chapter 9. plumbing equipment and...
TRANSCRIPT
CHAPTER 9. PLUMBING EQUIPMENT AND SYSTEMS
9.1 Water in Architecture
9.2 Water Supply and Treatment
9.3 Domestic Water Distribution Systems
9.4 Plumbing Fixtures and Components
9.5 Planning Plumbing Facilities
9.6 Sanitary Drainage Systems
9.7 Sewage Treatment and Disposal
9.8 Storm Drainage System
Throughout history, in nearly all climates and cultures, the designer’s major concern about water was how to keep it out of a building.
Only since the end of 19th century has a water supply within a building become commonplace in industrialized countries.
In the rest of the world today, running water is still not available within most buildings.
9.1 Water in Architecture
9.1.1 Water’s Contribution to Human Life and Architecture
Nourishment: Much of the human body is water, the most abundant chemical in our bodies as well as in our diet. The amount of pure (potable) water that we need for drinking and cooking is very small – only about 11.4 L/cd (per capita per day) in most developed countries.
Cleansing and Hygiene:Water is a nearly ideal medium for the dissolution and transport of organic waste. Much larger quantities of water are used for cleaning than for nourishment; in developed countries, about 53 L/cd is used for clothes washing and dishwashing, and another 79.5 L/cd is used for bathing and personal hygiene.
Ceremonial Uses:Largely through its association with cleaning, water acquired a ceremonial significance that remains particularly evident in religious services.
Transportation Uses:Water is used in buildings principally to transport organic waste. In most buildings, high-grade pure water is used for the low-grade task of carrying away wastes from human living. In typical homes in developed countries where water closets are generally used, about 121 L/cd of potable water is used just to flush toilets.
Cooling:Water has a remarkable cooling potential; it stores heat readily, removes large quantities of heat when it evaporates, and vaporizes readily at temperatures commonly found at the human skin surface.
Ornamental Uses:In almost any landscaping application, indoor or outdoor, water becomes a center of interest. Water is a very powerful design element recognized by landscape designers.
Protective Uses:Water is the best fire protection medium available in most buildings. The vast quantities of water potentially required for fire-fighting must be delivered quickly; the result is pipes of large diameter regulated by very large valves.
Another protective use of water has been as a means to control access to buildings; moats around castles are good examples. Designers still sometimes use water as a means of directing traffic over a bridge to an entry.
9.1.2 Historic Review on Public Water Supply
The Romans constructed numerous aqueducts to serve any large city in their empire, as well as many small towns and industrial sites.
The city of Rome had the largest concentration of aqueducts, with water being supplied by eleven aqueducts constructed over a period of about 500 years.
They served potable water and supplied the numerous baths and fountains in the city, as well as finally being emptied into the sewers, where the once-used gray water performed their last function in removing waste matter.
In addition to masonry aqueducts, the Romans built many more leats - channels excavated in the ground, usually with a clay lining. They could serve industrial sites such as gold mines, lead and tin mines, forges, water-mills and thermae(public baths).
Leats were very much more expensive than the masonry design, but all aqueducts required good surveying to ensure a regular and smooth flow of water.
9.1.3 The Hydrologic Cycle
There is a finite quantity of water in the Earth and its atmosphere. (This statement is challenged
by a controversial theory of a steady rain of small water-bearing comets from outer space)
The process whereby this water constantly circulates, powered by about one-fourth of the Earth’s solar energy, is called the hydrologic cycle.
More than 99% of this water is “inaccessible”-either because it is saltwater or because it is frozen in glaciers or polar ice caps. The most accessible sources of water are precipitation and runoff.
Providing water is among the most critical services in a modern building.
Generally, potable water is supplied from a public water system and the potable water must meet the quality standards prescribed by the governing public health agencies.
For use in a building, the water supply must meet a minimum quality based on several major characteristics:
- Physical characteristics: The water supply may contain only a limited amount of suspended material, as measured in terms of cloudiness, clarity, color, acceptable taste, odor, temperature.
- Chemical characteristics: The water supply may contain no more than the maximum content prescribed by health standards pertaining to hardness and dissolved matter, such as mineral and metals. The preferred hardness is lower than 200ppm of calcium carbonates.
- Biological and radiological characteristics: The water should be free of bacteria, viruses, and radioactive materials.
9.2 Water Supply and Treatment9.2.1 Water Quality
9.2.2 Water Treatment Process to Improve Water Quality
Process at water treatment plants:
Coagulation (Flocculation)
Sedimentation
Aeration (Oxidation)
Filtration
Disinfection
Fluoridation - optional
Water conditioning at buildings:
Softening
Purification (deionization, reverse osmosis, distillation)
Filtration
1) Process of Water Treatment Plant
Coagulation (Flocculation): Removes dirt and other particles suspended in water. Alum (hydrated aluminum sulfate, Al2(SO4)3) and other chemicals are added to water to form tiny sticky particles called “floc” which attract the dirt particles. The combined weight of the dirt and the alum (floc) become heavy enough to sink to the bottom during sedimentation. This process reduces turbidity and improves the color and taste of water.
