Refrigeration and Air Conditioning

Prepared By :MR. ABHISHEK SINGH

Heat Pump and Refrigerator PrincipleHeat Pump: Device that absorbs

heat from cold body and delivers it to hot body

Refrigerator: Device that absorbs heat from cold body and delivers it to surroundings.

Refrigerator DefinitionDevice used to maintain low

temperature below atmospheric temperature within required space.

‘Method of reducing the temperature of a system below surrounding temperature and maintains it at lower temperature by continuously abstracting heat from it.’

ApplicationsStorage and transportation of

food.Preservation of medicine and

syrups.Manufacturing of ice,

photographic films.Liquefaction of gases like N, O, HComfort

Properties of RefrigerantHigh latent heat of evaporation

and low specific volume.Good thermal conductivity for

rapid heat transfer.Non-toxic, non-flammable, non-

corrosive.Low saturation pressure.High COP.Economical

RefrigerantsMedium to absorb and reject

heat from required space and to the surrounding respectively.

A kind of working fluid for refrigeration cycle.

Refrigerants UsedNH3: Highly toxic flammable, good

thermal properties, highest refrigerating effect. Used for industrial and commercial refrigeration system like in ice plants, cold storage units.

Co2: Color-less, non-toxic, non-flammable and non-corrosive. Used in marine refrigeration.

Air: Economical, non-toxic, low COP. Used in air craft refrigeration.

Refrigerants Used R11/Trichloro-monofluro methane/Freon-

11: non-toxic, non-flammable. Used in office building air conditioning.

R12/Dichloro-difluro methane/Freon-12: non-toxic, non-flammable, non-corrosive, high COP. Used in domestic refrigeration. (VCRS)

R22/Monochloro-Trifluro methane/Freon-13: non-toxic, non-flammable, non-explosive, less compressor displacement. Used in commercial and industrial applications.

Unit of refrigerationOne ton of refrigeration is

defined as “Refrigerating effect produced by melting of 1 ton of ice from and at zero degree C in 24 hours”

“Amount of heat required to removed in order to form one ton of ice in 24 hours from water at Zero degree C”

Coefficient of Performance (COP)It is defined as Ratio of

refrigerating effect to the work done by compressor to compress the refrigerant in the compressor.

Inverse of efficiency of heat engine.

Its value is always greater than unity.

Types of RefrigeratorsNatural Refrigeration: In natural

refrigeration, cooling effect produced by evaporation of liquid or sublimation of solids.

Mechanical Refrigeration: Refrigeration effect is produced by external mechanical energy or heat energy source.

Types of Mechanical Refrigators:Air RefrigeratorVapour Absorption Refrigerator (VAR)Vapour Compression Refrigerator (VCR)

Vapour Compression Refrigerator (VCR)•It Uses vapour as a refrigerant which condenses and evaporates alternatively.•In evaporation it absorbs latent heat from the space to be cooled while in condensation, it rejects heat to atmosphere.

P-V and T-S Diagram for VCR

Functions of Various components of VCRCompressor: To remove vapour from

evaporator and increase the pressure and temperature, to be condensed in condenser.

Condenser: Surface for heat transfer from hot refrigerant vapour to condensing medium.

Expansion valve: To provide the proper amount of liquid refrigerant and reduces pressure of liquid refrigerant entering the evaporator.

Evaporator: To provide a heat transfer medium through which low temperature liquid refrigerant can absorb heat from the space to be cooled.

Domestic vapour Compression refrigerator:•Consists of and evaporator installed in freezing compartment.•One end of evaporator is connected to suction side of the compressor and other to the condenser through the throttle valve.•Delivery side is connected to condenser.•It is usually specified in terms of liters.

Vapour Absorption Refrigeration • In VAR refrigerant from evaporator is

absorbed in absorber.• Ammonia is generally used as

refrigerant due to its property of being absorbed easily by water at low pressure and temperature, and at high temperature its solubility in water is reduced.

• So when heated it gets separated from water.

• Water acts as an absorbent.

Vapour Absorption refrigerationLow pressure T and P vapour ammonia from evaporator enters absorber where it is absorbed by weak solution coming from generator through throttle valve.During absorption process, heat is released and rejected to cooling water. This solution is pumped back into generator, where it is heated and h3 separates from water and this water flows back into absorber where it is cooled by and external cooling source.

Air refrigeration (Bell Coleman Cycle)Process 1-2: Air fromcold storage enters aircompressor, due to which its pressure and temperatureincreases.Process 2–3: Hot airis cooled and temp. isreduced.

Air refrigeration (Bell Coleman Cycle)Process 3-4: Air is expanded isentropically, as a result T and P reduces and work is obtained.Process 4-1: From expander air passes through cold storagewhere heat is remove and again cycle is repeated.

P-V & T-S Diagrams

Advantages of Air refrigeration1. Free availability of air2. Weight of air refrigerator per ton

is low, so this can be used in air crafts and missiles cooling.

Disadvantages of Air refrigeration1. Very low COP2. Large power requirement3. More space4. Volume of air to be circulated is

more compared to other refrigerators. This sets the limitation of its usage to small capacity plants.

Characteristic Comparison

Air ConditioningAir conditioning is simultaneous

control of temperature, air humidity, air movement and air cleanliness.

Major Applications of AC: A) For human comfort B) For commercial use (industrial

air conditioning)

ComfortingTemperature and humidity that is

soothing for human life is called comforting of humans, and as listed below:

1. DBT 17 to 25 degrees2. RH 30 to 70%3. 0.1 to 0.25m/s air velocity

PrincipleAir conditioning device draws air

from the space to be cooled, cools it down and rejects back into the same cooling space.

Continuous circulation of air maintains the required low temperature in the room.

Components and functions of AC unit 1. Fan: air circulation2. Filters: cleanliness3. Heating system: heat of air

(Winter AC)4. Control System: automatic

temperature control5. Grille: Direction of flow air6. Tray: storage of condensed

water.7. Refrigerating plant: Cooling

effect.

Classification

Arrangement Purpose

Unitary Central Comfort

Industry

Arrangement

Winter AC

Summer AC

Window ACTwo major units1. Refrigeration Unit: evaporator,

condenser, compressor, expansion valve

2. Air circulation fan

Window AC Working

SPLIT ACWindow AC is split into two

halves1. Placed inside the room (Usually

wall mounted), includes evaporator, filter, grille.

2. Placed outside the room and includes condenser fan, compressor and condenser.

SPLIT AC

Advantages of SPLIT AC over Window ACNo noise.No window space required.Aesthetic view.