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Control devices 633Selection of two-port valves follows similar criteria as for the three-port variety.However, more detailed consideration is necessary in connection with the remainder ofthe circuit, because as the valves close the flow rate and pressure distribution around thecircuit will vary: this is particularly important since the installation is likely to have manytwo-port valves in the same pumped circuit. As the control valves throttle the flowthrough the controlled circuits the pump, if operated at constant speed, would tend todevelop an increased pressure which in turn would affect the authority of the valves.Added to which, this increase in pressure might affect the ability of the valves to open orclose fully and it may be necessary, therefore, to use either variable flow pumping or flowbypass valves with a system controlled by two-port valves.Steam control is a special application of the two-port valve. As the valve closes, the areaunder the seat decreases causing an increase in steam velocity, which tends to counter thedecrease in volume flow. The limiting condition, for practical purposes, is when thedownstream absolute pressure is 60% of the upstream pressure. When sizing a steamvalve, therefore, the pressure drop at full load is taken as 40% of the upstream absolutepressure, except when this pressure is less than 100 kPa, when impractical conditions arisefrom this rule of thumb and a smaller pressure drop is taken, with resulting loss ineffective control; reference to manufacturers' data is necessary in these circumstances.The heat exchanger surface area must, in consequence, be suitable for a steam supplylower than the mains pressure.Butterfly valves are, in effect, two-port control devices, but have poor control characteristicsequivalent to that illustrated as quick opening in Figure 22.11. Applicationis normally limited to two-position (open/closed) but standard equipment cannot beguaranteed to give total shut-off: special valves with liners are available for this purpose.Noise emanating from control valves should not be overlooked in the selection ofcomponents and in the design of the configuration of connecting pipework. The causemay be either unique or a combination of mechanical vibration, turbulence or cavitation.DampersControl of air flow follows the same principles as for water systems, and the function maybe either modulating or two (or more) ± position. There are two forms of control damper,parallel and opposed blade type, and their inherent characteristics are shown in Figure22.14. Dependent upon the damper authority (defined above for valves) the dampercharacteristic will vary when installed in a system (Figure 22.15). The closest to linearityis obtained where, for opposed blade dampers, the authority is 0.05 and, for parallel bladetype, 0.2. To limit the pressure drop in a system, therefore, opposed blade dampers, sizedfor an authority of about 0.05, would normally be selected.When used for controlling outside/exhaust/recirculating air in an air handling plant(Figure 22.16) the outside air damper (A), and the exhaust damper (B), would normally beopposed blade type, dimensioned at the duct size. However, for abnormal applicationswhere, for example, high resistance plant components are to be installed, a check shouldbe made from first principles. The function of the recirculation damper (C) is to impose aresistance in the bypass duct equivalent to the static pressure difference between thesupply and extract ducts and to have a characteristic to complement that of the outsideair damper in maintaining constant the mixed flow to the fan. This damper will ofnecessity have a high authority, up to 100%, and since the characteristic of the parallelblade type is better at higher authority (pressure drop in this case having no influence onrunning costs) the parallel blade type would be preferred. Where the pressure to be
634 Automatic controls and building management systemsFlow rate (percent)10050(A) Ideal(B) Parallel(C) Opposed(A)(B)(C)00 50 100Blade rotation (percent)Figure 22.14 Control damper characteristicsP1P2DamperControlledcomponentDamper authority =P1P+ 1 P2Figure 22.15 Basic control damper applicationAirintakeAControldampersPlantSupplyCExhaustBExtractFigure 22.16 Outside/exhaust/recirculating air control
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Faber and Kell's Heating andAir-con
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Faber and Kell's Heating andAir-con
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viiiContentsOther systems 396Altern
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xiiPreface to the ninth editionadvi
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2 FundamentalsBefore any part of th
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4 FundamentalsSpecific heat capacit
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6 Fundamentalsas insulators have a
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8 FundamentalsTable 1.4 Examples of
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10 FundamentalsIt has been suggeste
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12 FundamentalsTable 1.7 Wind-chill
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14 Fundamentalsthermometer, used fo
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16 Fundamentalsmeasure them, applic
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18 FundamentalsInletventilationTher
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20 The building in wintercoincide a
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22 The building in winter20GlassTem
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24 The building in winterFor the in
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26 The building in winterTable 2.2
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28 The building in winter4.0Plan8.5
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30 The building in wintermost commo
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32 The building in winterExposed el
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34 The building in winterFigure 2.4
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38 The building in winterInsulation
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40 The building in winterSurfaceAre
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42 The building in winterFrom Table
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44 The building in winterTemperatur
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46 The building in winterThe import
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50 The building in winterIntermedia
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52 The building in winterInside tem
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54 The building in winterDesigntemp
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56 The building in winterFrom earli
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60 The building in winterTemperatur
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62 The building in winterfollowing
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64 The building in winterIt has bee
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Chapter 3The building in summerThe
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68 The building in summerfrom simpl
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18070 The building in summerinforma
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72 The building in summerIncidence
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74 The building in summertime of pe
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76 The building in summerTable 3.2
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84 The building in summerFigure 3.9
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86 The building in summerAB B C a1
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88 The building in summerConduction
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92 The building in summerLossesMoto
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94 The building in summer(a)(b)Figu
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Chapter 4Survey of heating methodsH
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98 Survey of heating methodsTable 4
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100 Survey of heating methodsIndust
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102 Survey of heating methodsRadian
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104 Survey of heating methodsHeatex
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106 Survey of heating methodsReturn
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108 Survey of heating methodsReflec
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110 Survey of heating methodsCerami