Sedimentation: Allows suspended matter to settle out of water by precipitation. Reduces the turbidity of the water.
Aeration (Oxidation): Introduces air into water to oxidize impurities to improve its taste and color.
Filtration: Water passes through filters, some made of layers of sand, gravel, and charcoal to remove even smaller suspended particles. This process improve overall quality of the water, including turbidity, potability, color and taste.
Disinfection: A small amount of chlorine is added or some other disinfection method is used to kill any bacteria or microorganisms that may be in the water.
Fluoridation: Adds a fluoride chemical in water to prevent tooth decay of children. However, fluoride levels in the water supply must be carefully monitored, because fluoride is toxic chemical.
2) Water Conditioning at Buildings
When water quality does not meet the minimum standards for which it is to be used, it must be conditioned by the various treatment processes on the site, either within or outside the building. The treatment may be applied to the entire water source or to only a portion of the water supply.
Schematic diagram of a water distribution system for a large hospital:
① Cold-water supply to lower floors for general-purpose use
② Soft cold-water supply for building heating system
③ Soft domestic hot water for laundry and plumbing fixtures
④ Deionized cold water to laboratory⑤ Distilled or reverse osmosis(RO) water for
laboratory testing services⑥ Filtered water for swimming pool, therapeutic
pool, etc.⑦ Cold-water supply to upper floors, with pressure
booster pump as required to overcome static height and frictional losses
Water Softening System
Water from rain or snow usually contains no minerals; however, flowing through mountains or rivers dissolves minerals such as calcium or magnesium salts in the form of carbonates (炭酸鹽) or sulfates (黃酸鹽).
When the water is heated, carbonates precipitates from the solution, forming hard scale. This scale can reduce the efficiency of heat exchangers and the net cross-sectional area of the pipe, as well as corrode the equipment.
Carbonates in water are termed temporary hardness. When they are in excess of 200 ppm, they should be removed from the water.
The most popular water-softening process is the zeolite system. In this system, water is softened by an ion exchange process in which calcium or magnesium ions are replaced by sodium (Na) ions.
Sodium salts are much more soluble than magnesium or calcium salts and do not precipitate as easily.
Zeolites are microporous, aluminosilicate minerals commonly used in industry for water purification, as catalysts, and in nuclear reprocessing. Their biggest use is in the production of laundry detergents.
Operating principle of a mixed-bed deionizer
Water Purification System
A deionizing system is similar to the zeolite softener system, except that the tank or tanks contain a mixed bed of both cation- and anion-absorbing resins made of porous polymer minerals.
The deionizing system can produce water that approaches the theoretical limits of purity.
This system reduces both the mineral content and the hardness of water.
A reverse osmosis (RO) system is another effective way to purify water and reduce its
hardness.
The system operates on the principle of diffusion rather than ion exchange. Osmosis is a
natural phenomenon that occurs when water solutions of different concentrations are
separated by a semi-permeable membrane. Water tends to flow from lower concentrations to
higher concentrations of impurities.
RO works on the principle of reversing water flow by applying high external pressure
between 200 to 400 psi (1380 to 2760 kPa) to the side with the higher concentration to force
pure water to flow into the side with the lower concentration.
A reverse osmosis (RO) membrane is almost always made of a polymer.
Distillation is a traditional method of obtaining highly purified water. The water is heated to water vapor and condensed into highly purified water that is practically free of impurities.
Distillation systems are used in research, hospitals, and manufacturing; however, they are less energy efficient than the ionization and RO systems.
Water Filtration Systems
Water filtration systems differ from water purification systems in that the former remove (filter out) only the undissolved matter, such as dirt, suspended matter, and debris, and do not alter the dissolved matter in water, such as chlorine, calcium carbonates, and salt.
Filtration systems are used primarily for large bodies of water, such as swimming pools and fountains. There are two basic filtration systems for large bodies of water - sand filters and diatomaceous earth filters.
9.3 Domestic Water Distribution Systems
Water distribution systems provide ways to supply water throughout buildings at pressure sufficient to operate plumbing fixtures.
Smaller buildings may be served simply by the pressure available in water mains (or pressure tanks fed by pumped wells). This is called upfeed distribution.
For taller buildings, several other options are available;
- Downfeed: Pumps raise the water to storage tanks at the top of a building, and water then drops down to the plumbing fixtures.
- Pumped upfeed: Pumps supply the additional pressure needed.
- Hydropneumatic feed: Pumps force water into sealed tanks, compressing the air within the tanks to maintain the needed water pressure.
9.3.1 Upfeed Water Distribution
In cities with municipal water supply systems, water is distributed through street mains at pressure varying at the main from about 350 to 480 kPa. For low-rise buildings of two or three stories, these pressures are adequate to act against the static pressure of water standing in the vertical piping, overcome the frictional resistance of water flow in the pipes, and still deliver water at the pressure required to operate plumbing fixtures.
