ASHNuN. Fundamentals of HVAC Control Systems. Robert McDowell and Ross Montgomery are the authors of the

Transcription

1 Fundamentals of HVAC Control Systems Robert McDowell and Ross Montgomery are the authors of the 2009 edition of Fundamentals of HVAC Control Systems. This book is a revision of an earlier edition authored by Steven T. Taylor in ASHNuN 1791 Tullie Circle NE, Atlanta, GA 30329, USA

2 1 Introduction to HVAC Control Systems Why Do We Need Controls? A Brief History of Controls Control Loops Control Modes 9 Twoposition Control 10 Floating Control 14 Modulating Control 15 Pulsewidth Modulating, and Timeproportioning Control Gains and Loop Tuning Control Actions and Normal Position Control Range, and Sequencing Controls Documentation, Maintenance, and Operations 28 The Next Step 29 2 Basics of Electricity Simple Circuits and Ohm's Law AC Circuits Transformers and Power Services Relays Motors and Motor Starters Variable Speed Drives Relay Logic and Ladder Diagrams 54 The Next Step 60 3 Control Valves and Dampers 61 Introduction Twoway Control Valves 62 Styles and Principles of Operation Threeway Control Valves Selecting and Sizing Valves 76 Flow Characteristic Selection 81 Closeoff Pressure Control Dampers 87 Styles and Principles of Operation 87

3 Selfpowered vi 3.5 Selecting and Sizing Dampers 91 Twoposition Duty 91 Capacity Control Duty 92 Mixing Duty 98 The Next Step Sensors and Auxiliary Devices Introduction to Terms 107 Accuracy 107 Range 107 Reliability 108 Repeatability, Precision 108 Transmitter Temperature Sensors 109 Bimetal 109 Fluid Expansion 111 Electrical, Selfpowered 113 Electrical Resistance Humidity and the Psychrometric Chart 118 Indoor Air is a Mixture of Dry Air and Water Vapor 118 Relative Humidity Moisture Sensors 128 Relative Humidity Sensors Pressure Sensors Flow Sensors and Meters Auxiliary Devices 148 The Next Step Self and Systempowered Controls Principles of Operation Controls Examples of Selfpowered Controls 161 Thermopile Controls 161 Hot Water Control Valve 162 Selfpowered VAV Diffuser Systempowered Controls 164 Systempowered Air Valves 164 Systempowered Water System Valves 165 The Next Step Electric Controls Sensors Controllers, Twoposition Controllers, Modulating Example Application Actuators Auxiliary Devices 178 The Next Step 179

4 Direct Monitoring vii 7 Pneumatic Controls Principles of Operation Sensors Controllers Actuators Auxiliary Devices Compressed Air Supply Example Applications 198 The Next Step Analog Electronic Controls Principles of Operation Sensors Controllers Actuators Auxiliary Devices Example Applications 212 The Next Step Control Diagrams and Sequences Control Systems Design Criteria Control Systems Design Process Control Diagrams and Symbols Control Sequences Example Applications 222 Typical SingleZone System 222 Typical Constant Air Volume System with Face and Bypass Dampers 226 Typical Constant Air Volume System with Multiple Zones or Reheat 227 Typical Variable Air Volume System 227 Typical Constant Air Volume System, with Variable Speed Fan for Filter Loading 237 Chiller Plant, Pumps, and Boilers and Control 239 Temperature and Humidity Monitoring and Control 240 Carbon Dioxide Control 241 Exhaust Fan Control 242 Fume Hood Control 243 Condensate Management and Control 245 Ventilation Monitoring and Control 245 Filtration Monitoring and Control 246 Outside Air Monitoring and Control 246 DX Expansion Systems 246 Water Source Heat Pumps 247

5 To Making Transporting viii 10 DDC Introduction to Hardware and Software Introduction, and Input and Output Points I/O Point Characteristics Control Sequences Software Introduction Specific Programming System Features and Parameters Operator Terminal DDC Networks and Controls Protocols Interoperability System Hardware Architecture 288 Sample Controllers Network Standards 296 Ethernet (IEEE 802.3) 298 ARCNET 299 RS Wireless BACnet 301 What is a PICS? Devices Groups of Objects to Manage Activity Objects 3 Services 4 Network Represent Information 304 and Responding to Requests 305 Request and Responses Lon Works 308 The Next Step Digital Controls Specification Benefits and Challenges of DDC Design Bidding and Interoperability Monitoring Wiring 330 Network Wiring 330 Fiber Optic Cable 333 Power Wiring Commissioning and Warranty Resources 336 Index 339