Commercial Refrigeration: For Air Conditioning Technicians 2nd Edition

405 Pages·2016·22.5 MB·English

by  Dick Wirz

Commercial
Refrigeration
for
Air Conditioning
Technicians
This page intentionally left blank
Commercial
Refrigeration
for
Air Conditioning
Technicians
Second Edition
Dick Wirz
Australia • Brazil • Japan • Korea • Mexico • Singapore • Spain • United Kingdom • United States
Commercial Refrigeration for Air © 2010, 2006 Delmar, Cengage Learning
Conditioning Technicians, Second Edition
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Dick Wirz
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Printed in Canada
1 2 3 4 5 6 7 12 11 10 09
Contents
xv
PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Refrigeration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
CHAPTER 1
Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Temperature Ranges of Refrigeration . . . . . . . . . . . . . . . . . . 2
The Refrigeration Cycle. . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Low-Pressure Side of the System . . . . . . . . . . . . . . . . . . . . . . . . 3
How Is Heat Absorbed into the Evaporator? . . . . . . . . . . . . . . . . 3
How Does the Condenser Get Rid of the Heat
Absorbed by the Evaporator? . . . . . . . . . . . . . . . . . . . . . . . . 4
Comparing Commercial Refrigeration with AC. . . . . . . . . . . . . 4
Newer Refrigerants in Commercial Refrigeration. . . . . . . . . . . 6
The Four Basic Components of a Refrigeration System. . . . . . . 7
Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Condenser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Compressor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Metering Device. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Evaporators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
CHAPTER 2
Functions of the Evaporator. . . . . . . . . . . . . . . . . . . . . . . . .14
Evaporator Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Temperature Difference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Humidity and TD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Air Conditioning TD and Humidity. . . . . . . . . . . . . . . . . . . . . . 16
Walk-in TD and Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Reach-in TD and Humidity . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
Using TROT for TD and Troubleshooting . . . . . . . . . . . . . . . . . . 17
Heat Exchange Effi ciency . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Types of Evaporators . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Evaporator Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Measuring Superheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Flooding and Starving Evaporators. . . . . . . . . . . . . . . . . . . . . . 23
Hot Pull-Down. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
Evaporator Problems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
vi Contents
Medium-Temperature Evaporator Air Defrost. . . . . . . . . . . . . . . 24
When to Defrost . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
Defrost Operation of Freezers . . . . . . . . . . . . . . . . . . . . . . . . . 27
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
Condensers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
CHAPTER 3
Functions of the Condenser . . . . . . . . . . . . . . . . . . . . . . . . .42
Condenser Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Three Phases of the Condenser. . . . . . . . . . . . . . . . . . . . . . .43
De-superheat Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Condensing Phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
Subcooling Phase. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Flash Gas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Using Subcooling to Prevent Flash Gas. . . . . . . . . . . . . . . . . . . 44
Condenser Split . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46
Cleaning and Maintaining Air-Cooled Condensers . . . . . . . . . .47
Coil Cleaners. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
Maintenance Inspections . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
Low-Ambient Controls for Air-Cooled Condensers. . . . . . . . . . .49
Fan Cycle Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
Fan Speed Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Air Dampers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51
Condenser Flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Troubleshooting HPR Valves . . . . . . . . . . . . . . . . . . . . . . . . . . 53
Floating Head Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Water-Cooled Condensers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
Water-Regulating Valves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55
Cooling Towers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
Wastewater Systems. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
Service and Maintenance of Water-Cooled Equipment. . . . . . . . . 57
Proper Operating Conditions of a Water-Cooled Unit
on a Wastewater System. . . . . . . . . . . . . . . . . . . . . . . . . . . 59
Cleaning Water-Cooled Condensers . . . . . . . . . . . . . . . . . . . .59
Microchannel Technology . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Contents vii
Compressors. . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
CHAPTER 4
Functions of a Compressor. . . . . . . . . . . . . . . . . . . . . . . . . .68
How a Reciprocating Compressor Operates. . . . . . . . . . . . . . . . . 68
Hermetic Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70
Semihermetic Compressors . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
Compressor Lubrication . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Compressor Problems and Failures . . . . . . . . . . . . . . . . . . . . . . 73
Slugging. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
Diagnostic Chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
Compressor Capacity Control. . . . . . . . . . . . . . . . . . . . . . . . . . 79
Low-Temperature Applications. . . . . . . . . . . . . . . . . . . . . . . . . 86
Two-Stage Compound Systems. . . . . . . . . . . . . . . . . . . . . . . . . 86
Scroll Compressors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90