9.3.2 Downfeed Distribution
Water pumped directly from the street main (or from a basement “suction tank” filled by gravity from the main) is lifted to a storage tank located at the top of a building.
For medium-rise buildings, one elevated storage tank can serve all of the lower floors.
For taller buildings, it is advisable to separate groups of floors into zones with maximum height (for plumbing pressure limits) of about 45 m. The zone-height limitation is based on the height-to-static pressure relationship.
At the top of the zone (about 10 m below the storage tank), the minimum desirable pressure is about 103 kPa.
At the bottom of the zone, the maximum allowed pressure is about 553 kPa; above this pressure, damage to fixtures might occur.
552 kPa – 103 kPa = 449 kPa difference449 kPa x 0.1 m /kPa = about 45 m
9.3.3 Pumped Upfeed Distribution
This distribution system is for medium-sized buildings – too tall to rely on street main pressure but not so tall as to necessitate heavy storage tanks on the roof.
9.3.4 Determination of Domestic Water System Load
The required water capacity of a building depends on the coincidental peak load demand (CPLD) of all load categories, based on an assumed time of day in the heavy-demand season.
For example, the highest CPLD for an office building is fully occupied, plumbing facilities are in heavy use, and air conditioning is near its peak.
The highest CPLD for an apartment building would be around dinnertime in the summer, when most people are home taking showers, washing, and preparing meals.
Domestic water system loads may be grouped into the following categories:
- Plumbing facilities- Food service – preparation, refrigeration, washing, dining, etc.- Laundry- Heating and cooling systems- Exterior – lawn and plant irrigation, fountains, etc.- Pools – swimming pools, whirlpools, therapeutic pools- Research and process – laboratory equipment, commercial or industrial processes,
computer equipment- Fire protection (if combined with the domestic system)
Plumbing Facilities
Water demand for plumbing facilities depends on the number and type of fixtures actually installed. In practice, the actual number of fixtures in modern buildings exceeds the minimum required by codes, particularly in public buildings and high rise office buildings.
Each plumbing fixture is assigned a wsfu (water supply fixture unit) rating, representing the relative water demand for its intended operating functions.
For example, a lavatory that does not demand a heavy flow of water is given a wsfu of 1.
A flush-valve-operated water closet that demands a heavy flow of water is given a wsfu of 10.
1 wsfu = 1 to1.5 GPM (3.8 to 5.7 L/min)
Exteriors
Water demand load for exteriors depends on the size of the lot and the portion that is landscaped. No generalization can be made and the demand load must be determined on a project-by-project basis.
- Manual watering of plants and lawns: 5 to 15 GPM (18.9 to 56.8 L/min)- Landscape sprinkler system: 1 to 10 GPM (3.8 to 38 L/min)- Fountain: usually designed for recirculation (a 10% makeup capacity should be
provided)
Swimming Pools
Normally, the flow rate of the circulation pump is designed to turn over (circulate) the entire volume of water in the pool in 6~8 hours or 3~4 times in 24 hours.
About 1 to 2 percent of the pumped circulation rate should be provided as continuous makeup water demand to overcome losses from evaporation and spillage.
Research and Processing
The use of water for research and processing in special buildings could be very high . The demand water load should be obtained from building staff members who are familiar with the operation or by metering actual usage.
Fire Protection
Normally, the water supply for fire protection is not included in the domestic water system; however, two components of the fire protection system may be combined with the domestic water system.
When a standpipe system is connected to a domestic water system, the domestic system must be capable of supplying a minimum of 100 GPM (about 379 L/min)of additional demand for small buildings, to 500 GPM (about 1893 L/min) or more for large buildings.
For a sprinkler system, the flow rate of each sprinkler head can be estimated based on 30 GPM (about 114 L/min)
9.3.5 Sizing of Water Pipes
A water system must be maintained with positive pressure to establish a flow in the distribution system and through the plumbing fixtures or equipment.
Furthermore, positive water pressure prevents water from being contaminated by external sources, since at a positive pressure, water tends to leak out of the pipe.
Water pressure should be sufficient to overcome any pressure loss due to friction, differences in elevation, and flow pressure at outlets or equipment.
Minimum Flow Pressure for Fixture or Equipment
Every plumbing fixture or connection that uses water must have the proper pressure to maintain the required flow.
Minimum fixture pressures vary from 28 to 138 kPa (4 to 20 psi) for fixtures.
Because the pressure in street main is usually about 345 kPa (50 psi), it is possible to assure the minimum fixture pressure, provided that the water does not have to be lifted to too great a height and not too much pressure is lost by friction in distribution piping.
Excessive friction results from piping that is too long in developed length (actual distance of water flow) or that interposes too many fittings (such as elbows and tees), or is too small in diameter.
The pressure losses in an upfeed system served by street main pressure are as follows.
Minimum fixture flow pressure A (for the highest, most remote fixture from main)Pressure loss due to height +BPressure loss due to friction in piping +CPressure loss by flow through water meter +D------------------------------------------------------------Total required street main pressure = E
During design, items A, B, and E are known and are reasonably constant.
