Building Services Engineering 5th Edition Handbook

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Condensation in buildings 241 115 120 125 130 135 30 140 110 90 80 70 60 Percentage saturation 50 40 20 105 0.030 0.90 0.029 50 55 60 65 70 75 80 85 90 95 100 Based on a barometric pressure of 101.325 kPa 30 30 0.028 0.027 0.026 0.025 0.024 0.023 0.022 0.021 0.020 0.019 Moisture content kg/kg (dry air) 0.018 Specific volume m 3 /kg 0.017 0.85 0.016 Special enthalpy kJ/kg –10 –5 0 5 10 15 20 25 30 35 40 45 –10 –5 0 5 10 15 20 –10 –5 0 5 10 15 20 25 30 35 40 45 50 55 60 Dry-bulb temperature °C 45 50 55 20 25 30 35 40 –10 –5 0 5 10 15 Specific enthalpy kJ/kg 0.015 0.014 0.013 0.012 0.011 0.010 0.009 70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 0.6 0.7 0.8 0.9 1.0 0.9 0.8 0.7 0.6 0.4 0.5 0.5 Sensible/total heat ratio for water added at 30°C 0.4 0.3 0.2 0.1 0 °C (sling) 0.3 0.2 0.1 0 Wet-bulb temperature 0.008 0.007 0.006 0.005 0.004 0.75 0.80 0.003 0.002 0.001 0.000 60 65 Ó CIBSE London 1987 10.1 Psychrometric chart (reproduced by courtesy of the Chartered Institution of <strong>Building</strong> <strong>Services</strong> Engineers).
242 Condensation in buildings The warm internal atmosphere is able to hold more moisture than the cooler external air; thus the partial pressure of the vapour, that is, the vapour pressure p s , is higher inside than outside. This vapour pressure difference causes mass transfer of moisture out of the building through the porous structure and by the ventilation air flow. When dense materials such as precast concrete or impervious barriers form a major part of the construction, moisture removal from the normal habitation is slow and condensation occurs on cold surfaces. Brickwork or masonry that is already saturated has the same effect. Condensation and mould growth Condensation and mould may readily form on window sills and in the corners of rooms, where the surface temperatures are lower compared with large areas. Gloss paint stops the absorption of moisture into an otherwise porous plaster or wooden component and water droplets form on the surface. The production of surface condensation in heated rooms is generally avoided in structures with a U value lower than 1.4 W/m 2 K. Dampness in the timber of roofs, not caused by the ingress of rain, may be due to condensation on low-temperature surfaces. A well-insulated flat plaster ceiling may produce these low-temperature conditions in the roof construction. Natural ventilation through gaps between the tiles and roofing felt is normally sufficient to stop rot and damp patches on the plasterboard. Well-sealed roofs, with boarding under the felt, should have their ventilation increased by means of openings in the soffit of the eaves after extra thermal insulation. Humid air enters the roof space through gaps in the fiat plaster ceiling around access hatches and pipes. Sealing these substantially reduces condensation risk. Roof insulation should stop at the wall head and not be pushed into the eaves, or ventilation will be restricted (Saunders, 1981). Condensation forms within a structure or inside a solid material wherever the temperature falls below the dew-point of the moist air at that location. This is known as interstitial condensation. Vapour diffusion through building materials is calculated in a similar manner to the calculation of heat flow. Vapour diffusion The flow of water vapour through a porous building material or composite slab is analogous to the flow of heat through the structure. Convection currents transfer heat and moisture at the fluid–solid boundary. Conduction heat transfer is similar to vapour diffusion through a porous material, and its resistance to moisture flow varies with density, as does thermal resistance but in the opposite sense. The mass flow rate of moisture through a composite structure consisting of a number of plane slabs and surfaces in series is G = p s1 − p s2 R v where G is the mass flow rate of vapour (kg/m 2 s), R v is the vapour resistance of the structure (Ns/kg) and P s1 and P s2 are the vapour pressures on surfaces 1 and 2 on each side of the slab (N/m 2 or Pa). The total vapour resistance R v is given by R v = r v × l where R v is the total vapour resistance of a slab of homogeneous material (GN s/kg), r v is the vapour resistivity of a material (GN s/kgm), and l is the thickness of material (m). Surface films and
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Building Services Engineering
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Building Services Engineering Fifth
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Contents Preface to fifth edition A
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Contents vii Sick building syndrome
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Contents ix Circuit design 294 Cabl
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Preface to fifth edition Building S
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Acknowledgements I am particularly
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Units and constants xv Table 2 Mult
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Symbols xvii Symbol Description Uni
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Symbols xix Symbol Description Unit
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2 Built environment Introduction Th
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4 Built environment Ventilation The
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6 Built environment (a) At full occ
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8 Built environment Table 1.2 Compa
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10 Built environment Because of the
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12 Built environment Visual display
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14 Built environment v = 7 m/s t a
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16 Built environment 1.4 Sling psyc
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18 Built environment 1.7 Thermistor
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20 Built environment t res = t g (1
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22 Built environment great care wit
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24 Built environment 16. An hotel l
