Document Text Contents
Page 2
BUILDING SERVICES
HANDBOOK
Page 324
305
Velocity of flow † 0„75 m/s † is the accepted minimum to achieve self-
cleansing. It is recognised that an upper limit is required to prevent
separation of liquids from solids. A reasonable limit is 1„8 m/s for both
surface and foul water drainage, although figures up to 3 m/s can be
used especially if grit is present. The selected flow rate will have a
direct effect on drain gradient, therefore to moderate excavation costs
a figure nearer the lower limit is preferred. Also, if there is a natural
land slope and excavation is a constant depth, this will determine the
gradient and velocity of flow.
Hydraulic mean depth (HMD) † otherwise known as hydraulic radius
represents the proportion or depth of flow in a drain. It will have an
effect on velocity and can be calculated by dividing the area of water
flowing in a drain by the contact or wetted perimeter. Thus for half
full bore:
This table summarises HMD for proportional flows:
Depth of flow HMD
0„25 Pipe dia. (m) ÷ 6„67
0„33 Pipe dia. (m) ÷ 5„26
0„50 Pipe dia. (m) ÷ 4„00
0„66 Pipe dia. (m) ÷ 3„45
0„75 Pipe dia. (m) ÷ 3„33
Full Pipe dia. (m) ÷ 4„00
E.g. a 225 mm (0„225 m) drain flowing half bore:
HMD � � �0 225 4 0 05625. .
Drainage Design – Velocities and Hydraulic Mean Depth
Page 325
306
Drains are usually designed with a maximum flow condition of three
quarters full bore, i.e. depth of flow or proportional depth 0„75. It is
essential to maintain some air space within a drain to prevent pressure
variations. Half full bore is a more conservative design, allowing ample
space for future connections and extensions to the system.
The relationship between drain capacity or proportional depth of flow,
velocity of flow (m/s) and discharge (m 3 /s) is represented in graphical
format:
Taking the example on page 310 the drain is designed to flow at half
full bore with a flow velocity of 0„8 m/s and discharge of 0„052 m 3 /s. If
at some later date, additional buildings are connected to the drainage
system to produce an anticipated flow of up to 0„75 proportional
depth, the graph indicates revised relative velocity and discharge rates
of 114% or 0„912 m/s and 92% or 0„048 m 3 /s, respectively.
Drainage Design – Depth of Flow
Page 648
Index
629
Suction tank for sprinklers , 530
Suction tank for wet risers , 535 ,
537
Summer valve , 75
Sump pump , 285
Supatap , 25
Superheated steam , 130
Supervisory control of lifts , 500
Supply pipe , 29
Surface water drainage , 302 † 9
Suspended ceiling , 584
Sustainable Urban Drainage
Systems (SUDS) , 299
Swales , 299
Swinging type fire damper , 552
Tail end sprinkler system , 525
Tapping of water main , 29
Taps , 25
Taut wiring , 564 , 566
Telecommunications , 492
Telephone socket , 452 , 492
Temperature , 94 , 610 , 615
Temperature control valve , 133
Temperature relief valve , 67 † 70
Tempering valve , 343
Temporary hardness , 34 , 40
Terminal positions of gas flues ,
403 † 4 , 407 , 409 † 12
Terminal position of discharge
stack, 3360 , 363
Testing
of drains , 289
of sanitary pipework , 368
Thermal relief safety valve , 70 , 87
Thermal storage heating , 465 † 6
Thermal transmittance , 156
Thermal wheel , 260
Thermocouple , 392 † 4
Thermo-electric safety device , 394
Thermostatic control
of heating , 141 † 54
of hot water , 116 , 143 , 145 † 6 , 148
Thermostatic mixing valve , 120 ,
141 , 339 † 42
Thermostatic radiator valve , 110 ,
116 , 141 † 6
Thermostatic steam trap , 132
Thermostatic valves , 116 , 141 † 6
Thermostats for gas , 391 † 4
Thomas Box formula , 54 , 58
Three-phase generator , 432
Three-phase supply , 432 † 5
Time controller , 83 , 142 † 3 , 469 , 482