Item D depends upon flow and pipe size, neither of which is yet known. (See graph for Pressure losses in disk-type water meters)
Item D is estimated. For residences and small commercial building ,the meter size rarely exceeds 50 mm.
This leaves one unknown, the value of C: C = E – (A+ B+D)
Pipe size is based upon the graph for friction loss.
Pipe diameter is determined by the point of intersection of a horizontal line representing flow and a vertical line expressing friction loss.
To select a pipe size, we need to know the probable flow and the unit-friction loss in the pipe and fittings.
The noise created by water flow also must be considered. Flow above 10 fps (3.1 m/s) is usually too noisy. Flow above 6fps (1.8 m/s) may be too noisy in acoustical-critical locations (such as concert halls).
Example: Using the following data, find the proper size for a metered water supply main.
Street main pressure (minimum) = 345 kPa
Height of topmost fixture above main = 9 m
Topmost fixture type = Water closet with flush valve using 6 L water per flush
Fixture units in the system = 85 wsfu
Total length of the piping (to the highest and most remote fixture) = 30 m
Equivalent pipe length of fittings (elbows, tees and valves) = 15 m(commonly estimated at 50% of the developed length)
System uses predominantly = Flush valves
Solution:From the minimum street main pressure, subtract the sum of the fixture pressure, the static head, and the pressure lost in the meter. This sum is:
A: fixture pressure = 103.421 kPa
B: static head 9 m x 9.8 kPa/m = 88.2 kPa
D: pressure loss in meter (estimated) = 55.1 kPa
Subtotal (A+B+D) = 246.721 kPa
C: pressure loss due to friction in pipeC = E-(A+B+D)
= 345 – 246.721= 98.279 kPa
The pressure lost in 30 m (total length) of piping plus 15 m of piping equivalent to the pressure lost by friction in the fittings became 98.279 kPa.
The friction loss in the pipe (30 m) will be 98.279 kPa x 30/45 = 65.519 kPa/30m
Then, the friction loss per unit meter of pipe will be:65.519 kPa 30 m = 2.184 kPa/m (218.4 Pa/m)
From below figure, curve 1, a flush-valve system with 85 wsfu will have a probable flow of about 4.0 L/s.
Given this information, enter 4 L/s and 218.4 Pa/m.
At the intersection of these lines, the pipe diameter and velocity are determined.
Pipe diameter: between 38.1 to 50.8 mmWater velocity: about 2.75 m/s
Therefore, 50.8 mm supply pipe will be chosen with a 50.8 mm water meter.
Now, find the actual pressure loss in the 50.8 mm water meter for a flow of 4 L/s. From below graph it is about 24.5 kPa.
Because this is less than the estimated loss 55.1 kPa, the pressure at the fixture will be slightly higher than the minimum needed.
9.3.6 Hot-Water System
Source of energy: oil, gas, steam, or electricity
Hot-water demand (Quantity)
Hot-water demand (Temperature)
9.3.7 Design Considerations for Water distribution Systems
Piping Material
Copper: most commonly used water-piping material because of its strength, durability, and resistance to corrosion.
Stainless steel: sometimes used in lieu of copper when the sulfur content in the water or air is high, as in the area of hot springs.
Hot-dipped galvanized steel: economical to use for larger pipes.
Plastic: used for water distribution because of its lower cost, corrosion resistance, and low potential for scaling.
Thermal Insulation
Pipes are insulated with thermal material, such as fiberglass, mineral wool, or foam plastic, to maintain the temperature of water for either chilled or hot water.
Acoustic Isolation
Cold-and hot-water piping should be insulated for both thermal and acoustical purpose.
Expansion or Contraction
When the ambient temperature to which the piping system is exposed is changed, and the relative coefficient of expansion between the building and the piping material is different, the differential movement will be created between the piping and the building.
Differential movement will also occur when the water temperature in the pipe changes.
Flexibility must be built into the piping system to allow for such movement.
The methods commonly used involve installing expansion loops or joints to compensate for the physical expansion (or contraction) of the pipes.
Preventing Backflow
A check valve allows water to flow in one direction only.
(a)Wing-type check valve showing the check in closed and open positions(b) Center-pivoted design with reduced pressure drop
Vacuum breaker is installed at the branch connection to an equipment item or plumbing fixture, such as a sink, dishwasher, boiler, water closet, or urinal.
A vacuum breaker will automatically open the piping system to atmospheric pressure when pressure in piping drops below the atmospheric pressure level, to prevent foreign material or foul water in the equipment or fixture from being siphoned into the piping system.
The most positive way to prevent backflow of foreign material into the water system is by means of the air gap required on plumbing fixture installations at the end of a water outlet, such as a valve or faucet. An air gap must be installed at least two pipe diameters higher than the receptor (bowl or basin), so that in case water overflows above the receptor rim, foreign material will not get into the piping system.
