03.BE REFRIGERATION AND AIR CONDIONING,(Class Room).ppt

8/16/2019 03.BE REFRIGERATION AND AIR CONDIONING,(Class Room).ppt

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Heat Transfer Heat Transfer

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Types of refrigerants

Refrigerants are categorised by their chemical composition of

chlorine, fluorine, carbon and hydrogen. We have four

categories that we use and below is mentioned examples ofrefrigerants in the different groups and their composition.

CFC Chlorine!Fluorine!Carbon

HCFC Hydrogen!Chlorine!Fluorine!Carbon

HFC Hydrogen!Fluorine!Carbon

HC Hydrogen!Carbon

Category Type Trade name Mixture Chemical nameCFC R-11 Freon, Genetron, Frigen –11 R-11

(1! trichlorofluoromethane

CCl"F R-1# Freon, Genetron, Frigen –1# R-1#

(1! dichlorodifluoromethane (CCl#F#! 2


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Types of refrigerants, contd$T

ypes of refrigerants, contd$

HCFC R-## Freon, Genetron, %ol&ane –## R-## (1!

chlorodifluoromethane (C'CF#!

HFC R-#" Freon, Genetron, %ol&ane –#" R-#" (1!

trifluoromethane (C'F"!

R-1")a *lea, Genetron, %ol&ane –1")a R-1")a (1!

1,1,1,#-tetrafluoroethane (C'#FCF"!

R-))a %u+a '#, .tochem F/-0R-1#21)"a21")a ())2#2)! -

R-)1"a 3sceon )4 – Rodia

R-#1521")a2a (42552"! - R-)10a 3sceon 4 – Rodia

R-1#21")a2 (),22",)! - HC " natural

R-#4 ropane 'C-#4 (1! C'"C'#C'"

R-a 3so6utane R-a (1! C'(C'"!#-C'"

R-010 .mmonia R-010 (1! 7'"

R-0)) Car6on 8ioxide R-0)) (1! C9# 3


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%afety considerations%afet

y considerations

Refrigerants have to be handled correctly and one has to

observe the correct safety precautions to avoid accidents.

There are three factors that have to be ta#en intoconsideration

$. %oisonous products develop when refrigerants are

exposed to high temperatures, which is why smo#ing is

forbidden around refrigeration installations. &efore anysoldering or bra'ing is performed on piping or components the

system has to be emptied of refrigerant.

(. )ea#ing refrigerant can cause free'er burns as the boiling

point temperature of refrigerants at normal atmosphericpressure are well below the free'ing point. *oggles and gloves

have to be worn when handling refrigerants.

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+afety %recautions contd.

. -nhalation of larger amounts of refrigerant can cause

Headache, difficulty of breathing, irregular heart beat, narcosis,

di''iness and irritation of the respiratory system.

Glo6al :armingGlo6al :armi

ng

ne impact that the burning of fossil fuels has had on the earth/s

environment has been the increase of carbon dioxide 0C(

1 in the

earth/s atmosphere. The amount of atmospheric C( apparently

remained stable for centuries, at about (23 ppm 0parts per million1,

but over the past $33 years it has increased to 43 ppm.

The significance of this change is its potential of raising thetemperature of the earth through the process #nown as the

greenhouse effect. Carbon dioxide in the atmosphere tends to

prevent the escape of outgoing long!wave radiation from the earth to

outer space5 as more heat is produced and less escapes, the

temperature of the earth increases. 5


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*lobal Warming contd.

6 significant global warming of the atmosphere would have

profound environmental effects. -t would speed the melting of

polar ice caps, raise sea levels, change the climate regionallyand globally, alter natural vegetation, and affect crop

production. These changes would, in turn, have an enormous

impact on human civilisation.

+ince $743 there has been a mean rise in global temperature

of about $8 C. +ome scientists have predicted that rising levels

of C( and other 9greenhouse gases: will cause temperatures

to continue to increase, with estimates ranging from (8 to 28 Cby the middle of the ($st century. However, other scientists who

research climate effects and trends dispute the theories of

global warming, and attribute the most recent rise to normal

temperature fluctuations. 6


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9;one layer 9;one layer

The 'one )ayer , in nature, a region of the atmosphere from $; to


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9;one layer, contd$9;one layer, contd$

For several years, beginning in the late $;=3s, research scientists wor#ingin 6ntarctica detected a periodic loss of o'one in the atmosphere high

above that continent. The so!called o'one 9hole: develops in the 6ntarctic

spring and continues for several months before closing up again. therstudies, conducted using high!altitude balloons and weather satellites,

indicated that the overall percentage of o'one in the 6ntarctic o'one layer is

declining. Flights over the 6rctic regions found a similar problem developing

there.

-n $;74, a >nited ?ations convention #nown as the 9@ontreal %rotocol:,

signed by pper 6tmosphere Research +atellite. rbiting earth at

an altitude of 233 #m 0=( miles1, the spacecraft measures o'one variations

at different altitudes, and is providing the first complete picture of upper

atmosphere chemistry. 8


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9;one 8estruction9;one 8estruction

-n the $;=3s and $;73s, scientists began to find that human activity was

having a detrimental effect on the global o'one layer, a region of the

atmosphere that shields the earth from the sun/s harmful ultraviolet rays.

Without this gaseous layer, which is found at about


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6 thinning of the o'one layer exposes life on earth to excessive ultraviolet

radiation, which can increase s#in cancer and cataracts, reduce immune

system responses, interfere with the photosynthetic process of plants, and

affect the growth of oceanic phytoplan#ton.

&ecause of the growing threat of these dangerous environmental effects,

many nations are wor#ing towards eliminating the manufacture and use of

CFCs at least by the year (333. However, CFCs can remain in the

atmosphere for more than $33 years, so o'one destruction will continue to

pose a threat for decades to come.


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RefrigerantRefrigerant =ears =ears 9898 G>G>

R!$$ 0CFC1 23 $.33 $.33

R!$( 0CFC1 $(3 3.; .(3

R!(( 0HCFC1 $; 3.34 3.<

R!$


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-n the list the B% and *W% are relatively figures and made in

relation to CFC R$$, which is chosen as reference. 6ccording to this

for instance R(( is (3 times better than R$$ on B% and (.4 times

better on *W%.

6nother @ethod to calculate the environmental impact of refrigerants

is Total Auivalent Warming -mpact 0TAW-1, which is the sum of the

direct effect and the indirect effect. The indirect effect includes the

environmental impact during the energy production for the operation

of the refrigeration plant, and thus the efficiency of the refrigerant assuch is considered.

-f ! regionally or internationally ! an environmental duty based on

C(!emission is decided, it will be a calculation of the TAW- that

should be ta#en into consideration when choosing a refrigerating

plant andGor a refrigerant.

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Heat is a form of energy that is transferred from oneobject to another object.

Heat Is a form of energy transferred by a difference intemperature.

