similar uses

This procedure is the work of Joseph Ficek, Plumbing Designer, McGuire

En-gineers, as reported in Heating / Piping / Air Conditioning magazine, October, 1996.

SI values were added by the handbook editor

SIZING WATER-SUPPLY SYSTEMS FOR

HIGH-RISE BUILDINGS

A 102-family multiple dwelling, seven stories and basement in height, fronts on apublic street and is to be supplied by direct street pressure from an 8-in publicwater main located beneath the street in front of the building The public system

is of cast iron and a hydrant flow test indicates a certified minimum availablepressure of 75 lb / in2 (517 kPa) Top floor fixture outlets are 65 ft 8 in (20 m)above the public main and require 8 lb / in2flow pressure for satisfactory operation.Authoritative water analysis reports show that the public water supply has a pH

of 6.9, carbon dioxide content of 3 ppm, dissolved solids content of 40 ppm, and

is supersaturated with air Reports show that the public water supply has no nificant corrosion effect on red brass for temperatures up to 150⬚F (65.6⬚C).Cement-lined cast iron, class B, corporation water pipe, valves, and fittings havebeen selected for the water service pipe Red brass pipe, standard pipe size, hasbeen selected for the water distributing system inside the building

sig-Water supply for the building is to be metered at the point of entry by a pound meter installed in the basement The system is to be of the upfeed riser type

com-A horizontal hot water storage tank is to provide hot water to the entire building,and is to be equipped with automatic tank control of water temperature set for

140⬚F (60⬚C) The tank is to have a submerged heat exchanger

The most extreme run of piping from the public main to the highest and mostremote outlet is 420 ft (128 m) in developed length, consisting of the following:

83 ft (25.3 m) of water service, 110 ft (33.5 m) of cold water piping from the waterservice valve to the hot water storage tank, and 227 ft (69.2 m) of hot water pipingfrom the tank to the top floor hot water outlet at the kitchen sink Plans of theentire water supply system are available

The building has a basement and seven above-grade stories The basement floor

is 3 ft 8 in (1.1 m) below curb level, the first floor is 5.0 ft (1.5 m) above curblevel, and the public water main is 5.0 ft (1.5 m) below curb level Each of theabove-grade stories is 9 ft 4 in in height from floor to floor The highest fixtureoutlet is 3 ft above floor level

Fixtures provided on the system for the occupancies are as follows:

1 There are 17 dwelling units on each of the second, third, fourth, fifth, sixth, and

seventh floors; and each dwelling unit is provided with a sink and domesticdishwashing machine in the kitchen, and a close-coupled water closet and flushtank combination, a lavatory, and a bathtub with shower head above in a privatebathroom

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.15

2 This first floor is occupied for administrative and general purposes, and has the

following provisions for such occupancy: one flush-valve supplied water closetand one lavatory in an office toilet room; one flush-valve supplied water closet,one flush-valve supplied urinal and one lavatory in a men’s toilet room; twoflush-valve supplied water closets and one lavatory in each of two women’s toiletrooms; a sink and domestic dishwashing machine in a demonstration kitchen;one sink in an office kitchen; one sink in a craft room; and two drinking foun-tains in the public hall

3 The basement is occupied for building equipment rooms, storage, utility, laundry,

and general purposes and has the following provisions for such occupancy: oneflush-valve supplied water closet and one lavatory in a women’s toilet room; oneflush-valve supplied water closet, one lavatory, and one shower stall in a men’stoilet room; one service sink and six automatic laundry washing machines in ageneral laundry room; one faucet above a floor drain in the boiler room; andone valve-controlled primary water supply connection to the building heatingsystem

4 At each story and in the basement, a service sink is provided in a janitor’s closet

in the public hall

5 Four outside hose bibs (only two to be used at any time) are provided for lawn

watering at appropriate locations on the exterior of the building

Fixture arrangements are typical on the six upper floors of the building, and 24 sets

of risers are provided Of these, 5 sets are for back-to-back bathrooms, 2 sets arefor back-to-back kitchens, 4 sets are for back-to-back kitchen and bathroom groups,

9 sets are for separate kitchens, 3 sets are for separate bathrooms, and one set isfor a service sink on each floor above the basement Fixtures on the first floor areconnected to adjacent risers Basement fixtures are connected to overhead mains,which also supply directly the four outside hose bibs

Design a suitable water-supply systems for this building Choose pipe sizes foreach riser, fluid velocity, pressure drop, and piping material

Calculation Procedure:

