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Fundamentals of Refrigeration

Structure1.1 Introduction

1.2 Methods of Refrigeration

1.3 Ice refrigeration

1.4 Dry ice refrigeration

1.5 Air expansion refrigeration

1.6 Liquid gas refrigeration

1.7 Vapour compression refrigeration

Learning ObjectivitiesAfter studying this chapter, the student will be able to know,

• The various methods of refrigeration systems employed in Refrigerators and Air –Conditioners.

• How the artificial cooling is done by Ice Refrigeration.

• Why the Dry Ice refrigeration use for preservation of frozen food and ice creams in storage and transportation.

• Which Refrigeration system is used in Refrigerators and Air- Conditioners.

Mechanical Engineering Technician192

1.1 Introduction In olden days, natural ice was used for Refrigeration purposes which

was quite inconvenient and inadequate for large requirements. The differenttechniques are developed in last hundred years and now there are numerousapplications of refrigeration in our daily life as well as in many industries. Thedifferent types of the Refrigeration systems, some physical property of matteris used for producing cold.

Refrigeration is the process of removing heat from a space or substanceto reduce and maintain temperature lower than its surrounding. Before theadvent of mechanical refrigeration the natural phenomena was used produceand maintain a lower temperature in a space or product. The value of ice as apreservative was known and put to use thousands of years ago. Natural icefrom lakes and rivers was often cut during the winter and stored in saw dust-insulated buildings, and can be used as required. In the Middle east and Indiawater was cooled by evaporating it through porous clay pots. In favourableconditions it could be made cold enough to form ice.

The early machines the air system was probably the most successfuluntil the development of vapour compression and absorption system usingammonia as refrigerant. In 1859 ferdinand carre devised vapour absorptionsystem. And ammonia –water cyclel still used in absorption type domesticrefrigerators .Thomas Midgely and his associates Henne and McNarydiscovered dichlorodiflluoro methane, CCL2F2(Freon-12 which was) confirmedas super refrigerant with low –level of toxicity and non-flammable.

Principle of Refrigeration

Refrigeration is defined as the production of temperature lower thanthose of the surrounding and maintain the lower temperature within the boundaryof a given space. The effect has been accomplished by non cyclic processessuch as the melting of ice or sublimation of solid carbon dioxide . However,refrigeration effect is usually produced by transferring heat from a low temperaturesource to a high temperature source by spending mechanical work. To producethis effect requires certain machinery , hence, the method is called mechanicalrefrigeration. The working media of such machines are called refrigerants.

Classification of Refrigerators

Refrigeration implies the cooling of a system. It may be obtained byadopting the following methods.

1. Natural methods.

193Paper - III Refrigeration and Airconditioning

2. Artificial or mechanical methods

Mechanical refrigerators found wide industrial applications. They maybe further classified as

1. Air refrigerators

(a) Reversed carnot cycle

(b) Bell coleman cycle

2. Vapour refrigerators.

(a) Vapour compression refrigerator

(b) Vapour absorption refrigerator

1.2 Methods of Refrigeration The refrigeration effect may be produced by bringing the substance

to be cooled in direct or indirect contact with cooling medium such as ice. Thecommon methods of refrigeration are as follows.

1. Ice refrigeration

2. Dry Ice refrigeration

3. Air expansion Refrigeration

4. Evaporative refrigeration

5. Gas throttling refrigeration

6. Steam jet refrigeration

7. Liquid gas refrigeration

8. Vapour compression refrigeration

9. Vapour absorption refrigeration.

1.3 Ice RefrigerationThe ice refrigeration systems consists of an insulated cabinet equipped

with a tray or tank at the top, for holding blocks of ice pieces. Shelves for foodare located below the ice compartment. Cold air flows downward from icecompartment and cools the food on the shelves below. Air returns from thebottom of the cabinet up, the sides and back of the cabinet which is warmer,flows over the ice, and again flows down over the shelves to be cooled.

Refrigeration by ice is the most common form of artificial cooling. Inthis, the following methods are used


Direct method and Indirect method.

Direction Method : In the Direct method, the ice is kept in the samecompartment with the articles to be cooled . Ice is placed at elevated positionand cools the surrounding air. Cold air due to high density descends belowdisplacing warmer air towards the ice. In the storage space cold air is warmedby absorption of heat from the products to be cooled. And rises through thestorage space due to light density. It returns to the ice space. A circulation ofair is maintained so long as air cooled on ice space and the cycle is repeated.Direct method of ice refrigeration is shown in fig. This method is used in hotelsfor cooling the drinks.

Fig 1.1 Ice Refrigeration (Direct Method)

Indirect Method : In the indirect method, the ice is isolated from thestorage space and cooling of the articles is carried by circulation of brine. Theice is supplied to compartment D where it surrounds the vertical tubes containingbrine.

Fig 1.2 Indirect Refrigeration Method

IceIce Storage

Storage

Drip

A B C


Cold brine is circulated through the storage space A,B and C to coolthe articles, and finally the brine returns to ice compartment D. This cycle isrepeated.

This system is more suitable for large plants and no danger of foodinfection by impure ice.

1.4 Dry Ice Refrigeration

Dry ice is the solidified form of CO2. It evaporates directly fromsolid to vapour without liquid phase. This phenomena is called sublimation.In this, the dry ice in the form of flakes or slabs Is placed on the cartons containingfood stuffs. When dry ice sublimates, it will absorb heat from food stuff in thecartons and thus keeps them in a frozen condition. This is used for preservationof frozen foods and ice creams in storage and transportation. It has twice theheat absorbing capacity of ice refrigeration. However its cost is high.

1.5 Air Expansion Refrigeration

In this method, air is compressed to 5 bar and cooled down atconstant pressure. It is then expanded adiabatically to a pressure of 1 bar.This gives the maximum temperature reduction.

In a given pressure range, because work is done by expense of internalenergy which depends on the temperature. The cold air thus obtained iscirculated through the cold chamber to remove heat from the products storedin it.

Evaporative Refrigeration : In the evaporative refrigeration , waterevaporates by absorbing latent heat from the surrounding air. Thus the air iscooled, and circulated to the cold chambers.

Gas Throttling Refrigeration : In the gas throttling refrigerationprocess, there is no change in enthalpy and also for a perfect gas, there is nochange in temperature. However, for actual gases there is a substantial change,usually a decrease in temperature. This temperature drop depends upon theJoule- Thomas coefficient, the pressure drop, and the initial state of the gas.

High pressure gas is throttled through porous plug into the space tobe cooled and escapes outside after absorbing heat from the space. Thisproduces the refrigeration effect in the space or the product kept in the space.


The gas throttling refrigeration system is shown in Fig.

Fig 1.3 Gas Throttling Refrigeration

Steam – Jet Refrigeration : The steam – jet refrigeration is based onthe principle that the boiling point of water is lowered as the pressure isreduced. In this, water is a refrigerant and a steam ejector is used to lowerthe pressure and to reduce the boiling point of water. Water to be chilled isfilled in the flash chamber, steam generated in the boiler is expanded through anozzle and ejected out at high velocity. Due to this, low pressure is produced inflash chamber and water evaporates rapidly.

The steam ejector draws evaporated vapour from the chamber , andsends the fluid to condenser at a high velocity. The condensate is re circulatedto the boiler . The heat needed for the evaporation is taken from the water in thechamber. Thus its temperature is reduced. The cold water is circulatedthrough refrigerated space where it absorbs heat producing the refrigerationeffect. Water as refrigerant is very safe and widely used in air conditioningsystem.

1.6 Liquid gas Refrigeration In liquid gas refrigeration, liquid gas like nitrogen, which non-toxic is

used for producing refrigeration effect. It is filled in a well insulated cylinderwhich is connected to a pipe with intermittent perforations. Required quantityof liquid nitrogen is passed through the pie and sprayed through the perforationsinto the space to be cooled. The quantity of nitrogen is regulated by means ofvalve.

The temperature produced in the space may be -20C . Liquid gasvaporize after absorbing heat, and the gas is released to atmosphere. Thismethod is used for cooling fluids , vegetables, meat, fish and other food stuffs

Place to be cooled

High pressure gas

Porous plug


place in the cold storage. This type of cooling is also used in transportingvehicles carrying food stuffs.

1.7 Mechanical Refrigeration System or vapour Compression Refrigeration System.

Principle : The ability of a substance to change from a liquid to avapour under certain pressure and temperature conditions is physicalphenomenon called refrigeration cycle.In order for substance to boil fromliquid to a vapour or gas, it must absorb heat ; in the absorption of the heat ,thevaopourising substance cools the material, whether it be air or water fromwhich the heat is absorbed.

Components

Basic components parts of a mechanical refrigeration system are commonboth for refrigeration and air –conditioning systems. They are

1. Compression

2. Condersation

3. Expansion

4. Evaporation

Fig 1.4 Vapour Compression Refrigeration System

Compression : The low pressure vapour refrigerant in dry state is drawnfrom the evaporator during the suction stroke of the compressor. Duringcompression stroke pressure and temperature of the refrigerant increases.


Condensation : The high pressure and high temperature vapourrefrigerant enters in to the condenser through the discharge line . Heat will berejected in to the cooling medium and the refrigerant change its state from vapourto liquid.

Expansion

After condenser, the liquid refrigerant is stored in the liquid receiveruntil it passes through expansion valve. The function of the expansion is toallow the liquid refrigerant under controlled pressure in to the low pressure pathof the system.

Evaporation

The low pressure liquid refrigerant after expansion in the expansion deviceenters the Evaporator or Refrigerated space and absorbs its heat. Due to thisheat, the refrigerant changes its state from liquid to vapour and then suckedback by the compressor during its suction stroke .

The cycle is repeated till the required temperature gets inside therefrigerator.

Summary1. Refrigeration is the science of producing and maintaining

temperatures below that of the surrounding.

2. Vapour compression refrigeration system has four processes, they are,

1. Compression

2. Condensation

3. Expansion

4. Evaporation

Short Answer Type Questions1. Define refrigeration

2. What are the various method of Refrigeration ?

3. What is ice refrigeration ?

4. What is Dry ice refrigeration ?

5. What Air expansion refrigeration ?


6. What is liquid gas refrigeration ?

7. What is vapour compression refrigeration system ?

Long Answer Type Questions1. Explain Ice refrigeration

2. Write short notes on Dry Ice refrigeration

3. Write short notes on Air expansion refrigeration

4. Write short notes on Liquid gas refrigeration

5. Explain the Vapour compression refrigeration .


2UNIT

Refrigeration EquipmentStructure

2.1 Compressors

2.2 Condensers & cooling towers

2.3 Evaorators

2.4 Expansion devises

Learning ObjectivitiesAfter studying this chapter the student will be able to know

• The various types compressors employed in Refrigerators and Air- Conditioners.

• How the Condensers and cooling towers are working and where are they employed practically.

• Which type of Evaporators used in Refrigerators and Air-Conditioners and Industries.

• The various types of Expansion devices employed in House hold Refrigerators and Air-Conditioners

Basic Components of Vapour Compression Refrigeration System

Basic components parts of a mechanical refrigeration system arecommon both for refrigeration and air-conditioning systems. They are


1. Compressor

2. Condenser and Cooling tower

3. Expansion device

4. Evaporator or Freezer.

2.1 CompressorA compressor is that part in mechanical refrigeration system which

sucks the refrigerant vapours at low temperature and at low pressure andcompresses it to a lower volume at higher temperature and at higher pressure.Moreover , it creates the flow of refrigerant from one place to another.

A Compressor consists of an arrangement in which an electric motordrives it. The compressor is located near the condenser.

There are mainly two types of compressor are used . They are

1. Open type compressor

2. Semi-hermetically sealed ,

3. Hermetically sealed compressor.

2.1.1 Open type CompressorAn open type compressor is that in which the prime mover drives the

compressor by means of belt. In such a unit the prime mover and compressorare separately serviceable. In this, the compressor is enclosed in crank caseand crank shaft projects out through the compressor housing.

Fig 2.1 Open type Compressor

Base Plate

Compressor

MotorFan

Condenser


The projected end of crank shaft is connected directly or through thebelt to the driving motor. The compressor and motor can be mounted on thesame base plate. A seal must be used to prevent refrigerant leaking out orair from leaking in if the crank case pressure is lower than the atmosphericpressure. This is shown in Fig 2.1.