Heat transfer can occur, when there is a temperaturedifference between two or more objects. Heat will onlyflow from a warm object to a colder object.

The heat transfer is greatest, when there is a largetemperature difference between two objects.

If any liquid is allowed to pass through an orifice, thetotal heat energy of the liquid before expansion will besame as the total heat energy after expansion.

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Phase Change Diagram

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The Boiling Point Depends on the Liquid Temperatureand the Atmospheric Pressure

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The ?oiling oint 8epends on the i@uid Temperature and

the .tmospheric ressure

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p-h diagram (Mollier)p-h diagram (Mollier)


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Both start with a liquid and end with a gas. But they aredifferent proesses.

Evaporation:

!tritly a surfae pheno"ena#urs at any te"perature

Some hotter $faster%&than&a'erage partiles o'ero"e thefores they feel fro" their neigh(ors and esape the

liquid) ta*ing their heat energy with the".+ores only felt fro" partiles (eneath the"

Avaporation vs &oilingAvaporation vs &oiling

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apor %ressure and &oiling %ointapor %ressure and &oiling %oint

,'aporation in a losed ontainer will proeed until

there are as "any "oleules returning to the liquid

fro" the 'apor a(o'e the liquid as there areesaping & the 'apor is then said to (e saturated. -he

pressure of that 'apor is alled the saturated 'apor

pressure.

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B ili


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Boiling:

Happens throughout the liquid.

Occurs at the boiling point/temperature

Average motion of particles is fast enough tooercome the forces holding them closetogether ! all the particles are trying to escape! liquid turns to apor

"orces felt from particles all around them

#oiling point dependent on atmosphericpressure ! steam bubbles form in liquid onlywhen apor $steam% pressure exceedsatmospheric pressure $plus pressure of water

pushing down% 20

& l l 'i ti i


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&olecular 'inetic energy isgreater at highertemperature ! moremolecules can escape the

surface and the saturatedapor pressure iscorrespondingly higher.

If the liquid is open to theair, then the pressure of theair opposes the escape ofthe molecules.

The temperature at whichthe apor pressure is equalto the atmospheric pressureis called the boiling point.

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Heat of Fusion Measurement Heat of Fusion Measurement

(dd )* grams of ice $at *+ % to )** grams of water.

-hat is the heat of fusion of water &ass of water&

&ass of ice m

Hf heat of fusion of water

To initial temperature of ice Tw initial temperature of water

Tf final temperature of water

Heat required to melt the ice mHf

Heat required to raise the temperature of meltedice to final temperature of water cm 0T cm$Tf! To%

Heat absorbed from water c& 0T c&$Tw!Tf%22

P f l dP

i f li id i


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Properties of liquid at varying temperature Pro perties of liquid at varying temperature9+aturation Temperature: I can be defined as thetemperature of a liuid, vapor, or a solid, where if any

heat is added or removed, a change of state ta#esplace. 12atent Heat3! The heat required to change aliquid to a gas $or the heat that must be remoed

from a gas to condense it to a liquid%, withoutany change in temperature.( fluid requires and absorbs large quantities ofheat when it changes state from liquid to a

apour. The heat absorbed during this process iscalled the latent heat of eaporation. )iuification. 6 vapour or gas can be liuified bycompression and cooling . This process is called

liuification. 23


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REFR!ERAT"# A#D AR $"#D"##! REFR!ERAT"# A#D AR $"#D"##!The obJect of refrigeration is to prolong the storage life

of a perishable food product by lowering its temperatureso that metobolic detoriaration and decay caused by

micro!organism are retarded.

The perishable cargo being carried by sea underrefrigeration in refrigerated vessels and in containers.

%erishables materials are Fro'en produce, meats,

seafood , diary produce such as flowering bulbs andfresh flowers , confectionary, chemicals,pharmaceuticals

and photographic

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Refrigeration cycle Re frigeration cycle

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RefrigerationRefrigeration unit unit

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Cold RoomCold Room

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Flow diagram of vapour compression systemFlow diagram of vapour compression system

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V i tV

i t


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-he o"pressor re"o'es the 'apour fro" the e'aporator) the

te"perature and pressure of the 'apour are raised (yo"pression.

-he o"pressed 'apour flows thro the hot gas disharge line

in to the ondenser) using water or air as ooling "ediu".

-he 'apour in the ondenser first gi'es up its super heat and

then ooled fro" the disharge te"perature to the saturation

te"p orresponding to ondensing pressure then gi'es up itslatent heat as it ondenses (a* to liquid.-he liquid then flows

fro" the (otto" of the reei'er to o"plete the yle.

hen the liquid te"p is (elow the ondensing te"p it is said

to (e su( ooled.

Vapour compression systemVa pour compression system

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-he liquid refrigerant stored at high pressure in the reei'er.

/t flows through the liquid line to the flow ontrol 'al'e$-her"ostati epansion 'al'e%whih regulates the rate of

flow to the e'aporator to suit the e'aporation and also the

pressure of the liquid is redued to the e'aporating pressure so

that the te"perature of the refrigerant entering the e'aporatoris (elow that required in the refrigerated spae.

-he liquid 'apour refrigerant "iture then flows through the

e'aporator etrats heat fro" the refrigerated spae andhanges to a dry saturated 'apour at appro the sa"e te"p and

pressure at whih it left the flow ontrol 'al'e.

Vapour compression systemVa pour compression system

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Compressor types


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Compressor types

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&efrigeration Compressors:

Types:

1. eiproating o"pressors.

2. !rew o"pressors.

3. entrifugal o"pressors.

4. er"eti or !e"i&er"eti o"pressor.

5. !roll o"pressors

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The suction stro#e is when the


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Compressor Com pressor The suction stro#e is when the

piston moves downwards in the

cylinder, and when the pressure

in the cylinder is lower than the

pressure in the suction port, theinlet valve will open.

The refrigerant vapours are

suc#ed into the cylinder.

When the piston changes

direction the compression begins

and the inlet valve closes.

When the pressure in the cylinderis higher than the pressure in the

outlet port, the outlet valve will

open and the refrigerant vapours

are discharged.36


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ompressor bodiesFridge compressorFri

dge compressor


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ompressor bodiesare normally of closegrained castings ofiron or steel. &odern

ales are of thereed or disc typemounted in the headand are of high gradesteel on stainless

steel seats with ausual lift of about4mm. onnectingrods are aluminium

with steel bac'edwhite metal big ends.The cran'shaft isspheriodal graphiteiron.

Fridge compressor Fri dge compressor

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The pistons aremade from cast iron in older units, and

of aluminium alloy more recently.

The piston isattached to thecran'shaft by conrod in the normalmanner.

It should be notedthat the cran'caseis full of refrigerantgas at suctionpressure.


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Fridge compressor Fri dge compressor 2iners are made fromhigh tensile cast iron.

2ubrication is generallysplash only for smallercompressors with acran'shaft drien gear

pump supplying bearingson larger machines.