Shock Absorption
When the flow of water in a pipe is abruptly stopped, as by the closing of a faucet or a flushometer, the dynamic (kinetic) energy in the water must be absorbed. If it is not, the energy will be converted into a loud noise and vibration known as water hammer.
Water pressure required for water distribution is determined from a number of design parameters: water demand(flow rate), elevation, pipe sizes, material, routing, type of fittings, accessories, etc.
9.3.8 Water-Pumping System
1ftaq=0.43 psi1psi = 2.31 ftaq
9.4 Plumbing Fixtures and Components
Plumbing fixtures are receptacles, devices, or appliances that are supplied with water or that receive liquid-borne wastes and then discharge waters into the drainage system.
Commonly used plumbing fixture for building services include:
Water closets (WC)Urinals (UR)Lavatories (LAV or LV)Sinks (SK) - Kitchen sinks (KS), Service sinks (SS)Drinking fountains (DF)Bathtubs (BT)Showers (SH)Bidets (BD)
Plumbing fixtures are normally made of dense, impervious materials, such as vitreous china, enameled cast iron, stainless steel, or some other acid-resistant material.
9.4.1 Plumbing Fixtures
1) Water Closets(WC)
Water closets are normally made of vitreous china and are usually the most prevalent plumbing fixture in a building, both in number and in water demands; thus, they have the most impact on the capacity of water and drainage systems.
Water closets can be classified in terms of the following features:
Method of mounting: Floor-mounted and wall-mounted types.Cleansing action of the bowl: Siphon-jet, wash-down, and blowout types.Method of water control: gravity tank, flushometer, pressure tank, and vacuum type.
Flushing actions of water closets
Siphon-jet and wash-down types are the quietest in operation and are universally used in private and residential applications.
The blowout type is usually used in public facilities. This type is noisier, but more positive in cleansing action.
Method of water control
Gravity Tank WC
The water closets have 2- to 4-gal (7.5 to 15 L) water storage tanks. The water is discharged into the bowl by gravity.
Flushometer Valve WC
The water closets are equipped with a flushometer valve that admits a time-measured (adjustable between 5 and 10 seconds) amount of water into the bowl under the water pressure.
The amount of water admitted is between 2 and 4 gal (7 to 15 L) which is similar to that of gravity tank type of control. However, the instantaneous water demand rate is considerably higher (about 20 to 30 GPM, 75 to 114 L/min)
The flushometer type water closet can be ready for use immediately after flushing and therefore is mostly used in public applications.
When the flushometer valve is in the closed position, the segment diaphragm divides the valve into an upper and lower chamber with equal water pressure on both sides of the diaphragm.
Movement of the handle in any direction pushes the plunger, which tilts the relief valve and allows water to escape from the upper chamber.
Then, the water pressure in the lower chamber becomes greater than that of the upper chamber.
This greater water pressure in the lower chamber raises the relief valve and the diaphragm as a unit and allows water flow through the valve.
While the valve is operating, a small amount of water flows through the bypass orifice of the diaphragm, gradually refilling the upper chamber and equalizing the pressure once more.
As the upper chamber fills, the diaphragm returns to the seat to close the valve.
1) A continuous infrared beam is emitted from the valve sensor. As a user enter the beam’s effective range of 25 to 60 cm more than 7 seconds, the output circuit continues in a “hold” mode for as long as the user remains within the effective range of the sensor.
2) When the user leaves the sensing range, the unit automatically flushes the water closet.
Pressure tank WC
In the pressure tank type of control, the water closets are equipped with a pressurized tank within a conventional gravity tank.
The pressurized tank is charged with air and water under 25 psi (172 kPa) water pressure. When the plunger at the base of the tank is released, the air-water mixture is forced into the bowl to blow out its contents.
Because the blowout action is by pressure, 1.5 gal (5.7 L) of water is sufficient. Thus, a considerable amount of water is conserved.
However, pressure tanks are noisy, which must be taken into consideration.
Vacuum WC
The vacuum type of water closet operates on a central vacuum piping system.
When the valve below the bowl is opened, the contents of the bowl are sucked into the drainage piping system under vacuum using only 0.3 gal (1 L) of water per flushing.
This type of water closet is commonly used on airplanes, trains and oceangoing ships.
2) Urinals (UR)
Similar to water closets in construction and operating principle, they are either wall-mounted or floor-mounted.
Water flushing action should thoroughly clean the entire interior fixture surface.
3) Lavatory (LAV)
Lavatories are designed in a variety of size and shapes. Fittings, such as faucets, drains, and other accessories, are nearly unlimited in design and material.
4) Sinks (SK)
General purpose sinks and kitchen sinks are available in single-, double-, and triple-compartment models.
Stainless steel sinks are preferred because they are durable and easy to clean.
5) Drinking Fountains (DF)
Drinking fountains can be wall- or floor–mounted and are usually non-refrigerated.
6) Electric Water Coolers
Electric water coolers are individual drinking fountains with self-contained water-chilling units.
7) Bathtubs
The most popular bathtub is 5ft (1.5m) long with a net water basin dimension of 4 to 6 ft (1.2 to 1.8 m).
