1. Refrigeration & Air conditioning
Bangladesh University of Engineering and Technology (BUET)
ME 170: Fundamentals of Mechanical Engineering
(Model Lab)
Lecture 3
Refrigeration & Air conditioning
Md. Muntasir Alam
Lecturer
Department of Mechanical Engineering,
BUET, Dhaka-1000
address: ,
Md. Muntasir Alam (BUET)

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Refrigeration

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What is Refrigeration??
Refrigeration is the removal of heat from a material or space so that it’s temperature is lower than that of it’s surroundings.
Heat transfer from lower temperature to higher temperature.
But according to thermodynamics it is not possible until an extra work is done.

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How does it work??
High Temperature Reservoir
Low Temperature Reservoir R
Work Input
Heat Absorbed
Heat Rejected

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Applications
• Domestic Refrigeration
• Commercial Refrigeration
• Industrial Refrigeration
• Marine & Transportation Refrigeration
• Comfort Air Conditioning
• Industrial Air Conditioning

6. Domestic Refrigeration
Bangladesh University of Engineering and Technology (BUET)
Domestic Refrigeration

7. Commercial Refrigeration
Bangladesh University of Engineering and Technology (BUET)
Commercial Refrigeration

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Commercial Refrigeration
Meats, poultry and fish all must be kept in climate-controlled environments before being sold.

9. Industrial Refrigeration
Bangladesh University of Engineering and Technology (BUET)
Industrial Refrigeration

10. Cold storage: for Fruits, Vegetables, Fish, Meat etc.
Bangladesh University of Engineering and Technology (BUET)
Industrial Refrigeration
Cold storage: for Fruits, Vegetables, Fish, Meat etc.

11. Marine & Transportation Refrigeration
Bangladesh University of Engineering and Technology (BUET)
Marine & Transportation Refrigeration
In transportation temperature sensitive foodstuffs and other materials by trucks, trains, airplanes and sea going

12. Comfort Air-conditioning
Bangladesh University of Engineering and Technology (BUET)
Comfort Air-conditioning
Comfort air-conditioning is for human comfort.
It involves control of space temperature, humidity, ventilation and, air-motion and cleaning/filtering of air.

13. Industrial Air-conditioning
Bangladesh University of Engineering and Technology (BUET)
Industrial Air-conditioning
Air conditioning and dust removal of the machines is extremely important in the weaving mill.

14. Industrial Air-conditioning
Bangladesh University of Engineering and Technology (BUET)
Industrial Air-conditioning
Air conditioning and dust removal of the machines is extremely important in the weaving mill.

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Classifications
Based on Energy Input
Vapor-Compression Refrigeration System
Absorption Refrigeration System

16. Vapor-Compression Refrigeration Cycle
Bangladesh University of Engineering and Technology (BUET)
Vapor-Compression Refrigeration Cycle
Most common refrigeration cycle in use today
There are four principal control volumes involving these components:
Evaporator
Compressor
Condenser
Expansion valve
Two-phase
liquid-vapor mixture

17. The processes of this cycle are
Bangladesh University of Engineering and Technology (BUET)
Vapor-Compression Refrigeration Cycle
The processes of this cycle are
Process 4-1: two-phase liquid-vapor mixture of refrigerant is evaporated through heat transfer from the refrigerated space.
Process 1-2: vapor refrigerant is compressed to a relatively high temperature and pressure requiring work input.
Process 2-3: vapor refrigerant condenses to liquid through heat transfer to the cooler surroundings.
Process 3-4: liquid refrigerant expands to the evaporator pressure.
Two-phase
liquid-vapor mixture

18. Vapor-Compression Refrigeration Cycle
Bangladesh University of Engineering and Technology (BUET)
Vapor-Compression Refrigeration Cycle
Condenser
Evaporator
High Pressure Side
Low Pressure Side
Compressor
Expansion Valve 1 2 3 4

19. Key Components of a Refrigerator
Bangladesh University of Engineering and Technology (BUET)
Key Components of a Refrigerator
1.Evaporator
2.Suction line
3.Vapor compressor
4. Hot gas/discharge line
5.Condenser
6.Receiver tank
7.Liquid line
8.Refrigerant flow control device

20. Ideal Vapor-Compression Refrigeration Cycle
Bangladesh University of Engineering and Technology (BUET)
Ideal Vapor-Compression Refrigeration Cycle

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Ammonia-Water Absorption Refrigeration
Absorber
coolant
Absorption refrigeration systems have important commercial and industrial applications.
The principal components of an ammonia-water absorption system are shown in the figure.