These compressors are used in the plants employed for ice making,cold storage and food processing applications.

2.1.2 Hermetically Sealed CompressorIn ordinary compressor the crank shaft extends through compressor

housing and it is connected to the driving motor . A seal must be provided at theplace where the shaft comes out through the compressor housing . This isnecessary to prevent the leakage of refrigerant outside or leakage of air inside.To avoid this problem , the compressor and motor are enclosed in one housingwhich known as Hermetically sealed compressor. These types of compressorsare normally used for small capacity Refrigerating systems as house holdRefrigerator or small capacity coolers. The main parts of a sealed unit are1. Electric motor, 2. Compressor, 3. Muffler, 4. Dome. The Hermetically sealedReciprocating compressor is shown in Fig 2.2.

Fig 2.2 Hermitically sealed Compressor

The advantages of hermetically sealed compressor s over ordinary typecompressors as follows,

1.The leakage of refrigerant is completely avoided

2. It is less noisy,

Oil

Motor

SuctionValves

Discharge

Motor


3.It requires less space.

4. The motor is cooled more efficiently

Disadvantages

1. Maintenance is not easy

2. The welded joints has to be broken or cut for reparing the compressor.

3. The pressure of moisture in the refrigerant may harm the winding of the motor.

4. A separate vaccum pump is required for evacuation and charging the refrigerant.

The motor and compressor assembly is mounted in the unit in such waythat usually the motor is fitted on the top and the compressor on the bottom.But at present in a specially designed sealed unit,for keeping the motor cool, it isdipped in to the oil and bottom of the compressor is fitted at the top.The oil isforced to the compressor, through the shaft of the motor. Some times the motorand compressor and assembly is hung on the springs in the unit and sometimesit is press fitted.

As the motor is energised, it drives the compressor. The compressorsucks the low temperature and low pressure gas, compresses it into hightemperature and high pressure gas and discharges it through the discharge line.

Some of the examples of refrigeration machines in which sealed unitsare used are

1. Refrigerator,

2. Bottle cooler,

3. Window-type Air conditioner,

4. Water cooler.


2.1.3 Difference Between open type Compressor and sealed unit Compressor Open type Compressor

1.Prime mover drives the compressor through v-belts.

2. Prime mover may be a Diesel engine , AC motor or DC motor

3. In case of ac single phase , split phase induction motor, for disconnecting starting winding a centrifugal switch is used.

4. Compressor and motor are generally mounted in vertical and horizontal positions respectively on the base.

5. Revolution per minute of the motor differ with the compressor.

6. Speed of the compressor can be adjusted.

7. Shaft seal is used for preventing the leakage around the shaft of the compressor.

8. Any type of refrigerant control device can be used.

9. Receive is used in the case.

10. Possibility of gas exists.

11. Dust and moisture can come in contact with it.

12. Occupies much space.

13. Used for domestic and commercial purposes.

14. Can be easily repaired.

Sealed unit Compressor

1.Electric motor and compressor aredirectly connected on the same shaftand enclosed in a welded dome.

2.Generally AC 50 cycles, single phasesplit –phase induction motor used.

3.In this case, a relay is used for thispurpose.

4. Motor and compressor assemblycan be mounted in any position butgenerally the motor remains on thetop

5. RPM is the same for motor andcompressor.

6. Speed of the compressor can notbe adjusted.

7. No shaft seal is used.

8. No service valve is used.

9. Capillary tube is used as a refrigerantcontrol device.

10. No receiver is used.

11. No possibility of gas leakage.

12. It is dust and moisture proof unit.

13. It occupies less space.

14. Used for domestic purposes.

15. Cannot be easily repaired.


2.2 CondenserA condenser is an heat exchanger in which heat transfer takes place

from high temperature vapour refrigerant to low temperature air or water whichis used as cooling medium. Its purpose is to covert all the vapour refrigerant toliquid refrigerant delivered by the compressor.

Types of Condenser

1. Air cooled condenser.

2. Water cooled condensers

3. Evaporative type condensers..

2.2.1 Air Cooled CondensersAir is used as the cooling medium in the air cooled condenser. Heat

transfer takes place air convection around the condenser surface. There aretwo types of air cooled condensers are used.

(a) Natural air cooled condensers (b) Forced air cooled condensers.

In the Natural air cooled condensers large condensing surface area isrequired as the circulated air quantity is less. This type of condensers are usedin domestic refrigerator, deep freezer , etc.,

These are cooled by natural air or atmospheric air. These are providedat the back of the refrigerator.

This is shown in Fig 2.3

Fig 2.3 Natural Convection Air Cooled Condenser

Hig

h Pr

essu

reH

igh

Tem

pera

ture

Refri

gera

nt

From Comp


In the case of Forced air cooled condensers , air is circulated by meansof a fan or blower. This type of condensers are compact in design and arerelatively more efficient. This is shown in Fig 2.4

Fig 2.4 Forced Convection Air Cooled Condenser

These are commonly used for water coolers, bottle coolers and airconditioners.

Merits of Air Cooled Condensers

1. Cheap due to simplicity of construction

2. Low maintenance cost.

3. No piping work involved.

4. Negligible corrosion effect.

5. Disposal of air is easier in comparison to disposal of water.

6. High flexibility.

Demerits of Air Cooled Condensers

1. It is restricted to small capacity refrigeration units.

2. Rate of heat transfer is low.

3. Distribution of air on the condenser surface area is uneven.

4. Increase in ambient temperature causes reduction in the capacity Of the condensers.

The air cooled condensers are preferred under the followingcircumstances

High press. Liquid Refrigerant

Receiver

Fan


Minimum corrosion is the major requirement.

Inadequate supply of cooling water

Expensive means of water disposal.

2.2.2 Water Cooled CondenserThe condenser which cooled by water, is called water cooled condenser.

These are always preferred where adequate supply of and inexpensive meansof water disposal are available. These condensers are used in large capacityrefrigerant plant such as, cold storage, ice plants and central air-conditioners.

There are three types of water cooled condenser

(a) Shell-and-tube condensers

(b) Shell and coil condensers

(c) Double pipe condensers.

Shell and Tube Condenser

A shell and tube condenser consists of a cylindrical shell, in which alarge number of parallel tubes are fitted and connected with tube sheets onboth ends of these tubes. These tubes are made of steel or copper tubes.These tubes are generally finned to increase their surface area. The diameter ofthese tubes are 19mm,25mm,30mm etc.. The lengths are in between 1.5 m and5.5m. These condensers have the capacity ranging from 2 ton to 1000 ton.Cooling water enters through the heads which are baffled to make one ormore passes through the tubes. Refrigerant vapour from the compressor entersshell at the top and gives its heat to cooling water. After the completion ofcondensation , the liquid refrigerant flows down and remain in the lower part ofthe shell. Which act as a liquid receiver. This is shown in Fig 2.5

Fig 2.5 Shell and Coil type Condenser

RemovableHead

Hot waterout

Cold waterout

Ref. liquid to exp.device Finned Tubes

Ref. Vapour fromcompressorShell


Fig 2.6

Shell and coil type condenser are used for small tonnage low pressureunits. It consists of shell that contains a coil for circulating the water . The shellends are not removable and the water side of the coil may ;be cleaned withchemicals. In case of a coil leakage the entire coil must be replaced. Theseare preferable where clean water is available because its coil cannot be cleanedeasily.

These can be cleaned only by circulating acids or other chemicalsthrough them. In this, the water enters at the bottom and flows up through coilas shown in fig. Vapour refrigerant from the compressor enters at the top andflows down, the shell giving its heat to cool water. Refrigerant vapour getscondensed and liquid refrigerant is collected at the bottom of the shell whichacts also as receiver. These are used upto 50 ton capacity plants. Shell and coiltype condenser is shown in Fig 2.6

Double tube type Condenser

A double type condenser has the condensing water tube in side therefrigerant tube. The refrigerant flows in the space between the tubes whilewater is pumped through inner tube. Water flows in the opposite direction tothe refrigerant. The refrigerant vapour from the compressor enters at the topand flows downwards in the clearance space between the two tubes. As resultof heat transfer from refrigerant to water, the refrigerant gets condensed. Theliquid refrigerant leaves the condenser at the bottom. The scales formed intubes are removed by chemical treatment.

Since copper tubes cannot be used with ammonia. These are madeof steel pipes for ammonia. This is shown in Fig 2.7

RefrigerantVapour fromCompressor

Condensedliquid

refrigerant

Water

Water


Fig 2.7 Double Tube type Condenser

These condensers are difficult to clean and do not provide enough spacefor separation of gas liquid. Its capacity is about 2.5 kw.

Evaporative Condenser

The Evaporative condenser combines the function of the condenserand cooling tower. Its works on the principle of Evaporative cooling. Thewater evaporation when it comes in contact with the refrigerant flowing in thecondensing coil. In this, both air and water are used as the cooling media.

The condensing coil are encased in galvanized steel cabinet. Water issprayed over the condensing coil through which hot refrigerant vapour flowing.A pump is utilized for this purpose. An exhaust fan is fitted at the top of thecondenser. It sucks air from side opening. Eliminators are provided in thecondenser to prevent the escaping of water particles with air.

The air carries away the heat taken from refrigerant by the water vapourat about 3 to 5% of water circulated evaporates, make up water is admitted totank through float operated valve. Water treatment should also be used toreduce the scale formation in the coil. The atmospheric air enters at the bottomand drawn over the coils by a fan. The air flowing up words through the waterspray carries out the heat from the refrigerant . It is shown in Fig 2.8

These are used where there is scarcity of water, draining facilities are inadequate. The use of cooling tower is un economical. It is suitable forrefrigerant plants above 100 ton capacity.

Refrigerant vapour from compressor

Liquid ref toreceiver

Water

Water


Fig 2.8 Evaporative Condenser

Difference Between Air Cooled and Water Cooled Condenser

2.2 A. Cooling TowerCooling tower is a device used to cool the hot water coming from the

water cooled condenser of large refrigerating machine.

Principle: The water goes in to the air in the form of vapour taking itslatent heat from the remaining and causes the reduction in temperature.

Air Cooled Condenser

1. Its construction is simple and cheap.

2. Maintenance cost is very low.

3. No problem of water and pipe.

4. Low heat transferring capacity.

5. Used for low capacity plants.

6. Air distribution is not uniform

7. No corrosion effect and fouling effect is low

8. High flexibility

Water Cooled Condenser

1. It construction is complicated andexpensive

2.Maintenance cost is high

3.Pipe is required to take water

4.High heat transfer capacity

5.Used for high capacity plants

6. Even distribution of water

7. Pipes corrode due to presence ofmoisture and more fouling effect

8.No flexibility

Exhaust FanAir out

Refrigerant vapourfrom comp

Liquid Refrigerant

Air in

Make up waterconnection

EliminatorHeader with spraynozzles

Pump


Classification of Cooling tower

According to the method of air circulating , cooling towers areclassified in to two main types

1. Natural draft cooling towers

2. Mechanical draft cooling tower

(a) Induced draft cooling tower

(b) Forced draft cooling tower

Natural draft Cooling tower

This is also called as open tower or atmosphere tower. This towercools water by moving air at low velocities through tower, so they are constructedin open places and cover large area.

In this the hot water of condenser is sprayed from the top of the towerand is cooled by the movement of natural air through it.

A natural cooling tower is metallic tank connected with water mainthrough float valve. On the bottom of the tank, a pipe connection is made to thecondenser water inlet through centrifugal pump. The condenser water outlet ispiped to the top of cooling tower , from where hot condenser water is sprayedthrough nozzles. This is shown in Fig. 2.9



Mechanical Draft Cooling Tower

Mechanical draft cooling tower is also called as closed type coolingtower. In this method, air is forced mechanically through the tower. Smalltowers may be located indoor and be constructed to a source of out door air.Large towers are located on the building roof.

These are mainly two types.

1. Forced draft cooling tower

2. Induced draft cooling tower.

Forced draft type Cooling Tower

The walls of this tower are totally enclosed by a wooden or metal shellfrom all four sides, air is sent down wards. This air is forced top to downwardswith force by a fan as shown in fig . Spray eliminator is used under the fan sothat air goes down after cleaning and it prevent excessive drift losses. Underthese are fixed spray nozzles through which water comes out in the form ofshower and becomes cool. The water is collected after getting cooled. This isshown in Fig 2.10



Induced Draft Cooling

In the Induced draft cooling tower a eliminator is provided at the topand the water falls down through nozzles. Fan is located at the bottom asshown in fig . As the water comes in the form of showers, it become cool dueto fan fixed at the bottom. This water sent into condenser through centrifugalpump so it may be reused.