1. Assemble the information needed for the design

Obtain data on the applicable plumbing code, characteristics of the water supply,location and source of the water supply, pressure available at the water entrance tothe site, elevations associated with the height of the building, minimum pressurerequired at the highest water outlets, and any special water services required in thebuilding Contact local responsible authorities for any missing data over which theyhave control You must have as much pertinent information as possible before thedesign job is started

2. Prepare a schematic elevation of the building water-supply system

Figure 10 shows a schematic elevation of the building water-supply system beingdesigned in this procedure This drawing was developed using the building andsystem plans All piping connections are shown in proper sequence for the system.The developed lengths for each section of the basic design circuit are determinedfrom the building and system plans Fixtures and risers are identified by combi-nations of letters and numbers Those fixtures and branches having quick-closingoutlets are specially identified by an asterisk Important information for establishing

a proper design basis are shown on the left side of Fig 10

4. List the demand in gal / min (L / s) adjacent to the fixture-unit load

Use Table 1 to determine the demand in gal / min (L / s), applying the values shownunder the heading ‘‘Supply Systems Predominantly for Flush Tanks’’ for all pipingexcept for the short branch piping which supplies water to water closets and urinalsequipped with flush valves on the first floor and in the basement (This procedure

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.19

TABLE 2 Demand at Individual Water Outlets

Type of outlet

Demand gal/min L / s

1 ⴖ (25.4 mm) flush valve [25 lb/in 2 (172 kPa) flow pressure] 35.0 2.210 1ⴖ (25.4 mm) flush valve [15 lb/in 2 (103 kPa) flow pressure] 27.0 1.703

3 ⁄ 4 ⴖ (19.0 mm) flush valve [15 lb/in 2 (103 kPa) flow pressure] 15.0 0.946

Laundry machine [8 lb (3.6 kg) or 16 lb (7.3 kg)] 4.0 0.252

uses both flush tanks and flush valves to show how to handle both in design.Remember: Flush tanks are still widely used in developing countries around theworld.)

5. Determine the water demands of any special fixture

The special fixtures in this building are the four outside hose bibs, Fig 10 Onlytwo of these hose bibs will be used at the same time Show this on the designsheet, along with the flow in gal / min (L / s) Obtain the normal demand for thesefixtures from Table 2

6. Size the individual fixture supply pipes to water outlets

Use Standard Code Regulations to size these pipes, as given in Table 11, later inthis section of the handbook Choose the minimum sizes recommended in Table 11

7. Using velocity limitations established for the design, size the remainder of the system

The velocity limitations adopted for this system are 8 ft/s (2.4 m / s) for all piping,except 4 ft/s (1.2 m / s) for branches to quick-closing valves as noted by asterisks

on Fig 10 Size each line using the total fixture units of load corresponding to thetotal demand of each section For those sections of the cold-water header in thebasement which convey both the demand of the intermittently used fixtures and thecontinuous demand of hose bibs, the total demand in gal / min (L / s) was converted

to equivalent water-supply fixture units of load and proper pipe sizes determinedfor them Proper sizing could also have been done simply on the demand rate ingal / min (L / s)

8. Calculate the amount of pressure available at the topmost fixture

Assume conditions of no flow in the system and calculate the amount of pressureavailable at the topmost fixture in excess of the minimum pressure required at such

TABLE 3 Pressure Calculations for Basic Design Circuit

Excess static pressure at top outlet available for friction loss 38.6 lb/in 2

Friction loss through 4-in compound meter at 227 gal/min flow rate

32.8 lb/in 2

Friction loss through horizontal hot water storage tank assumed for

Maximum pressure remaining for friction in pipe, valves, and

fittings

32.1 lb/in 2

Developed length of circuit from public main to top outlet 420 ft

Equivalent length for valves and fittings in circuit (based on sizes

established on velocity limitation basis)

363 ft

Maximum uniform pressure loss for friction in basic design circuit

⫻ 0.433 lb/in2/ ft of water)⫽ 38.6 lb / in2(266 kPa) (Note: 1 ft of water column

⫽0.433 lb/in2and 1 m of water column⫽9.79 kPa pressure)

9. Determine which piping circuit of the system is the basic design circuit (BDC)

The basic design circuit (BDC) is the most extreme run of piping through whichwater flows from the public main, or other pressure source of supply, to the highestand most distant water outlet Heavy lines in Fig 10 show the BDC for this struc-ture