8) Showers
Showers can be integrated with a bathtub or be independently constructed into shower stalls or a group of showers.
One major concern is the control of water temperature by a mixing valve between cold and hot water. Thermostatic valves mix the water for the desired outlet water temperature.
9) Bidets
Bidets are small baths, having the same size and shape of a water closet, used primarily for personal hygiene.
Bidets are popular in Europe.
9.4.2 Traps
To prevent the backup of sewer gas into a building through the drainage connection of plumbing fixtures, every plumbing fixture must be connected by means of a trap seal.
As a rule, all water closets, bidets, and urinals are manufactured to have an internal trap, whereas other plumbing fixtures use external traps.
Water column in a trap is normally between 5 and 10 cm deep.
A water trap is always filled with water if the fixture is regularly used. However, if a building is unoccupied for long periods of time, water in the trap may dry out by evaporation .
In such a case, the trap should be filled with some lighter-than-water but non-evaporative fluid, such as glycerin or mineral oil, to cover the water seal surface, thus retarding the rate of water evaporation.
The water supply fixture unit (wsfu):
The wsfu is a measure of the probable hydraulic demand on the water supply by various types of plumbing fixtures.
The wsfu depends on the rate of supply, the duration of a single operation, and the frequency of operation of the fixture.
1 wsfu: A 1/2 in. (12.7 mm) residential type lavatory faucet is rated for 1 wsfu which is equivalent to about 1 to 1.5 GPM (5.7 L/min) flow rate.
The drainage fixture unit (dfu) :
The dfu is a measure of the probable discharge into the drainage system by various types of plumbing fixtures.
The dfu depends on the rate of drainage discharge, the duration of a single operation, and the frequency of operation of the fixture.
1 dfu: The rate of discharge of an ordinary lavatory with a nominal 1-1/4 in. (32 mm) outlet and trap is about 7.5 GPM (28 L/min or 0.5 L/s) and it is assigned a dfu = 1.
9.4.3 Fixture Units
9.5 Planning Plumbing Facilities
Plumbing facilities for buildings are primarily toilets, bathrooms, washrooms, and lockers for private or public use.
The requirements for such facilities are normally analyzed and planned by the architect to fulfill the needs of the building’s occupants; however, planned facilities must equal or exceed the minimum code requirements.
In practice, the plumbing facilities in high-quality buildings are more than are required by the code, for the following reasons:
- To improve convenience- To accommodate the fluctuation in a building occupants- To avoid congestion
9.5.1 Minimum Requirements by Code
Plumbing fixtures shall be installed to afford easy access for cleaning and maintenance.
More space is required for the physically disabled.
Toilets and washrooms should be located near building entries, waiting areas, elevator lobbies, stairways, telephone stations, etc.
Men’s and women’s toilets should be located in the same general area. When they are placed back to back, sharing one separating wall, the cost of piping is substantially reduced for small and low-rise buildings.
The cost of piping for large and high-rise buildings may not be significantly affected, since the large number of fixtures to be installed will probably require multiple stacks and risers in any case.
The designer must be careful to provide a visual barrier between the public passageway and the interior of the toilets when the door to the room is opened and there is a possibility that a reflected image may be seen through a mirror.
Allow ample distance between fixtures and room surfaces.
9.5.2 Substitution for Water Closets
Urinals may be substituted for water closets in male toilets on a one-for-one basis, but the substitution should not be more than 50 percent of the required water closets.
9.5.3 Planning Guidelines
9.6 Sanitary Drainage Systems
Drainage in buildings consists of three major components: sanitary waste (잡배수雜排水), storm water (우수雨水), and specialty waste (폐수廢水) (toxic, radioactive, chemical, or other processing wastes).
Sanitary waste and storm water may be piped separately or combined, depending on the public sewer system to which the drainage is connected.
Combined storm and sanitary sewer systems still exist in some major cities, carried over from the early practice of discharging untreated sewage into rivers.
This practice is no longer permitted in most developed, as well as developing, countries.
Because of their pollutants, specialty wastes must be piped and treated separately.
Definitions of several terms commonly used in drainage systems:
Waste (liquid): Liquid discharged from water consuming equipment. (잡배수雜排水)
Sanitary waste: Liquid discharged from plumbing fixtures. (잡배수雜排水)
Soil (waste): Liquid discharged from plumbing fixtures that contains or potentially contains fecal matter, such as liquid from a floor within a toilet. (오수汚水)
Sanitary drain: Main drain(배수구排水口) of the sanitary drainage within a building.
Sanitary sewer: Extension of the sanitary drain at the exterior of a building to the public sewer or to a sewage disposal system.
Storm water: Rainwater collected from building roofs and from exterior areas.
Storm drain: Main drain of the storm water drainage within a building.
Storm sewer: Sewer that is exterior to a building and that contains storm water only.
Combination sewer: Sewer that contains sanitary waste and storm water
9.6.1 Drainage-Waste Venting (배수통기관 排水通氣管)
When the sanitary drainage system is connected to a public sewer, the entry of sewer gas, insects, or rodents through the system must be avoided.