Fig 2.11 Induced Draft Cooling

Difference between Natural Draft and Mechanical Dragt Cooling Tower

Natural Draft

1. Water is cooled by natural air

2. It sides are open

3. It can be installed where enough space and natural air is available.

4. It is cheap

5. It is less efficient.

6.It occupies large space.

Mechanical Draft

1. Water is cooled by a fan or blower

2. It sides are closed.

3. It can be installed any where.

4. It is expensive.

5. It is more efficient.

6. It occupies less space.

Drift eliminatorWater sprays

Hot gas fromrefrig machine

Condensed liquidto Refrig. machine

AirMake up

Air/Watervapour dirft

Circulating pump

Bleed off


2.3 Evaporataor The Evaporator is a device in which the heat is removed from the

substance to be cooled . It is part of the system in which the refrigerantevaporates or boils; It is the cooling unit and some times called the cooling coilOr freezing coil or liquid cooler .

Classification of Cooling Evaporator

There are many types of evaporators used in the refrigeration and Airconditioning systems;

They may be classified

1. According to the refrigerant feed

(a) Flooded evaporator

(b) Dry-Expansion evaporator

2. According to the type of construction

(a) Bare tube coil evaporator

(b) Finned tube evaporator

(c) Plate evaporator

(d) Shell and tube evaporator

(e) Shell and coil

(f) Tube- In-Tube evaporator or Double tube evaporator

3. According to the mode of heat transfer

(a) Natural convection evaporator

(b) Forced convection evaporator

4. According operative condition

(a) Frosting evaporator

(b) De-Frosting evaporator.

2.3.1 Dry –Expansion Evaporation In this, the liquid refrigerant is fed by expansion valve. The refrigerant

entered in to one end of the tube and the other end of tube is connected tosuction line. The evaporator is filled with mixture of liquid and vapour refrigerant.


As refrigerant passes through the evaporator, more and more liquid is vapourised.Thus, the refrigerant leaves the evaporator in dry state. A Feeder bulb is providedto control the flow of refrigerant in to the evaporator . It is shown in Fig 2.12

Fig 2.12 Dry - Expansion Evaporation

It is used in small capacity units of below 150 tons.

2.3.1 Flooded type Evaporator

In a Flooded type evaporator a constant refrigerant liquid level ismaintained. A float valve is used as throttling device which maintains a constantliquid levlel in the evaporator. It consists of a shell in to which the refrigerantliquid is fed through the float valve. The shell is connected to the top and bottomof the coil. The liquid flows from the bottom of the shell by gravity to coil tubesin which it evaporates by absorbing heat from the surrounding. The liquid vapourmixture from the coil returns to the shell. In the shell, the liquid and vapour areseparated. The vapour is collected at the top of the shell (Flash chamber) fromthere it enters into the compressor through suction line.

Flooded type evaporators provide rapid cooling and used in largecapacity equipment . It is shown in Fig 2.13

Fig 2.13 Flooded type Evaporator

Liq. Refrigerant fromreceiver

Ref. Control Evaporator Coil

Feeler Bulb

To Compressor

Flash ChamberLiq. Ref

Float control

Surge chamber

BufflesEvaporator coiltubes Liq. vapourrefrigerant


2.3.2 Bare tube EvaporatorBare tube evaporators are constructed of either steel pipe or copper

tubing. Steel pipe is used for large evaporators and copper tube is used forsmall evaporator. Using Freon as refrigerant these are also used with secondaryrefrigerant as in the case of water chiller and ice making plants. This is shown infig These are used where the temperature is maintained below 0C. The Baretube evaporator is shown in Fig 2.14

Fig 2.14 Bare tube Evaporator

2.3.3 Finned Tube EvaporatorFinned coils are bare tube coils upon which metal plates or fins are

installed. Fins increase the surface area of the evaporator and there by improveseffective cooling. The number of fins provided depends on the capacity ofevaporator. These evaporators are mostly used in Air-Conditioning system.This is shown in fig. 2.15

Fig 2.15 Finned Tube Evaporator

2.3.4 Plate Surface Evaporator

In this, the coils are welded together at the edges. It increases thesurface area of evaporator and hence, higher rate of heat transfer fromsurrounding to the refrigerant. It is easily clean and defrosted manually. It isused in domestic Refrigerator or Freezes. This is shown in Fig

Refrigerant IN

Refrigerant OUTAir


2.3.5 Shell and Tube EvaporatorShell and tube evaporator consists a steel cylindrical shell fitted with a

large number of parallel tubes. These are used for chilling water or brine. Theseare mainly two types

1. Flooded shell and tube type

2. Non-Flooded shell and tube type.

2.3.6 Flooded Shell and Tube EvaporatorIn flooded shell and tube type evaporators, the fluid to be cooled flows

through the tubes and refrigerant flows over the tubes. Liquid refrigerant absorbheat from water and evaporates completely. The dry refrigerant vapour issucked in the compressor. This is shown in Fig 2.16

These are used for refrigerating units of capacity at about 100 ton.

Fig 2.16 Flooded Shell and Tube Evaporator

2.3.7 Non - Flooded Shell and Tube type Evaporator

Fig 2.17 Non - Flooded Shell and Tube type Evaporator

Baffles

To compressor

Liquid refrigerant fromcondenser

Fluid to be chilled Chilled fluid

Tube

Water in

Chilledwater out

ShellRefrigerantvapour

Liquid


In Non-Flooded shell and tube evaporator, the refrigerant flows insidetubes and evaporates as it abstract heat from the fluid being cooled flows overthe tubes as shown in fig. In this , the baffles are provided to improve the heattransfer. These are used upto 50 ton capacity. It is shown in Fig 2.17

2.3.8 Shell and Coil EvaporatorShell and coil evaporator consists of shell and helical coil. The fluid to

be cooled enters at the top and leaves the bottom of the shell. The refrigerantflows through the coil . The fluid to be cooled , comes in direct contact withcoil. These are used in water cooler and small capacity units ranging from 2 to10 ton capacity. This is shown in Fig 2.18

Fig 2.18 Shell and Coil Evaporator

2.3.9 Tube – in – Tube Evaporator

Fig 2.19 Shell and Coil Evaporator

Liquid Ref

Water OUT

Ref vapour tocompressor

Water IN

Warm Brine Condensate fromcondenser

To compressor

Chilled Brine


These are called as double tube evaporators. It consists two concentrictubes. The fluid to be cooled flows through inner tube where as the refrigerantflows through the annual space between the two tubes as shown in fig. Thisarrangement improves the heat transfer. These are used in dairy, beveragesand oil plant. This is shown in Fig 2.19

2.4 Expansion Deveices or ValveExpansion device or valve is a dev ice which regulates or meters flow

of liquid refrigerant to an evaporator. It also divides high pressure side from lowpressure side of the system.

Functions

It reduces the pressure of the refrigerant coming from condenser andtemperature as per the requirement of system It regulates the flow of refrigerantas per the loan on the evaporator.

The various types of evaporators are

Capillary tube

Pressure control or automatic expansion valve

Thermostatic expansion valve

High-side float valve

Low-Side float valve

Solenoid valve

2.4.1 Capillary TubeCapillary tube is a coil or length of fine tube that has a very small orifice

usually 0.5 to 2.25mm inside diameter and length is about 1 to 6 m. It is aconstant restrict type expansion device, because the opening through which therefrigerant flow is constant. It controls the flow of refrigerant in to the evaporator.It is used with smaller hermitic units such as room Air-Conditioners and itsapplication extends up to refrigerating capacity about 10 kw. The usual formof capillary tube installed in refrigerating plant is shown in Fig 2.20

One end of capillary tube is connected to filler at the outlet of thecondenser. The other end is connected to evaporator. The capillary tube reducesthe pressure of the refrigerant from high-side pressure to low-side pressure.Liquid refrigerant from condenser enters in to the capillary tubes and as it flowthrough the tube pressure drops due to friction.


Fig 2.20 Capillary Tube

The capillary tube replaces thermostatic expansion valve for smallunits such as Domestic Refrigerator, Room Air-Conditioner and deep Freezers

The advantages of capillary tubes are

It is simple in construction and requires no maintenance

When the compressor stops, the refrigerant continues to flow from highpressure side to low pressure side unless pressure is equalized.

This requires low starting torque to start the compressor so a lowstarting torque motor can be used with these unit.

No receiver is required for systems using this device.

Its cost is much less as compared to other devices.

Disadvantages

The refrigerant must be free from moisture and dirt other wise it willchoke the tube and stop the flow of refrigerant . It cannot be used with highfluctuating loads.

2.4.2 Solenoid Valve The solenoid valve is shut off valve that is actuated by a

electromagnetic coil when the coil is energised . It is shown in Fig 2.21

An armature or plunger placed inside the coil. A stem or pin attached toplunger open or close. When the coil energised by passing current through it ,the magnetic field attracts the plunger up into the core of the coil which causesthe opening of the valve. When the coil is deenergised due to break in thecircuit, the plunger fall of its own weight and pin closes the valve. These valvesfitted vertical and allows the fluid flow in one direction.

Liquid refrigerant fromcondenser enterscapillary tube

Metered liquid refrigerantlieaves capillary andentersevaporator coil

Gas leavesevaporator


Fig 2.21 Solenoid Valve

Solenoid valve is installed in the liquid line just a head of the expansionvalve. They are used to control the condensing fluid when ever solenoid valveis used in a system, it is essential that the strainer should be installed ahead of itto prevent the entry of any contaminants.

SummaryThe main parts of refrigeration system are

1. Compressor

2. Condenser

3. Expansion Device

4. Evaporator

Compressor is device which delivers the high pressure refrigerant tothe condenser and maintains continuous flow of refrigerant through the refrigerantsystem.

• Condenser is a device in which heat absorbed by the refrigerant isremoved, and thus vapour refrigerant is condensed back to liquid form.

• Expansion device is used to control the flow refrigerant and toreduce the pressure from the condenser pressure to evaporator pressure.

• Evaporator is a device in which refrigerant evaporates by extractingheat from the surrounding medium.

Cover

Valve

Plunger

Stem

Ref out

Valve seat

Solenoidcoil Supply

Body

Ref In


Short Answer Type questions1. What are the main components the refrigeration system ?

2. What is the function of compressor in refrigeration system ?

3. What are the advantages of hermitically sealed compressor over open unit ?

4. State the function of condenser and classify the condenser.

5. Distinguish between water cooled condenser and air cooled condenser.

6. What is the function of evaporator in refrigeration system. List out different types of evaporator ?

7. State the differences between bare-tube evaporator and finned tube evaporator.

8. What is the function of expansion device in the refrigeration system?

9. State the function of capillary tube.

10. State the advantages and limitations of capillary tubes.

Long Answer Type Questions1. Explain the working Hermitically sealed compressor used in

Refrigeration system with neat sketch.

2. Write the differences between open unit and hermetically sealed unit.3. What are the merits and demerits of Air cooled condensers ?

4. Explain the working shell and tube condenser .

5. Draw a shell and coil type condenser and explain its working.

6. Explain the working of double tube condenser.

7. Explain the working of evaporative condenser.

8. Write the differences between Air cooled condensers and Water cooled condensers.

9. Explain the working of Natural draft cooling tower.10. Explain the working of mechanical draft cooling tower.

11. Write the differences between Natural draft and mechanical draft cooling tower.

12. Explain the working of any one expansion device with neat sketch.

3UNIT

Refrigeration ApplicationStructure

3.1 Applications of Refrigeration

3.2 Definition of Refrigeration.

3.3 Unit of RefrigerationI

3.4 Domestic Refrigerator

3.5 Water cooler

3.6 Ice plant

3.7 Cold storage

Learning Objectivities

After studying this unit, the student will be able to know

• How the Domestic Refrigerator works

• The various parts of Water cooler and how it works.

• How the Ice plant works

• How the cold storage works and where it is used.


