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140 Chapter 4 Quantities of Water and Wastewater Flows
of three dwellings per acre (7.415 unit/ha), an average market value of USD 125,000 per dwelling
unit, and a potential evaporation of 0.28 in./d (7.11 mm/d) on the maximum day.
Solution 1 (U.S. Customary System):
Average maximum and peak daily domestic demands per dwelling unit:
By Eq. 4.20: Q domestic 157 3.46 M 157 3.46 125 590 gpud
By Eq. 4.19: A 0.803 D 1.26 0.803>3 1.26 0.20 acre per dwelling unit
4
4
By Eq. 4.18: Q sprinkling 1.63 l0 A (E P) 1.63 l0 0.20 (0.28 0)
913 gpud excluding precipitation
For management:
Q max day Q domestic Q sprinkling 590 913 1,503 gpud.
By Eq. 4.21: Q peak h 334 2.02 Q max day 334 2.02 1,503 3,640 gpud
For design based on 200 dwellings:
From Table 4.11: Q max day 1,503 0.4 (1,000) 1,903 gpud
From Table 4.11: Q peak h 3,640 0.7 (1,000) 4,340 gpud
Solution 2 (SI System):
Average maximum and peak daily domestic demands per dwelling unit:
By Eq. 4.20a: Q domestic 594 13.1 M 594 13.1 125 2,232 Lpud
By Eq. 4.19a: A 1.016 D 1.26 1.016>(7.415) 1.26 1.016>12.4836 0.08138 ha/unit
By Eq. 4.18a: Q sprinkling 6,003 A (E P) 6,003 0.08138 (7.11 0)
3,473 Lpud excluding precipitation
For management:
Q max day Q domestic Q sprinkling 2,232 3,473 5,705 Lpud.
By Eq. 4.21a: Q peak h 1,264 2.02 Q max day 1,264 2.02 5,705.2 12,789 Lpud
For design based on 200 dwellings:
From Table 4.11: Q max day 5,705 0.4 (1,000) 3.785 7,219 Lpud
From Table 4.11: Q peak h 12,789 0.7 (1,000) 3.785 15,438 Lpud
4.5 DEMAND AND DRAINAGE LOADS OF BUILDINGS
The demand load of a building depends on the number and kinds of fixtures and the prob-
ability of their simultaneous operation. Different fixtures are furnished with water at differ-
ent rates as a matter of convenience and purpose. Expressed in cubic feet per minute
3
(ft /min), or liter per second (L/s) for fixture units, these rates become whole numbers of
small size. Common demand rates are shown in Table 4.15.
It is quite unlikely that all fixtures in a building system will draw water or discharge it
at the same time. A probability study of draft demands leads to the relationships plotted in
Fig. 4.5. In practice, the values shown are modified as follows:
1. Demands for service sinks are ignored in calculating the total fixture demand.
2. Demands of supply outlets, such as sill cocks, hose connections, and air conditioners,
through which water flows more or less continuously for a considerable length of
time, are added to the probable flow rather than the fixture demand.