Heating Systems, Plant and Control

Contents
1 Introduction1
1.1Heating: the fundamental building service1
1.2Low-pressure hot water1
1.3The need for ef?cient heating systems2
1.4Scope of the book3
1.5Content of the book: an overview37

PART AHEAT GENERATION
2 Boilers and Burners9
2.1De?nition of a boiler9
2.2Principal functional elements of a boiler9
2.2.1Gas-?red boilers9
2.2.2Oil-?red boilers10
2.2.3Solid fuel boilers12
2.3The boiler block12
2.3.1Function of the boiler block12
2.3.2Configuration and design12
2.3.3The multi-pass principle15
2.3.4Water content and temperature differential16
2.3.5Wet-base and dry-base types18
2.4The burner18
2.4.1Function of the burner18
2.4.2Boiler fuels and the combustion process18
2.4.3Burner design23
2.4.4Atmospheric natural gas burners25
2.4.5Fan-assisted and forced-draught natural gas burners29
2.4.6Premix natural gas burners32
2.4.7Other natural gas burners34
2.4.8Burners for other gases34
2.4.9Pressure-jet oil burners36
2.4.10Other atomizing oil burners38
2.4.11Dual-fuel burners39
2.5Burner operation and control39
2.5.1Functions of burner control39
2.5.2Modes of control for burner output40
2.5.3On/off control of burner output40
2.5.4High/low/off control of burner output42
2.5.5Modulating control of burner output45
2.5.6Control of burner safety46
2.6The burner gas line47
2.7The boiler control system49
2.7.1Boiler controls and system controls49
2.7.2Control of the burner50
2.7.3Boiler safety and limit controls52
2.7.4Reporting functions: remote monitoring54
2.8The boiler casing55



3Types of Boiler and Their Needs56
3.1Types of boiler56
3.2Boiler construction materials56
3.2.1Range of materials56
3.2.2Cast-iron56
3.2.3Steel57
3.2.4Copper and aluminium58
3.3Methods of construction59
3.3.1Cast-iron sectional boilers59
3.3.2Fabricated steel boilers61
3.3.3Copper boilers65
3.4Fire-tube and water-tube boilers67
3.5Modular boiler installations67
3.5.1Types of modular boiler installation67
3.5.2Modular boiler systems67
3.5.3True modular boilers69
3.6Heating, hot water service and combined applications72
3.7Condensing operation73
3.7.1Principles and bene?ts73
3.7.2Requirements of condensing operation78
3.7.3Condensing boilers79
3.7.4Condensing economisers84
3.8Boiler ef?ciency87
3.8.1Choosing the correct de?nition87
3.8.2Basis of the de?nition87
3.8.3Gross and net calori?c value88
3.8.4Overall ef?ciency89
3.8.5Combustion ef?ciency90
3.8.6Seasonal ef?ciency91
3.9Carbon intensity92
3.10The needs of the boiler installation93
3.11Hydraulic stability93
3.12Return water temperature94
3.13Pressure in the boiler circuit94
3.14Fuel supply96
3.14.1Natural gas96
3.14.2LPG99
3.14.3Oil100
3.15Ventilation of the boiler plant room105
3.16Water treatment108
4 Alternative Means of Heat Generation113
4.1Scope of the alternatives113
4.2Combined heat and power units113
4.2.1The concept113
4.2.2Application to building services114
4.2.3Principal elements of a small-scale packaged
CHP unit114
4.2.4Typical energy balance for a small-scale  packaged CHP unit116
4.2.5Fuels for CHP117
4.2.6The economic case119
4.2.7The CHP unit as part of a boiler installation122
4.3Heat pumps126
4.3.1Principle of operation126
4.3.2Heat sources126
4.3.3Coef?cient of performance128
4.3.4Refrigerants129
4.3.5Application to LPHW heating systems130
4.3.6Cost and environmental performance133
4.4Energy crops and bio-diesel135
4.5Waste as a fuel136

5 Flueing137
5.1Purpose of the ?ue137
5.2Flue and chimney137
5.3Types of ?ue138
5.4Flue draught138
5.5Natural-draught ?ues144
5.6Mechanical-draught ?ues144
5.7Balanced ?ues149
5.8Flue dilution systems153
5.9Sizing of the ?ue156
5.10General design and construction of the ?ue159
5.11Flues for condensing boilers161