3.1 Few applications of the Refrigeration• Central air conditioning

• Food storage

• Making of ice

• Ice-Cream plants

• Industrial applications

• Hospital operation theatre

• Research laboratories

• Computer rooms

• Storage and transportation of food stuff

• Cooling of concrete for special application like dams

• Production of Rocket fuels

3.2 Definition of RefrigerationRefrigeration is the process of removing heat from substance or space

to reduce its temperature and transferring that heat to another substance orRefrigeration is providing and maintaining the temperature below that of thesurrounding temperature.

3.3 Unit of RefrigerationThe capacity of a Refrigeration unit is expressed in terms of Ton. One

ton of refrigeration is equivalent to the rate of heat transferred needed toproduce 1000Kg of ice at 0 water in 24 hours.

One ton of refrigeration= 55 kcal/min

A refrigerant is the substance used for heat transfer in a refrigerationsystem. It absorbs heat (latent heat and sensible heat) from the source at alow temperature and pressure and gives up this heat at a high temperature andpressure. The refrigerant which transfer heat in the form of latent heat is moreefficient than the air refrigerant which transfer heat in the form of sensible heat.The refrigerant in the first group continuously change its phase from liquid tovapour and vapour to liquid.

However in the second group, the refrigerant exist in the gaseousphase only. The refrigerant which absorb heat in the form of latent heat aremore suitable and widely used in the refrigeration system. In selecting a


refrigerant for a particular purpose its characteristic must be considered andthe selection must be made on the of its compatibility with the system.

Secondary refrigerants are those which are cooled first by the primaryrefrigerants and then employed for cooling purposes. Indirect method of coolingis produced by absorption of sensible heat.

3.4 Domestic RefrigeratorThe domestic refrigerator works on vapour compression cycle. It is

compact and more efficient in use of electric energy. The refrigerant used inthis is Freon 12. Its main function is to provide low temperature space for thepreservation of food. The domestic Refrigerators also used in medical shops,hospitals, hotels, offices, laboratories etc.

The domestic refrigerators capacity is the internal volume of the unitand is expressed in litres. The various common sizes of refrigerators availableare 100,165,200 and 300 litres.

Components

The main components of a domestic refrigerator are

1. Compressor

2. Air-Cooled condenser

3. Receiver

4. Drier

5. Evaporator

6. Accumulator

7. Capillary tube.

The refrigerant vapour drawn from the evaporator is compressed incompressor and deliver to the condenser. It is then expanded in capillary tubeand passed on to the evaporator. Capillary tubes is used as throttling device isused to reduce the pressure of the refrigerant. The low pressure refrigerantevaporates as absorbing its latent heat and thus producing refrigerating effectin the evaporator.

It consists a hermetically sealed compressor fitted at the base of thecabinet. Condenser is air cooled coil. The evaporator is placed at the top ofinside cabinet. The evaporator produce low temperature about -15C andtemperature around 7 to 10C can be maintained in the refrigerating space.


Heavy cold air from freezer moves down wards and becomes warmair after cooling the products. This warm air moves upward. Thus the airmovement is maintained continuously in the refrigerated space.

The freezer is a mini cold storage in which ice-cubes , ice-creams ,frozen foods, meat poultry and fish can be preserved. A thermostat is providedto control the temperature in the freezer. Chiller tray is provided below thefreezer to prevent the accumulation of water drops in the freezer.

Below the freezer, it consists adjustable shelves to preserve fruits,vegetables, cooked foodEtc. Egg tray, dairy bins ,bottle shelves are providedin side the door of refrigerator. It should be placed in a clean and well ventilatedarea and kept on the leveled place. It is important to check thefunctioning of thermostat, door switch, light etc., and a separate plugmust be provided for the refrigerator. This is shown in Fig 3.1

Fig 3.1

Fig 3.2

Suction line

Evaporator

AccumulatorDischarge Line

Condenser

Capillary

Drier

Freezer

Evaporator freshfood compartment

Crisper

Drain Tray

Light switch

Thermostatknob

Push button


Fig 3.3

The various functions of the components of domestic refrigerator are:

Compresser

In this, rotary type compressor is used and is sealed unit. It compressesthe refrigerant gas to high pressure and temperature .

Evaporator

The evaporator cools the air in its surrounding in the cabinet. The coldair being heavier moves downwards to cool the food stuff and becomes warm.This warm air being lighter moves upward to take the place of cold air. Theconvection currents are formed in the cabinet which enable the maintain of uniformtemperature.

Drier : A drier is connected between the receiver and the evaporatorto eliminate the traces of moisture, if any.

Accumulator : It is connected between the evaporator andcompressor, which accumulates liquid droplets of the refrigerant and preventthe compressor from any possible damage.

Capillary Tube : The throttling device is a capillary tube. In this, thepressure equalizes through out the system during off- cycle, and hence a lowstarting torque motor can be used.

Condenser

Compressor


3.5 Water CoolerWater cooler is a device which is used to cool and supply this water at

temperature about 7 to 13 *C. Water coolers may be classified in to

1. Storage type water cooler

2. Instantaneous water cooler.

In a storage type water cooler, a cooling coil is wrapped around thewater storage tank and the cold water is available always in the tank.

In instantaneous cooler, the cooling coil is wrapped around the pipeline. Water is cooled to desired temperature and reaches the tank.

Water Cooler

Fig 3.4 Water Cooler

Water cooler consists the following components

1. Water storage tank

2. Compressor

3. Condenser

4. Evaporator

5. Thermostat

6. Water inlet pipe

7. Cold water outlet

Evaporator coil

Suction linedischarge lineCompressor

Condenser

InsulationCold water outlet

Waste water

Thermostat

Storage tank

Water Inlet

Waste water outletHeat exchanger basin

Capillary tube

Strainer


8. Insulation

9. Waste water outlet

10. Heat exchanger

11. Strainer

12. Capillary tubes.

Water cooler consists a water storage tank in which water is filled. Thewater is maintained at constant level with the help of float valve. Insulation isprovided around the tank as shown in fig ( 3.3 ).The insulation is provided toprevent the heat transfer from the surrounding into it. In this, The vapourcompression system is usd and Freon-12 is used as refrigerant. The high pressureand temperature vapour refrigerant enters the condenser where it is convertedin to liquid refrigerant. Then, the liquid refrigerant enters the capillary tubesthrough strainer. It gives out heat to vapour in the suction line where heatexchanger is provided. The liquid refrigerant expands in capillary tubes andthen its pressure is reduced.

The low pressure and low temperature refrigerant flows throughevaporator coil which is around the storage tank. The refrigerant absorbsheat from water and evaporates. In this way the water is cooled in the storagetank. A Thermostat is provided to control the temperature of the water in thetank. The vapour refrigerant from evaporator is entered in to the compressor,where it is compressed to high pressure and high temperature refrigerant. Thishigh pressure refrigerant enters the condenser and thus the cycle is completed.This is shown in Fig

3.6 Ice PlantIce is made by Ice plant. The ice is produced by natural form and

artificial system. The ice is produced with contact of cold air at the peakmountain. This Ice is called snow. When water freezes on the tree ,plant etc.with the coldness of air in plant, this is called frost. Ice making is to freeze thesimple water, this is called crystal ice.

The water required mainly for ice making should be quiet clean but itcontains many impurities such as dissolved gases and solids. It should not containany kind of impurities of chemical such as carbonic acid, sulphurated hydrogen,lime,salt etc. Water should be given preliminary chemical treatment and filteredbefore using. The distilled water or rain water is the best for making goodquality ice because, it has no possibility to mix the air or other impurities but dueto its high cost, it is not widely used.


The essential components of a ice plant machine are compressor,expansion coil, liquid receiver , refrigerant and condenser.

Compressor : It pumps the refrigerant vapour towards the condenserby which condenser coverts the vapour into liquid form. This liquid refrigerantenters the evaporator through the expansion coil where the liquid converts in tovapour. The compressor sucks this vapour and compressed and send towardsthe condenser again. During the operation of compressor, cylinders becomehot which reduce the efficiency of compressor. So for cooling, compressorhave water jackets around the cylinder.

Expansion Coil : It is a direct expansion freezing coils and the coil is inU form as shown in Fig

Fig 3.5 Ice Plant

The refrigerant is circulated in this coil. When the refrigerant from thereceiver in liquid form comes out through expansion valve, open space shouldbe provided to expand the refrigerant. This coil should be placed around theice can. This coil is also called as evaporation. It is shown in fig

Liquid Receiver

It is a storage tank which receives the liquid refrigerant from thecondenser and supplies it to evaporator according to the requirement. It is acylindrical shell made cast steel with suitable inlet and outlet. The inlet is connectedwith the condenser and outlet of receiver is connected with the expansion coil.A gauge glass is provided for indicating the liquid level. In receiver, the liquidlevel should not exceed than two third part of it.

It almost all the ice manufacturing plants, ammonia is used as primaryrefrigerant and brine as secondary refrigerant. Ammonia is colour less liquid.It is a combustible or explosive when mixed with air in certain proportion and

FreezingTank

Receiver

Compressor


much more so when mixed with the oxygen. It is very toxic and requires heavysteel fittings.

Condensor

It consists of U-type tubes. The ammonia vapour circulates in thesetubes. The water is sprayed over the surface of these for the reasons theammonia vapour converts into liquid form and this liquid stores in liquid receiver.

3.7 Cold StorageCold storage is a process of preserving perishable food stuffs on the

large scale by refrigeration. It is a mechanical refrigeration system which ismostly used now days because daily used food stuffs such as fruit, vegetable,meat eggs, etc. are to be kept in a preserved condition up to the longer period.Refrigeration has not only saved incalculable quantities of food stuffs fromspoilage but has played an important part in changing the diet of the world.

The seasonal fruits and vegetable are to be preserved and stored tomake their availability for the whole year around. The perishable product areplaced in cold storage for their preservation in original fresh state not to thespoiled. The food stuff can be kept in a preserved condition for a long periodin a cold storage. Some of these food stuff can be preserved the cololur andfreshness but the taste of some product have changed with respect to the freshproduct.

In this, mechanical refrigeration is used for preserving the useful foodstuff from spoilage. Mechanical refrigeration is done through the process ofcold storage. In this process there is a big room in which the perishable foodand drink stuffs are kept. Its temperature of the cold storage is kept low andalso moisture is about 80 to 90%.

The essential components of cold storage plant are compressor,condenser, expansion device and evaporator. In this, the room is cooled by air.The warmed air from the room is drawn and it passes over the evaporatorcoils and cool air is blown out through louvers in the room. The layout of suchcold storage is shown in Fig

In such units the refrigerant use directly in thin cooling coils or brinecirculate in which secondary coils are provided. The compressor, condenser,receiver, expansion valve and charging valve are provided in this unit. From hispart, the refrigerant goes towards evaporator in which evaporator remainsseparate from above part. The air enters through the evaporator and therefrigerant absorbs the heat of the air and air is to be cooled. This cooled airis blown out by the blower in the whole room and room become cold.


Fig 3.6 Cold Storage

SummaryRefrigeration is the science of producing and maintaining temperature

below that of the surroundings.

Refrigerant is the substance used for heat transfer in a refrigerationsystem. Vapour refrigerants are more efficient than air refrigerant.

Primary refrigerants directly produce the refrigerating effect where assecondary refrigerant are first cooled by primary refrigerants and then employedfor cooling purposes.

Some of the applications refrigeration are

1. Domestic Refrigerator

2. Ice plant

3. Water cooler

4. Cold storage

Domestic refrigerator works on vapour compression cycle with Freon-12 as a refrigerantIce is manufactured artificially from clean water by chilling .Ice plant uses vapour compression system with ammonia as a refrigerant.Brine is used as secondary refrigerant.

Water cooler uses vapour compression system with R-12 asrefrigerant.Cold storage prevents the spoilage of perishable products. It workson vapour compression cycle.

Condenser

Condenser

RefrigeratedSpace chilled air

WaterWater

ExpValve

Blower

Evapora-tor CoilCooling

Coil

Air Intake


Short Answer Type Questions1. Define Refrigeration.

2. Write the various applications of refrigeration.

3. What are the components of the domestic refrigerator ?

4. Mention the parts of the water cooler.

5. State the various parts of ice plant.

6. What is the function of Cold storage.

Long Answer Type Questions1. Explain the working House hold refrigerator with neat sketch.

