1. PLUMBING SYSTEMS

2. Introduction
Plumbing systems compromise major subsystems for conveyance of liquids and gases in pipes within a building
The plumbing subsystems have different objectives and must be kept independent of each other

3. Subsystems Water supply systems Water distribution systems
Waste water removal and rainwater
Heating gas

4. Water supply and Distribution systems
Water supply and distribution components
They consist of three major parts:
Fixtures
Distribution components
Distribution accessories

5. Fixtures
These fixtures are used in a building according to codes , owners choice, or architect/engineer decision
They constitute the device which use water such as:
Water closets (eastern and western)
Lavatories (sink with hot and cold water)
Hose bibs
Water fountains
Bathtubs
Janitor sinks

6. Distribution components
These include piping connecting fixtures to the water sources, valves, tanks and other components
Piping : Ferrous (include iron) rust Non-ferrous (include copper) Plastic
Other components: valves, shock absorbers, pressure regulating equipment

7. Distribution accessories
These include
Heaters
Pumps
Water softeners
Etc.

8. Water supply systems Include the following:
Water sources : public (mains), private (wells)
Hot and cold service water
Domestic hot water (DHW) systems

9. Need to determine
Estimation of hot water demand in a building (Table 21.7)
Temperature at which hot water should be provided (Table 21.6)

10. Heat sources Natural gas Electricity Oil and coal fired boilers
Solar energy
Heat pump
Heat recovery
Heating methods: direct heating and indirect heating)

11. Both methods can be utilized in a variety of equipment
Storage tank water heater: common for residential and small commercial uses
Circulating storage water heaters: in which water is first heated by a coil, then circulated through the storage tank
Tank-less heaters: in which water is very quickly raised to a desired temperature within a heating coil and immediately sent to the point of usage

12. Water distribution systems
Water is supplied through out the buildings at pressures sufficient to operate plumbing fixtures
Water is distributed through street mains at pressure varying from : 345(50) to 483 (70) k Pa (psi)

13. Water pressure should be enough to overcome
Water static pressure (in vertical pipes)
Frictional resistance in pipes, fittings and valves
And to operate plumbing fixtures in the case of up-feed pumping
Flow pressure required at fixtures range from: 35 to 210 k Pa (Table 8 ASHRAE.F33.7)

14. Static pressure
The pressure exerted at the bottom of a stationary “head” of water is directly related to its height
One cubic meter of water weighs 1000 kg ( 1 cubic ft. weighs 62.4 lb.)

15. Consider a “cube” of water (1mx 1mx1m)
Its weight is 1000 kg rests on a bottom of 1 m2
The static pressure at the bottom is therefore:

16. In other words:

17. Up-feed Distribution Distribution systems up-feed distribution
Pumped up-feed distribution
Up-feed Distribution
Pressure available in water mains is used to achieve flow pressure at fixtures
Applicable in small, low buildings of moderate water demand

18. Pumped up-feed distribution
1. Pumps are used to deliver water to various parts of the building
2. Pumps are of variable speed type operating in sequence according to water demand as called for by a pressure sensor at the base of the riser ( meets the requirements for increasing supply at nearly constant pressure

19. 3. Used for medium size buildings – those too tall to rely on street main pressure but not so tall to necessitate heavy storage tanks on the roof
4. A surge tank , filled by casual flow from street main, can be used to avoid suction demand on the street min at full operation. This could seriously reduce the available water pressure in the neighborhood
5. Up-feed pumping eliminates the house tank problems of weight, volume , and periodic cleaning. However , it lacks reverse storage in case of electric power failure unless emergency pumping is arranged

20. Down-feed Distribution
1. Water from street main or from basement “suction tank” is pumped directly to a roof-storage tank 2. The roof storage tank is usually placed in a penthouse that encloses many equipment and technical facilities needed to serve the building ( i.e. A/C e.g. , exhaust blowers, ….) 3. Water pressure increases with height above plumbing fixtures

21. 4. For tall buildings , it is necessary to separate groups of floors into zones with a maximum height ( for plumbing pressure limits). This minimizes problems of pipe expansion, excessive pipe sizes, and high pressure in lower stories
5. The “Suction Tank” is a buffer between the system and the street mains. It holds enough reserve to allow the pumps to make up the periodic depletion in the house tank. It refills automatically by gravity from street mains
6. Excessive pressure on bottom plumbing fixtures can be reduced by using pressure reducing valves
7. Top fixtures require minimum head to operate of about 10 m
The static pressure for 10 m head is 9.81 k Pa /m x 10 m= 98 k Pa