It is important tounderstand that actual

pumped lube oil pressureis the indicated pressureless this cran'casepressure.

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The properties of the2ubricating oil used inare compressors are

critical and specific tothe refrigerant gasused.


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Advantages of Reciprocating compressor:


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Advantages of Reciprocating compressorThis is ideal for refrigerant plant having small displacementand high condensing pressure.As the valve area is limited it is uneconomical for low-pressure

refrigerant.Economical in manufacture and durable.

Advantages of Screw Compressor:•Unaffected by load variation.

•Oil injection etends the wor!ing range.•"ibration free operation.•#ontinuous capacity control from $%%& to $%&.•'eriod between successive overhauls can be etended.•(ue to faults in line) if the *reon is drawn in) it will passthrough without damaging the compressor.

Disadvantage:•A large and efficient oil separator is needed due to injection

of oil.


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Compressor shaft seal Compressor shaft seal

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MechanicalMechanical sealseal


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Mechanical Mechanical seal seal The carbon seal andflexible bellows is

fixed in way of themounting plate andthe hard runningsurface is allowed torotate.

This is the opposite tothe set up for sealsmounted on pumps.

The finish of the runningsurface of the seal isextremely fine.

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Mechanical sealMechanical seal


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when the surface has been

damaged say by the deposit

of copper, it is possible to lapthe face of the carbon.

The method recommended

is metal polish such asbrasso, on a true flat surface

on which is laid chart paper.

The chart paper absorbs thewear particles as they are

removed an a reasonable

finish is possible

Mechanical seal Mechanical seal

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-n semi!hermetic compressorsSemi Hermetic


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p

the electrical motor and the

compressor are built together

and the shaft seal is avoided

The electric motor is cooled by

means of the refrigerant

vapours being suc#ed through

the motor before entering the

cylinder. The whole compressoris usually air cooled, e.g. on

reefer containers by means of

air from the condenser

ventilator or on stationarysystems by means of a

separate ventilator.

)ubrication by forced lubrication

system

Semi Hermetic

Compressors

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%


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%


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er"eti o"pressors are

her"etially sealed "eaning that

the asing of the o"pressor is

fully welded.

sed in s"aller refrigeration

plants as s"all air onditioning

units) do"esti refrigerators and

do"esti freeers.

+ro" the fatory these plants are

filled with an adequate a"ount of

refrigerant and lu(riating oil.

+f the compressor brea!s+f the compressor brea!sdown it has to be renewed asdown it has to be renewed as

you can not repair it. you can not repair it.

Hermetic compressor

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-he refrigerant 'apours areH ti


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g p

su*ed into the asing) through

the eletri "otor for ooling and

into the ylinder.

+ro" the ylinder theo"pressed 'apours are

disharged through the outlet

pipe on the o"pressor.

-he surrounding air usually pro'ides suffiient ooling of the

o"pressor.

s with the other o"pressors the

lu(riation oil is in ontat with

the refrigerant and "ust (e

o"pati(le with the refrigerant

(eing used.

Hermetic compressor

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HERMETIC -HERMETIC -


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The advantage of the scrollcompressor is that it weightsabout $G of a piston compressor

with the same output.There are fewer movable parts andmuch less vibration and noiselevels compared to the pistoncompressors.

The scroll compressor is becomingmore freuently used as bettermaterials have been developedfor the helices, ma#ing thecompressor more reliable.

with the scroll compressor thedemand for lubrication of thehelices are very high and that theoutlet temperatures of thevapours are very high as well.

HERMETIC -HERMETIC

SCROLLSCROLL

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Hermetic scroll compressorsHermetic scroll co

mpressors


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Hermetic scroll compressorsHermetic scroll compressors

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scroll compressorsscrol

l compressors


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scroll compressorsscrol l compressors

o"pression in the sroll is reated (y the intersetion of an or(iting

spiral. as enters an outer opening as one of the spirals or(its55

Sliding vane compressorSlidi

ng vane compressor


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Sliding vane compressor Slidi ng vane compressor

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Rolling piston compressorsRolli

ng piston compressors


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Rolling piston compressors$Rolli ng piston compressors$

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R lli i tRolli

ng piston compressor


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Rolling piston compressor Rolli ng piston compressor

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These compressors

R t CR

t C


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are used mainly in

house hold

applications but

modern practice sees

there use in cargo

conditioning.

( ariation on this isthe multi blade type

where the rotor has

slots cut in it, fitted to

which are springloaded blades.

(lternately the blades

may rely on

centrifugal force.

Rotary Compressor R otary Compressor

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#oth these types , when theRotary Compressor

Rotary Compressor


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compressor is stopped thesealing pressure and oil filmare bro'en and there fore

the suction and dischargeare common. This reducesstarting loads but requires asuction non return ale to

be fitted.-here these are fitted tolarge refrigeration systemsit is possible to use ariable

speed thyristor controlledelectric motors. Thereby thecompressor can run atoptimal reolution tomaintain plant efficiency.

Rotary Compressor Rotary Compressor

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Centrifugal compressorCentrif

ugal compressor


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Centrifugal compressor Centrif ugal compressor

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Centrifugal compressorCentrif

ugal compressor


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Centrifugal compressor Centrif ugal compressor

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2 Stage Centrifugal compressor2 St

age Centrifugal compressor


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2 Stage Centrifugal compressor 2 St age Centrifugal compressor

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#y the nature of the system apossibility exists whereby liquidmay be passed to thecompressor suction

To preent serious damage,some form of unloading deice isnormally fitted.

In this case the suction aleassembly is held on the liner bya heay gauge spring.

In the eent of liquid passing tothe compressor the suction alewill lift against this spring

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unloader unloader


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5ormal oilpressure moing

sleee downagainst the springpressure.

6nloadedcondition the oil

pressure isreleased pin

moes upward bythe springpressure causesthe ale to lift

from its seat. 67

unloaderunloader


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unloader unloader

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Bifferent types of oil are available for lubrication and inrefrigeration systems the two most used types are mineral oil


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refrigeration systems the two most used types are mineral oiland synthetic oil.

@ineral oil is produced by refining crude oil and was used as

lubricant with the old types of refrigerants 0CFC and HCFC1because these refrigerants and mineral oil are soluble. When introducing HFC!refrigerants 0e.g. R $


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g p p

2. rise in ran*ase pressure (eause of rise in

e'aporator load inrease the pressure against the (ellows

and o"presses the range adusting spring.

3)o"pression of the range adust"ent springs allows

the 'al'e springs to "o'e the push pins and 'al'e

needle point toward the 'al'e seat

4 . -he 'al' e throttle the flow of ontrol oil to the

ran* ase ausing the ontrol oil pressure to (uild

up ) oil enters apaity ontrol iruit thro orifie

fro" o"pressor oil pu"p iruit.