There are 26 sections in the BDC in Fig 10 For each of these sections, thedeveloped length is computed as shown in Fig 10, for a total of 420 ft (128 m).Then, using the BDC length and other data for the installation, the pressure loss inthe BDC, is found thus, as shown in Table 3

10. Mark on the system schematic the pressure loss through any special

fixtures in the system

Obtain from the special fixture manufacturer(s) the rated pressure loss due to tion corresponding to the computed demand through any water meter, water soft-ener, or instantaneous or tankless hot-water heating coil that may be provided inthe basic design circuit

fric-Thus, the rated pressure loss through the compound water meter selected forthis system was found from the manufacturer’s meter data to be 5.8 lb / in2(40 kPa)for the peak demand flow rate of 227.6 gal / min (862.6 L / min) Note this on thedesign sheet, Fig 10 The rated pressure loss for flow through the horizontal hot-

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.21

water storage tank, i.e., entrance and exit losses, is assumed to be about 1.6 ft head

(0.49 m), 0.7 lb / in2(4.8 kPa)

11. Calculate the amount of pressure remaining

We must now calculate the amount of pressure remaining and available for pation as friction loss during peak demand through the piping, valves, and fittings

dissi-in the basic design circuit Deduct from the excess static pressure available at thetopmost fixture (determined in step 8) the rated friction losses for any water meters,water softeners, or water heating coils provided in the basic design circuit, as de-termined in step 10

Thus, the amount of pressure available for dissipation as friction loss duringpeak demand through the piping, valves, and fittings in the BDC is: 38.6⫺5.8⫺0.7⫽32.1 lb / in2(221 kPa)

12. Compute the total equivalent length of the basic design circuit

Pipe sizes established on the basis of velocity limitations in step 7 for main linesand risers must be considered just tentative at this stage, but may be deemed ap-propriate for determining the corresponding equivalent lengths of fittings and valves

in this step Using the tentative sizes for the BDC, compute corresponding alent lengths for valves and fittings Add the values obtained to the developed length

equiv-to obtain the equiv-total equivalent length of the circuit

The equivalent length of valves and fittings, using the methods given elsewhere

in this handbook, is 363.2 ft (110.7 m) When added to the developed length, wehave a total equivalent length of the BDC of 420⫹363.6⫽783.2 ft (238.7 m)

13. Calculate the permissible uniform pressure loss for friction in the piping

Thus, the maximum uniform pressure loss for friction in the basic design circuitis: 32.1 / 783.2 ft⫽0.04 lb/in2/ ft, or 4.0 lb/in2/ 100 ft (0.9 kPa / 100 m) This is thepipe friction for the BDC Apply it for sizing all the main lines and risers supplyingwater to fixtures on the upper floors of the building

14. Set up a pipe sizing table showing the rates of flow for the system

Set up the sizing table showing the rates of flow based on the permissible uniformpressure loss for the pipe friction calculated for the basic design circuit determined

in step 13 In Table 4, the flow rates have been tabulated for various sizes of brasspipe of standard internal diameter that correspond to the velocity limit of 4 and 8ft/s (1.2 and 2.4 m / s), and to the friction limit of 4.0 lb/in2/ 100 ft (0.9 kPa / 100m) of total equivalent piping length The values shown for various velocity limi-tations were taken from the data cited in step 7 Values shown for friction limitationswere taken directly from Fig 11 This chart is suitable, in view of the water-supplyconditions and a ‘‘fairly smooth’’ surface condition

15. Adjust the chosen pipe sizes, as necessary

All the main lines and risers on the design sheet have been sized in accordancewith the friction limitation for the basic design circuit Where sizes determined in

TABLE 4 Sizing Table for System

Red brass pipe, standard pipe size

Note: Apply the column headed ‘‘Velocity limit, l⬘ ⫽ 4 ft/s,’’ to size branches to quick-closing valves Apply the

column headed ‘‘Velocity limit, l⬘ ⫽ 8 ft/s,’’ to all piping other than individual fixture supplies Apply the column headed ‘‘Friction limit,’’ just for sizing piping that conveys water to top floor outlets Where two columns apply and two different sizes are indicated, select the larger size.

FIGURE 11 Water-piping pressure-loss chart.