22. Pressure Tank Pump selection Serving also for water storage
These tanks are frequently used both to maintain a constant pressure on a pump-supplied water system and to allow for temporary peaks in water supply rates that exceed the capacity of the pump
Pump selection
Table 21.4

23. The capacity of pressure tanks usually is small in comparison to the daily total water consumption, they provide short-term responses to peak flow demands
The pressure tank should be sized to deliver about 10 times the pump’s capacity in gpm.
For a typical residence allow 10 to 15 gal tank capacity per person served

24. For larger installation, the size of a pressure storage tank can be calculated by
Where Qm is 15 minutes of storage at peak usage rate
P1 and P2 are the minimum and maximum allowable operating pressure

25. Example 21.1 Pump and a well The peak demand is 50 gpm P1=50 psi
What is size of the tank?

26. Solution

27. The capacity of the elevated tank is usually equal to at least 2 days of average water usage.

28. Table 21.6 represents the hot water temperature
Table 21.7 domestic hot water consumption
Table 21.8 HUD-FHA (Housing and Urban Development) (Federal Housing Administration), minimum water heater capacities , residential
21.10 domestic hot water consumption

29. Example 21.2
Select a natural gas water heater for a five bedroom house with three baths.
From Table 21.8: 50 gal, Btu/h, 90 gal draw per hour and 40 gph recovery

30. Solution
From fig and Table a model BTH 120 is selected since it exceeds all the minimums

31. Example 21.3
A women’s dormitory housing 300 students, with a cafeteria serving 300 meals in one hour, is to be built.
Find the required hot water storage size for two conditions:
Assuming a minimum recovery rate for both dorm and cafeteria and
Assuming a dorm recovery rate of 2.5 gph, which is half the maximum hourly given in table and a cafeteria recovery rate of 10 gph which is two-third of the maximum hourly value given in table 21.21

32. Solution Use the figures.
Figure a, the minimum recovery rate for women’s dormitories is 1.1 gph
For 300 students:
300 x 1.1 =330 gph recovery
At this rate from figure a, the minimum usable storage capacity is 12 gal/student. Assume that 70% of the total capacity is usable capacity. This means that 70% of the stored hot water is withdrawn , the remaining water has been cooled (by incoming water) to an unusable low temperature.
Storage tank size must be increased by
100%/70%=1.43

33. At this rate the minimum usable storage capcity is 7 gal/meal. Thus
Thus 12x300x1.43=5150 gal storage
From figure e, the minimum recovery rate for the cafeteria (serving full meals Type A) is 0.45 gph. For 300 meals,
300 x 0.45=135 gph recovery
At this rate the minimum usable storage capcity is 7 gal/meal.
Thus
300 x7 x 1.43=3000 gal storage
Combining the requirements for dorm and cafeteria:
Recovery= =465 gph
Storage = =8150 g

34. At the specified dorm recovery rate of 2.5 gph,
Faster recovery:
At the specified dorm recovery rate of 2.5 gph,
300 x 2.5=750 gph
And the minimum usable storage required is 5 gal/student
Thus
300 x 5 x1.43=2150 gal
And the specified cafeteria recovery rate of 1.0 gph,
300 x 1.0 =300 gph
And the minimum usable storage required is 2 gal/meal. Thus:
300 x 2.0 x 1.43 = 860 gal

35. Combining these requirements for dorm and cafeteria:
Recovery = =1050 gph
Storage = = 3010 gal

36. For this example , an increase in heater size of 225% for faster recovery allows the size of the tank to be reduced to only 37%

37. Expansion air chambers
Absorb and reduce the shock of “water hammer” when faucets are shut off abruptly. On hot water run-outs , they also allow for the expansion of the hot water as it increases in volume with increasing temperature

38. Vacuum Breakers
Prevent back-flow of polluted water into pipes carrying potable (hot or cold) water
Treatment is most often performed to reduce hardness that could clog piping and equipment, or to neutralize acidity- a source of corrosion