To overcome this problem, all drainage equipment (including all plumbing fixtures) connected to the sanitary drainage system must be separated by a liquid seal trap that acts to separate the building from the sewer.
Each trap must be adequately vented to the atmosphere to prevent the liquid seal from being siphoned or sucked dry.
One important purpose of venting is to ventilate the system by allowing air from the fresh-air inlet to rise through the system and carry away offensive gases.
Because of the importance of venting, a sanitary drainage system is often referred to as drainage-waste-venting (DWV) system.
Important terms associated with a DWV systems and definitions are:
Stack: Vertical portion of a DWV-piping system.
Waste stack: Vertical portion of a waste-piping system.
Soil stack: Vertical portion of a soil-piping system.
Stack vent: Open-end extension of a waste or soil stack above the highest horizontal drain connected to the stack.
Brach interval: Section of a soil or waste stack corresponding to one story in height, but in no case less than 8 ft (2.4 m).
Vent: Pipe open to the atmosphere.
Vent stack: Stack that does not carry waste of any kind and that is installed primarily for providing circulation of air to and from any part of the DWV system.
Brach vent: Brach of the venting system.
Common vent: Vent connected at the common connection of two fixtures.
Circuit vent: Branch vent that serves two or more traps and that extends from the downstream side of the highest fixture connection of a horizontal branch to the vent stack.
Crown vent: Vent connected to the crown of a trap
Developed length: Total length of a pipe, measured along the centerline of the pipe.
9.6.2 Sizing of Vent Pipes
The capacity of vent pipes depends on three major factors: the size of the stack, the number of dfu connected on the stack, and the developed length of the vent pipe.
In general, vents should comply with the following rules:
- Individual vents shall not be smaller than half the diameter of the required drainpipe served.
- No vent shall be smaller than 1-1/4 in. ( 32 mm) diameter.
- Vents exceeding 40 ft (12 m) in developed length shall be increased by one nominal pipe size. The nominal pipe sizes are 1-1/4 in. (32 mm), 1-1/2 in. (38 mm), 2 in. (51 mm), 3 in. (76 mm), 4 in. (102 mm), 5 in. (127 mm), 6 in. (152 mm), 8 in. (203 mm), 10 in. (254 mm), 12 in. (305 mm), and 15 in. (381 mm).
- Vents exceeding 100 ft (30.5 m) in developed length shall be increased by another nominal pipe size.
The minimum size of DWV pipes is governed strictly by the plumbing code. When cast iron (C.I.) pipe is used, it is good practice to use minimum 2 in. (51 mm) pipe for branch drain and vent pipes.
The layout of the toilet is usually determined by the architectural plan; however it is responsibility of the plumbing engineer to determine the need for floor drains and to coordinate with the architect on the location of cleanouts, etc.
Indirect waste shall be provided for all equipment that contains toxic or harmful chemicals.
All traps must be vented.
All horizontal drainage piping shall be installed in alignment at a uniform slop (pitch) not less than 1/4 in. per foot for a diameter of 3 in. and less, and not less than 1/8 in. per foot for a diameter of 4 in. or more. (21mm / 1 m for a diameter of 76 mm or less, and 10 mm / 1m for a diameter of 102 mm or more)
9.6.3 Design Guidelines for a DWV System
Cleanouts shall be installed at the base of drainage stacks and at the beginning of main horizontal branch so that the entire DWV system can be cleaned and cleared to prevent clogging.
Grease-laden waste from kitchens should be piped directly to the building drain or stack. A grease trap shall be installed for commercial kitchens, prior to connection to the waste pipe.
Waste containing high volumes of insoluble matter, such as sand, plaster, etc., shall be intercepted by sediment basins or catch basins prior to discharging into the sewer.
Waste containing oil, such as drains from a commercial garage, shall be connected through an oil interceptor.
A 4 in. (102 mm) waste and soil horizontal branches shall be used for a WC outlet even though plumbing codes do allow the user of 3 in. (76 mm) branch for a tank type of WC in public buildings and up to two bathroom groups in private residences. Experience indicated that the increased horizontal branch will substantially reduce the chance of blockage.
EXAMPLE:
Design, lay out, and size the piping for the sanitary drainage system for the sample house.
SOLUTION:
9.7 Sewage Treatment and Disposal
To protect water resources and the greater environment, all waste from buildings and industrial processes must be treated to meet certain standards of quality.
Domestic sewage (汚水) from dwellings and DWV systems in buildings are permitted to be discharged into the public sewer (下水道) system, which provides the necessary treatment prior to its discharge into nature.
When public sewers are not accessible, or when there is no public sewer system in the vicinity of a building or buildings, a private sewage treatment system must be constructed.
General schemes for sewage treatment and disposal:
1) Building mains sewer pump station sewage treatment plant
2) Building septic tank mains sewer pump station sewage treatment plant
3) Building septic tank drain field, seepage pit, or sand mount
9.7.2 Sewage Treatment Plants and Process
Modern sewage treatment plants require considerable mechanical equipment and controls in order to be efficient and reliable.