2. Draw a neat sketch of Water cooler and explain its working.

3. Explain the Iceplant.

4. Eexplain the cold storage plant.


4UNIT

Fundamental of AirConditioning

Structure4.1 Introduction

4.2 Meaning of Air conditioning

4.3 Psychrometry & Its properties

4.4 Dry Air

4.5 Moist Air

4.6 Dry bulb temperature

4.7 Wet bulb temperature

4.8 Dew point temperature

Learning Objectives

After studying this unti, the student will be able to know

• The meaning of Air-Conditioning

• What is psychrometry and its properties.

• The various psychrometry properties required for human comfort.


4.1 Introduction

Air-conditioning is necessary to provide a controlled atmosphere inbuildings where industrial process are to be carried out and in private andpublic buildings such as offices and cinema halls for human comfort. Thehumidity of air was to be responsible for human comfort and number ofexperiments were conducted with variable humidity and temperature and it wasfound that a particular temperature and humidity of air was comfortable forlarge percentage of people.

In tropical and subtropical countries cooling by means of air conditioningis necessary features of modern development. Besides human comfort , airconditioning is used in industries for efficient functioning of machines, in coldstorage to preserve food products, in textile industry for better product qualityand pharmaceuticals.

Air –Conditioning is a process by which the temperature, humidity,flow and purity of the air is controlled simultaneously to meet the requirementsof the conditioned space.

Control of temperature means the maintaining of temperature forhuman comfort, i.e, it needs increasing the temperature in winter where asdecreasing the temperature in summer. Control of humidity means increasing ordecreasing the moisture content in the air. The moisture content in the airincreases in winter and decreases in summer. Cleanlyness of air means improvingthe purity of air by removing dust and other undesirable elements. Distributionof air means the circulation of pure air through the controlled space or room.

The application of air conditioning can be sub divided as

1. Human comfort air-conditioning means to provide the inside conditions which are comfortable to the occupants.

Industrial Air - Conditioning

Industrial air-conditioning provides air at required temperature andhumidity to perform a specific industrial process successfully. Examples ofapplication in this category are research laboratories, control rooms in powergenerating stations, operation theatres in hospitals, electronic industry etc.


4.2 Meaning of Air conditioning

Air conditioning is a process of simultaneous control of temperature,humidity, cleanliness, and distribution of air to meet the requirements of theconditioned space. Control of temperature means maintain the temperaturefor human comfort. It requires heating in winter or cooling in summer.

Control of humidity means increasing or decreasing the moisturecontent in the air. It depends on weather conditions. Moisture content in theair is increased in winter and decreased the moisture in summer. Control ofcleanliness means improving the purity of air by removing dust and otherundesirable elements. Cleanliness of air is ensured through the use of filter.

Distribution of air means the circulation of controlled air uniformlythrough the controlled space or room. The quality of air depends on thetemperature to be maintained and the volume of enclosed space.

Classification of Air - Conditioning

The air-conditioning systems are classified as

1. According to the purpose

(a) Comfort air-conditioning system

(b) Industrial air conditioning system

2. According to the season of the year

(a) Winter air conditioning system

(b) Summer air conditioning system

(c) Year round air conditioning system

3. According to the arrangement of equipment

(a) Unitary air conditioning system

(b)Central air conditioning system.

4.3 Psychrometry Psychrometry is a science dealing with behavior of water vapour

present in air. atmosphere. Humidity is a prime factor in air conditioning forhuman comfort.


Phychrometric Properties

4.4 Dry AirThe dry air is considered as a mixture of Nitrogen and Oxygen and

neglecting the percentage of other gases

4.5 Moist AirThe moist air considered as a mixture of dry air and water vapour.

The quantity of water vapour present in air depends upon the temperature ofthe air. When water vapour contains dry air , it become cold. Moist air isheavier than the dry air.

Atmospheric Air : It is called as air in psychrometry. It is a mixtureof dry air and water vapour.

4.6 DBT (Dry bulb temperature) When there is no moisture in the air, it is dry air and human does not

feel comfort. Dry air contains dust also. Its temperature is dry bulb temperatureand is recorded by an ordinary thermometer. This temperature increases anddecreases according to the dryness of the air. The DBT for human comfort is25C.

4.7 WBT (Wet bulb temperature)Wet bulb temperature is temperature at which liquid or solid water , by

evaporating into the air, can bring the air to saturation at the same temperaturewet bulb temperature is measured by an ordinary thermometer whose glassbulb is covered with wet cloth.

4.8 Dew Point TemperatureThe quantity of moisture contained in air having a relative humidity; of

less than 100% is less than the maximum possible at some lower temperature.This lower temperature is the dew point and if the air is cooled to a temperatureslightly below the dew point moisture will to condense. Dew point temperatureis the saturation temperature corresponding to existing humidity ratio andbarrow metric pressure.

Humidity

Moisture in the air is measured in terms of humidity . In the presence ofmoisture , the atmosphere becomes cold. The dry air dries sweat of the bodybut not dried by moist air. There are two types of humidity: Absolute humidityand Relative humidity.


Absolute Humidity : The weight of the water vapour which is associated witha unit quantity of air. Absolute humidity is the actual quantity of water vapourpresent in the air. It is indicated by kg per cub m of air vapour mixture.

Relative Humidity : It is the ratio of the actual weight of water vapour presentin a given volume of air at a given temperature to the weight of water vapoursrequired to saturate the same volume of air at the same temperature.

Relative humidity = Weight of water vapour present in a volume of airat t c/Weight of water vapour requires to saturate the same volume of air at tc.

SummaryAir conditioning is defined as the process of simultaneous control of

temperature, humidity, cleanliness and distribution to meet the requirements ofconditioned space.

Comfort is the condition at which human body feels an absence ofexcess of sensation. The feeling of comfort for human beings depends oneffective temperature , purity of air and air motion.

Psychrometry is a science dealing with behavior of water vapou present in atmosphere.

Dry air is mixture of nitrogen and oxygen and small percentage of other gases.

DBT is the temperature shown by ordinary room temperature.

WBT is temperature measured with a thermometer with its bulb covered with wet wick or cotton around it.

Short Answer Type Questions1. Define air conditioning.

2. What is meant by air conditioning ?

3. Write the classification of air conditioning.

4. What is dry air ?

5. What is Moist air ?

6. Define DBT

7. Define WBT

8. What is Dew point temperature.

5UNIT

Air - ConditioningEquipment

Structure5.1 Fans & Blowers

5.2 Ducts

5.3 Supply Air out lets

5.4 Return Air out lets

5.5 Filters and Dust collectors

5.6 Heating & Cooling coils

Learning ObjectivesAfter studying this unit, the student will be able to know

• Which type of fans and blowers are used in Air conditioning equipment

• The functions of ducts

• The meaning supply air outlet and which type of grills used in Air conditioning equipment.

• The functions of Filters and Dust collectors

Air taken from atmosphere carries harmful ingredients, and it is necessaryto remove these ingredients from air before supplied to the air conditioning system.To control the air and supply the controlled air to conditioned space or roomneed various equipments such as fans and blowers, ducts, filters, dust collectors


etc. The main equipment and devices used in air conditioned plants are brieflydescribed in this chapter.

5.1 Fans and BlowersFans and Blowers are used for circulation of air in Air- Conditioning

plants which create positive pressure in the air and maintained desired speedand rate in the desired space or room. The fan is used to handle small quantityof air where as the blower is used to handle large quantity of air.

Fans may be classified according to the direction of air flow as

1. Axial fan- In this air moves parallel to the impeller shaft.

2. Centrifugal fan – In this air moves radial direction or perpendicular to the impeller shaft.

5.1.1 Axial FanAxial fans are those in which air flows in the direction parallel to impeller

shaft. These are used for handling large quantity of air at low pressure. Theypossesses higher efficiency but these are not suitable for duct air conditioningsystem.

Axial fans are further classified as

1. Propeller fan

2. Tube axial fan

3. Vane axial fan

Propeller Fan

Propeller fan consists a propeller or disc type wheel which is fitted onthe motor shaft which operates with in mounting ring or plate as shown inFig5.1

The ring surrounding the propeller does not permit the back flow ofdischarged air. It produces propulsive force and moves the air in an axial direction.These fans are designed to develop low pressure and are used there where theresistance of air movement is small.

Propeller fans are used for ventilation of rooms made on roofs, toremove gas or odour from kitchen, for the ventilation of latrines and bathroomsand similar applications where duct work is not involved.


Fig 5.1 Propeller Fan

Tube Axial Fan

Tube axial fan consists a disc type wheel or an axial flow wheel attachedwith motor is operated in cylindrical cover in it which is supported on bearing.This is shown in Fig 5.2

Fig 5.2 Tube Axial Fan

These fans produce a wide range of air volume against medium dischargepressure or air moves in large space. This wheel is wide at tip and smalldiameter at hub so the air produces of uniform velocity. The air of this fandischarge follows a spiral path as it leaves the cylindrical housing.

1. Vane Axial Fan : A Vane axial Fan consists of a axial type wheelattached with cylindrical cover. A set of guide vane is at both sides in it asshown in fig. The flow of air produced from this fan has no turbulence. Itsefficiency is better and low noisy. It is more efficient than the tube axial fan. Itcan be installed in the duct system.

Mounting Ring or plate

Gas Flow

Motor

Propeller or Disctype wheel

Motor

Gas Flow Gas Flow

CylindricalCover


5.1.2 Centrifugal Fan In Centrifugal fan , blades are fitted to impeller or rotor that rotates

with in spiral casing . In centrifugal fan the air enters the impeller axially anddischarged radially at the periphery. These fans are used for duct air conditioningsystem. They deliver any quantity of air over a greater range of operating pressure.The centrifugal force produces in it so the air passes rapidly and spread to allsides. Such fan has one or two inlets which , fan has only one inlet is calledexhauster and which have two inlets are called blowers.

The centrifugal fans are quiet and more efficient at high pressures. Theirperformance is largely depends on the type of the blades used. Centrifugal fanswith the following types of blades are normally used in air conditioned systems.

a. Back ward blades

b. Radial blades

c. Forward blades.

Backward Curved Blades : These blade tips are inclined away fromthe direction of rotation, and the blade angle is less than 90. They give low noiseand their efficiency is greater than 90%. These back ward curved blade fansare used in Air-conditioning system. This is shown in fig 5.3

Fig 5.3 Centrifugal Fan

Radial or Straight Blades : Radial blade tips are straight and theblade angle is 90. They provide vey high pressure at high speeds but theirefficiency is low. This is shown in Fig 5.4

Forward Curved Blades : These blade tips are inclined towards thedirection of rotation and blade angle is greater than 90. These blades increasethe efficiency up to 75%. They reduce the noise level. These are smaller and

(a) Backward curved (b) Radial (c) Forward curved


operate at low speed. These are used in window air-conditioning systems.This is shown in fig 5.5

The selection of the fan is determined with the operation of therequirements. If no duct system is required, the propeller fan is commonly usedbut on employed the duct system, the centrifugal or axial fan is used. Theimportant factor to select the fan is minimum noise level.

The following important factors are considered for the selection of fan.

1. Capacity requirement

2. The air density

3. Static pressure

4. Nature of load

5. Type of application or service.

6. Shape and size of equipment room

7. Sound level permissible.

5.2 Ducts The duct system convey the conditioned air from the air-conditioning

system to the space being conditioned and carry the return air from rooms orconditioned space to the air conditioning equipment for reconditioning andrecirculation. Like any other fluid passing through a pipe , air in passingthrough a duct suffers a pressure drop due to friction. Larger quantity of airpassing through a given cross sectional area of the duct, greater will be thefrictional loss and pressure drop.

Fan has to deliver the required quantity of air overcoming the resistanceoffered by the various components in the air distribution system, such as coolingcoil / air-washer , filters, supply and return air –outlet, dampers and the resistanceoffered by the duct system. The system resistance increases the H.P of Fan todeliver the required quantity of air against the system head or pressure. Asvelocity increases noise level due to the air in motion also increases. Thus, thevelocity of air in the duct has to be kept at a reasonably low level. With lowerair velocities the size of the duct increases.

The initial cost depends on the size of the duct. A smaller sized ducthas low cost. But with a smaller duct the air velocity will increase and sopressure loss due to friction also will increase. The fan will use more power toovercome the head, increasing the operating cost.


Ducts are defined as the passage way provided for conveying theconditioned air to specified location in order to provide comfort conditions.Smooth surface are desirable for ducts as they offer minimum resistance to theflow of air. The system should also be air tight so that the conditioned air doesnot leave out to the space not being conditioned.