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112 Survey of heating methodsTubula
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114 Survey of heating methodsthey a
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116 Survey of heating methodsFactor
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118 Survey of heating methodsrelian
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Chapter 5Electrical storage heating
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122 Electrical storage heatingTable
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124 Electrical storage heatingR 3
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126 Electrical storage heatingAs wi
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128 Electrical storage heatingWet c
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130 Electrical storage heatingStora
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132 Electrical storage heatingCasin
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134 Electrical storage heatingFinis
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136 Electrical storage heatingTable
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138 Electrical storage heatingVentI
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140 Electrical storage heatingUtili
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142 Electrical storage heatingExpan
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Chapter 6Indirect heating systemsIt
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146 Indirect heating systemsTable 6
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148 Indirect heating systemsin cont
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150 Indirect heating systemsHGIDEAC
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152 Indirect heating systemsLow tem
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154 Indirect heating systemsColdwat
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156 Indirect heating systemsRadiato
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158 Indirect heating systemsRadiato
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160 Indirect heating systemsCondens
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162 Indirect heating systems200800T
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164 Indirect heating systemssuccinc
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166 Indirect heating systemsTable 6
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168 Indirect heating systemsHigh ve
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170 Indirect heating systemsAs will
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172 Indirect heating systems0.080.0
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174 Indirect heating systems(a)(b)(
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Chapter 7Heat emitting equipmentWit
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178 Heat emitting equipmentTable 7.
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180 Heat emitting equipmentRadiant
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182 Heat emitting equipmentHeated g
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184 Heat emitting equipmentHangerIn
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186 Heat emitting equipmentpipes: e
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188 Heat emitting equipmentOpen fro
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190 Heat emitting equipment(a)(b)(d
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192 Heat emitting equipmentTable 7.
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194 Heat emitting equipmentConvecti
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196 Heat emitting equipmentDamperOu
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198 Heat emitting equipmentFilterOu
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200 Heat emitting equipmentSwivelno
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202 Heat emitting equipmentcovered
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204 Pumps and other auxiliary equip
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Chapter 9Piping design for indirect
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234 Piping design for indirect heat
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Chapter 10Boilers and firing equipm
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262 Boilers and firing equipmentcom
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264 Boilers and firing equipmentEss
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266 Boilers and firing equipment100
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268 Boilers and firing equipmentAs
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270 Boilers and firing equipmentFlu
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272 Boilers and firing equipmentFlo
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274 Boilers and firing equipmentFig
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276 Boilers and firing equipmentof
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278 Boilers and firing equipment. a
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280 Boilers and firing equipmentIt
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282 Boilers and firing equipmentFue
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284 Boilers and firing equipmentNoz
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286 Boilers and firing equipmentof
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288 Boilers and firing equipmentNea
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290 Boilers and firing equipmentpor
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292 Boilers and firing equipmentSaf
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294 Boilers and firing equipmentIgn
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Chapter 11Fuels, storage and handli
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298 Fuels, storage and handlingvehi
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300 Fuels, storage and handlingRese
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302 Fuels, storage and handlingtank
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304 Fuels, storage and handlingTank
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306 Fuels, storage and handlingabcd
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308 Fuels, storage and handlingTabl
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314 Fuels, storage and handlingstor
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318 Combustion and chimneysTable 12
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320 Combustion and chimneysTable 12
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322 Combustion and chimneysHence, b
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324 Combustion and chimneys. The te
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326 Combustion and chimneys. Draugh
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328 Combustion and chimneysClean Ai
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330 Combustion and chimneysMechanic
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332 Combustion and chimneysFire bri
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334 Combustion and chimneysMaterial
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336 Combustion and chimneysCombusti
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338 Combustion and chimneysFlueterm
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Chapter 13VentilationThe act or art
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342 VentilationTable 13.1 Ventilati
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344 Ventilationnormal circumstance
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346 Ventilationof air which could b
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348 Ventilationsimilar plant. This
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350 VentilationFlueCrackleaksInduce
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352 VentilationCapSuction bandLouvr
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354 VentilationTable 13.6 Air volum
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356 VentilationCowlBelt driveHinged
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358 VentilationTo fans at roof leve
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360 Ventilationboiler plant in wint
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Dining hall362 VentilationCafeteria
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364 Ventilationthis arrangement, as
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366 Ventilationbe noted that, as a
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368 VentilationTable 13.9 Air veloc
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370 Ventilationvelocity. An increas