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26 Built environment 37. Are any of
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28 Built environment building has a
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30 Built environment 73. What was t
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32 Energy economics Introduction Bu
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34 Energy economics 16. air-to-air
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36 Energy economics 1 kWh = 1 kWh
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38 Energy economics 2. Heat transfe
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40 Energy economics For solid fuel
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42 Energy economics gas cost = 1.80
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44 Energy economics Table 2.5 Carbo
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46 Energy economics EXAMPLE 2.8 A h
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48 Energy economics annual cost = u
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50 Energy economics EXAMPLE 2.12 Ex
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52 Energy economics l = 0.035 ( 1 0
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54 Energy economics Table 2.11 Valu
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56 Energy economics From Table 2.4
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58 Energy economics 3. Minimum outs
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3 Heat loss calculations Learning o
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62 Heat loss calculations Table 3.1
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64 Heat loss calculations Table 3.6
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66 Heat loss calculations Where onl
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68 Heat loss calculations The venti
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70 Heat loss calculations The surro
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72 Heat loss calculations The speci
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74 Heat loss calculations where R m
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76 Heat loss calculations The addit
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78 Heat loss calculations operation
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80 Heat loss calculations 2. The fo
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82 Heat loss calculations internal
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84 Heat loss calculations 27. Which
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86 Heating Key terms and concepts a
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88 Heating 4.2 Electrically heated
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90 Heating Sheet steel case Removab
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92 Heating Floor finish Screed with
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94 Heating Flue Return air plenum F
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96 Heating Table 4.1 Classification
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98 Heating Table 4.2 Heat output fr
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100 Heating Table 4.3 Flow of water
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102 Heating and, maximum available
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104 Heating This means that one vol
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106 Heating Performance testing A r
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108 Heating Electrical power genera
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110 Heating Combined heat and power
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112 Heating 3. A building energy ma
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114 Heating Connections are made to
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116 Heating remotely the MWh consum
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118 Heating 13. The two-pipe heatin
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120 Heating 27. Which is not correc
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122 Heating 39. Which of these is t
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124 Heating 4. Heat supplied is cha
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126 Ventilation and air conditionin
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6 Hot- and cold-water supplies Lear
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180 Hot- and cold-water supplies Wa
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182 Hot- and cold-water supplies po
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184 Hot- and cold-water supplies Ce
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186 Hot- and cold-water supplies st
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188 Hot- and cold-water supplies 0.
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Page 213 and 214: 192 Hot- and cold-water supplies an
Page 215 and 216: 194 Hot- and cold-water supplies Ta
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Page 219 and 220: 198 Hot- and cold-water supplies (a
Page 221 and 222: 200 Hot- and cold-water supplies 3.
Page 223 and 224: 202 Hot- and cold-water supplies 5.
Page 225 and 226: 204 Hot- and cold-water supplies 49
Page 227 and 228: 206 Soil and waste systems Introduc
Page 229 and 230: 208 Soil and waste systems Open to
Page 231 and 232: 210 Soil and waste systems 7. Bends
Page 233 and 234: 212 Soil and waste systems The inte
Page 235 and 236: 214 Soil and waste systems 40 mm wa
Page 237 and 238: 216 Soil and waste systems Table 7.
Page 239 and 240: 218 Soil and waste systems 50 mm ve
Page 241 and 242: 220 Soil and waste systems 3. Long
Page 243 and 244: 222 Surface-water drainage Table 8.
Page 245 and 246: 224 Surface-water drainage Rectangu
Page 247 and 248: 226 Surface-water drainage The solu
Page 249 and 250: 228 Surface-water drainage 7. A PVC
Page 251 and 252: 230 Below-ground drainage Design ca
Page 253 and 254: 232 Below-ground drainage Manhole:
Page 255 and 256: 234 Below-ground drainage From Fig.