The important requirements of duct system are

To convey specified rate of air flow to the prescribed location,economical and should occupy less space and should not transmit or generateobjectionable noise.

Ducts are usually made of Galvanized Iron sheets or aluminium sheets.Ducts are also made with non-metallic material such as glass fibre, cementasbestos. Glass fibre ducts are easy to manufacture to the required shape andsize. They are used in low velocity applications. Cement asbestos ductsused for underground air distribution and for exhausting corrosion materials.These are made in circular, rectangular, square cross-sections. The Circularducts are preferred because they carry more air in less space. The Rectangularducts are easier to manufacture and are preferred for good look.

Classification of Ducts

Ducts may be classified as

(a) Supply air duct: Supply air duct carry the conditioned air from equipment to the space or room to be conditioned.

(b) Return air duct: Return duct carry the return air from the space or room to the equipment for reconditioning or recirculation.

(c) Fresh air duct: Fresh air duct carries the atmospheric air in to the air-conditioned equipment.

(d) Low pressure duct: In this, the static pressure is less than 50 mm of water gauge.

(e) Medium pressure duct: In this, the static pressure is from 50mm to 150 mm water gauge.

(f) High pressure duct: In this, the static pressure is from 150mm to 250 mm of water gauge.

(g) Low velocity duct: In this , the velocity of air less than 600 m/min

(h) High velocity duct: In this, the velocity of air is more than 600m/ min.


5.3 Supply Air Out LetThe conditioned air enters the conditioned space through supply air

outlets. These are designed to distribute air uniformly and prevent noise.

According to their design and construction, they may be classified as

1. Grill out lets

2. Slot diffuser out lets

3. Ceiling diffuser outlets

4. Perforated ceiling panels.

Grill outlets

Grill is a perforated covering for an air inlet or outlet, and is made ofscreen. It can be adjustable type which consists of a set of horizontal andvertical vanes. In this, the air flow can be controlled both in vertical andhorizontal directions. In the fixed bar type grilles, the vanes are not adjustable,but they are either straight or inclined at an angle. Grills are used in high sidewall location. They are not suitable for ceiling locations as they cause draftconditions. Grilles are provided with various accessories for uniform distributionas shown in Fig 5.6

Fig 5.6 Grill Out Let

A combination of a grill and a damper is called register.

Slot Diffuser

It consists one or more slots and are installed in a continuous lengths.The maximum height of outlet is 75 mm with aspect ratio of 25:1. They are used

(a) Opposed blade dampers (b) Multishuffer damper

(d) Individually adjustableturnine vanes

(c) Gang-operated turning vanes

BranchDuct

BranchDuct

CollarCollar


in high side wall location or perimeter installation in the floor. They should notbe installed in ceiling.

Ceilong Diffuser

Ceiling diffusers are mounted in the ceiling . The most common typesare round, square and rectangular diffusers. They consists of series of flaringrings or louvers which form a number of air passages. They may also be fittedwith dampers.

Perforated Ceiling Outlet

Perforated ceiling outlets use the confined space above the ceiling as asupply plenum. The plenum pressure ranges from 0.025 to 3.5mm of watergauage, and flow rates are from 0.3 to 4.5 cub.mm/sq m of floor area. Theseoutlets have perforated face and deflection aids to discharge air in any desireddirection. They are suited to large zones of uniform temperature.

5.4 Return Air OutletReturn air outlets are the openings in a room space which allow the

exhaust air to enter the return duct. Return duct may be connected to airconditioning equipment if recirculation is necessary to the atmosphere if thesystem is designed for 100 percent fresh air. They can be mounted on ceiling,walls or floor. The selection of outlets depends on the size of the room, quantityof air required and discharge velocity of air.

5.5 Filters and Dust CollectorThe basic requirement of air conditioned system is that the conditioned

air must be free from dust, dirt, smoke, bad odour etc. One of the majorfunction of an air conditioning system is to clean and purify the air. As theheating and cooling coils are used for controlling the temperature and humidityof the air similarly various cleaning devices are used for controlling the dust,pollen, odour and smoke. Filters and dust collectors are installed in air-conditioning system to clean the contaminated air. Air used in an air conditioningsystem must be filtered to clean the contaminated air, outside air contains alwayscontaminants such as bacteria, pollens, insects, soot, ash, dust, and dirt. Thereturn air contains contaminants such as dust, lint, soot ash etc.

The various types of filters are commonly used in air conditioning systemas follows

1. Dry filters

2. Viscous filters


3. Wet filters

4. Electronic filters

Dry Filters

Dry filters or mechanical filters are used to remove dust particles abovecertain size. These are constructed by fibrous materials such as felt, fabric, cotton,wool, or metallic filters. The air to be cleaned is passed through these filters.The filters traps the dust particles from the air passing through it. The surfacearea of the filter should be large to eliminate the pressure drop. To clean thisdust , the plates are taken out and are turned round in the opposite directionwith any support, in such a way all the dust is cleaned . This is shown in Fig5.7

Fig 5.7 Dry Filters

These filters are not suitable to remove smoke and have little effect onsmall particles.

Viscous Filters

Viscous filters consists of a metal frame which is filled with wool orfibre, wire screen etc. These material s are coated with sticky oil which captureand holds the dust particles from air that flows through the filter. The dustparticles must be uniformly distributed throughout the filter area. These filtershave a large dust holding capacity and require less maintenance. However theirefficiency is low and are expensive. These are suitable for industrial applicationswhere a high degree of atmospheric pollution.

The various types of viscous filters are commonly used in air conditioningsystem are as follows

Moving Air

Moving Air

Holes

Aluminiumplates


1. Replaceable type filters : It is made of cheap material , discarded after specific period of use.

2. Manual cleaned type filters : It can be cleaned and reused; Cleaned filters must be coated with viscous oil.

3. Automatic or self cleaned type Filters : Automatic or self cleanedtype filters are made in the form of a continuous roll of material coated with oil.It is driven by a motor across the air stream. The roll passes over the rollersand moves through a trough of oil and air stream. The oil trough serves thedual purpose of cleaning the dirt and recoating the filter with clean oil. This isshown in Fig 5.8

Fig 5.8 Viscous Filter

Wet Filters

In this, the air to be conditioned is made wet by water spray. The dustparticles in air gain additional weight and fall down in the water sump. Wetfilters are used in Industrial area where dust and smoke particles likely to bepresent in the air.

Electronic Filters

Electronic filters are based on the principle of electrostatic on whichunlike electrical charges attract one another. The air to be cleaned is passedbetween parallel plates, one set charged positively and other set of platesnegatively charged. The dust particles in the air stream acquire positive chargeand are attracted to the negative charged plates or collector plates. A stickyadhesive coating is given to collector plates to hold the dust particles. Theseplates must be cleaned periodically. These are very efficient. It works effectivelyon finer dust particles. It is useful in large installations where adequate safety

Roll

Oil Trough


measures can be taken because of the high voltage involved. This is shown inFig 5.9

Fig 5.9 Electronic Filter

Air Washer

Air washer serves as a air cleaner. The air steam flows through filtersthat separate dust and then to water sprays that remove the remaining impuritiesby washing.

5.6 Heating and Cooling CoilThese are used to increase and decrease the temperature of air

respectively. Heating and Cooling of air without changing its moisture contentis termed as sensible heating and sensible cooling respectively. Sensible coolingof air takes place when it flows over cooling coil whose surface temperature islower than the temperature of air. The cooling medium may be chilled water orbrine as the secondary refrigerant. This is shown in Fig 5.10

Fig 5.10 Air Washer

Dirty Air

Dust Particles

Clean Air

Steam Out Chilled water out

Air In Air Out

Steam In

Air Out

Chilled water IN


Summary• The function of air conditioning equipment is to control the air and

supply the controlled air to conditioned space . The air conditioning equipmentconsists fan and blowers, ducts, filters and dust collectors.

• Fan and Blower create positive pressure and maintains circulation ofair through the conditioned space.

• Ducts are passage way to convey the conditioned air to prescribedlocation and carry the return air to air- conditioning equipment for reconditioningand recirculation.

• Filters and dust collectors in air-conditioning system are used toclean the contaminated air.

Short Answer Type Questions1. List out the air-conditioning equipment.2. State the function of Fan.3. Write the differences between axial fan and centrifugal fan.4. Define duct and write the requirements of the duct system.5. What is the function of Supply air outlet ?6. State the classification of Supply Air outlet.7. State the function of Return air outlet.8. State the function of Filters and Dust collectors.9. What are the various types of filters used in Air-Conditioning system?10. State the function of Heating and Cooling Coil in Air-Conditioning system.

Long Answer Type Questions1. Explain the various types of Axial fans with neat sketches.2. Write short notes of the following questions:

(a) Centrifugal fan(b) Propeller fan

3. Describe various types of duct system used to supply conditioned air to outles.

4. How are filters classified? Describe dry collector with neat sketch.

5. Explain the working Heating and Cooling coil with neat sketch.

6UNIT

Air - Condition ApplicationStructure

6.0 Introduction

6.1 Air Cooler

6.2 Air-Conditioning systems.

6.3 Window Air-Conditioner

6.4 Split Air-Conditioner

6.5 Packaged Air-Conditioner

6.6 Differences between Window Air-Conditioner and Split Air- Conditioner

Learning ObjectivitiesAfter studying this chapter the student will be able to know

• How the Air cooler works

• Under stand the special features of Air cooler.

• How the Window Air-Conditioner works

• How the split Air-Conditioner works.

• The differences between window Air-Conditioner and Split Air- Conditioner.


6.0 Introduction Air conditioning is a process by which the temperature , humidity,

flow and purity of the air are controlled simultaneously. Control of thesefactors depends on the application to which the air conditioning system isemployed . There are different types of air conditioner units and various methodsto use them.

There are two applications of air-conditioning

1. Comfort air-conditioning

2. Industrial air-conditioning

The comfort air conditioning intends to provide a comfortableenvironment for human beings round the year. This involves sensible heat gainsduring summer and sensible heat looses in winter. This further involvesdehumidification in summer and relative humidity in the conditioned space isallowed to be reduced during winter. Human beings are comfortable in widerange of relative humidity varying from 30 to 70%. The temperature range forhuman comfort is 22 to 26.5 ‘C.

The factors which determine the effectiveness of air conditioning forhuman comfort are

Air purity and removal of moisture emitted by occupants, removal ofheat emitted by occupants, sufficient air motion and uniform air distribution,supply of oxygen and removal of Carbon dioxide, control of moisture content ofair.

The air conditioning for industrial application is different, as well definedinside conditions are strictly to be maintained, within permissible limit, otherwisethe work to performed suffers. A few applications of industrial applications arecomputer centers, research laboratories, control rooms, in power generatingstations, operation theatres in hospitals, electronic industrial establishments etc.

6.1 Air CoolerFor conditioning the room, the air cooler instead of air conditioner is

used also. These are called as space cooler. Air humidified when quantity ofwater mixed with dry air and humid air is cold than dry air. In this, quantity ofwater will be more needed. There is no use of refrigerant as the air conditioner.

Air cooler works on the principle of evaporating cooling. In this, wateris used as a cooling medium. The temperature of air is decreased by the waterwhen air is brought in contact with water. Water absorbs heat from the air and


evaporates. The make up water is added to compensate the loss of water dueto evaporation.

The components of air cooler are fan, water pump and pads throughwhich air enters the cooler, Air deflectors, water trays, Electric motor, pipe ,Blower, switch and regulator.

The electrical driven pump pumps the water from the bottom tank tothe top headers. The headers have holes through which water trickles downand pass through pads fitted on three sides of the cooler. Air sucked throughpads from three sides gets cooled. The cool air is discharged by the motordriven fan into the room or space to be cooled. The direction of air flow can beadjusted with the help of grills fitted on the discharge side of the cooler. Forbetter performance pads to be changed every year and water tank should becleaned from time to time. This is shown in Fig 6.1

Fig 6.1 Air Cooler

Main Features of Air Cooler

1. Sturdy design : Air cooler is made of thermoplastic material having excellent aesthetic appeal and corrosion free life.

2. Four way Air deflection system : This feature enables uniformcirculation of air by motorized louvers to maintain same cool temperaturethrough out the room.

3. Uniform Water distribution pads : Water is distributed to wet thewood wool through a pump and valve arrangement that delivers water to theshower pipes. Independent humidifier control is provided which controls quantityof water released on the wood wool pads.