5.the inreased oil pressure pushes the relay piston

against the spring opens passages (etween the oil

pu"p and the unloader power ele"ents)

6.the pu"p oil pressure in the unloader power

ele"ents fores the piston upwards pi'oting the lifting

for*

7. -he lifter pins drop and seat the sution 'al'e

loading the ylinder 71


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Condenser Condenser

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&affle plate arrangement'( type)&affle plate arrangement'( type)


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&affle plate arrangement'( type)&affle plate arrangement'( type)

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T % i *

i *


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Tu%eTu%e repair wor* r epair wor*

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Tu%e stac*Tu%e stac*


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Tu%e stac* Tu%e stac*

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Condenser+Condenser+


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7enerally a water cooled tube cooler.

( safety ale and ent are fitted. The purpose of theent is to bleed off non!condensibles such as air whichcan enter the system when the suction pressure isallowed to fall below atmospheric or can be containedwithin the top up gas.

The presence of non!condensibles is generally indicatedby a compressor discharge pressure considerably aboethe saturation pressure of the refrigerant.

The coolant flow to the condenser is sometimestemperature regulated to preent too low a temperaturein the condenser which can effect plant efficiency due tothe reduction in pressure.

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h l

Si h Gl


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9ight glass are often of the #ulls eye form.This allows the operator to ensure that it is onl

liquid, and not a liquid/gas mix going to the expansioales.

On some designs a water indicator is incorporatedthis is a coloured ring in contact with the liquid, whewater is detected it changes colour, typically from pin' tblue.

Sight GlassSight Glass

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The moisture indicator serves todetect if there is moisture leaving

Moisture indicator


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detect if there is moisture leaving

the filter drier and is usually

situated in the liuid line Just after

the filter drier.

-t is of vital importance that the

moisture indicator indicates dry

as we donKt want moisture

entering the TL. -n the TL wehave a pressure and temperature

drop and here the moisture will

free'e to ice. The ice will bloc#

the flow in the TL and norefrigerant can enter the

evaporator thus hindering the

refrigeration unit from removing

heat from the cargo space

(ello ) *et+reen ) Dry

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S!#,N!(, V-#V, S!#,N!(, V-#V, The solenoid valve is aelectro magnetic valve which


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electro magnetic valve which

provides automatic opening

and closing of liuid and gas

lines. 6 solenoid valve is anelectrically activated valve

that can either be open or

closed

When the coil 01 isenergised the pilot orifice 0


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Filter (rier Filter (rier


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an be either a compacted solid cartridge or bags ofdessicant. The main purpose of this unit is to remoe the

moisture from the refrigerant.&oisture cause two main problems.

"irstly it can free


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Filter (rier Filter (rier 1

10.asing


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1.auge

onnetion

2.o'er

3.:oint

4.ithdrawing

handle.

5.spring

6.;istane piee

7.;i'ision plate.8.+elt washers.

9.aue plates.

10.asing

11./nlet

onnetion

12.#'al flange.

13.harging

onnetion

14.enter (olt.

15;rying agent.

16.etaining

slee'e.

17.#utlet

onnetion.

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Filter (rier Filter (rier


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Briers are used in the

liuid line to remove

any water moisture

accidentally admitted

to the system.

The common drying

agents are silica gel

and activated 6lumina

which can be activated

by heating

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,-TE&' -/ &E,&-+E&0T-%/ C-&C-T,-TE&' -/ &E,&-+E&0T-%/ C-&C-T


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& The 'lters are removed from location by

shutting the inlet and outlet valves of theequipment.& The 'lters are cleaned using electro cleanerand later (ushed with low pressure air.

& The drying agent is renewed if found to besaturated with moisture. )if silica gel is thedrying agent, a change in colour will con'rmsaturation with moisture*& The 'lters are 'tted bac% to its originallocation+ the air trapped is purged and 'lter putin operation.


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The system shown is

typical of that fitted on

many ships other than it

is more common to

hae two low

temperature rooms

rather than one.

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Compressor safety devicesC

ompressor safety devices The compressor is protected by three safety switchesA


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The compressor is protected by three safety switchesA

The 9 s:itch or 9il 8ifferential ressure s:itch compares

the measured lubricating oil pressure to the 9uction$cran'case% pressure. 9hould the differential pressure fallbelow a pre!set minimum $about ).4 bar% then thecompressor will trip and require a manual reset to restart.( time delay is built into the circuit to allow sufficient time

for the lubricating oil pressure to build up when startingbefore arming the circuit.

The ' or 'igh ressure s:itch, is fitted to the outlet ofthe compressor before the isolating ale. On oer

pressurisation $dependent on the refrigerant, up to about4;bar bar for @44% the switch will trip the compressor anda manual reset is required before restart.

The or o: ressure s:itch when actiated $ at about )91

Compressor control devicesC

ompressor control devices


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This normally ta'es the form of an 2B cut out pressure

switch with automatic reset on pressure rise. The cut outset point is just aboe the 2B trip point say at about).;bar. (n adjustable differential is set to about ).;bar togie a cut in pressure of around 4.C bar. The electricalcircuit is so arranged that een when the switch has

reset, if no room solenoid ales are open the compressorwill not start. This is to preent the compressor cyclingdue to a lea'y solenoid ale.

In addition to this extra 2B switches may be fitted whichoperate between the extremes of the 2B cut in and cutout to operate compressor unloaders.

9ome modern systems contain a rotary ane compressor

with ariable speed $frequency changing% control92

The aim of the thermostatic expansion valve is to ta#e care of thegreatest possible filling of the evaporator, in a way that liuid not


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g p g p , y

will escape out into the suction pipe of the compressor.

This is done by regulating the supply of refrigerant to theevaporator, so it Just euals the amount that evaporates during

absorption of heat in the evaporator.

6s the valve is controlled by the super!heating temperature at the

outlet of the evaporator, and the change of this, it is necessaryto use some of the last part of the evaporator for the

superheating of the refrigerant.

The thermostatic expansion valve consists of a small bulb

containing liuid refrigerant 0same type as in refrigerationsystem1.

The bulb is mounted on the outlet pipe of the evaporator and feels

the temperature of the refrigerant vapours leaving the

evaporator.93

To determine the superheating of the refrigerant the valve also needs

t th i th t hi h b d


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to measure the pressure in the evaporator which can be made

inside the TL 0internal pressure eualisation1 or by means of a

separate pipe 0external pressure eualisation1.

When the temperature is increasing the pressure in the bulb will

increase, and by decreasing temperature the pressure will

decrease.

The pressure from the bulb, is via a capillary tube, lead to the top of

the valve. -n the top of the valve there is a membrane which will

move up! or downwards depending of the changes in the pressure

in the bulb.

&elow the membrane there is a spring and a valve stem, which have

connection to the no''le thus opening the valve with increasingpressure and closing the valve with decreasing pressure.

94


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?ernoulli


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For hori'ontal fluid flow, an increase in the velocity offlow will result in a decrease in the static pressure.

