Modern Refrigeration and

1
Modern Refrigeration and Air Conditioning
Althouse Turnquist Bracciano
PowerPoint Presentation by Associated
Technical Authors
PublisherThe Goodheart-Willcox Company,
Inc.Tinley Park, Illinois
2
Chapter 3
Basic Refrigeration Systems
3
Learning Objectives
? Explain the operation of a simple ice
refrigerator. ? Explain how evaporation provides
a cooling effect. ? Name the basic mechanical
refrigeration systems. ? Explain various
applications for mechanical refrigeration
systems. ? Describe the operation of various
mechanical refrigeration systems.
4
Learning Objectives

• Compare compression- and absorption-type systems.
• Discuss refrigeration systems using icemakers and
  water coolers.
• Explain how a system using an expendable-type of
  refrigerant works.
• Discuss and compare domestic and commercial
  refrigeration systems.

5
Learning Objectives

• Explain the operation of thermoelectric
  refrigeration.
• Compare the differences between hot-gas and
  electric defrost systems.

6
Ice Refrigeration
3.1

• Consists of an insulated cabinet with tray at top
  to hold ice.
• Food located below ice compartment.
• Cold air flows downward, cooling the food.
• Maintains a fairly high humidity level.
• Temperatures range between 40F and 50F (4.4C
  and 10C).

7
Ice Refrigeration
3.1
8
Evaporative Refrigeration(Desert Bag)
3.2

• Moisture on surface of the bag evaporates
  rapidly.
• Heat that causes the evaporation comes from the
  desert bag and its water.
• This heat removal cools the drinking water.

9
Evaporative Refrigeration(Snow Making)
3.3

• Water flows from nozzle.
• Air under high pressure breaks water into tiny
  droplets.
• Surrounding temperature near or below freezing.
• Water droplets evaporate and rapidly cool.
• Ice is formed.

10
Low-Side FloatRefrigerant Control
3.4

• Pressure on low side of flooded system will vary
  with temperature.

11
Low-Side FloatRefrigerant Control
3.4
Note the float needle, low-side float, and
pressure motor control.
12
External-Drive(Open) Refrigeration System
3.5

• Compressor usually belt-driven from an electric
  motor.
• Compressor must have crankshaft seal to avoid
  refrigerant flowing out or air flowing in.

13
External-Drive(Open) Refrigeration System
3.5
14
High-Side Float(Flooded) System
3.6

• Capillary tube refrigerant line frequently used
  in conjunction with the high-side float system.
• Frequently specified in commercial applications
  where high operating efficiency is desired.
• Easy to service.
• Charge must be accurately measured.
• This is a critically charged system.

15
High-Side Float(Flooded) System
3.6
16
Questions

• What is the temperature range for ice
  refrigeration?

40 to 50F.

• Would the humidity level of ice refrigeration be
  high or low?

High.

• What causes the cooling effect on a desert bag?

Evaporation.

• What are two important features used for snow
  making?

High-pressure air and freezing temperatures.
17
Questionscontinued

• What type of evaporator uses a low-side float?

A flooded evaporator.

• What is used to prevent refrigerant from escaping
  to the atmosphere on an open-type compressor?

A crankshaft seal.

• Which of the following is a critically charged
  system, high- side float or low-side float?

High-side float.
18
Compression System Using Automatic Expansion
Valve (AEV)
3.7

• The refrigerant can flow through the AEV only
  when the compressor runs and reduces evaporator
  pressure.
• Pressures do not balance on the off cycle.
• Motor compressor must start under load.
• Used widely in small commercial applications.
• Must be used with a temperature control.

19
Compression System Using Automatic Expansion
Valve (AEV)
3.7
20
Using Thermostatically ControlledExpansion Valve
(TEV)
3.8

• Operation of thermostatically controlled
  expansion valve (TEV) controlled by
• Temperature of TEV control bulb.
• Pressure in the evaporator.
• Spring pressure.
• Pressures do not balance on-off cycle, so
  compressor often starts under load.
• Used on large commercial refrigerators as well as
  in many air-conditioning applications.
• Can be controlled by pressure or temperature
  control.

21
Using Thermostatically Controlled Expansion Valve
(TEV)
3.8
22
Compression System Using Capillary Tube
3.9

• One of the most popular compression-type systems.
• Capillary tube maintains a pressure difference
  while compressor is operating.
• Must be operated by temperature control.
• Capillary tube allows high- and low-side
  pressures to balance during the off cycle.
• Used in refrigerators, freezers, air
  conditioners, and dehumidifiers.

23
Compression System Using Capillary Tube
3.9
24
Multiple Evaporator Systems
3.10

• One condenser connected to two or more
  evaporators.
• Two-temperature valve located in suction line of
  warmer evaporator.
• Check valve located in suction line of colder
  evaporator.
• Sight glass often included in liquid line.
• Pressure motor control operates as a safety
  device.
• Commonly used in commercial refrigeration
  applications.

25
Multiple Evaporator Systems
3.10
26
Questions

• Which type of motor control is used with an AEV?

