Presents Practical Fundamentals of Heating, Ventilation and Air Conditioning (HVAC) for Engineers and Technicians Revision 11.2 Website: www.idc-online.com E-mail: idc@idc-online.com
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Contents 1 Introduction to HVAC 1 1.1 General 1 1.2 Principles of thermodynamics 2 1.3 Temperature and its measurement 6 1.4 Pressure and temperature relationship 7 1.5 Laws of thermodynamics 7 1.6 Fundamentals of heat transfer 8 1.7 Fundamentals of fluid flow 11 2 Psychrometry 17 2.1 Introduction to psychrometry 17 2.2 The properties of air 17 2.3 Understanding the psychrometric charts 26 2.4 Psychrometric processes 32 2.5 Air conditioning systems-summer and winter 40 3 Requirements of Comfort air conditioning 49 3.1 General 49 3.2 Air purification methods 52 3.3 Thermodynamics of the human body 53 3.4 Role of clothing 54 3.5 Comfort and comfort chart 56 3.6 Design considerations 60 3.7 Requirements of temperature and humidity-high heat load industries 61 3.8 Recommended inside design conditions 61 3.9 Outside summer design conditions for some foreign cities 63 3.10 Types of Ventilation Systems 65 3.11 Effect of vertical temperature gradient & corrective measures 71 3.12 Factors considered in air distribution systems indoor 73 3.13 Indoor Air Quality 75 3.14 Design of ventilation systems 84
4 Heating & Cooling Load Calculation Procedure 105 4.1 General 105 4.2 Definitions 106 4.3 Design considerations 106 4.4 Internal Sensible and Latent Heat Load components 107 4.5 Design condition - indoor & outdoor conditions 108 4.6 External Load components 109 4.7 Miscellaneous heat sources 117 4.8 Fresh air load 118 4.9 Design of air-conditioning system 119 4.10 By-pass factor (bf) consideration 124 5 HVAC Systems 129 5.1 Heating systems 129 5.2 Warm air heating systems 130 5.3 Sizing heating systems 134 5.4 Hot water heating system 134 5.5 Steam heating systems 137 5.6 Electric heating systems 138 5.7 District heating system 139 5.8 Warm air curtains 140 5.9 Air-conditioning systems: General 144 5.10 Air Handling Units 161 5.11 Functional variations in the design 164 5.12 Fan coil unit 178 5.13 Capacity calculation of an air handling unit 180 6 Variable air volume (VAV) systems 185 6.1 General 185 6.2 System concept 185 6.3 Different VAV systems 187 7 Duct design, air flow and its distribution 195 7.1 Air flow and pressure losses 195 7.2 Dynamic losses in ducts 198 7.3 Duct design 201 7.4 Duct arrangement systems 203 7.5 Air distribution system inside space 206 7.6 Ventilation systems 210 7.7 Effect of vertical temperature gradient and corrective measures 212
8 Insulation of Air-conditioning systems 219 8.1 Introduction 219 8.2 Desired properties of an ideal insulating material 219 8.3 Factors affecting thermal conductivity 221 8.4 Types of insulation materials 222 8.5 Heat transfer through insulation 226 8.6 Economical thickness of insulation 226 8.7 Insulated systems 227 8.8 Importance of relative humidity for the selection of insulation 230 9 Air-conditioning equipment 233 9.1 Air filters 233 9.2 Humidifiers 243 9.3 Dehumidifiers 249 9.4 Fans and blowers 254 9.5 Grills and registers 260 10 Refrigeration 263 10.1 General 263 10.2 Methods of refrigeration 263 10.3 Air refrigeration system 269 10.4 Vapor compression refrigeration system 272 10.5 Absorption refrigeration system 274 10.6 Refrigerants 279 10.7 Refrigerant nomenclature 284 10.8 Important refrigerants 285 10.9 Refrigeration equipment 289 11 Controls and Instrumentation 309 11.1 Objectives 309 11.2 Introduction 309 11.3 Definitions 310 11.4 Elements of control 313 11.5 Types of control system 322 11.6 Methods of control 325 11.7 Selection of a control system 330 11.8 Typical control systems 331 11.9 Control specifications 335 11.10 Conclusion 336
12 Installation, Commissioning, Operation, Testing & Maintenance 337 12.1 Objectives 337 12.2 Installation 337 12.3 Charging the refrigeration unit 338 12.4 Adding oil to the compressor 340 12.5 Commissioning 340 12.6 Other service operations 346 12.7 Operational activities 349 12.8 Do s and don ts 352 12.9 Maintenance 353 12.10 Economics 359 13 Fault finding and troubleshooting 363 13.1 Objectives 363 13.2 Introduction 363 13.3 Faults 363 13.4 Troubleshooting 366 14 Green House effect and future refrigerants 373 14.1 Objectives 373 14.2 General 373 14.3 The greenhouse effect 374 14.4 History of CFCs 377 14.5 Ozone depletion by CFCs and the greenhouse effect 378 14.6 Global warming potential (GWP) and Ozone depleting potential(odp) 379 14.7 Montreal protocol (1987) 381 14.8 Kyoto protocol 382 14.9 Future refrigerants to replace CFCs 383 Appendices 389 Appendix A: Symbols and units used in psychometric tables 389 Appendix B: Properties of refrigerants 397 Appendix C: Practical exercises 405 Appendix D: Equations 425 Appendix E: Testing, Adjusting and Balancing in HVAC systems 485 Appendix F: Conversion Tables 501 Appendix C1: Practical Exercises-Supplement 507 Appendix C2: Practical Exercises-Supplement-Psychrometric Chart Plotting 587