TN-S and TN-C-S systems , 437
Towel rail , 75 , 116
Traction sheave , 496 † 7 , 502
Transformer , 149 , 432 † 6 , 470 † 1 ,
483 † 4
Trace element , 149
Traps
sanitation , 355 † 7
steam , 132
Travelator , 519
Trickle ventilator , 200 † 2 , 205
Trunk water mains , 22
TT system , 436
Tundish , 87 , 91 , 117 , 124 , 146 , 195 ,
405
Two-pipe heating , 114 † 15
drop heating system , 115
high level return heating system ,
115
parallel heating system , 114
reverse return heating system , 114
upfeed heating system , 115
Two-pipe sanitation , 364
Two-way switching , 448 † 50
U-duct , 414
̀ U ' values , 156 , 158
Ultrasonic detector , 564 , 568
Ultra-violet heat detector , 548
Under floor heating , 2 , 120 † 3 , 465
Underground coal gasification , 598
Underground heating mains , 135 † 7 ,
592
Unfilled soakaway , 290
Unvented hot water storage
system , 67 † 9
Page 649
Index
630
Unventilated stack , 270
Urinals , 345 † 6 , 364
Valves , 23 † 5 , 50 , 70 † 1 , 110 , 116 ,
130 , 147
Vapour compression cycle , 241 ,
246
Vapour expansion thermostat , 391
Vapourising oil burner , 186 † 7
Variable air volume a/c , 236
Velocity of water in drains , 304 † 6
Velocity of water in pipes , 58 † 60 ,
97 † 8 , 162 , 164
Ventilated one-pipe sanitation ,
363
Ventilated light fitting , 236 , 477
Ventilated stack , 362
Ventilation, Building Regulations ,
198 , 200 † 2
Ventilation
of buildings , 198 † 209
design , 218 † 30
of drains , 268 † 9
duct materials , 211
duct profile , 210
for gas appliances , 418 † 20
for oil appliances , 188 † 9
heat losses , 158
rates , 198 † 9
requirements , 198 † 202
system characteristics , 224
Venturi , 89
Venturimeter , 60
Verifiable backflow preventer , 43
Vibration detector , 564 , 567
Viscous air filter , 216
Voltage drop , 460
Walkway , 581
Wall flame burner , 187
Warm air heating , 155 , 207 , 467
Warning pipe , 31 † 2 , 41 , 44 , 124
Wash basins , 337 , 339 † 41 , 359 † 66
Wash-down W.C. pan , 325 , 359 † 65
Washer for air , 234 † 5
Washing machine waste , 367 , 370
Washing trough , 338
Waste disposal unit , 318
Waste pipes , 356 , 359 † 67
Waste valve , 358
Water
conditioners , 36 † 9
disinfection , 107
hardness , 33 † 6
Industry Act , 4 , 11
mains , 28 † 9
meter , 30
pressure and head , 54 , 57 , 613
pressure test , 169
Regulations Advisory Scheme , 11
seal loss in traps , 356 † 7
softener , 21 , 35 † 6
sources , 18
supply for sprinklers , 530
test on drains , 289
treatment , 40 , 106 † 8
tube boiler , 78
power , 586 , 590
Wavering out of trap seals , 356
WC pan , 325 † 6
Wet bulb temperature , 232 , 248 † 55
Wet pipe sprinkler system , 525 ,
527 † 8
Wet riser , 537
Wet steam , 130
Whirling hygrometer , 248
Whole building ventilation , 200 † 2
Wind power , 586 , 589
Wind pressure diagrams , 203 , 410
Wireless heating controls , 150
Wiring systems for central
heating , 151
Work at Height Regulations , 5 , 8
Workplace (Health, Safety and
Welfare) Regulations , 5 , 6 , 245 ,
261 , 350
Yard gully , 264 † 5
Zone controls , 143 † 4 , 148
BUILDING SERVICES
HANDBOOK
Page 324
305
Velocity of flow † 0„75 m/s † is the accepted minimum to achieve self-
cleansing. It is recognised that an upper limit is required to prevent
separation of liquids from solids. A reasonable limit is 1„8 m/s for both
surface and foul water drainage, although figures up to 3 m/s can be
used especially if grit is present. The selected flow rate will have a
direct effect on drain gradient, therefore to moderate excavation costs
a figure nearer the lower limit is preferred. Also, if there is a natural
land slope and excavation is a constant depth, this will determine the
gradient and velocity of flow.