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Ammonia-Water Absorption Refrigeration
The left-side of the schematic includes components familiar from the discussion of the vapor-compression system: evaporator, condenser, and expansion valve. Only ammonia flows through these components.
Absorber
coolant

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Ammonia-Water Absorption Refrigeration
The right-side of the schematic includes components that replace the compressor of the vapor-compression refrigeration system: absorber, pump, and generator. These components involve liquid ammonia-water solutions.
Absorber
coolant

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Ammonia-Water Absorption Refrigeration
A principal advantage of the absorption system is that – for comparable refrigeration duty – the pump work input required is much less than for the compressor of a vapor-compression system.
Absorber
coolant

25. Ammonia-Water Absorption Refrigeration
Bangladesh University of Engineering and Technology (BUET)
Ammonia-Water Absorption Refrigeration
Specifically, in the absorption system ammonia vapor coming from the evaporator is absorbed in liquid water to form a liquid ammonia-water solution.
The liquid solution is then pumped to the higher operating pressure. For the same pressure range, significantly less work is required to pump a liquid solution than to compress a vapor.
Absorber
coolant

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Ammonia-Water Absorption Refrigeration
However, since only ammonia vapor is allowed to enter the condenser, a means must be provided to retrieve ammonia vapor from the liquid solution.
This is accomplished by the generator using heat transfer from a relatively high-temperature source.
Absorber
coolant

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Ammonia-Water Absorption Refrigeration
Steam or waste heat that otherwise might go unused can be a cost-effective choice for the heat transfer to the generator.
Alternatively, the heat transfer can be provided by solar thermal energy, burning natural gas or other combustibles, and in other ways.
Absorber
coolant

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Refrigerant
Desirable properties:
High latent heat of vaporization - max cooling
Non-toxicity (no health hazard)
Desirable saturation temp (for operating pressure)
Chemical stability (non-flammable/non-explosive)
Ease of leak detection
Low cost
Readily available
Commonly use FREON (R-12, R-114, etc.)

29. Performance Parameter
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Performance Parameter

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Air Conditioning

31. Refrigeration system is at heart of AC system
Bangladesh University of Engineering and Technology (BUET)
Introduction to Air Conditioning
The process of controlling & maintaining the properties of air like temperature, humidity , purity , direction of flow etc. in a closed space.
Refrigeration system is at heart of AC system
HVAC = Heating, Ventilation and Air Conditioning
ASHRAE = American Society of Heating, Refrigerating, and Air-Conditioning Engineers

32. Factors Influencing Thermal Comfort
Bangladesh University of Engineering and Technology (BUET)
Factors Influencing Thermal Comfort

33. Basic Air Conditioning System
Bangladesh University of Engineering and Technology (BUET)
Basic Air Conditioning System

34. Basic Air Conditioning System
Bangladesh University of Engineering and Technology (BUET)
Basic Air Conditioning System

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HVAC Components

36. HVAC Components - Condenser
Bangladesh University of Engineering and Technology (BUET)
HVAC Components - Condenser
1 Expansion valve
2 Fan
3 Compressor
4 Heat exchange coils

37. HVAC Components – Air Handler
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HVAC Components – Air Handler 1 2
1 Heat exchange coils
2 Fan

38. HVAC Components – Duct System
Bangladesh University of Engineering and Technology (BUET)
HVAC Components – Duct System

39. HVAC Components – Duct System
Bangladesh University of Engineering and Technology (BUET)
HVAC Components – Duct System
Supply Ducts
Supply
Plenum
Air
Handler
Return Grille
Return
Plenum

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Typical HVAC System
Cooling coil
Heat transfer from air to refrigerant
Extended surface coil
Drain Pan
Removes moisture condensed from air stream
Condenser
Expansion valve

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Typical HVAC System
Heating coil
Heat transfer from refrigerant to air
Heat pump
Furnace
Boiler
Electric resistance

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Typical HVAC System
Blower
Overcome pressure drop of system
Adds heat to air stream
Makes noise
Potential hazard
Performs differently at different conditions (air flow and pressure drop)

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Typical HVAC System
Duct system (piping for hydronic systems)
Distribute conditioned air
Remove air from space
Provides ventilation
Makes noise
Affects comfort
Affects indoor air quality

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Typical HVAC System
Diffusers
Distribute conditioned air within room
Provides ventilation
Makes noise
Affects comfort
Affects indoor air quality

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Dampers
Change airflow amounts
Controls outside air fraction
Affects building security
Typical HVAC System

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Filter
Removes pollutants
Protects equipment
Imposes substantial pressure drop
Requires Maintenance
Typical HVAC System

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Controls
Makes everything work
Typical HVAC System
Temperature
Pressure (drop)
Air velocity
Volumetric flow
Relative humidity
Enthalpy
Electrical Current
Fault detection

48. Conventional Air Conditioning System
Bangladesh University of Engineering and Technology (BUET)
Conventional Air Conditioning System

49. Window type Air Conditioner
Bangladesh University of Engineering and Technology (BUET)
Window type Air Conditioner

50. 3 4 2 1 Outside Building Inside Building Anatomy of a Window type A/C
Bangladesh University of Engineering and Technology (BUET)
Anatomy of a Window type A/C
Outside
Building
Low pressure
Cold gas
Hot, high
Pressure gas
Hot, high
Pressure liquid 1 2 3 4
Inside
Building
Room Temp
Low Pressure gas

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Split System A/C
Condenser separates from the evaporator.
It enables to locate the condenser elsewhere.

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Enough for today.