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.23

this step were larger than previously determined in step 7, based on velocity tation, the increased size was noted directly on the design sheet Increased sizeswere made in all risers and in some parts of the main lines in this system Forexample, in the BDC, sections J-K, K-L, and L-M were increased from 2-in (50.8-mm) to 2.5-in (63.6-mm); sections O-P and P-Q were increased from 1.5-in (38.1-mm) to 2-in (50.8-mm); sections Q-R, R-S, and S-T were increased from 1.25-in

limi-to 1.5-in (31.8-mm limi-to 38.1-mm); T-U, U-V, and V-W were increased from 1-in limi-to1.25-in (25.4-mm to 31.8-mm); section W-X was increased from 0.75-in to 1.25-

in mm to 31.8-mm); and section X-Y was increased from 0.75-in to 1-in

(19-mm to 25.4-(19-mm)

16. Determine if the water supply is such that pipe sizing must be changed

From the characteristics of the water supply given by the municipal authority, it isrecognized that the water is relatively noncorrosive and nonscaling Hence, there is

no need for additional allowance in sizing in this case

Related Calculations. The method given here is valid for a variety of supply designs for apartment houses, hotels, commercial and industrial buildings,clubhouses, schools, hospitals, retirement homes, nursing homes, and residences ofall sizes As a designer, you should be certain to follow all applicable plumbingcodes so the system meets every requirement of the locality

water-This procedure is the work of L C Nielsen, as given in his Standard Plumbing Engineering Design, McGraw-Hill SI values were added by the handbook editor.

for this system Use the National Plumbing Code (NPC) as the governing code for

the plant locality The branch piping and house drain will be pitched 1⁄4 in (6.4mm) per ft (m) of length

Calculation Procedure:

1. Select the upper-floor branch layout

Sketch the layout of the proposed plumbing system, beginning with the upper, orsecond, floor Figure 12 shows a typical plumbing-system sketch Assume in thisplant that the second-floor urinals, water closets, and lavatories are served by onebranch drain and the showers by another branch Both branch drains discharge into

a vertical soil stack

FIGURE 12 Typical plumbing layout diagram for a multistory building.

2. Compute the upper-floor branch fixture units

List each plumbing as in Table 5

Obtain the data for each numbered column of Table 5 in the following manner.(1) List the number of the floor being studied and number of each branch drainfrom the system sketch Since it was decided to use two branch drains, numberthem accordingly (2) List the name of each fixture that will be used (3) List the

number of each type of fixture that will be used (4) Obtain from the National Plumbing Code, or Table 6, the number of fixture units per fixture, i.e., the average

discharge, during use, of an arbitrarily selected fixture, such as a lavatory or toilet.Once this value is established in a plumbing code, the discharge rates of other types

of fixtures are stated in terms of the basic unit Plumbing codes adopted by variouslocalities usually list the fixture units they recommend in a tabulation similar toTable 6 (5) Multiply the number of fixtures, column 3, by the fixture units, column

4, to obtain the result in column 5 Thus, for the urinals, (3 urinals)(4 fixture unitsper urinal fixture) ⫽ 12 fixture units Find the sum of the fixture units for eachbranch

3. Size the upper-floor branch pipes

Refer to the National Plumbing Code, or Table 7, for the number of fixture units

each branch can have connected to it Thus, Table 7 shows that a 4-in (102-mm)

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.25

TABLE 5 Floor-Fixture Analysis

branch pipe must be used for branch drain 1 because no more than 20 fixture unitscan be connected to the next smaller, or 3-in (76-mm) pipe Hence, branch drain 1will use a 4-in (102-mm) pipe because it serves 42 fixture units, step 2

Branch drain 2 serves 9 fixture units, step 2 Hence, a 21⁄2-in (64-mm) branchpipe will be suitable because it can serve 12 fixture units or less (Table7)

4. Size the upper-floor stack

The two horizontal branch drains are sloped toward a vertical stack pipe that

con-ducts the waste and water from the upper floors to the sewer Use Table 7 to sizethe stack, which is three stories high, including the basement The total number ofsecond-floor fixture units the stack must serve is 42⫹ 9 ⫽51 Hence, for a 4-in(102-mm) stack, Table 7 must be used

5. Size the upper-story vent pipe

Each branch drain on the upper floor must be vented However, the stack can be

extended upward and each branch vent connected to it, if desired Use the NPC,

or Table 8, to determine the vent size

TABLE 6 Fixture Units per Fixture or Group ⬚

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.27

TABLE 7 Horizontal Fixture Branches and Stacks ⬚

TABLE 8 Sizes of Building Drains and Sewers⬚

As a guide, the diameter of a branch vent or vent stack is one-half or more ofthe branch or stack it serves, but not less than 11⁄4(32 mm) Thus branch drain 1would have a 4 / 2 ⫽ 2-in (51-mm) vent, whereas branch drain 2 would have a