Pads

Warm air

Water In

Header

Cool Air

Cabinet

Floor


4. Speed control : Independent controls for three different air speeds.LED indicator is used for indicating power on.

5. Special wood wool pads : Wood wool pads are provided forodourless and fresh cool air.

6. Auto water level controller : The air cooler when connected bythe water inlet to the over head tank maintains the required water level in thetank by the float valve arrangement .

7. Water level indicator : An easy to view water level indicator on the front panel . You can easily check the water level in the tank.

8. Safe : The body is electrical shock proof plastic material and earthing is provided on the fan motor.

6.2 Air - Conditioning SystemAn air-conditioning systems consists of assembly of different component

to produce design conditions of air within the required space. The essentialparts of air-conditioning system are

1. Air intake for ventilation

2. Pre heater to increase to increase the temperature of air,

3. Filter to remove contaminants from air.

4. Dehumidifier to decrease the moisture content.

5. Humidifier to increase the moisture content.

6. Heating coil to control the temperature and humidity,

7. Refrigeration system to produce and maintain low temperature.

Classification of Air Conditioning System

Air conditioning systems classified as

1. According to season of the year

(a) Summer air conditioning

(b) Winter air conditioning

(c) Year round air conditioning

2. According to the applications of the system

(a) Comfort air conditioning


(b) Industrial air conditioning

3. According to location of equipment

(a) Unitary system

(b) Central station system

(c) Combination system

Summer air conditioning system

Summer air conditioning is used to provide comfort conditions duringsummer seasons. The comfort conditions required are 24 C and 60% relativehumidity, irrespective of out door conditions.

Winter Air –conditioning system

In winter air conditioning, the air is heated and humidified to achievedesigned cnotitions.

Year round air conditioning system

This system consists of heating and cooling equipment with automaticcontrol to produce desired conditions irrespective of climatic conditions. Inwinter, heating and humidification of air achieved by the heating coils andhumidifier and cooling is made in operative. The conditioned air is distributedinto the space to be conditioned. In summer, Cooling and dehumidification isachieved by a cooling coil whose DBT is below the dew point temperature ofentering air. In this case heating coil is made in operative. The conditioned aircirculated through the space to be conditioned.

Central air conditioning system

In this system, all the major components are located at the centralplace, away from the area to be conditioned. The conditioned air is suppliedto different rooms by ducts. The exhaust air can be returned and partly reused.

Unitary system

All the components of the unit air conditioning system are assembledin the factory itself. The unit air conditioner are usually installed in or immediatelyadjacent to the space to be conditioned. They are preferred for low capacityrequirements.


6.3 Window Air - Conditioner Window Air-Conditioner is also called as room air conditioner, which

is installed on the window of a room or wall opening. It works on principle ofvapour compression refrigeration system. The refrigerant used is Freon-12(R-12) or Freon 22(R-22).

Construction: It consists of steel chasis. In the centre of it, a hermeticallysealed compressor motor unit is fitted. The Reciprocating type compressor isused in it. A discharge line, fin and tube type condenser and remote bulb orcapillary tubes are fitted at one end and suction line and fin and tube typeevaporator on the opposite end. The complete refrigeration system is chargedwith Freon-22 refrigerant.

The shaft is fitted on the both side of the sealed motor. A blower isfitted behind the evaporator on one side of the motor shaft and on the otherend, a fan with water splashing ring or belt his fitted behind the condenser.Evaporator and blower housing are insulated with the felt . The bottom tray ofthe evaporator is connected with the condenser by means of rubber tube. Anair filter is fitted in front of the evaporator for cleaning the air. A grill is fitted onthe front portion of the air conditioner in which having provision for changing thedirection of the air.

Working of Window Air - Conditioner

An electric motor drives the fan to circulate air through condenser coiland runs a blower. Blower sucks air through the filter and forces it through theevaporator coil which cools as well as dehumidifies the air. The conditioned airis circulated through the room or the space to be conditioned. Dampers areused for the appropriate air distribution in the room. It is also provided withthermostat to maintain the desired temperature by means of an on-off control ofthe compressor.

Window air conditioners are available in sizes up to 2 ton capacity. Itis employed to condition the air of a given space such as office rooms, salons,bed rooms, drawing offices etc. This is shown in Fig 6.2

The window air conditioner is divided into two parts. Out door partand Indoor part.

Out door part : This part consists of hermetically sealed compressorand motor unit, condenser and motor driven fan.

Indoor part : This part consists of a filter , evaporator, motor drivenfan and remote bulb refrigerant control.


Fig 6.2 Window Air - Conditioner

Hermetically sealed motor and compressor unit : The compressorand motor are mounted on the only one shaft and are enclosed in welded dome.Compressor and motor work on the same shaft. There is arrangement so thatdirt, moisture, etc. cannot enter in this. The refrigerant vapour enters directly into the compressor and then goes to the suction tube fixed inside. This tubefitted on the top end of the oil bath surface. Oil goes to the tube and thecompressor starts.

Condenser : In this, the refrigerant vapour comes from compressorand cool with air or water or both.

Fan operating motor : A single phase capacitor run motor is fixed tooperate the condenser fan, out side air is forced over the condenser coil by thisfan.

Filter : Filters are used for purifying air because the air supplied to theconditioned space must be free from all foreign matter such as dirt, fumes andharmful bacteria. Carbon filters absorbs the smell of different gases.

Evaporator : Evaporator absorbs heat and liquid refrigerant changesinto vapour. The heat inside the room absorbs by the refrigerant and roombecomes cold. The pressure of vapour refrigerant becomes less and goestowards compressor.

Blower : A Blower is driven by single phase motor and used to drawair through the filter and forces it over the evaporator coils. The condenser fanand blower may be operated by the same motor or each may have a separatemotor.

CondenserEvaporator Fan

CondenserFan

Evaporator

Fan MotorDrier Filter

Capillary Tube

Compressor

Accumulator


6.4 Split Type Air - ConditionerSplit type air-conditioner consists the indoor and outdoor sections.

These are separated into two units. Indoor unit consists of evaporator, blower,air filter, grills etc. and is installed inside the room to conditioned. It may beceiling suspended , wall mounted or kept on floor as console model.

Out door unit consists of compressor, air cooled condenser, fan and isinstalled outside the room. The distance between the indoor and outdoor unitsof a split air-conditioner should kept as small as possible other wise the increasein distance increases the pressure drop in the suction line and liquid line. This isshown in Fig 6.3 & Fig 6.4

Fig 6.3 Split Type Air Conditioner

The split air-conditioner has certain advantages over the window air-conditioner. Since the compressor is installed away from the room to be air-conditioned, the noise level will be very lower than in case of a window air-conditioner. It is used in bed rooms, design offices etc.

6.5 Packaged Air - ConditionerPackaged air –conditioner is a self contained unit with all needed

equipment in a single cabinet. This available up to 20 ton capacity. In this, theevaporator, condenser, and compressor are all located in one cabinet. This isusually placed on roof. Air supply and return ducts come from indoors throughthe house exterior wall or roof to connect with the packaged air conditioner,which is located outdoor. The system is usually water cooled. It is used inrestaurants, stores, banks, laboratories etc.

Outdoor Unit

4 Way valve

Accumulator

FanMotor

Capillarytube

Drier Filter

Indoor Unit

IndoorFan


6.6 Differences between Window air conditioner and Split air conditioner

Summary• In Air Conditioning System, conditioned air is supplied to the room or space to be conditioned.

• Air Cooler

• Works on evaporating cooling. Water is used to the circulating air.

• Window Air-Conditioner

• It works on the principle of Vapour compression refrigeration system.

• Split Air-Conditioner

It consists the out door section and indoor section. Indoor unit consistsevaporator , Blower, air filter and grills etc., mounted at indoor.

Out door consists of compressor, air cool condenser and fan mountedat out door

Window type air-conditioner

1. It is a single unit having a cooling and condensing unit fitted on the same base plate.

2. It has only one motor having a double shaft. A blower is fitted at one end of the shaft and condenser fan at the other end of the shaft.

3. It is installed mostly in the window of the room.

4. It produces a little noise while working.’

5. It is cheaper than split air- conditioner.

6. Less copper tube is used with window type air-conditioner.

Split type air-conditioner

1. It is called split unit, as there are two separate units, a cooling unit and other condensing unit which are fitted on separate base plate.

2. It has two motors, one blower motor and the other condenser fan motor.

3. It is installed anywhere in the room.

4. Its working is noise free.

5. It is costlier than window type air- conditioner.

6. The length of the copper tube is morein split type air-conditioner.


• Packaged air-conditioner

• Packaged air-conditioner contained a single unit with all need equipment in a single cabinet.

Short Answer Type Questions1. List out the essential parts of Air Cooler.

2. What are the main features of Air cooler?

3. What are the main components of air conditioning system?

4. Write the advantages of mechanical draft cooling tower over natural draft cooling tower.

5. Describe the classification of air-conditioning system.

Long Answer Type Questions1. Explain the working of Air Cooler with neat sketch

2. Describe the working Window Air-Conditioner with neat sketch.

3. Explain the working of Split Air-Conditioner

4. Describe the working packaged Air-Conditioner.

5. Write the differences between Window-Air conditioner and Split Air-Conditioner.

7UNIT

Servicing and Maintanance ofRefrigeration & Air - Conditioning

EquipmentStructure

7.1 Introduction

7.2 Maintenance of Refrigeration system.

7.3 Maintenance of Air-Conditioning system

7.4 Symptoms of Refrigerant shortage

7.5 Gas leakage detective methods

7.6 Trouble shootings in Refrigeration system.

7.7 Trouble shootings in Air-Conditioning system.

Learning Objectives

After studying this unit, the student will be able to know

• The Servicing and maintenance of Refrigerator

• The Servicing and maintenance of Air-Conditioner.

• The various trouble shootings in Refrigerator.

• The various trouble shootings in Air-Conditioner.


7.1 Introduction The Refrigeration and Air-Conditioning systems require proper

maintenance, i.e, Daily , weekly ,monthly and yearly maintenance. Themaintenance details are supplied by the manufacturers of each equipmentshould be followed to ensure trouble free service. Periodic checking ofcontrol and safety devices is essential to ensure their good working. The variousdefects frequently occurred in refrigeration and air conditioning equipment arediscussed in this chapter.

7.2 Maintenance of Refrigeration systemPlanned maintenance schedule for Refrigeration system is given below.

Daily maintenance

(a) Check and ensure that all equipment is free from noise and vibration

(b) Check suction, discharge and oil pressure

Weekly maintenance

(a) Check running amperage of all main motors

(b) Check and ensure that air cooled condensers are free from obstruction.

Monthly maintenance

(a) Check all belts for proper tension and alignment

(b) Check compressor oil levels, if it is provided with crankcase sight glass

Yearly maintenance

(a) Examine all bearings

(b) Clean all water strainers

(c) Clean and repair all cooling tower and condenser surface as necessary

(d) Check all operating and safety control for correct setting and operation

(e) Check and lubricate fan and motor fan bearing

(f) Conduct leak test the refrigerating system using electronic leak method.


7.3 Maintenance of Air-Conditioning systemDaily maintenance

(a) Check and ensure that all equipment is free from noise and vibration

(b) Check suction , discharge and oil pressures

Weekly maintenance

(a) Check running amperages of all main motors

(b) Check and ensure that air cooled condenser are free from obstructions.

(c) Check air filters- clean/ replace them if necessary

(d) Check the condition of air intake grill and filters.

Quarterly maintenance

(a) Check finned heat exchanger surface for freedom from blockages

(b) Lubricate motor and fan bearings if necessary

(c) Wash out condensate trays

(d) Inspect humidifiers and ensure that they are free from scale

(e) Check and clean sensors of thermostat and humidi stats.

Yearly maintenance

(a) Reactivate sensing elements of hair-type humidstats in accordance as per the manufacturer instructions

(b) Check all the bearings

(c) Clean all water strainers

(d) Clean and repair all cooling tower and condenser surface if necessary

(e) Check all operating and safety controls for correct setting and operation.

7.4 Symptoms of Refrigerant ShortageThe symptoms of refrigerant shortage are,

• In sufficient cooling in the equipment

• Frequent tripping of compressor motor


• Power consumption is high

• low suction pressure

• Excessive heating of compressor parts

• Gas shortage is mainly due to leakage in the system.