Temperature control.

• Which pressures control a TEV?

Bulb, evaporator, and spring.

• Does the compressor on a TEV system start under a
  load?

Yes.

• Which type of motor control can be used on a TEV
  system?

Pressure or temperature control.
27
Questionscontinued

• What type of motor control can be used on a
  capillary tube system?

Temperature control.

• In a multiple evaporator system, where would the
  two- temperature valve be located?

At the outlet of the warmer evaporator.

• In a multiple evaporator system, where would a
  check valve be located?

At the outlet of the colder evaporator.
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Compound Refrigerating System
3.11

• Consists of two or more compressors connected in
  series.
• Usually requires an oil separator for each
  compressor to increase system capacity during low
  temperatures.
• A single-temperature motor control operates all
  motors.
• A TEV controls liquid refrigerant flow into
  evaporator.
• Pressures do not balance on the off cycle. Motors
  must start under load.
• Requires heavy maintenance.

29
Compound Refrigerating System
3.11
30
Cascade Refrigerating Systems
3.12

• Two refrigeration systems connected in series.
• Both systems operate at the same time.
• Each system has a TEV.
• One motor control is used.
• Motors must be capable of starting under load,
  since pressures do not balance on-off cycle.

31
Cascade Refrigerating Systemscontinued
3.12

• Condenser-evaporator is usually of shell-and-tube
  flooded evaporator type.
• Refrigerant must be very dry.
• Often used in industrial process where objects
  must be cooled below 50F (46C).
• One condenser gives up heat to the others
  evaporator.

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Cascade Refrigerating Systems
3.12
33
ModulatingRefrigeration Cycle
3.13

• Matches machine capacity to needed heat load.
• May use two or more compressors connected in
  parallel.
• Each compressor is operated by a pressure-type
  motor control.
• Commonly uses TEV.
• Same evaporator is connected to all the
  compressors.

34
ModulatingRefrigeration Cycle
3.13
35
Ice Maker
3.14

• Motor compressor and condenser usually located in
  bottom of cabinet.
• Note the accumulator, ice cube mold, and electric
  defrost.
• Most surfaces in contact with water and ice are
  stainless steel.

36
Drinking Water Cooler
3.15

• Uses a hermetic (airtight) compression
  refrigerating system.
• Uses a capillary tube system.
• Water pressure regulator adjusts the water flow.
• Condensing unit is air-cooled.
• Condenser fan increases capacity.
• Thermostat maintains desired water temperature
  approximately 50F (10C).

37
Drinking Water Cooler
3.15
Note water heat exchanger.
38
Questions

• In a compound refrigeration system, are the
  compressors connected in series or in parallel?

In series.

• In a compound refrigeration system, do the
  pressures balance during the off cycle?

No.

• On a cascade refrigeration system, how are the
  two systems connected, in series or in parallel?

In series.

• What are the operating temperatures of a cascade
  refrigeration system?

Below 50F.
39
Questionscontinued

• Are the compressors of a modulating refrigeration
  system connected in series or in parallel?

Parallel.

• From which material is the evaporator of an ice
  machine most commonly made?

Stainless steel.

• What is the desired water temperature of a water
  cooler?

Approximately 50F.
40
Expendable Refrigerant Refrigeration System
3.16

• Often called a chemical refrigeration or
  open-cycle refrigeration system.
• Used on trucks or other vehicles to transport or
  store refrigerated or frozen foods.
• Consists of a heavily insulated space cooled by
  liquid nitrogen.
• The system discards the refrigerant after it has
  evaporated.
• Excellent for shipping frozen foods, since it
  maintains 20F (29C) temperature.

41
Expendable Refrigerant Refrigeration System
3.16
Note temperature-sensing element, control
box, and liquid control valve.
42
Thermoelectric Refrigeration
3.17

• Transfers energy from one place to another using
  electrons, rather than refrigerants.
• A thermoelectric couple moves heat from the
  inside of an insulated space to a heat exchanger.
• Electrons carry the heat.
• Fins on the evaporator increase heat flow. Fins
  on the heat exchanger give off heat to the
  surrounding air.
• Contains no moving parts.
• Thermal efficiency is low.

43
Thermoelectric Refrigeration
3.17
This system uses a simple thermoelectric couple.
44
Thermoelectric Refrigerationcontinued
3.17

• Semiconductors are of two types.
• N-type semiconductors conduct electricity by flow
  of negatively charged particles (usually
  electrons).
• P-type semiconductors conduct electricity by the
  flow of positively charged particles (often
  called holes or electron holes).
• Several N-P paired junctions are connected in
  series to produce significant cooling.
• Often used in electronic equipment (computers,
  aerospace devices, etc.).

45
Thermoelectric Refrigerationcontinued
3.17
46
Dry Ice Refrigeration
3.18

• Dry ice is solid carbon dioxide.
• Dry ice changes from solid directly to vapor
  through sublimation.
• Dry ice is packed beside or on top of food.
• Carbon dioxide, as it changes to a vapor, keeps
  the food frozen.
• Safety Note Never handle dry ice with bare
  hands. It will cause instant freeze burns. Always
  wear heavy gloves.