98

In addition it also reduces theinternal heat absorption

ThermostaticThermostatic,.pansion valve,

.pansion valve


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internal heat absorptionprocess that occurs during theexpansion stage which is due toa small degree of flash off aslatent heat $of aporisation% isabsorbed from surroundingliquid to reduce the

temperature of the bul' liquidto the new correspondingsaturation temperature for thereduced pressure.

#y this process of boiling$apouri


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e.pansion valvee .pansion valve The expansion process iscontrolled by the action ofthe bellows and push pinsacting on the orifice aleplate.

The bellows is controlled by

a bulb which measures thetemperature of the gas atoutlet from the eaporator.

To ensure no liquid passes

through to the compressor,the expansion ale is setso that the gas at outletfrom the eaporator has 4to : degrees of superheat.

100


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Thermostatic e.pansion valveThermostatic e

.pansion valve


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103

as rom e sys em o e pumpe own o econdensercondenser&-ircuit brea%er of the compressor switched o and-ircuit brea%er of the compressor switched o and


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104

&-ircuit brea%er of the compressor switched o and-ircuit brea%er of the compressor switched o and

sign board /men at wor%0 to be placed.sign board /men at wor%0 to be placed.

&-lose the compressor discharge valve and release-lose the compressor discharge valve and releasethe pressure by slac%ening the drain plug of the oilthe pressure by slac%ening the drain plug of the oil

separator.separator.&pen the (oat valve and ta%e out the (oat out ofpen the (oat valve and ta%e out the (oat out of

the chamber carefully and clean internals thoroughlythe chamber carefully and clean internals thoroughlywith a clean rag and blow dry air such that thewith a clean rag and blow dry air such that the

partition mesh is cleaned.partition mesh is cleaned.&verhaul the oil return needle valve and 't bac% theverhaul the oil return needle valve and 't bac% the

(oat as original with new gas%ets and seal rings.(oat as original with new gas%ets and seal rings.&After tightening all the 'ttings, open the compressorAfter tightening all the 'ttings, open the compressor

discharge valve one turn and close bac% to pressuriedischarge valve one turn and close bac% to pressurie

the oil separator for lea% test.the oil separator for lea% test.&nce lea% test is satisfactory, the suction andnce lea% test is satisfactory, the suction and

ELECTRONIC TEMPERATURE CONTROL ELECTRONIC TEMPERATURE CONTROL

SYSTEMSYSTEM


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%peration:

-he te"perature sensor "easuresthe te"perature of the ooled air

lea'ing the e'aporator. -he

registered te"perature is

ontinuously o"pared in the

ontroller) with the pre&set

referene te"perature. s soon as

a differential ours (etween the

"easured and required

te"peratures) the ontroller sendseletri i"pulses to the "otor)

whih "o'es the spindle of the

pilot 'al'e up or down.

SYSTEM SYSTEM

105


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Safety controls and devices$Safet

y controls and devices$

& t f th t l l t i it h t t d b


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&ost of these controls are electric switches actuated bybellows moement ia amplifying leerage.

The bellows moes in response to pressure changestransmitted from the sensing point ia a connecting tube.

High pressure safety cut outF

used to protect against high discharge pressure which willoerload the compressor and may damage components.

The control is set to stop the compressor motor at apressure of about G*E of the maximum wor'ing pressure

of the system.

9ome controls restart the compressor automatically ondrop in pressure others hae a manual reset mechanism.

111


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Thermostats these are temperature controlled electricswitches can be used for both safety and control

functions.

$. When fitted to compressor discharge lines they areset to stop if the compressor discharge temp is too

high.

(. used to control the temp in a refrigerated space bycycling the compressor on and off or by opening and

closing a solenoid valve in the liuid line.

113

High pressure safety

High pressure safetycut out cut out

used to protect against highdischarge pressure which will

overload the compressor and


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overload the compressor and

may damage components.

set to stop the compressormotor at a pressure of about

;3N of the maximum wor#ing

pressure of the system.

+ome controls restart the

compressor automatically on

drop in pressure others have

a manual reset mechanism.

6.&ellow &. %ressure pipe connection C.*uide washer B.Catch

A.Catch spring F.+witch arm *.+pring contact O.@ain +pring

P.+crewed spindle for 6dJusting pressure114


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Hp cut out H

p cut out


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116


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#p cut out

#p cut out -he push pinoperates the swith thro

hi h i


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a ontat whih is

flipped open or lose

thro a oiled spring

plate

ith the ontat open

the spring is oiled

#utward "o'e"ent

of the pin o"presses

the spring and this thenflips the ontat to

lose the o"pressor

starting iruit.120


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>sed to protect against too lowoil pressure in forced lubrication

system -t is a differential control

!il pressure safety!il

pressure safetycut out$cut out$


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system.-t is a differential control

using two bellows, one side

represents low side pressure andthe other responds to the oil

pressure.The oil pressure must always

be greater than the low side

pressure for the oil to flow. -f the oil pressure falls below a

minimum value the control stops

the compressor after a certain

time has lapsed

cut out$cut out$

1.@icro switch (.*land nut

. Ring seal


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&ac* pressure regulator valve&ac*

pressure regulator valve This ale is fitted to the higher temperature rooms,egetable and flour $?Do% only and not to the &eat and


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egetable and flour $?Do% only and not to the &eat and"ish rooms $!4*o%.

They sere two main purposes.

"irstly when all solenoid ales are opened they act assystem balancing dierters, that is they restrict the liquid flow to the rooms which can be 'ept at the higher

temperature and delier the bul' to the colder rooms.9econdly they sere to limit the pressure drop across theexpansion ale by giing a set minimum pressure in theeaporator coil. This in turn limits the temperature of the

refrigerant thereby preenting delicate foodstuffs such asegetables from being damaged by haing air at ery lowtemperatures blown oer them. 6ltimately they may alsobe set to proide a safety limit to the room temperature by restricting the pressure to gie a corresponding

minimum saturation tem erature of *o.125


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&RECIPROCATIN COMPRESSOR LUBRICATIN OIL

S"STEM:


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131


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COMPRESSOR STARTIN AND STOPPIN TOO OFTENCOMPRESSOR STARTIN AND STOPPIN TOO OFTENON LO#- PRESSURE S#ITCH!ON LO#- PRESSURE S#ITCH!

CAUSESCAUSES


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133

C US S&@vaporator coils clogged with frost.

&7iquid, suction or expansion valve 'lters clogged.&!ensing bulb on expansion valve has lost charge.& The delivery valves of the compressor lea%ing.&7ea%y solenoid valve.&@xpansion valve choc%ed with ice.

RECTIFICATIONRECTIFICATION&6efrost coils.&2ump down and clean 'lters.&4f delivery valves are lea%ing, remove cylinder head,

examine, replace if necessary.&6etach thermal bulb from suction line and hold in palmof one hand, with the other hand gripping the suction line+if (ow of refrigerant is felt, bulb has not lost its charge. 4fno (ow is noticed, replace expansion valve.

& 4nsucient gas in system.& Too much oil circulating in system.