PART BSYSTEMS AND CONTROL 163
6 Room Heat Emitters165
6.1Introduction165
6.2General description of heat emitter types165
6.2.1Natural convectors165
6.2.2Fan convectors167
6.2.3Radiators168
6.2.4Radiant panels170
6.2.5Heated ?oors171
6.3Typical heat output rates172
6.3.1Natural convectors173
6.3.2Fan convectors174
6.3.3Radiators and radiant panels175
6.3.4Heated ?oors177
6.4Effect on thermal comfort177
6.5Heat loss rate and energy consumption178
6.6Safety issues181
6.7Controlling heat output rate181
6.7.1Modulation of water ?ow rate181
6.7.2Flow temperature modulation182
6.7.3Combined ?ow rate and temperature modulation183
6.8Under?oor heating183
6.8.1Upward heat ?ow183
6.8.2Downward heat ?ow184
6.8.3Thermal capacitance184
Appendix 6.1Thermal Comfort186
Appendix 6.2Emitter Heat Output Rate Analysis189

7Heating Circuits195
7.1Choice of ?ow and return water temperatures195
7.2Insulation of pipework196
7.2.1Economic insulation thickness197
7.2.2Environmental considerations198
7.2.3Other considerations198
7.3Pipework arrangements199
7.3.1Secondary circuit200
7.3.2Compensated temperature circuit201
7.4Variable volume ?ow201
7.4.1Variable volume pumping203
7.4.2Variable speed drives204
7.4.3Control of variable speed pumps205
7.5Control valves209
7.5.1Valve inherent characteristic211
7.5.2Installed characteristic212
7.5.3Recommended valve authorities213
7.6Forces acting on pipework213
7.6.1Types of support215
7.6.2Spacing of supports215
7.6.3Expansion and contraction216
7.6.4Forces arising from the ?uid218
Appendix 7.1Heat Loss from Pipework220
Appendix 7.2Idealised Pump Characteristics223
Appendix 7.3Forces Due to Fluid Flow225

8 Hot Water Services227
8.1Instantaneous versus storage227
8.2Central versus local systems228
8.3Sizing229
8.3.1Peak instantaneous demand229
8.3.2Time-averaged demand231
8.3.3CIBSE sizing charts for storage systems232
8.4Systems233
8.4.1Domestic storage systems233
8.4.2Non-domestic storage system235
8.4.3Unvented systems237
8.4.4Pumped storage237
8.4.5Hot water generators238
8.4.6Instantaneous239
8.5Solar hot water239
8.5.1Integration with HWS system239
8.5.2Ef?ciency and output of panel240
8.5.3Sizing of the system242
8.6Legionella242
Appendix 8.1Solar Panel Ef?ciency244

9 Sizing Central Boiler Plant247
9.1Design heat output247
9.2Traditional sizing approaches249
9.2.1CIBSE guidance249
9.2.2Plant size and intermittent operation250
9.2.3An economic approach to sizing255
9.3Optimum start control261
9.3.1Optimum start and compensator interaction265
9.3.2Optimum stop265

10 Matching Output to Demand267
10.1Relationship between heating demand, system sizing  and boiler capacity267
10.1.1Boiler ef?ciency267
10.1.2System seasonal ef?ciency269
10.2Designing the central plant arrangement269
10.2.1Plant con?guration270
10.3System con?guration272
10.3.1Weather compensation control272
10.3.2Calculating room and emitter temperatures  for practical schedules274
10.3.3The implications of compensator control for  the central plant278
10.4Primary ring main279
10.5Controlling boiler output280
10.5.1Temperature sensing281
10.5.2Single boiler with ?ow sensing281
10.5.3Multiple units with common header284
10.5.4Sequencing285
10.5.5Common ?ow temperature control286
10.5.6Temperature dilution effects287
10.5.7Flow prevention through un?red boilers287
10.5.8Injection systems288
10.5.9Large systems with cascade control or heat  metering289
10.5.10Heat metering290
10.5.11High/low ?ring291
10.5.12Multiple units with modulating burners291
10.5.13Condensing boilers292
10.5.14Anti-cycling and add-on devices292

11Energy Consumption of Heating Systems295
11.1Degree-day based estimates295
11.1.1Calculating degree-days297
11.1.2Calculation errors298
11.1.3Base temperature correction300
11.1.4Application of degree-days300
11.1.5Uncertainty304
11.2Monitoring and targeting of existing systems307
11.2.1Performance lines307
11.2.2Scatter in the performance line308
11.2.3Applying the performance line309
11.2.4Base temperature and the performance line309
11.3Benchmarking311
11.4Normalisation312
11.5Minimising energy use in heating systems313
11.5.1Design313
11.5.2Hot Water Services (HWS)314
11.5.3Management314
Index316















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