1 Introduction Objectives 1.1 General After reading this chapter the student should be able to: Refresh his knowledge on the engineering basics Understand the laws of thermodynamics Air conditioning for human comfort was considered a luxury a few decades ago, but now it has become a necessity in life. The air conditioning industry is rapidly developing throughout the world. More than 10 million window installations are being installed each year and residential central cooling installations are enjoying similar popularity. Apart from reasons for comfort alone, air conditioning is commonly used nowadays in various industries such as food, automobiles, hotels, textiles and many more. On Earth, not only pollution from smoke is on the rise but pollution from dust is also playing havoc with our lives. Air conditioning plays a vital role in keeping out smoke and dust which could harm our health. Similarly, air conditioning has an important role to play in the preservation of food. At present, there is hardly any sector of the economy that is not dependent on this industry. In fact in most areas of industry, HVAC systems are considered to be a basic necessity. It is thus important to become part of this industry and this course is targeted at providing you with the basic knowledge and technology to play a role in designing, installing and commissioning HVAC systems. The following gives an overview of the basic principles of thermodynamics, which play a key role in understanding HVAC systems.
2 Practical Fundamentals of Heating, Ventilation & Air-conditioning (HVAC) For Engineers and Technicians 1.2 Principles of Thermodynamics 1.2.1 Force, Newtons In simple language, force is defined as a push or a pull. It is anything that has a tendency to set a body into motion, to bring a body to rest or change the direction of any motion. 1.2.2 Pressure, Pascals Pressure is the force exerted per unit area. It may be described as the measure of intensity of a force exerted on any given point on the contact surface. Whenever a force is evenly distributed over a given area the pressure at any point on the surface is the same. It can be calculated by dividing the total force exerted by the area (on which the force is exerted). Atmospheric pressure The Earth is surrounded by an envelope of air called the atmosphere, which extends upward from the surface of the earth. Air has mass and due to gravity exerts a force called weight. The force per unit area is called pressure. This pressure exerted on the Earth s surface is known as atmospheric pressure. Gauge pressure Most pressure measuring instruments measure the difference between the pressure of a fluid and the atmospheric pressure. This is referred to as gauge pressure. Absolute pressure Absolute pressure is the sum of gauge pressure and atmospheric pressure. Vacuum If the pressure is lower than the atmospheric pressure, its gauge pressure is negative and the term vacuum is applied to the magnitude of the gauge pressure when the absolute pressure is zero (i.e. there is no air present whatsoever). The relationships among absolute pressure, gauge pressure, atmospheric pressure and vacuum are shown graphically in the Figure 1.1.
Introduction 3 1.2.3 Density 1.2.4 Work 1.2.5 Energy Figure 1.1 Relationship between absolute, gauge and vacuum pressures In the above figure P a is the atmospheric pressure P gauge is the gauge pressure P ab is the absolute pressure P vacuum is the vacuum pressure It is defined as the mass of a substance divided by its volume or the mass per unit volume. ρ = mass/volume Specific Volume is defined as the reciprocal of density or volume per unit mass. v = V/m Specific Weight (Ws) is defined as the weight of a substance divided by its volume or the weight per unit volume. Ws = m/v If a system undergoes a displacement under the action of a force, work is said to be done; the amount of work being equal to the product of force and the component of displacement parallel to the force. If a system as a whole exerts a force on its surrounding and a displacement takes place, the work that is done either by or on the system is said to be external work. A body is said to possess energy when it is capable of doing work. In more general terms, energy is the capacity of a body for producing an effect. Energy is classified as