39. Pipe and tube expansion
As the temperature of water rises in pipes and tubes from shut-down status (21 o C) to hot water operating status (71 o C), EXPANSION in water and pipes occur
This expansion, and therefore elongation in pipes, can be appreciable in tall buildings and can be controlled by the use of expansion joints (Table (21.12))

40. Example
A 20 story zone in a tall building has a height of 80 m. what will be the elongation in a copper tube carrying “service hot water” when heated from 21 to 71 o C

41. Solution Table 21.12 elongation is: (0.44+0.67)/2=0.555 mm/m
T= 50 o C
Table elongation is:
( )/2=0.555 mm/m
Expansion = 80 x mm/m= 44.4 mm

42. Maintenance Issues
Corrosion/scaling are the major problems which normally result in leaks
Water leakage from plumbing systems can cause damages and extensive repair actions and expenses
Paper selection of materials specifications, and proper installation are key issues in the operation and maintenance of these sub-systems

43. Access for maintenance of these components can reduce maintenance efforts and expenses
Provision of adequate isolation valves to permit maintenance of some components without interrupting the operation of others is important
Water treatment is critical for proper operation of these sub-systems as good health of occupants

44. Breakdown maintenance may be most appropriate for plumbing fixtures since multiple fixtures provide diversity
Breakdown maintenance is most appropriate approach for distribution components , although regular inspections may be used in preventing secondary materials damage

45. Breakdown maintenance is often practiced for distribution accessories , although corrective maintenance using inspections is probably a preferable approach

46. Sizing of water pipes
Equations are used to calculate pressure drop in hot and chilled water piping. However, charts were developed based on the equations to provide ways determination of pressure drops for specific fluids and pipe standards
Pipe friction loss is in the range of 100 and 400 Pa/m. A mean value for most systems is 250 Pa/m.

47. Valve and fitting pressure drop can be listed in elbow equivalent to a length of straight pipe
Tee fittings pressure drop varies with flow through the branch

48. Service water System pipe sizing procedure
Sketch the main lines , rises and braches and indicate all fixtures to be served
Determine the rate of flow of each fixture. The rate of flow desired for many common fixtures and the average pressure necessary to give this rate of flow are given in table 8 of 1993 ASHRAE Handbook of Fundamental-33

49. 3. Determine the probable rate flow in any particular section of the piping. Rarely , all fixtures will operate at the same time. Therefore, the rate of flow in the service line, risers, and main branches , rarely equals the sum of the rates of flow of all connected fixtures
4. Find the demand weights of the fixtures in fixtures.
5. Determine the total demand in fixture units en

50. 6. Determine the equivalent length pipe in main line , risers and branches . Add the equivalent lengths, starting at the street main and proceeding along the device line, the main line of the building and up the riser to the top fixture in the building.
Since the sizes of the pipes are not known , the exact equivalent length of various fittings cannot be made
A frequently used rule of thumb is to assume design length of pipe 50 to 100% longer than actual to account for fitting losses for initial pipe sizing

51. 7. Determine the average minimum pressure in the street main and the min. pressure required for the operation of the top most fixtures. This should be 50 to 170 k Pa above atmospheric
8. Calculate the appropriate design value of the average pressure drop per unit length of pipe in the approximately determined equivalent length of pipe:

52. Where:
P= average pressure loss per meter of equivalent length of pipe, k Pa/m
Ps=pressure in street main, k Pa
Pf=minimum pressure requires to operate topmost fixture, k Pa
Pm= pressure drop through water meter, k Pa

53. H= height of highest fixture above street main, m
L = equivalent length of pipe , m
The pressure due to height of water is 9.8 H, k Pa)

54. If the system is down feed supply from a gravity tank, the term 9
If the system is down feed supply from a gravity tank, the term 9.8 H is added rather than subtracted and replaces Ps:
H is the vertical distance of the fixture below
the bottom of the tank, m

55. 9. From the expected rate of flow , as determined in 5 above , and the value of ∆P (k Pa/m) calculated in 8 above, the proper sizes of pipes can be selected

56. Example
Assume a min. street main pressure of 375 k Pa above atmospheric, a height of topmost fixture ( shower of 20 m above street main); pipe length of 40 m from water main to highest fixture units. The water closest are flush value operated. Find the required size of supply main. Assume 40-mm water meter.