47
Dry Ice Refrigeration
3.18
48
Intermittent Absorption System
3.19

• Uses a generator charged with water and ammonia.
• Heat source (usually a kerosene flame) heats
  solution in generator.
• Piping is welded steel, due to high pressures on
  the generating cycle.
• Intermittent absorption systems are popular in
  areas where electric power is not available.

49
Intermittent Absorption System
3.19
50
Continuous-CycleAbsorption System
3.20

• Operated by limited amount of heat furnished by
  gas, electricity, or kerosene.
• No moving parts are employed.
• Operation based on Daltons Law.
• Consists of four main parts boiler, condenser,
  evaporator, and absorber.
• Unit charge consists of quantity of ammonia,
  water, and hydrogen.
• Widely used in domestic refrigerators and
  recreational vehicles.

51
Continuous-CycleAbsorption System
3.20
52
Solid Absorbent Refrigeration
3.21

• Based on the principle of an experiment done by
  Michael Faraday.

53
Solid Absorbent Refrigeration
3.21
54
SophisticatedCommercial Systems
3.22

• Various conditions and refrigeration requirements
  require accessory (add-on) devices.
• Accessory devices can make systems safer and more
  efficient.

55
SophisticatedCommercial Systems
3.22
Note the pressure regulator, vibration damper,
crankcase heater, filter-drier, suction service
valve, crankcase heater, oil separator, liquid
desuperheater valve, and defrost control device.
56
Hot-Gas DefrostDuring Refrigerating Cycle
3.23

• Timing mechanism directs hot high-pressure vapor
  through the evaporator to remove frost and ice.

57
Hot-Gas DefrostDuring Refrigerating Cycle
3.23
Note Solenoid valve No. 1 is open during
refrigerating cycle.
58
Hot-Gas DefrostDuring Defrost Cycle
3.23

• Solenoid valve No. 1 is closed no liquid
  refrigerant is flowing through the TEV into the
  evaporator.
• Solenoid valve No. 2 is open hot compressed
  refrigerant vapor flows through it directly into
  the evaporator.
• As the hot vapor passes through the evaporator,
  it melts ice from the evaporator surface.

59
Electric Defrost Duringthe Refrigerating Cycle
3.24
Note Refrigerant flow and electric heating
elements alongside the evaporator surface are
green.
60
Electric Defrost Duringthe Defrost Cycle
3.24
Note Refrigerating unit is not running. There is
no flow. Note Resistance heating elements are
shown in red alongside the evaporator surface.
61
Questions

• What is another name for an open cycle
  refrigeration system?

Expendable refrigeration system.

• How is heat transferred in a thermoelectric
  refrigeration system?

By electrons.

• Name two types of semiconductors that are
  commonly used in thermoelectric refrigeration
  systems.

N type and P type.

• What is sublimation?

A process in which a substance changes from a
solid directly to a vapor, skipping the liquid
state.
62
Questionscontinued

• From which substance is dry ice made?

Carbon dioxide.

• In an intermittent absorption system, what is the
  generator commonly charged with?

Ammonia and water.

• On which law is the operation of a continuous
  cycle absorption system based?

Daltons law.

• What controls the hot gas that flows to
  evaporator during a hot gas defrost cycle?

A solenoid valve.
63
Safety

• Wear goggles and gloves at all times, especially
  when charging or discharging refrigerant.
• R-717 (ammonia) is very irritating to the eyes
  and lungs. Avoid exposure to it.
• Dry ice will cause instant freeze burns. Never
  handle it with bare hands.

64
Glossary

• capillary tube
• Control system in which pressure difference is
  maintained through the use of a thin tube.
• continuous-cycle absorption system
• System that has a continuous flow of energy
  input.
• dry ice refrigeration
• Use of a refrigerating substance made of solid
  carbon dioxide, which changes directly from a
  solid to a gas (sublimates). Its subliming
  temperature is 109F (78C).
• Faraday, Michael
• Scientist who found that silver chloride absorbs
  ammonia when cool and releases it when heated.
  This is the basis on which some absorption
  refrigerators operate.

65
Glossary

• intermittent absorption system
• Refrigerant system using a kerosene burner and
  ammonia, used in situations where gas and
  electricity are not available.
• modulating refrigeration cycle
• Refrigerating system of variable capacity.
• pressure motor control
• Device that opens and closes an electrical
  circuit as pressures change.
• semiconductors
• A class of solids whose ability to conduct
  electricity lies between that of a conductor and
  an insulator.

66
Glossary

• sublimation
• Condition in which a substance changes from a
  solid to a gas without becoming a liquid.
• thermoelectric refrigeration
• Direct current flowing through an electrical
  junction between unlike metals produces heating
  or cooling effect, depending on direction of
  current flow.
• thermostatically controlled expansion valve (TEV)
• Control valve operated by temperature and
  pressure within evaporator. It controls flow of
  refrigerant. Control bulb is attached to outlet
  of evaporator.