Variable Frequency Drives. . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
Metering Devices. . . . . . . . . . . . . . . . . . . . . . . . .99
CHAPTER 5
Functions of a Metering Device . . . . . . . . . . . . . . . . . . . . .100
Superheat. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .102
What Is the Proper Superheat? . . . . . . . . . . . . . . . . . . . . . . . 102
How a TEV Operates. . . . . . . . . . . . . . . . . . . . . . . . . . . . .104
TEV Body Styles. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
Equalized Valves, Internal and External. . . . . . . . . . . . . . . .106
Adjusting Superheat. . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
TEV Bulb Placement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .108
How the System Affects TEVs. . . . . . . . . . . . . . . . . . . . . . .111
TEV Sizing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112
Reading an Expansion Valve . . . . . . . . . . . . . . . . . . . . . . .114
Troubleshooting TEVs . . . . . . . . . . . . . . . . . . . . . . . . . . . .115
Flooding. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Starving. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
TEV Hunting. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115
Balanced Port Expansion Valves. . . . . . . . . . . . . . . . . . . . . . . 116
Capillary Tube Metering Devices. . . . . . . . . . . . . . . . . . . . .116
viii Contents
How a Cap Tube Works . . . . . . . . . . . . . . . . . . . . . . . . . . .118
How Cap Tubes Respond to System Conditions. . . . . . . . . . . . . 120
Troubleshooting Cap Tubes . . . . . . . . . . . . . . . . . . . . . . . .121
Automatic Expansion Valves . . . . . . . . . . . . . . . . . . . . . . .122
Electric Expansion Valves . . . . . . . . . . . . . . . . . . . . . . . . .123
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127
Controls and Accessories. . . . . . . . . . . . . . . . .133
CHAPTER 6
Temperature Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . .134
Compressor Service Valves. . . . . . . . . . . . . . . . . . . . . . . . .138
Solenoid Valves for Pump-down and Hot Gas Bypass . . . . . . .141
Hot Gas Bypass Valves . . . . . . . . . . . . . . . . . . . . . . . . . . .143
Crankcase Pressure Regulators. . . . . . . . . . . . . . . . . . . . . .144
Evaporator Pressure Regulators . . . . . . . . . . . . . . . . . . . . .146
Low-Pressure Controls. . . . . . . . . . . . . . . . . . . . . . . . . . . .148
High-Pressure Controls . . . . . . . . . . . . . . . . . . . . . . . . . . .150
Oil Separators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .151
Oil Safety Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .152
Receivers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156
Accumulators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
Filter Driers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .157
Sight Glass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .160
Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .161
Vibration Eliminator. . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .162
Refrigeration System Troubleshooting . . . . . .169
CHAPTER 7
Review and Preview . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170
Evaporator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Compressor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
Condenser. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
Metering Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173
How Fixed Metering Devices React to System
Conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .173
How a TEV System Reacts to System Conditions . . . . . . . . . .175
Contents ix
Summary of How External Temperature Changes
Affect the Refrigeration System . . . . . . . . . . . . . . . . .176
Summary of How Pressure Changes Affect the
Refrigeration System. . . . . . . . . . . . . . . . . . . . . . . . .177
Superheat and Subcooling. . . . . . . . . . . . . . . . . . . . . . . . .177
Diagnosing Nine System Problems . . . . . . . . . . . . . . . . . . .178
Undercharge of Refrigerant . . . . . . . . . . . . . . . . . . . . . . . .180
How an Undercharge Affects a Reach-in with
Cap Tube System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180
How an Undercharge Affects a TEV System . . . . . . . . . . . . . . . 181
Overcharge of Refrigerant . . . . . . . . . . . . . . . . . . . . . . . . .182
How an Overcharge Affects a Cap Tube System . . . . . . . . . . . . 182
How an Overcharge Affects a TEV System . . . . . . . . . . . . . . . . 183
Condenser Airfl ow Problems. . . . . . . . . . . . . . . . . . . . . . . .184
Condenser Problems on a Cap Tube System . . . . . . . . . . . . . . . 184
Condenser Problems on a TEV System. . . . . . . . . . . . . . . . . . . 184
Noncondensables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .186
Ineffi cient Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . .188
Restricted Metering Device. . . . . . . . . . . . . . . . . . . . . . . . .190
Partially Restricted Capillary Tube. . . . . . . . . . . . . . . . . . . . . 190
Partially Restricted TEV . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
Restriction in the Liquid Line after the Receiver. . . . . . . . . .192
Restriction in the High Side Before the Receiver . . . . . . . . . .192
Dirty Evaporator, Iced Evaporator, or Low Airfl ow. . . . . . . . .193
Evaporator Problems on a Cap Tube System. . . . . . . . . . . . . . . 193
Evaporator Problems on a TEV System . . . . . . . . . . . . . . . . . . 194
Getting the Right Information . . . . . . . . . . . . . . . . . . . . . .195
Using a Diagnostic Chart. . . . . . . . . . . . . . . . . . . . . . . . . .195
Evaporator Oil Logging. . . . . . . . . . . . . . . . . . . . . . . . . . .198
Troubleshooting without Gauges . . . . . . . . . . . . . . . . . . . . . . 199
Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .201
Compressor Motor Controls. . . . . . . . . . . . . . .211
CHAPTER 8
Three-Phase Motors . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212
Contactors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .212
Motor Starters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214
Single-Phase Motors. . . . . . . . . . . . . . . . . . . . . . . . . . . . .214