57. Solution
From fig , the peak water demands ( for number of fixtures 50) is 3.2 L/s
The min pressure to operate topmost fixture, Pf is 85 k Pa.
The pressure drop through water main ( assuming 40 mm meter) for a flow of 3.2 liter /sec is:
Pm=45 k Pa

58. The pressure drop available for overcoming friction in pipes and fittings is:

59. To find the pressure drop per unit length of the pipe , the equivalent pipe length of fittings on the direct line from street main to the highest fixture needs to be estimated. Velocity in branches leading to pump suction should be limited to 1.5 m/s

60. Example 21.7
Using the following data , find the proper size for a metered water supply main:
Street main pressure k Pa
Height, topmost fixture above main 10 m
Topmost fixture type water closet flush valve
Fixture units in the system 85 wsfu
Developed length of the piping (to the highest and most remote fixture) 30 m
Pipe length equivalent to fittings (commonly estimated at 50% of developed length) 15 m
System uses predominantly flush water

61. Solution
For 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 (Table 21.14) 103 k Pa
B: static head 10 m x 10 k Pa/m 100 k Pa
D: Pressure loss in meter (estimated, fig.21.63) k Pa
Subtotal k Pa
E: pressure in street main k Pa
(A+B+D)
E-(A+B+D) k Pa

62. Total equivalent length is 45 m.
The pressure lost in 30 m (developed length) of piping plus the 15 m of piping equivalent to the pressure lost by friction in the fittings can total 87 k Pa.
Total equivalent length is 45 m.
This procedure assures 103 k Pa at the critical fixture
The unit friction loss, k Pa/100 m of pipe , will be:
87 k Pa x 100/45 (total equivalent length)=193 k Pa/100

63. From figure b , curve 1, a flush valve system with 85 wsfu (water supply fixture units) will have a probable flow (diversified demand) of about 4 L/s.
Given this information, enter Fig b horizontally at 4 L/s and vertically at 193 k Pa/100 m
At the intersection of these lines, the pipe diameter and velocity are determined
Between 38 mm and 51 mm diameter pipe:
Velocity = about 2.4 m/s ( less than 3 m/s, so it is OK)
Therefore , a 50 mm diameter supply

64. At this point, exact pipe sizes are not known and equivalent length has to be approximated, to tentatively select pipe sizes

65. If the computed pipe sizes differ from those assumed in determining the equivalent length of pipe fittings , a recalculation would necessary, using the computed pipe sizes for the fittings
Assuming equivalent length of fittings=20 m
∆P permissible = 49/(40+20)=0.817 k Pa/m
∆P=8.7 Pa /m
We choose a pipe diameter of 50 mm where the velocity is about 1.9 m/s

66. Sizing of branches of the building main, the risers and fixtures branches follows these principles
For example , assume a branch of the building main carrying cold water with a demand of 2.4 L/s. Using the permissible pressure loss of k Pa/m, and the charts for 2.4 l/s flow rate, the required branch pipe size is 40 mm (1.7 m/s)

67. For actual piping layout of a building, calculate actual losses of all fittings
The general range of pipe friction loss in hydronic systems is between 100 and 400 Pa/m ( 250 Pa/m as a mean value)

68. Liquid waste Waterless toilets and urinals
This includes toilets in which chemicals or oil are substituted for water
These devices are commonly used in airplanes, vehicles, and boats as well as in environmentally sensitive areas
The chemicals must be frequently recharged and the waste products removed

69. Design of residential waste piping
In residential applications and in other relatively small buildings, standard size of 4 in soil stack and building drain is adequate
Table 22.2 through 22.5 list minimum pipe sizes to carry waste and serve for venting

70. Example 22.1
Design , lay out and size the piping for the sanitary drainage system for the house shown in figure 22.22

71. Solution
The first step is to identify the location where hot and cold water is needed at fixtures and where soil or waste drains must be provided
Fig 22.23a illustrates how this is done
A plan layout for the drains in both levels follows (fig22.23b)

72. Next comes the plumbing section (fig 22.24
The local administrative authority usually requires this to be submitted for approval
Sizes of all piping are determined from table 22.2 through 22.5
Drainage fixture units (dfu) for this system are summarized in table 22.6 from data given in Table 22.2

73. Residential Fixture
Drainage Fixture Units (dfu)
Bar sin 2
Kitchen sink with dishwasher
Lavatory 1
Water closet 4
Automatic clothes washer
Master bathroom group 6
Extra lavatory
Shower
Lower floor bathroom group
Total 26