Page 257 and 258: 236 Below-ground drainage storage v
Page 259 and 260: 238 Below-ground drainage 14. The f
Page 261: 240 Condensation in buildings mould
Page 265 and 266: 244 Condensation in buildings EXAMP
Page 267 and 268: 246 Condensation in buildings This
Page 269 and 270: 248 Condensation in buildings Tempe
Page 271 and 272: 250 Condensation in buildings and,
Page 273 and 274: 252 Condensation in buildings EXAMP
Page 275 and 276: 254 Condensation in buildings Tempe
Page 277 and 278: 256 Condensation in buildings For t
Page 279 and 280: 258 Condensation in buildings 4. Ev
Page 281 and 282: 11 Lighting Learning objectives Stu
Page 283 and 284: 262 Lighting Table 11.1 Typical val
Page 285 and 286: 264 Lighting Light sources 9 9 9 Wi
Page 287 and 288: 266 Lighting Utilization factor The
Page 289 and 290: 268 Lighting From Table 11.3, for a
Page 291 and 292: 270 Lighting Table 11.4 Lamp data.
Page 293 and 294: 272 Lighting number of lamps = 12.8
Page 295 and 296: 274 Lighting 3. Sketch and describe
Page 297 and 298: 276 Lighting 4. Insufficient inform
Page 299 and 300: 278 Lighting 3. 800 lm/m 2 . 4. 260
Page 301 and 302: 12 Gas Learning objectives Study of
Page 303 and 304: 282 Gas Open to atmosphere Rubber p
Page 305 and 306: 284 Gas EL = (1.25 × 34) m = 42.5
Page 307 and 308: 286 Gas become exhausted. SNG will
Page 309 and 310: 288 Gas are ignited and an air flow
Page 311 and 312: 290 Gas 3. The pipe from a gas mete
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292 Electrical installations Key te
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294 Electrical installations curren
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296 Electrical installations 1 Volt
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298 Electrical installations power
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300 Electrical installations For1mm
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302 Electrical installations Table
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304 Electrical installations Incomi
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306 Electrical installations energi
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308 Electrical installations Starte
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310 Electrical installations Ethyle
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312 Electrical installations Test o
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314 Electrical installations Joint
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316 Electrical installations 4. 100
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318 Electrical installations 39. Wh
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320 Electrical installations 51. Wh
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322 Room acoustics 20. understand t
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324 Room acoustics pump blades and
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326 Room acoustics ceiling, Q is 4.
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328 Room acoustics Table 14.2 Solut
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330 Room acoustics Table 14.3 Fan s
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332 Room acoustics Table 14.4 Illus
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334 Room acoustics (Sound Research
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336 Room acoustics The target room
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338 Room acoustics Table 14.6 Noise
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340 Room acoustics 100 90 80 70 Sou
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342 Room acoustics 24. A forced-dra
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344 Room acoustics The room directi
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346 Room acoustics 3. Multiple sour
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348 Room acoustics 55. Which is not
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350 Fire protection computer monito
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352 Fire protection halogen gas, wh
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354 Fire protection the reach of tu
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356 Fire protection Range pipe Spri
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358 Fire protection Fire compartmen
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360 Fire protection 16. Which are c
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362 Plant and service areas Key ter
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364 Plant and service areas 2.0 1.5
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366 Plant and service areas Fuel st
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368 Plant and service areas a minim
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370 Plant and service areas An unde
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372 Plant and service areas Air cha
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374 Plant and service areas 100 mm
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376 Plant and service areas Fire co
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378 Plant and service areas Table 1
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380 Plant and service areas 11. Wha
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17 Mechanical transportation Learni
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384 Mechanical transportation Table
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386 Mechanical transportation Crowd
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388 Mechanical transportation Hydra
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390 Mechanical transportation 4. Co
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18 Question bank Learning objective
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394 Question bank 8. Which correctl
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396 Question bank 5. This building
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398 Understanding units Questions 1
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400 Understanding units 15. Which i
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402 Understanding units 29. Which o
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404 Understanding units 43. Which i
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Appendix: answers to questions Chap
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408 Appendix Chapter 3 Heat loss ca
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410 Appendix 4. 0.007469 kg H 2 O/k
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412 Appendix 32. 5 33. 5 34. 3 35.
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414 Appendix 23. Lighting 1200 h/ye
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416 Appendix 27. 37 dB. 28. 39 dB.
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418 Appendix 15. 5 16. 2 17. 5 18.
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References Action Energy, Departmen
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Index Absorption 154, 324 Absorptio
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424 Index Gas burner controls 289 G
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426 Index Sensible heat gains 137 S
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