The flow scheme of a sewage treatment plat is generally the same for all countries.
Mechanical treatmentInflux (Influent)Removal of large objectsRemoval of sandPre-sedimentation
Biological treatmentOxidation bed or aeration systemsPost-sedimentationEffluent
Chemical treatmentThis step is usually combined with sedimentation and other processes to remove solids, such as filtration.The combination is referred as physical-chemical treatment.
The sewage treatment process is divided into three major steps:
1) Primary treatment:
Primary treatment is to reduce oils, grease, fats, sand, grit, and coarse (settleable) solids. This step is done entirely with machinery, hence this process is called “mechanical treatment.”
Retention: To remove large objects by racked screen.Sand and grit removal: To remove sand and grit to avoid damage to pumps and other equipment.Sedimentation: To settle fecal solids.Skimming: To remove floating material such as grease and plastics.Aeration: To accelerate the decomposition of organic matter.Sludge removal: To remove settled fecal solids.
Secondary treatment
Secondary treatment is designed to substantially degrade the biological content of the sewage such as are derived from human waste, food waste, soaps and detergent. The majority of municipal and industrial plants treat the settled sewage liquor using aerobic biological processes.
After aerobic biological process, the waste water flows through a series of filters, which cleans all the little things, such as bacteria and algae. There are several types of filters, including trickling filters and biological aerated filters.
Tertiary treatment – Nutrient removal and disinfection
Waste water may contains high content of nutrients such as nitrogen and phosphorus, which can be very dangerous in large doses. Nitrogen is removed by oxidation, which converts it into nitrate, and then to nitrogen gas, which stands out from the water, releasing into the air. Phosphorus is removed by using chemicals such as salts of iron and aluminum.
As the last step, the water is treated by chlorine or ultraviolet for disinfection, and the water is released to nature.
9.7.3 Septic Tank System
In rural areas for small capacity applications, the septic tank system is most commonly used, rather than a sewage treatment plant.
9.8 Storm Drainage System
A storm drainage (우수배수雨水排水) system conveys rainwater or melting snow from a building or site to the points of disposal.
The locations to be drained are roofs, patios, and areaways of buildings and parking lots, and roadways, lawn, and gardens on the site.
In general except for small or incidental areas, all exterior storm drainage should be connected externally to the building storm drainage system.
Commonly used terms related to storm drainage system :
Roof drain: Device installed on a roof to receive water collected on the surface of the roof
Area drain: Similar to a roof drain, except that it is installed in an exterior area
Conductor or downspout: Vertical portion of a storm drainage system installed in the interior of a building
Gutter: Exterior trough, installed below a roof, that collects rainwater from the roof and discharges it to the point of disposal through a leader
Leader: Vertical portion of a storm drainage system installed at the exterior of a building
Subsoil drain: Drainpipe that collects subsurface water and conveys it to a place of disposal
Controlled storm drainage system: Storm drainage system that collects storm water on a roof and release the flow slowly to the drainage system to allow the load to drain in a longer time
Primary drainage system: Basic storm water drainage system designed for normal use
Secondary drainage system: Additional storm drainage system that will handle any storm water overflow that may occur when heavier storms occur
Sump: Receiver or pit that receives liquid waste, storm water, or ground-water located below the elevation of a gravity system
Sump pump: Pump that removes liquid from a sump
Projected roof area: Horizontal component of a sloping or pitched roof
The fundamental principle behind the design of storm water system is to install a piping or conductor system to lead the storm water away from the building and site in a reasonable time.
The size of the system depends on the rate of rainfall, rather than the total rainfall in a day or in a year.
The rate of rainfall varies with intensity and frequency of occurrence.
Exterior drainage must be closely coordinated with the capability of the public sewer or public drainage system.
In many cases, the instantaneous drainage of storm water on a large exterior area may overtax the public sewer system. If this occurs, a method of delaying the runoffs may be necessary.
Delaying methods include undersizing the drainpipes, letting the ground gradually absorb water, and creating a storm water holding area, a technique known as “ponding”
9.8.1 Design Principle
The selection of a design value for the intensity of rainfall is usually governed by code and the economic and safety factors of the project
9.8.2 Data on Rainfall
1) First determine where drainage is required:
Other than roofs, areaways, driveways, and walkways toward space of lower elevation, entrances into and exits from buildings are areas that should be considered.
2) Determine the location of roof drains:
Roof drains should be located at lower spots or in depressed area of the roof.A minimum of 0.5% slope toward each roof drain is necessary.Structure must be designed to carry the extra weigh of water.
3) Determine the roof drain design criteria based on or exceeding the code requirements for the rate of rainfall for primary and secondary roof drain systems
4) Select the appropriate drainage fittings
5) Finally, select the piping materials and method of installation.
9.8.3 Design of Storm Drainage System
Sand interceptor Combination storm and sanitary basin with duplex submersible sump pumps