Hydraulic mean depth (HMD) † otherwise known as hydraulic radius
represents the proportion or depth of flow in a drain. It will have an
effect on velocity and can be calculated by dividing the area of water
flowing in a drain by the contact or wetted perimeter. Thus for half
full bore:
This table summarises HMD for proportional flows:
Depth of flow HMD
0„25 Pipe dia. (m) ÷ 6„67
0„33 Pipe dia. (m) ÷ 5„26
0„50 Pipe dia. (m) ÷ 4„00
0„66 Pipe dia. (m) ÷ 3„45
0„75 Pipe dia. (m) ÷ 3„33
Full Pipe dia. (m) ÷ 4„00
E.g. a 225 mm (0„225 m) drain flowing half bore:
HMD � � �0 225 4 0 05625. .
Drainage Design – Velocities and Hydraulic Mean Depth
Page 325
306
Drains are usually designed with a maximum flow condition of three
quarters full bore, i.e. depth of flow or proportional depth 0„75. It is
essential to maintain some air space within a drain to prevent pressure
variations. Half full bore is a more conservative design, allowing ample
space for future connections and extensions to the system.
The relationship between drain capacity or proportional depth of flow,
velocity of flow (m/s) and discharge (m 3 /s) is represented in graphical
format:
Taking the example on page 310 the drain is designed to flow at half
full bore with a flow velocity of 0„8 m/s and discharge of 0„052 m 3 /s. If
at some later date, additional buildings are connected to the drainage
system to produce an anticipated flow of up to 0„75 proportional
depth, the graph indicates revised relative velocity and discharge rates
of 114% or 0„912 m/s and 92% or 0„048 m 3 /s, respectively.
Drainage Design – Depth of Flow
Page 648
Index
629
Suction tank for sprinklers , 530
Suction tank for wet risers , 535 ,
537
Summer valve , 75
Sump pump , 285
Supatap , 25
Superheated steam , 130
Supervisory control of lifts , 500
Supply pipe , 29
Surface water drainage , 302 † 9
Suspended ceiling , 584
Sustainable Urban Drainage
Systems (SUDS) , 299
Swales , 299
Swinging type fire damper , 552
Tail end sprinkler system , 525
Tapping of water main , 29
Taps , 25
Taut wiring , 564 , 566
Telecommunications , 492
Telephone socket , 452 , 492
Temperature , 94 , 610 , 615
Temperature control valve , 133
Temperature relief valve , 67 † 70
Tempering valve , 343
Temporary hardness , 34 , 40
Terminal positions of gas flues ,
403 † 4 , 407 , 409 † 12
Terminal position of discharge
stack, 3360 , 363
Testing
of drains , 289
of sanitary pipework , 368
Thermal relief safety valve , 70 , 87
Thermal storage heating , 465 † 6
Thermal transmittance , 156
Thermal wheel , 260
Thermocouple , 392 † 4
Thermo-electric safety device , 394
Thermostatic control
of heating , 141 † 54
of hot water , 116 , 143 , 145 † 6 , 148
Thermostatic mixing valve , 120 ,
141 , 339 † 42
Thermostatic radiator valve , 110 ,
116 , 141 † 6
Thermostatic steam trap , 132
Thermostatic valves , 116 , 141 † 6
Thermostats for gas , 391 † 4
Thomas Box formula , 54 , 58
Three-phase generator , 432
Three-phase supply , 432 † 5
Time controller , 83 , 142 † 3 , 469 , 482