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134

g y&4mproper ad8ustment of expansion valves.

&Bloc%age in liquid pipe, expansion valve orsuction 'lters.

RECTIFICATIONRECTIFICATION

1. @vacuate, isolate, remove, inspect and clean'lters.". -harge with more refrigerant.$. 4nspect to see whether oil has accumulated

anywhere in the system. 4f accumulated, thenretrieve the collected oil bac% into compressor5. !et the expansion valves to feed more

refrigerant


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(efrost system(efrost

system &oisture free


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restriction and reducing the efficiency of the plant. Thismust be periodically remoed.

"or >eg and "lour rooms, were restricted to *o minimumby the bac' pressure ale, this is carried out once perday.

"or the &eat and "ish rooms this has to be carried out

two or more times. ue to the low temperature in therooms it is necessary to fit a drain heater.

-hen on defrost the solenoid ale is shut and the fan isoff.

On some systems at end of defrost the solenoid ale isopened momentarily before the fan is started. This allowsmoisture to be snap fro


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The effects of oercharge are a full condenser/receiergauge glass. 9ystem pressures are not effected until

highly oercharged when a possibility of excessie HBpressure exists.

6ndercharge causes failure to maintain cold roomtemperatures and compressor short cycling. ompressor

cycling is caused by there being insufficient gas tomaintain the compressor loaded een with all roomsolenoids open.

In extreme the compressor will cut in and out.

6ndercharge is detected by low leels in thecondenser/receier gauge glass/ bubbles in liquid sightglass, compressor short cycling and low suctionpressures. 137


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CAUSESCAUSES-ondition may be due to4 i t t ( i th h d


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139

&4nsucient water (owing through condenser.&-logged condenser.&


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140

& There are possibilities of small air bubbles in the liquidsight glass of the condenser.

&-ondensing pressure of the refrigerant in the condenserwill be high.&4f there is excessive air, it may reduce the coolingcapacity of the system, ma%ing the compressor to run for

the extended period of time.&4t may cause the gauge pointer of the pressure gauge to8ump inde'nitely.CAUSES:&6uring charging refrigerant or oil, air may enter into thesystem.&4f ;reon=1" is used air may lea% into the suction linebecause the wor%ing pressure of the ;reon=1" refrigerantis close to the atmospheric pressure.

&6uring standby mode air may enter into the system & , &%$ !

0CT-%/:

&Air in the system can be removed by collecting the


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141

&Air in the system can be removed by collecting thesystem gas in the condenser, leaving the condenser

cooling water on and venting out the air from the top ofthe condenser because air will not be condensed in thecondenser but remain on top of the condenser above theliquid refrigerant.

-onnect the collecting cylinder to the purging line of thecondenser, open the valve, and collect air in the cylinder.&After purging the air from the system don’t forget to shutthe purging valve.&-hec% the level of the refrigerant in the system. 4f

required, charge the system with fresh refrigerant.&9estart the compressor with all safety precautions.

&ur ng c arg ng o re r geran an u r ca ng oand after renewal of any components li%e

solenoid valve, exp valve, drier air may enter into


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142

the system.

&4f ;reon=1" is used air may lea% into the suctionline because the wor%ing pressure of the ;reon=1"refrigerant is less than the atmospheric pressure.&6uring standby mode air may enter into the

system .& Through the system valve glands and lea%ycompressor seal during pumping down operation&4f the 72 cut out does not function then vacuum

conditions could be produced as a result ofcompressor not stopping C this could induce airinto the system.

Re'%3 %6 &%$*'i$*e+ re6riger$*Re'%3 %6 &%$*'i$*e+ re6ri

ger$*$. The pumping down of the gas to be carried out to collect the completesystem gas to the condenser and later close the condenser outlet valve. 7witch off the circuit brea!er


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143

. 7witch off the circuit brea!er.1. The empty *reon gas cylinders must be cooled in a fish room to bring

the temperature appro. ()* deg C+2. The cooled cylinders are connected to the charging valve between thecondenser and filter drier unit.3. Open the empty cylinder valve and condenser outlet valve) the li8uefiedgas from the condenser is transferred to the bottle due to the

differential pressure.5. 4enew bottles to collect all the gas present since single bottle would notbe enough to collect the gas.6. The reason for more gas bottles is that temperature of bottles riseduring collection process e8uali. #harge fresh *reon gas to the system to normal condenser level.$%. +t may be re8uired to renew silica gel couple of times even afterrenewing the refrigerant) d,e to -eft over moist,re adhering to the

wa--s of condenser

INDICATIONINDICATIONThe rese$&e %6 '%is*ure is i$+i&*e+ i$ *he sigh*gss 1**e+ i$ *he i8ui+ i$e&Doisture in the !ystem comes with the ingress of air in


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144

&Doisture in the !ystem comes with the ingress of air inthe system.

CAUSESCAUSES&Doisture will tend to develop inter crystalline embrittlement of brassor copper bellows, such as used in the high pressure control switch+and leads to corrosion on compressor valves, pistons, shaft, etc&Doisture may freee at the expansion valve, giving some of the

indication of under charging. Doisture will contribute to the corrosionin the system and may cause lubrication problems and brea%down ofthe lubricating oil in the reciprocating compressor.&Doisture can freee to ice in the evaporator and cause bloc%ageinside the evaporator coil.

&Doisture can form acids by reaction with ;reon refrigerant. This acidattac%s the copper lines and deposits in the other parts of thesystem.& Thus moisture causes adverse troublesome eects when it isdeposited on the compressor mechanical seal faces leading to

damage and lea%age and the 'ne particles could possibly bloc% the

1. 4n a refrigeration system it is essential toreduce the moisture content of refrigerant to aminimum by careful drying of components and


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145

minimum by careful drying of components andby 'tting 'lter drier units with drying agents in

the system.". The operation of the 'lter drier in refrigerationis to remove moisture and to prevent othercontaminants entering and bloc%ing theexpansion valve or deposit in the compressor,mechanical seal faces leading to damage andlea%age.

nder harging "eans either the syste" is harged with lesserrefrigerant) or it has lea*ed out fro" the syste". -he syste" runs with

less a"ount of gas in irulation.


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146

-/D-C0T-%/:&-ompressor is running hot and performance of thecompressor falls o due to high superheat temperatureat the suction side of compressor.&!uction and discharge pressure of the compressor is

low.&7arge vapor bubbles in the liquid sight glass.&7ow gauge readings in the condenser.&Ammeter reading for the compressor motor is lower

than normal.&9ise in temperature of the room which is to be cooled.&-ompressor is running for extended period of time.

&%$*+!

CAUSES: 7ea%age of refrigerant at the1 !h f l


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147

1. !haft=seal". ;lange couplings and 8oints$. Ealve glands etc.4. ea*age of gas through the ondenser tu(es due to orrosion.

0CT-%/:

&4dentify and rectify the lea%age of refrigerant from thesystem.&-lean the 'lter and drier.&-harge the system with fresh refrigerant if required.