7.5 Gas Leakage Detective MethodsLeakage cannot be tolerated in any refrigeration system. Test must be

conducted for leak detection during maintenance of equipment. The variousmethods can be used with specific refrigerant are given below:

1. Ammonia : Ammonia leakage from the system can be identified by two methods.

(a) Using Sulphur sticks : This method is used to identify exact locationof leak. When it is lit and its flame is exposed to ammonia , it gives off a whitesmoke of ammonium chloride or ammonium sulphide.

(b)When red litmus paper is exposed to ammonia vapour , it turns blue.

2. Freon : The leakage of Freon (Halogenated refrigerants) like, R - 11, R-12, R-22, etc. can be identified by two methods,

(a) Soap solution : When soap solution is applied over the suspectedleak , it will be identified by the formation of bubbles from leakage point.

(b) Halide test lamp : The flame is supported by oxygen in the airused as a sensing agent. When it is passed over the leakage point or surfacebeing leak tested, the colour of flame will be changed in to green or deep blue,depending upon the quantity of gas leaked.

3. Sulphur dioxide : When a small piece of ammonia soaked clothfastened to the end of stick and placed at the leakage point or surface beingleak tested, It will give off thick white smoke at the point of leak.

Electronic Leak detector

It is very sensitive device and is used to detect leak of any refrigerantgas. It consists tube through which refrigerant is suck in to the instrument. Aheating element in the tube heats the refrigerant gas. The refrigerant gas bringchange in the current flow. This is indicated on instrument which gives amountof leakage of gas. The gas leakage is also identified by an audible sound.


7.6 Trouble Shooting in Refrigeration SystemThere are various types of trouble shootings in the refrigerating system.

Trouble shooting is not as complex as it seems. In order to get accurateservice, the technician must have a basic knowledge about the system. Thereare standard procedure to follow that make it relatively easy.

1. Refrigerating unit does not run

Possible causes Possible Remidy

2.Refrigerating unit gives humming and stops

Possible causes Remidy

1. Check fuse if it is blown, replace.

2. Check voltage by volt meter. Adjust thestabilizer.

3. Check voltage at relay, if there is novoltage, check the line continuity.

4. Check capacitor by testing lamp. If lampdonot burnt or find leakage, replace it.

5. Start the refrigerator by correct supplyvoltage with out relay. If starts the unit,replace relay.

6. Start the refrigerator to with outthermostat. If this works and connection iscorrect then either repair the thermostat orreplace it.

7. Change the broken wire or repair.

1. Fuse blown

2. Low supply voltage

3. Connection broken

4. Capacitor defective

5. Relay defective

6. Thermostat defective

7. The wire of compressor or thermostat is broken.

1. Check the voltage by volt meter. If it is lessor more than 10% of medium voltage. Shortthe length of wire or adjust the stabilizer.

2. Check capacitor with test lamp, and replacethe capacitor if necessary.

3. Check relay operation and replace it ifnecessary

1. Too low voltage

2. Capacitor defective

3. Relay defective


3.The Refrigerator runs very fast

Possible causes Remedy

4.The Refrigerator makes noise


1. Interior lamp lighted

2. Gasket seal defective

3. Improper air circulation

4. Gas unit leakage

5. Loose connection in the thermostat valve from evaporator.

6. Defective thermostat.

7. Shortage of the refrigerant

8. Moisture in the unit.

1. Check the lamp after closing the door of the unit cabinet. If it is lighted, check the switch and replace.

2. Check the door gasket and replace if necessary.

3. Check the location of unit. It should be located at proper distance from the walls.

4. Check the leakage. Repair or replace if necessary

5. Check the connection and tight if it is loosely connected.

6. Start the unit with out thermostat connection, if it runs properly, replace the thermostat.

7. Check the refrigerant ,charge it if shortage, repair leak .

8. Check the moisture in the unit. If find it, replace by dry filter

1. Tighten any loose components.

2. Check the motor . If rotor rubs with stator or bolts of motor are loose. Repair and tighten the loose components.

3. Check the level of the cabinet and correct the level of the cabinet if necessary.

4. Check the compressor and lubricate the compressor bearing s or replace it if necessary.

1. Not proper installation

2. Motor is noisy

3. Improper level of the cabinet

4. Noise in the compressor


5. No or poor cooling efficiency or low refrigerating effect


6. Low suction pressure –high super heat


7. High Suction pressure –low superheat


1. Thermostat defective

2. Loss of refrigerant charge

3. Poor condenser efficiency

1. Check operation , replace if necessary

2. Fit new cooling system

3. Check condenser and remove any obstructions to air flow

1. Less quantity of refrigerant in system or loss of refrigerant

2. Compressor suction strainer clogged.

3. Excess oil in the system.

1. Trace and repair leak, recharge .

2. Clean or replace the strainer

3. Drain excess oil from condenser and evaporator

1. Plant under capacity

2. Excessive liquid refrigerant from expansion valve

3. Suction valve leaking

4. In correct super heat setting

5. Bulb not properly fixed

1. Reduce load

2. Adjust the expansion valve

3. Check valve plates, replace if necessary

4. Adjust setting

5. Secure the bulb to suction line andis not affected by other sources.


8. Suction pressure fluctuates


9. High discharge pressure


10. Low discharge pressure


1. In correct super heat setting

2. Un even load at evaporator

3. Equaliser line restricted

4. Oil in suction line affecting temperature sensed by valve bulbs

1. Adjust setting

2. Check condition of distributor

3. Clean or replace line

4. Do not locate valve sensing element in a section of line likely to form an oil trap

1. Discharge valve is not properly open

2. Air or non-condensable gases present in system

3. Cooling water through condenser is not sufficient

4. Temperature of water entering the condenser is high

5. Scale formation in condenser tubes.

1. Open the discharge valve

2. Purge the condenser

3. Increase the circulation of water

4. Check cooling tower and ensure that water at proper temperature enters the condenser

5. Clean the condenser tubes

1. Discharge valve leaking

2. Excess water supply

3. Low water temperature

4. Compressor not getting loaded.

1. Check valve plates , replace if necessary

2. Reduce the water supply

3. Regulate water supply at correct temperature

4. Follow the loading pattern


11. Ice formation is slow


12. Moisture formation on exterior


13. Works, but cabinet is not cold enough i.e cabinet


1. Temperature control is not properly set

2. Door opened too frequently

3. Thermostat knob is not set on to colder settings

1. Check and reset temperature control

2. Avoid opening of door unnecessarily

3. Due to some obstruction doormay not closed. Check and repair

1. Wipe the moisture periodically

2. Check the door gasket forproper door sealing

1. High humid weather

2. Defective door gasket

1. Temperature control is not properly set

2. Out side temperature may be very high

3. Door kept open for long period

4. Circulation of air is blocked by the items on shelves

1. Check and reset temperaturecontrol

2. Reset thermostat to maximumknob setting

3. Close the door immediatelyafter use

4. Rearrange the items soted.


14. Moisture collection inside


15. Refrigerator gives mild shocks

Possible causes

1. Earthing is not proper

Remedy

1. Check the earthing rectify if defective, If the refrigerator gives shock, remove the plug from the wall socket and call authorized technician

7.7 Trouble Shooting in Air - Conditioning SystemAir-Conditioning system is very expensive and it must be maintained

properly. Proper maintenance schedule must be followed to avoid breakdown. Some of the problems related to air-conditioning system with possiblecauses and remedies are discussed below.

1. Compressor and condenser fan motor will not start.

Possible causes Remedies

1. Humid weather

2. Storage of hot food

3. Under utilization of refrigerator compartment

1. Avoid opening door frequentlymoisture carried by air condenseson the surface of inner body.

2. Avoid storage of hot food.

3. Follow loading pattern

(i) Call fuse off call office

(ii) Replace defective fuse- check for possible high voltage and short circuits.

(iii) Repair or replace thermostat

(iv) Check wiring and kake necessaryrepairs

(v) Check controls, replace defectivecontrols

(i) Power failure

(ii) Fuse blown

(iii) Defective thermostat

(iv) Faulty wiring

(v) Defective controls


2. No air flow, compressor runs

Possible Causes Remedies

3. Compressor will not start, but condenser fan runs


4. System short of capacity


(i) Bending of the fan-motor shaft or blades

(ii) Defective fan motor

(iii) Defective relays or capacitors

(i) Check fan motor shaft and blades, repair or replace the blades

(ii) Replace fan motor

(iii) Check for short circuits, replace relays or capacitors as required

(i) Check compressor wiring and repair

(ii) Replace the compressor

(iii) Replace the capacitor

(iv) Check and repair, replace thermostat

(i) Circuit to compressor open

(ii) Defective compressor motor

(iii) Defective compressor starting capacitor

(iv) Defective circuit to thermostat if defective

(i) Low refrigerant charge

(ii) Defective expansion valve

(iii) Dirty condenser

(iv) Compressor valve leaking

(v) Expansion valve or strainer plugged.

(i) Check for leaks, repair leaks andcharge refrigerant

(ii) Repair or replace expansion valve

(iii) Clean the condenser

(iv) Replace valve plate assembly

(v) Clean expansion valve and strainer


5. Compressor is noisy


6. Compressor losses oil


7. Compressor runs continuously


8. Evaporator fan runs compressor will not start


(i) Worn compressor bearings

(ii) Over charge of oil

(iii) Broken compressor valves

(i) Replace the compressor

(ii) Remove excess oil

(iii) Replace valve plate assembly

(i) Oil trapped in the system

(ii) Leakage through piston rings

(iii) Excessive super heat

(i) Check oil separator, if it correct,replace the refrigerant piping

(ii) Replace the piston rings

(iii) Adjust super heat setting

(i) Low refrigerant charge

(ii) Excessive load

(iii) Thermostat setting too low

(iv) Compressor valve leaking

(v) Dirty condenser

(i) Check the system for leaks, repair leaks and add refrigerant

(ii) Check for excessive infiltration and excessive source of moisture

(iii) Reset the thermostat

(iv) Replace valve plate assembly

(v) Clean condenser

(i) Compressor electrical interlocks not completed

(ii) Compressor safety control open circuit

(iii) Defective compressor

(i) Locate and rectify the fault

(ii) Locate and rectify the fault

(iii) Check and replace if necessary


9. Insufficient cooling


10. Humidity too low


Summary• Refrigerant equipment and Air-Conditioned equipment should be

maintained properly for good functioning

• The symptoms are the sign of troubles in the system. The mainsymptoms of gas shortage are

(i) Insufficient cooling

(ii) Power consumption is high

(iii) Excessive heating of compressor parts

(i) Insufficient chilled water supplied to cooling coil

(ii) Restricted air flow over cooling coils

(iii) Excessive cooling load

(iv) Internal sealing of chilledwater system.

(i) Check chilled water valve

(ii) Check air filters, cooling coil clean lines and fan operation, rectify the defects

(iii) Check the space for doors , windows and other heat sources, reduce the cooling load

(iv) Clean entire system chemically recharge chilled water system.

(i) Defective controls

(ii) Humidified capacity is low for given conditions

(iii) Cooling system defect

(i) Check controls , replace if necessary

(ii) Check the requirements; arrange booster humidifier if necessary

(iii) Check cooling coils, replace if necessary


• Gas shortage is mainly due to leakage in the system. The variousmethods of leak detection for specific refrigerant are

(i.)Ammonia - Sulphur candle test

Litmus paper test

(ii) Freons - Soap solution test (Bubble test)

Halide test lamp

Electronic leak detector is a very sensitive instrument. It is used todetect leak of any refrigerant.

Short Answer Type Questions1. What are the various symptoms of gas shortage in the system?

2. How the leakage test conducted for Ammonia refrigerant?

3. Describe the working principle of Halide test lamp.

4. State any four causes and remedies for Refrigerator unit does not run.

5. Write four causes and remedies for Refrigerator runs very fast.

6. State any four causes and remedies compressor and condenser fan motor will not start.

Long Answer Type Questions1. Describe the different methods for leak testing of the following refrigerant.

(a) Ammonia

(b) Freon

(c) Sulphur dioxide

2. Explain the possible causes and remedies for the following problems

(i) Noisy operation

(ii) Suction pressure fluctuates

(iii) High discharge pressure.

3. Explain any six Trouble shootings in Refrigeration system.

4. Write any six trouble shooting s in Air-Conditioning system.

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