Transcript Student CD for Commercial Refrigeration for Technicians

Student CD for
Commercial Refrigeration for A/C Technicians
Chapter 1
Refrigeration Principles
Chapter 1 Overview
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•
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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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2
Common Space & Product Temperatures
•
•
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Air Conditioning = 75°
High temperature refrigeration = 55°
Medium temperature refrigeration = 35°
Low temperature refrigeration = -10°
Extra low temperature refrigeration = -25°
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3
Simple A/C System
•
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
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4
Simple A/C System
AMBIENT AIR 95o
165o
RETURN AIR 75o
175o
60o
50o
40o
125o
125o
115o
40o
105o
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40o
5
Simple Medium Temperature
Refrigeration System
• 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?
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Simple Medium Temperature Refrigeration System
AMBIENT AIR 95o
165o
RETURN AIR 35o
175o
45o
35o
25o
125o
125o
115o
25o
105o
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25o
7
“Standard” A/C System
with fixed metering device
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
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Standard A/C System R-22
175º
60º
40º
125º
CONDENSER
125º
EVAPORATOR
115º
40º
50º
AMBIENT AIR 95o
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RETURN AIR 75o
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Standard A/C System R-22
Total Superheat 20°
Super Heated Vapor
175º
60º
40º
125º
Evaporation Starts
CONDENSER
Condensing Starts
EVAPORATOR
125º
Fully Evaporated
Fully Condensed Liquid
Sub-Cooled Liquid
115º
Coil Superheat 10°
AMBIENT AIR 95o
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40º
50º
RETURN AIR 75o
10
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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Typical Walk-In Refrigerator (R22)
175º
45º
125º
25º
TEV
CONDENSER
125º
EVAPORATOR
115º
25º
35º
AMBIENT AIR 95o
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BOX TEMPERATURE 35
12
Total Superheat 20°
Typical Walk-In Refrigerator (R22)
Super Heated Vapor
175º
45º
25º
125º
TEV
Evaporation Starts
CONDENSER
Condensing Starts
EVAPORATOR
125º
Fully Evaporated
Fully Condensed Liquid
Sub-Cooled Liquid
115º
25º
Coil Superheat 10°
AMBIENT AIR 95o
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35º
BOX TEMPERATURE 35
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Current refrigerants used in most new
refrigeration systems
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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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14
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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15
Basic Components and Piping
Discharge Line
Compressor
Suction
Line
Condenser
Metering
Device
Liquid 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
“Baseball Diamond”
Metering
Device
Evaporator
Condenser
Compressor
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