INDICATION:& The liquid level in the condenser is too high )high


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148

q g gcondenser gauge reading*. This will reduce the available

condensing surface, with corresponding increase in thesaturation temperature and pressure.&


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149

connecting a cylinder to the liquid line charging valve,

starting the compressor, and then operating the chargingvalve.&2urge the air from the system and maintain eectivecooling. Fhile purging there is always some gas will passalong with air hence the regulation says the purging hasto be collected in recycling cylinders and same has to berecorded.&9emove ice from the regulator by using any of thedefrosting methods


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150

TR"U.'E S%""TIN&TR"U.'E S%""TIN&

1. AIR IN T%E SYSTE#:AIR IN T%E SYSTE#:


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$.igh condenser pressure.$.igh condenser pressure.

2.2.'resence of small bubbles in the sight glass'resence of small bubbles in the sight glass

/+ #"ISTURE IN T%E SYSTE#/+ #"ISTURE IN T%E SYSTE# ??

$.igh condenser pressure.$.igh condenser pressure.

. /ow evaporator pressure.. /ow evaporator pressure.

1. #ompressor stops.1. #ompressor stops.

0+UNDER C%AR&E:0+UNDER C%AR&E:

$./ow condenser pressure.$./ow condenser pressure.

. /arge bubbles in the sight glass.. /arge bubbles in the sight glass.1. #ompressor wor!s hot.1. #ompressor wor!s hot.

2. 4oom temperature goes up.2. 4oom temperature goes up.

151


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15'E %, '%06 'D'

T d f t ti d t


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153

& To prepare soap suds for testing, use a soap and watersolution of about the consistency of liquid hand soap,which will lather freely, or wor% up a lather on the brushby rubbing the wetted brush on a ca%e of soap.&A few drops of glycerine added to the solution will causethe lather to remain wet longer.

&Fhen applying the soap suds, paint the soap lather onthe 8oint all the way around, and examine the 8ointthoroughly for bubbles.&Fhen the 8oint is located so that a part of it is not visible,

use a poc%et mirror. 4t will sometimes ta%e a full minute ormore for bubbles to appear at a small lea%.&Guestionable spots should be covered with lather andexamined again.

&!mall ;reon=1" lea%s are detected by a special designedtorch %nown as a HHi+e T%r&h!&Atmosphere suspected of containing ;reon=1" gas isdra n through an e ploring hose into the burner b an


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154

drawn through an exploring hose into the burner by anin8ector action.& The air sample passes over a copper reactor plate in theburner chamber, which is heated to incandescence by the(ame.&4f there is even a minute trace of ;reon=1" present, the

torch (ame will turn from its normal blue or neutral colourto a characteristic green colour as it comes in contactwith the reactor plate.& The shade of green will depend upon the relative amount

of ;reon=1" present, being paler for small concentrations,and dar%er for heavier concentrations. @xcessivequantities of ;reon=1" will colour the (ame a vivid purple,and may even extinguish it by crowding out the supply ofoxygen in the air.

e can es n ca e e presence o ammon a gas ygiving o a cloud of dense white smo%e.4.Litmus, or other indicating papers: (for AmmoniaPlants

)


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155

)

The paper, when wet, indicates the presence of ammonia

gas by change in colour, e.g. red litmus paper turns blue.9outine 4nspections 7ea% detection should be carried outevery 1,III hours of operation, special attention beingpaid to braed 8oints, welded 8oints, gas%ets, (anges,

valve stems, compressor shaft seals, and areas wherethere are signs of an oil lea%. The high=pressure side ofthe system may easily be tested with the plant running,but it may be necessary to stop the compressor, andallow the pressure in the low=pressure side to rise

suciently. The amount of refrigerant in the systemshould also be strictly monitored as a drop in level mayindicate the presence of a lea%.4n the event of a ma8or lea%, the initial lea% test should be

made using the soap bubble method


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RefrigerantsR

efrigerants


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Besirable properties of a refrigerant%& #ow %oiling point 'otherwise operation at high vacuam

%ecomes a necessity)

1$ #ow condensing pressure 'to avoid heavy machine plant

scantling and reduce the lea*age ris*)

2$ High specific enthalpy of vaporisation ' to reduce the 3uatity of

refrigerants in circulation and lower machine speeds4 si5es

etc$)

6$ #ow specific volume in vapour state 'reduces si5e and

increases efficiency)

157

5 High critical temperature (temperature a!"e #hich "ap!ur

RefrigerantsRefri

gerants


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5.High critical temperature (temperature a!"e #hich "ap!ur

cann!t e c!n$ense$ % is!thermal c!mpressi!n&

'.!n c!rr!si"e an$ n!n s!l"ent (pure an$ mi)e$&

*.Stale un$er #!r+ing c!n$iti!ns

8.!n ,lammale an$ n!n e)pl!si"e. ! acti!n #ith !il ( the ,act that m!st re,rigerants are

miscile ma% e a$"antage!us e.e. the rem!"al !, !il

,ilms l!#ering p!ur p!ints etc pr!"i$e$ separat!rs are

,itte$/0.Eas% lea+ $etect

11.!n t!)ic

/1 chea easil st!re$ an$ !taine$

158

@)4 is halogenated hydrocarbon deried frommethane $H % with the hydrogen being displaced by

Refrigerant +1 Ref

rigerant +1


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methane $H;% with the hydrogen being displaced by

chlorine and fluorine. The resulting compound isichlorodifluoromethane $l4"

4% also 'nown as "reon

)4@)4 is considered non!toxic except in high

concentration producing oxygen deficiency. Howeer oncontact with flame it brea's down to form chlorine gasand phosgene $Ol

4%.

@)4 escaping under pressure can cause s'indamage on contact. It is non!irritant and not considered

flammable.-or'ing pressures and temperatures are moderate

and the high critical temperature $))4o% is well aboethe wor'ing range

159

+esig$! The &ri*i& *e' %6 *he gs is %0 : >?%C$+ *his &uses r%be's 6%r &%%i$g i$ res0here *he se *e'er*ure is high! I* s% hs %0 &%e@&ie$* %6 er6%r'$&e The gs is $%*


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160

%0 &%e@&ie$* %6 er6%r'$&e! The gs is $%*e5%si3e %r .''be bu* e4 is %*e$*i/+$ger%us s i* &uses sh/5i*i%$ $+ is s%*%5i&!

