Drainage Calculations

Discharge Unit Values BS.5572 :1978 Type of Sanitary Fitting

Interval between Use Domestic Public Peak Flow Discharge Unit (min) (min) (min) Value

Automatic Washing Machine 5

4 20 40

5

7 14 28

5

6 14 27

5

1 3 6

-

7 18 -

10

WC (9 Litre Cistern)

20 10

Sink

20 10

Wash Basin

20 10

Bath

75 10

Shower (Per Head) 1 2

Domestic Public

Urinal Bowl

20

0.3

Discharge Unit Maximum Values BS.5572 :1978 Internal diameter of pipe (mm)

Fall 1 in 111 1 in 45

1 in 22

100mm

230

430

1050

125mm

780

1500

3000

150mm

2000

3500

7500

Rates of Discharge from Sanitary Fittings BS.5572 :1978 Type of Fitting

Discharge (litres per second)

Basin

0.60

Bath

1.00

Sink (32mm Diameter Waste)

0.50

Sink (38mm Diameter Waste)

1.00

Sink (50mm Diameter Waste)

2.00

Urinal

0.15

WC (9 or 14 litre cistern)

2.30

Shower

1.00

Equipment Washer

5.70

Steam Steriliser

0.95

Peak Simultaneous Demand Simultaneous Demand Factor The discharge unit value takes into account the number of fittings discharging simultaneously compared with the total number of fittings installed. m = np + 1.80 [2 np (1 - p] 0.5 Where m = number of fittings discharging simultaneously p=t T,

known as the usage ratio

n = total number of fittings installed t = time in seconds fittings are discharging T = time in seconds between usage

Total number of fittings installed (n) = 30 It has been assumed that each fitting will take 10sec to discharge their contents, and will be used at 900sec intervals p = 10 900

.= 0.11

m = (30 x 0.11) + 1.80 [2 x 30 x 0.11 (1 - 0.11)] 0.5 .= 5.10 + square root of 5.874 .= 5.10 + 2.42 .= 7.52 Simultaneous Demand Factor = 7.52%

Residual Drainage Network Pipe Sizing The following calculations indicate the pipework sizes of the main horizontal sections. The size of branch mains is calculated on the basis that the discharge pipe shall be at least equal to the diameter of the outlet on the appliance to which it is connected.

Section 1. Sink (38mm waste) Sink (50mm waste)

4 x 1.00 l/s = 4.00 l/s 4 x 2.00 l/s = 8.00 l/s

12.00 x 7.52% = 0.90 l/s or 0.0009m3/s Q = VA

= V x π/8 D 2 (Half Bore) D = Square Root Q x 8 / V x π 0.0009 x 8 = 0.0072 0.0072 / 1 x 3.142 = 0.0023m Square root of 0.0023m = 0.048m 0.048m x 1000 = 48mm Suggested horizontal pipe size is 80mm Nominal Bore

Section 2. Sink (38mm waste) Sink (50mm waste) Equipment Washer

4 x 1.00 l/s = 4.00 l/s 5 x 2.00 l/s = 8.00 l/s 1 x 5.70 l/s = 5.70 l/s

17.70 x 7.52% = 1.33 l/s or 0.0010m3/s Q = VA

= V x π/8 D 2 (Half Bore) D = Square Root Q x 8 / V x π 0.0010 x 8 = 0.008 m3/s 0.008 / 1 x 3.142 = 0.0025m

Square root of 0.0025m = 0.05m 0.05m x 1000 = 50mm Suggested horizontal pipe size is 80mm Nominal Bore

Section 3. Sink (38mm waste) Sink (50mm waste) Equipment Washer Steam Steriliser

2 x 1.00 l/s = 2.00 l/s 7 x 2.00 l/s = 14.00 l/s 2 x 5.70 l/s = 11.40 l/s 3 x 0.95 l/s = 2.85 l/s

30.25 x 7.52% = 2.27 l/s or 0.0023m3/s Q = VA

= V x π/8 D 2 (Half Bore) D = Square Root Q x 8 / V x π 0.0023 x 8 = 0.0184 m3/s 0.0184 / 1 x 3.142 = 0.0059m Square root of 0.0059m = 0.077m 0.077m x 1000 = 77mm Suggested horizontal pipe size is 80mm Nominal Bore

Section A. 17 Sinks @ Peak Flow = 17 x 27 = 459 Loading Units 1 Washer @ Peak Flow = 1 x 40 = 40 Loading Units Total Loading Units = 499 LU From BS 5772 :1978 100mm Nominal Bore @ 1:22

Section B. 8 Sinks

@ Peak Flow = 8 x 27 = 216 Loading Units

5 Washer @ Peak Flow = 5 x 40 = 200 Loading Units Total Loading Units = 416 LU From BS 5772 :1978 100mm Nominal Bore @ 1:45