Module 8 Calculations

1.

A light commercial building is installed with four flush tank type water closets, two urinals with flushometers, and four lavatories. What is the total water supply fixture units (wsfu)? What is the probable water demand?

Table 8.6 Table 8.3B

Water closets: (4) WC x 5 wsfu 20
Urinals: (2) UR x 5 wsfu 10
Lavatories: (4) LV x 2 wsfu 8
Total WSFU 38

From Table 8-3B, the probable water demand is 55 gpm.

2.

What is the pressure at the base of a water pipe feeding a plumbing facility 500 feet above the base due to static height alone?

The water column equivalent is 1 psi = 2.31 feet. With a water column of 600 feet, the static pressure at the base of the column (pipe) is: $\frac{500 f t}{2.31}$ = 216 psi.

3.

If the roof area is 1500 sq. ft., and the roof is adjacent to three vertical walls of 100, 200 and 500 sq. ft. each. What shall the roof drain or drains be designed for?

The equivalent projected roof area plus 35% of the two largest vertical adjacent walls which are 500 and 200 sq. ft. respectively. The equivalent area is:

1500 + 0.35 × 700 = 1745 sq. ft.

Note that not all codes are consistent on this calculation.

4.

A building is installed with 300 tons of air conditioning. The air conditioning unit is water cooled through a cooling tower. How much make-up water should be provided?

Based on $0.35 \frac{g p m}{t o n}$ , the makeup water rate is: $300 t o n s \times 0.35 \frac{g p m}{t o n} = 10.5 g p m .$

5.

What is the pressure at the base of a water pipe feeding a plumbing facility 500 feet above the base due to static height alone?

The water column equivalent is $1 p s i = 2.31 f e e t$ . With a water column of $600 f e e t$ , the static pressure at the base of the column (pipe) is: $\frac{500 f e e t}{2.31} = 216 p s i$ .

6.

What is the minimum number of roof drains for any size building? For a building over 10,000 sq. ft. of roof area?

The minimum roof drains for any roof is 2, and that for buildings over 10,000 sq. ft. is 4.

7.

What size horizontal storm drain pipe should be installed for a building having 16,000 sq. ft. of projected roof area, in a region having 2-inch rainfall rate, and the drain pipe is laid with $\frac{1}{16”}$ /ft. slope? With $\frac{1}{4”}$ /ft. slope?

There should be a minimum of 4 roof drains, assuming each carries $\frac{1}{4}$ th of the storm water of 4000 sq. ft.
Each drain pipe shall be minimum 5-inch diameter at $\frac{1}{16”}$ slope and 4” diameter at $\frac{1}{4”}$ slope.

8.

What is the maximum number of fixture units (dfu) that may be connected to a 4-in. drain line with $\frac{1}{4}$ in. per foot slope?

A maximum of 840 dfu’s may be connected to the line.

MODULE 8 Plumbing Equipment and Systems