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372 VentilationLastly under this he
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374 Air-conditioningBecause refurbi
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376 Air-conditioningThe installatio
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378 Air-conditioningThe type of sys
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380 Air-conditioningAn extension of
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382 Air-conditioningZone unitsSuppl
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384 Air-conditioningSupply airOptio
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386 Air-conditioningoutput of the c
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388 Air-conditioningDischargeto spa
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390 Air-conditioningAirdischargeExt
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392 Air-conditioningin the wall in
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394 Air-conditioningPrimaryair2 Pip
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396 Air-conditioningThe induction s
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398 Air-conditioningsensor as an en
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400 Air-conditioningfan-coil system
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402 Air-conditioningVariable refrig
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404 Air-conditioningChilled water P
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406 Air-conditioningAir supply to h
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408 Air-conditioningTable 14.1 Fact
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410 Air distributionUpward systemTh
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412 Air distributionInlet at 50ºCm
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414 Air distributionExtract airSupp
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416 Air distributioninlet is at a h
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418 Air distribution(a)(b)Figure 15
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420 Air distributionconnections to
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422 Air distributionOpposed bladesD
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424 Air distributionVelocity profil
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426 Air distributionAir supplyPerfo
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428 Air distributionair temperature
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430 Air distributionTable 15.4 Typi
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432 Air distributionFrameSpring cli
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434 Air distributionenergy consumpt
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Chapter 16Ductwork designHaving dec
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438 Ductwork designthe duct with no
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440 Ductwork designFlat ovalStandar
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442 Ductwork designconstruction met
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444 Ductwork designDuctlengthDDRDDu
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446 Ductwork design6mm Plate damper
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448 Ductwork design+Pressure0Veloci
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450 Ductwork designatmospheric pres
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452 Ductwork designTable 16.2 Corre
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454 Ductwork design. Any allowances
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456 Ductwork designBy these means,
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458 Ductwork designTable 16.7 Minim
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460 Ductwork designxAmplitudeyFigur
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462 Ductwork designNoise criteriaIt
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464 Ductwork designL w ˆ 10 ‡ 10
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466 Ductwork design3 64Plant527 8 3
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468 Ductwork designwhereD ˆ perime
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470 Ductwork designArrows show dire
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472 Ductwork designALNORAJAFLOW(a)(
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Chapter 17Fans and air treatment eq
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476 Fans and air treatment equipmen
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PressurePowerPowerPressure482 Fans
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Chapter 18Calculations for air-cond
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Figure 18.1 Psychrometric chart (as
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518 Calculations for air-conditioni
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20mFoyer520 Calculations for air-co
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Chapter 19Refrigeration: water chil
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Absolute pressure MPa532 Refrigerat
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534 Refrigeration: water chillers a
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564 Hot water supply systemsObvious
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566 Hot water supply systemswith a
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568 Hot water supply systemswhich i
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600m m M in570 Hot water supply sys
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572 Hot water supply systemsThe meg
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574 Hot water supply systemsVentDra
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576 Hot water supply systemsPrimary
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578 Hot water supply systemsCistern
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580 Hot water supply systemsFor use
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Page 601 and 602: 584 Hot water supply systemsThe hea
Page 603 and 604: 586 Hot water supply systemsTable 2
Page 605 and 606: 588 Hot water supply systemsStorage
Page 607 and 608: 590 Hot water supply systemsStorage
Page 609 and 610: 592 Hot water supply systemsadequat
Page 611 and 612: 594 Hot water supply systemsA compl
Page 613 and 614: 596 Hot water supply systemsInsulat
Page 615 and 616: Chapter 21Piping design for central
Page 617 and 618: 600 Piping design for central hot w
Page 629 and 630: Water flow rate in energy units kW/
Page 637 and 638: Chapter 22Automatic controls and bu
Page 639 and 640: 622 Automatic controls and building
Page 649: 632 Automatic controls and building
Page 677 and 678: 660 Running costsPence per kWh4.03.
Page 679 and 680: 662 Running costsAfter allowance ha
Page 681 and 682: 664 Running costsTable 23.3 Part L
Page 683 and 684: 666 Running costsTable 23.4 Degree-
Page 685 and 686: 668 Running costsTable 23.5 Approxi
Page 687 and 688: 670 Running costsaddition, consider
Page 689 and 690: 672 Running costsRunning hours for
Page 691 and 692: 674 Running costs20%. The variables
Page 693 and 694: Air temperature (ºC)Mass flow rate
Page 695 and 696: 678 Running costsEnergy auditsAn en
Page 697 and 698: 680 Running costs. Preventative. Pl
Page 699 and 700: 682 Running costsTable 23.14 Econom
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3Oil consumption(litre / month x 10
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686 Running costsTable 23.15 Presen
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Chapter 24Combined heat and power (
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690 Combined heat and power (CHP)Fi
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698 Combined heat and power (CHP)to
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700 Combined heat and power (CHP)we
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Appendix ITemperature levelsDegrees
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Appendix IIIConversion factorsImper
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708 IndexAuxiliaryequipment (costs)
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710 Indexdegree-hour 676heat pumps
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712 Indexcleaning 489±93, 489±93d
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714 IndexIndirect hot water supplys
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716 IndexPharmaceuticalcleanrooms 4
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718 IndexSol-air temperatures 12sol
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720 Indexextract grilles 430±1indu
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