Building Services Engineering 5th Edition Handbook

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Ventilation and air conditioning 141 The heated or cooled air supply may also have its humidity modified by an air-conditioning plant so that the percentage saturation of the room air is controlled. A water spray or steam injector can be used for humidification. The refrigeration cooling coil lowers the air temperature below its dew-point to condense the moisture out of the air. Figure 5.4 shows how the properties of humid air are determined from a psychrometric chart. If g r and g s are the moisture contents of the room and the supply air respectively, then a heat balance can be written for the latent heat gain absorbed by the previously calculated supply air flow rate Q: latent heat gain to room = latent heat equivalent of moistures removed by the conditioned air LH kW = moisture mass flow rate kg kJ × latent heat of evaporation s kg = air mass flow rate kg s × moisture absorbed kg H 2O kg dry air × 2453.61 kJ kg H 2 O LH kW = Q m3 s Q = × 1.205 kg 273 + 20 × × (g m3 r − g s ) kg H 2O kJ × 2453.61 273 + t s kg air kg H 2 O LH g r − g s × 273 + t s 866 284 m3 /s The denominator can be rounded to 860 000 with an error of less than 1.0%. Percentage saturation 100 50 14.8°C w.b. Dew-point temperature R Typical room air condition Moisture content g kg water kg air 0.0078 –10 t dp 21.0 60 Dry-bulb air temperature t (°C d.b.) 5.4 Sketch of the CIBSE psychrometric chart.
142 Ventilation and air conditioning EXAMPLE 5.6 The people in the office in Example 5.4 each produce 40 W of latent heat. Find the supply air moisture content to be maintained, given that the room air is to be at 50% saturation and the corresponding moisture content g r is 0.008905 kg H 2 O/kg air. W LH = 30 people × 40 person × 1kW 10 3 = 1.2 kW W t s = 13 ◦ C Q = 2.13 m 3 /s air mass flow rate = 2.13 m 3 /s × 1.205 kg/m 3 = 2.57 kg/s Q = We obtain, LH g r − g s × 273 + t s 860 000 m3 /s g r − g s = Hence, 1.2 × (273 + 13) 2.13 × 860 000 kg H 2O/kg air g s = 0.008905 − 0.000187 kg H 2 O/kg air = 0.008718 kg H 2 O/kg air Psychrometric cycles Heating and cooling processes in air-conditioning equipment can be represented on the psychrometric chart in the following manner. Heating Heating is performed with a low- or high-pressure hot-water, possibly steam, finned pipe heating coil, electric resistance heater or fuel-fired heat exchanger as shown in Fig. 5.5. SE is the specific enthalpy, total heat content, of the air, as read from the chart. Cooling Cooling is performed by passing chilled water, brine solution or refrigerant through a finned pipe coil. When the coolant temperature is below the air dew-point, condensation occurs and the air will be dehumidified. Figure 5.6 shows the two possible cycles. Mixing Mixing of two airstreams occurs when the fresh air intake joins the recirculated room air. The quantity of each air stream is regulated by multi-leaf dampers operated by electric or pneumatic motors under the direction of an automatic control system. Varying the intake of fresh
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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
Page 111 and 112: 90 Heating Sheet steel case Removab
Page 113 and 114: 92 Heating Floor finish Screed with
Page 115 and 116: 94 Heating Flue Return air plenum F
Page 117 and 118: 96 Heating Table 4.1 Classification
Page 119 and 120: 98 Heating Table 4.2 Heat output fr
Page 121 and 122: 100 Heating Table 4.3 Flow of water
Page 123 and 124: 102 Heating and, maximum available
Page 125 and 126: 104 Heating This means that one vol
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Page 129 and 130: 108 Heating Electrical power genera
Page 131 and 132: 110 Heating Combined heat and power
Page 133 and 134: 112 Heating 3. A building energy ma
Page 135 and 136: 114 Heating Connections are made to
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Page 141 and 142: 120 Heating 27. Which is not correc
Page 143 and 144: 122 Heating 39. Which of these is t
Page 145 and 146: 124 Heating 4. Heat supplied is cha
Page 147 and 148: 126 Ventilation and air conditionin
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Page 199 and 200: 6 Hot- and cold-water supplies Lear
Page 201 and 202: 180 Hot- and cold-water supplies Wa
Page 203 and 204: 182 Hot- and cold-water supplies po
Page 205 and 206: 184 Hot- and cold-water supplies Ce
Page 207 and 208: 186 Hot- and cold-water supplies st
Page 209 and 210: 188 Hot- and cold-water supplies 0.
Page 211 and 212: 190 Hot- and cold-water supplies 53
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192 Hot- and cold-water supplies an
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194 Hot- and cold-water supplies Ta
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196 Hot- and cold-water supplies Ta
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198 Hot- and cold-water supplies (a
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200 Hot- and cold-water supplies 3.
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202 Hot- and cold-water supplies 5.
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204 Hot- and cold-water supplies 49
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206 Soil and waste systems Introduc
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208 Soil and waste systems Open to
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210 Soil and waste systems 7. Bends
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212 Soil and waste systems The inte
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214 Soil and waste systems 40 mm wa
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216 Soil and waste systems Table 7.
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218 Soil and waste systems 50 mm ve
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220 Soil and waste systems 3. Long
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222 Surface-water drainage Table 8.
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224 Surface-water drainage Rectangu
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226 Surface-water drainage The solu
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228 Surface-water drainage 7. A PVC
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230 Below-ground drainage Design ca
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232 Below-ground drainage Manhole:
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234 Below-ground drainage From Fig.
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236 Below-ground drainage storage v
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238 Below-ground drainage 14. The f
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240 Condensation in buildings mould
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242 Condensation in buildings The w
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244 Condensation in buildings EXAMP
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246 Condensation in buildings This
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248 Condensation in buildings Tempe
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250 Condensation in buildings and,
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252 Condensation in buildings EXAMP
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254 Condensation in buildings Tempe
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256 Condensation in buildings For t
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258 Condensation in buildings 4. Ev
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11 Lighting Learning objectives Stu
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262 Lighting Table 11.1 Typical val
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264 Lighting Light sources 9 9 9 Wi
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266 Lighting Utilization factor The
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268 Lighting From Table 11.3, for a
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270 Lighting Table 11.4 Lamp data.
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272 Lighting number of lamps = 12.8
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274 Lighting 3. Sketch and describe
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276 Lighting 4. Insufficient inform
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278 Lighting 3. 800 lm/m 2 . 4. 260
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12 Gas Learning objectives Study of
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282 Gas Open to atmosphere Rubber p
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284 Gas EL = (1.25 × 34) m = 42.5
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286 Gas become exhausted. SNG will
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288 Gas are ignited and an air flow
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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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