TN-S and TN-C-S systems , 437
Towel rail , 75 , 116
Traction sheave , 496 † 7 , 502
Transformer , 149 , 432 † 6 , 470 † 1 ,
483 † 4
Trace element , 149
Traps
sanitation , 355 † 7
steam , 132
Travelator , 519
Trickle ventilator , 200 † 2 , 205
Trunk water mains , 22
TT system , 436
Tundish , 87 , 91 , 117 , 124 , 146 , 195 ,
405
Two-pipe heating , 114 † 15
drop heating system , 115
high level return heating system ,
115
parallel heating system , 114
reverse return heating system , 114
upfeed heating system , 115
Two-pipe sanitation , 364
Two-way switching , 448 † 50
U-duct , 414
̀ U ' values , 156 , 158
Ultrasonic detector , 564 , 568
Ultra-violet heat detector , 548
Under floor heating , 2 , 120 † 3 , 465
Underground coal gasification , 598
Underground heating mains , 135 † 7 ,
592
Unfilled soakaway , 290
Unvented hot water storage
system , 67 † 9
Page 649
Index
630
Unventilated stack , 270
Urinals , 345 † 6 , 364
Valves , 23 † 5 , 50 , 70 † 1 , 110 , 116 ,
130 , 147
Vapour compression cycle , 241 ,
246
Vapour expansion thermostat , 391
Vapourising oil burner , 186 † 7
Variable air volume a/c , 236
Velocity of water in drains , 304 † 6
Velocity of water in pipes , 58 † 60 ,
97 † 8 , 162 , 164
Ventilated one-pipe sanitation ,
363
Ventilated light fitting , 236 , 477
Ventilated stack , 362
Ventilation, Building Regulations ,
198 , 200 † 2
Ventilation
of buildings , 198 † 209
design , 218 † 30
of drains , 268 † 9
duct materials , 211
duct profile , 210
for gas appliances , 418 † 20
for oil appliances , 188 † 9
heat losses , 158
rates , 198 † 9
requirements , 198 † 202
system characteristics , 224
Venturi , 89
Venturimeter , 60
Verifiable backflow preventer , 43
Vibration detector , 564 , 567
Viscous air filter , 216
Voltage drop , 460
Walkway , 581
Wall flame burner , 187
Warm air heating , 155 , 207 , 467
Warning pipe , 31 † 2 , 41 , 44 , 124
Wash basins , 337 , 339 † 41 , 359 † 66
Wash-down W.C. pan , 325 , 359 † 65
Washer for air , 234 † 5
Washing machine waste , 367 , 370
Washing trough , 338
Waste disposal unit , 318
Waste pipes , 356 , 359 † 67
Waste valve , 358
Water
conditioners , 36 † 9
disinfection , 107
hardness , 33 † 6
Industry Act , 4 , 11
mains , 28 † 9
meter , 30
pressure and head , 54 , 57 , 613
pressure test , 169
Regulations Advisory Scheme , 11
seal loss in traps , 356 † 7
softener , 21 , 35 † 6
sources , 18
supply for sprinklers , 530
test on drains , 289
treatment , 40 , 106 † 8
tube boiler , 78
power , 586 , 590
Wavering out of trap seals , 356
WC pan , 325 † 6
Wet bulb temperature , 232 , 248 † 55
Wet pipe sprinkler system , 525 ,
527 † 8
Wet riser , 537
Wet steam , 130
Whirling hygrometer , 248
Whole building ventilation , 200 † 2
Wind power , 586 , 589
Wind pressure diagrams , 203 , 410
Wireless heating controls , 150
Wiring systems for central
heating , 151
Work at Height Regulations , 5 , 8
Workplace (Health, Safety and
Welfare) Regulations , 5 , 6 , 245 ,
261 , 350
Yard gully , 264 † 5
Zone controls , 143 † 4 , 148
