chapter 01 - refrigeration principles.ppt
TRANSCRIPT
Student CD for Commercial Refrigeration for A/C Technicians
Chapter 1
Refrigeration Principles
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Chapter 1 Overview
• Temperature ranges of refrigeration• Refrigeration cycle• Relate refrigeration to air conditioning• Relationship between a refrigerant’s pressure
and its temperature• Newer refrigerants used in commercial
refrigeration systems• Relationship between the 4 basic components
of a refrigeration system
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Common Space & Product Temperatures
• Air Conditioning = 24° C
• High temperature refrigeration = 12°C
• Medium temperature refrigeration = 2°C
• Low temperature refrigeration = -23°C
• Extra low temperature refrigeration = -32°C
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• A compressor + two tanks + metering device is used to illustrate a simple A/C system:
– High pressure stays the same, but . . . • Refrigerant:
1. Temperatures drop as discharge gas cools
2. Condenses as heat is rejected
3. Sub-cools before entering the TEV
– Low pressure stays the same, but . . . • Refrigerant:
1. Temperatures rise as liquid vaporizes and absorbs heat in the evaporator
2. Then the vapor superheats after all refrigerant has evaporated
Simple A/C System
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165o
125o
125o
115o
50o
40o
RETURN AIR 75oAMBIENT AIR 95o278psig
69psig
Simple A/C System
105o 40o
40o
175o 60o
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• Compare the previous A/C system illustration to the following refrigeration system:– Are the high side pressures and temperatures of
both systems different? Why or why not?– Are the low side pressures and temperatures of
the two systems different? Why or why not?
Simple Medium Temperature Refrigeration System
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165o
125o
125o
115o
35o
25o
RETURN AIR 35oAMBIENT AIR 95o278psig
49psig
Simple Medium Temperature Refrigeration System
105o 25o
25o
175o 45o
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The following slide is an example of what happens to refrigerant in an A/C system:
• Compressor discharges hot gas
• Gas condenses to liquid, releasing heat
• Metering device lowers pressure
• Refrigerant vaporizes, absorbing heat
• Returns to the compressor
“Standard” A/C Systemwith fixed metering device
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AMBIENT AIR 95o
Standard A/C System R-22
RETURN AIR 75o
40º
40º
69psig
278psig
115º
50º
EVAPORATOR
CONDENSER
125º
125º
175º60º
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AMBIENT AIR 95o
Standard A/C System R-22
RETURN AIR 75o
40º
40º
69psig
278psig
115º
50º
EVAPORATOR
CONDENSER
125º
125º
175º
Condensing Starts
Sub-Cooled Liquid
Fully Condensed Liquid
Super Heated Vapor
Evaporation Starts
Coil Superheat 10°
60º
Total Superheat 20°
Fully Evaporated
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Commercial Refrigeration System with a TEV metering device
Comparing A/C to Refrigeration systems:
• Same ambient, same high side pressures and temperatures
• Lower space temperature, low side pressures and temperatures are lower than those on the A/C system
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AMBIENT AIR 95o
Typical Walk-In Refrigerator (R22)
BOX TEMPERATURE 35
25º
25º
50psig
280psig
115º
35º
EVAPORATOR
CONDENSER
125º
125º
175º45º
TEV
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AMBIENT AIR 95o
Typical Walk-In Refrigerator (R22)
BOX TEMPERATURE 35
25º
25º
50psig
280psig
115º
35º
EVAPORATOR
CONDENSER
125º
125º
175º45º
TEV
Condensing Starts
Sub-Cooled Liquid
Fully Condensed Liquid
Super Heated Vapor
Evaporation Starts
Coil Superheat 10°
Total Superheat 20°
Fully Evaporated
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Current refrigerants used in most new refrigeration systems
• Walk-in refrigerators – R22 and R404A• Walk- in freezers – R404A• Reach-in refrigerators – R22, R404A, 134a• Reach-in freezers – R404A• Note: after 2010, manufacturers will not be
allowed to produce equipment with R22• Note: R404A must be charged in a liquid
state
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The Four Basic Components of a Refrigeration System
1. Metering device• Lowers the refrigerant temperature below the space
temperature
2. Evaporator• Absorbs heat as refrigerant evaporates
3. Compressor• Increases the refrigerant temperature above the
ambient temperature
4. Condenser• Rejects heat from the refrigerant as vapor condenses
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Basic Components and Piping
Compressor
Metering Device
Condenser
Discharge Line
Liquid Line
Suction Line
Evaporator
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Refrigeration System“Baseball Diamond”
• The 4 components can be illustrated in the shape of a baseball diamond
• Half the system is high pressure
• Half the system is low pressure
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Basic Components
Low Side High S
ide
“Baseball Diamond”
Compressor
Metering Device
CondenserEvaporator
Disch
arge
LineSuction Line
Liquid Line
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