21⁄2/ 2⫽11⁄4-in (32-mm) vent

6. Select the lower-floor branch layout

Assume that the six urinals, three water closets, and three lavatories are served byone branch drain and the six showers by another Indicate these on the systemsketch Further, arrange both branch drains so that they discharge into the verticalstack serving the second floor

7. Compute the lower-floor branch fixture units

Use the same procedure as in step 2, listing the fixtures and their respective fixtureunits in the lower part of Table 5

8 Size the lower-floor branch pipes

By Table 7, branch drain 3 must be 4 in (102 mm) because it serves a total of 54fixture units Branch 4 must be 3 in (76 mm) because it serves a total of 18 fixtureunits

9. Size the lower-floor stack

The lower-floor stack serves both the upper- and lower-floor branch drains, or atotal of 42 ⫹9 ⫹ 54 ⫹ 18 ⫽123 fixture units Table 7 shows that a 4-in (102-mm) stack will be satisfactory

10. Size the lower-floor vents

By the one-half rule of step 5, the vent for branch drain 3 must be 2 in (51 mm),whereas that for branch drain 4 must be 11⁄2in (38 mm)

11. Size the building drain

The building drain serves all the fixtures installed in the building and slopes downtoward the city sewer Hence, the total number of fixture units it serves 42⫹9⫹

54 ⫹18 ⫽123 This is the same as the vertical stack Table 8 shows that a 4-in9102-mm) drain that is sloped 1⁄4-in / ft (21 mm / m) will serve 216 fixture units.Thus, a 4-in (102-mm) drain will be satisfactory The house trap that is installed

in the building drain should also be a 4-in (102-mm) unit

Related Calculations. Where a local plumbing code exists, use it instead of

the NPC If no local code exists, follow the NPC for all classes of buildings Use

the general method given here to size the various pipes in the system Select piping

materials (cast iron, copper, clay, steel, brass, wrought iron, lead, etc.) in accordance with the local or NPC recommendations Where the house drain is below the level

of the public sewer line, it is often arranged to discharge into a suitably size sump pit Sewage is discharged from the sump pit to the public sewer by a pneumatic

ejector or motor-drive pump

With the increased emphasis on the environmental aspects of plumbing, manylarge cities are urging building owners to convert water closets to Ultra-Low-Flow(ULF) units These ULF closets use 1.6 gal (6.06 L) per flush, as contrasted to 5

to 7 gal (18.95 to 26.5 L) per flush for conventional water closets Thus, in abuilding having 300 water closets the water savings could range up to [(300 ⫻7)⫺(300⫻1.6)]⫽1620 gal (6140 L) with just one flush per unit per day With

an average of ten flushes per day per water closet, the daily saving could be (10⫻1620) ⫽ 16,200 gal (61,398 L) Using a 5-day week for an office or industrialbuilding and a 52-week working year, the water savings could be (5 days)(52weeks)(16,200 gal / day)⫽4,212,000 gal (15,963,480 L) per year

When water savings of this magnitude are translated into reduced pumpingpower, lower electricity costs, and smaller piping sizes, the savings can be signif-icant This is why many large cities around the world are urging building owners

to install ULF water closets and urinals, along with reduced-flow shower heads,and lavatories

Once disadvantage of ULF units is that the reduced water flow can cause cumulation of solids in horizontal drain piping To remove solids, the horizontalpipes must be snaked out at regular intervals, depending on the system usage While

ac-PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.29

FIGURE 13 Building roof areas.

this does not occur in every installation of ULF units, it is being studied to mine possible remedies

deter-Building owners in one large city are currently receiving a bonus of $240 foreach ULF water closet installed in an existing structure This is leading to wide-scale replacement of existing water closets which use excessive amounts of water,

in view of today’s new environmental laws and regulations

A further benefit of the ULF units is the smaller amount of water that must betreated for each flush The reduced water flow allows the central sewage treatmentplant to handle more buildings and their water closets, showers, sinks, and otherfixtures As cities grow, it is important that sewage-treatment plants be able tohandle and process the increased waste flow Thus, the ULF unit saves water duringusage and reduces the post-usage need for waste-water treatment It is for thesetwo reasons that large cities are urging building owners to install ULF units

DESIGN OF ROOF AND YARD RAINWATER

DRAINAGE SYSTEMS

An industrial plant is 300 ft (91.4 m) long and 100 ft (30.5 m) wide The roof ofthe building is flat except for a 50-ft (15.2-m) long, 100-ft (30.5-m) wide, 80-ft(24.4-m) high machinery room at one end of the roof Size the leaders and hori-zontal drains for this roof for a maximum rainfall of 4 in / h (102 mm / h) Whatsize storm drain is needed if the drain is sloped1⁄4in / ft (2.1 cm / m) of length?

Calculation Procedure:

1. Sketch the building roof

Figure 13 shows the building roof and machinery room roof Indicate on the sketchthe major dimensions of the roof and machinery room

2. Compute the roof area to be drained

Two roof areas must be drained, the machinery-room roof and the main roof Therespective areas are: machinery room roof area⫽50⫻100⫽5000 ft2(464.5 m2);main roof area⫽250⫻ 100⫽25,000 ft2(2322.5 m2)

TABLE 9 Sizes of Vertical Leaders and Horizontal Storm Drains⬚

The wall of the machinery room facing the main roof will also collect rain tosome extent This must be taken into consideration when the roof leaders are sized

Do this by computing the area of the wall facing the main roof and adding half this area to the main roof area Thus, wall area⫽80⫻100⫽8000 ft2(743.2

one-m2) Adding half this area to the main roof area gives 25,000⫹8000 / 2⫽29,000

ft2(2694 m2)

3. Select the leader size for each roof

Decide whether the small roof area, i.e., the machinery room roof, will be drained

by separate leaders to the ground or to the main roof area If the small roof area

is drained separately, treat it as a building unto itself Where the small roof drainsonto the main roof, add the two roof areas to determine the leader size

By treating the two roofs as separate units, Table 9 shows that a 5-in (127-mm)leader is needed for the 5000-ft2(464.5-m2) machinery room roof This same tableshows that an 8-in (203-mm) leader is needed for the 29,000-ft2 (2694-m2) mainroof, including the machinery room wall

PLUMBING AND DRAINAGE FOR BUILDINGS AND OTHER STRUCTURES 15.31

TABLE 10 Size of Gutters⬚

4. Size the storm drain for each roof

The lower portion of Table 9 shows that a 6-in (152-mm) storm drain is neededfor the 5000-ft2(464.5-m2) roof A 10-in (254-mm) storm drain (Table 9) is neededfor the 29,000-ft2(2694-m2) main roof

When any storm drain is connected to a building sanitary drain or storm sewer,

a trap should be used at the inlet to the sanitary drain or storm sewer The trapprevents sewer gases entering the storm leader

Related Calculations. Size roof leaders in strict accordance with the National Plumbing Code (NPC) or the local applicable code Undersized roof leaders are

dangerous because they can cause water buildup on a roof, leading to excessiveroof loads Where gutters are used on a building, size them in accordance withTable 10

When a roof leader discharges into a sanitary drain, convert the roof area toequivalent fixture units to determine the load on the sanitary drain To convert roofarea to fixture units, take the first 1000 ft2(92.9 m2) of roof area as equivalent to

256 fixture units when designing for a maximum rainfall of 4 in / h (102 mm / h).Where the total roof area exceeds 1000 ft2 (92.9 m2), divide the remaining roofarea by 3.9 ft2 (0.36 m2) per fixture unit to determine the fixture load for theremaining area

Thus, the machinery room roof in the above plant is equivalent to 256⫹4000/3.9⫽ 1281 fixture units The main roof and machinery room wall are equivalent

to 256⫹ 28,000 / 3.9 ⫽ 7436 fixture units These roofs, if taken together, wouldplace a total load of 1281⫹7436⫽8717 fixture units on a sanitary drain.Where the rainfall differs from 4 in / h (102 mm / h), compute the load on thedrain in the same way as described above Choose the drain size from the appro-priate table Then multiply the drain size by actual maximum rainfall, in (mm) / 4

If the drain size obtained is nonstandard, as will often be the case, use the next

larger standard drain size Thus, with a 6-in (152-mm) rainfall and a 5-in

(127-mm) leader based on the 4-in (102-(127-mm) rainfall tables, leader size⫽ (5)(6 / 4)⫽7.5 in (191 mm) Since this is not a standard size, use the next larger size, or 8 in(203 mm) Roof areas should be drained as quickly as possible to prevent excessivestructural stress caused by water accumulations

To compute the required size of drains for paved areas, yards, courts, and yards, use the same procedure and tables as for roofs Where the rainfall differs