#h/ A''%$i is $%* re6erre+#h/ A''%$i is $%* re6erre+ : The g%%+ 8ui*ies%6 ''%$i s re6riger$* is %7se* b/ i*s *%5i&i*/,

.''bii*/, $+ u$ge$* %+%ur! A''%$i 0he$'i5e+ 0i*h 0*er &%rr%+es brss, br%$e $+si'ir %/s, 6%r *his res%$ ''%$i s/s*e's use%$/ s*ee i$ *heir &%$s*ru&*i%$!This '4es i*

+i@&u* 6%r *he ir &%$+i*i%$i$g 'r4e* 0here&%er hs bee$ *he bse '*eri 6%r ii$g $+$*!A''%$i is $%r'/ &%$si+ere+ *% be *he '%s*+$ger%us %6 *he ri'r/ re6riger$*s $+ hs


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To protect the global enironment an international

Refrigerant and the environment

Refrigerant and the environment


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To protect the global enironment, an internationalagreement, &ontreal protocol signed in )GC= controls theuse and production of " refrigerant and other o


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The production of R1# and R11 has now stopped underthe &ontreal Brotocol and 6 regulation on o


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currently limited to @44,ammonia$@=)=% and @):;a.@44will continue to be the first choice for all new marineinstallations.

(mmonia $@)=% is receiing serious consideration as analternatie refrigerant as it has OB and 7-B of *.

@):;a has been deeloped as an alternatie for @)4, ithas an OB of * and 7-B of one tenth that of @)4. #ut ithas a drawbac' in being un suitable for use with mineraloil, and is expensie.

(t present @):;a is considered to be an acceptablerefrigerant for small system $below Dhp% operating at higheaporating temperature and low condensingtemperature.

165


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167


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169


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contro s t e rate o ow to t e evaporator to su t t e rate o

evaporation.& The pressure of the liquid is reduced to the evaporating pressureso that thetemperature of the refrigerant entering the evaporator is below


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171

temperature of the refrigerant entering the evaporator is belowthan that required in the refrigerated space.

& The liquid vapour refrigerant mixture then (ows through theevaporator, extracts heat from the refrigerated space andchanges to a dry saturated vapour at approx the sametemperature and pressure at which it left the (ow control valve.& The compressor which receives the low pressure, low

temperature superheated vapour from the evaporator and duringthe compression stro%e the gas is compressed to a high pressure,high temperature, superheated vapour.&4f the condition of the refrigerant leaving the evaporator andentering the compressor exists in liquid state /7iquid %noc%0 can

ta%e place in the compressor during compression stro%e and thiscan cause serious damage to the compressor.

&The res%$s 6%r i8ui+ re6riger$* *he e$*eri$g *he&%'ress%r

&

FITTED IN A APOR COMPRESSION S"STEMFITTED IN A APOR COMPRESSION S"STEM

&


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172

&7ow=pressure cut in3cut out switch7ow=pressure cut in3cut out switch

&6ierential il pressure safety cut out switch6ierential il pressure safety cut out switch&2ressure control on the condenser2ressure control on the condenser&9efrigeration compressor abnormal alarm and9efrigeration compressor abnormal alarm and

stop .stop .&9efrigeration compressor motor overload stop9efrigeration compressor motor overload stop&!afety spring on the discharge valve of!afety spring on the discharge valve of

reciprocating compressor to prevent damage duereciprocating compressor to prevent damage due

to entry of liquid refrigerant.to entry of liquid refrigerant.

&De6r%s*i$g is *er'e+ s *heDe6r%s*i$g is *er'e+ s *he removal of frost in theevaporator coils which is formed due to presence ofmoisture in the system& The method of defrosting in the system is done manually


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173

e e od o de os g e sys e s do e a ua yor automatically&I$ '$u %er*i%$I$ '$u %er*i%$,, the evaporator unit is isolatedand opened. The frost formed is removed with the help ofblowing the compressed air over the evaporator coils andthe defrosted water is drained

&I$ u*%'*i& %er*i%$I$ u*%'*i& %er*i%$ ,a electric heater placed insidethe evaporator activates according to the set=timer in thetime cloc%.& The electric heater which is activated periodically

according to the pre set=timer melts the frost formed andthe defrosted water gets collected at the drip tray )placedat the bottom of evaporator*and passes overboardthrough a non=return drain pipe&ther methods of defrosting are


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Compressor usedare may bereciprocating orrotary. In nearly allcases a method ofarying the quantity

of deliery isincorporated.

"or reciprocatingcompressors this may

ta'e the form of anunloader and forrotary ariable speed drie.

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The compressors haeprotection systemssimilar to their fridge

System Protection


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gcounterparts with HighBressure and 2owBressure cut outs thatrequire manual resets.

In addition to this an

interloc' is fitted sothat the compressorcannot be started if theair handling unit fan is

not running. 9houldthe fan be stopped thecompressor will cutout.

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(n alternatie to thisis to fit solenoidales before the

System Protection


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ales before the

compressor, as inthe diagram aboe,which open onlywhen the fan isrunning.

The compressor willtrip on 2ow suctionpressure.

The purpose of boththese systems is topreent liquidreturning to the

compressor

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( single unit containstwo indiidualeaporators which areindependently suppliedb

Air Handling Unit Air Handli

ng Unit


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by a compressor.

( belt drien fandeliers air to theeaporators ia a finemesh air filter.

This filter is remoed ona regular basis andwashed in a soapysolution containing

disinfectant.

The air passes oer theeaporator where it iscooled and releases

water a or

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The water condenses andis fed away ia a drip trayand pipe wor', the wateris quite clean and can be

f

Air Handling Unit Air Handl

ing Unit


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used for domestic

purposes after treatmentalthough this practice isnot common. On theaboe design a catcherhas been fitted to remoewater droplets entrained inthe air, these are notalways fitted.

( perforated pipe is fittedafter the eaporatorallowing low quality steamto be fed into the airimproing its humidity

when too dr

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Cooler unit (dehumidifier!!

Ineffectie drainage can allow water to stagnate in theh l h l h h

Contamination of ships air Contamination of shi

ps air


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catchment sumps. (lso, where air elocities are high oer

the bloc', air can become entrained and carry moistureinto the air stream. (n efficient moisture eliminator isrequired.

'umidifier !

9team humidifiers, where fitted, do not appear to be aproblem.

Howeer, adiabatic humidifiers of which the water spraytype appears to offer a special ha


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Recommended countermeasures.Filters!9hould be washed in D*ppm solution on a regularbasisCoolers!9pecial attention to drainage arrangements aswell as super chlorinating the condensate sump eery

:months.lenum insulation-Insulation to be examined anddamaged areas resealed

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Central system-chilled :ater distri6utedCentral s

ystem-chilled :ater distri6uted


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Central system twin air ductCentral s

ystem twin air duct..


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ea& detection e@uipmentsea& detection e

@uipments1.Electronic lea7 detectorsA-he detetor ontains an internal pu"p that

draws air into a pro(e. /f the gas is present in the sa"ple) the eletrode in

the sensing ele"ent generate a urrent and an output signal is o(tained


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the sensing ele"ent generate a urrent)and an output signal is o(tained.

/n "odern refrigerated argo installations lea* detetor sensors fitted in

the holds and "ahinery spaes ati'ate audi(le and 'isual alar"s

loated in the ontrol roo" in the e'ent of refrigerant lea*age.

ea7 detector torchA-he "ethod used is (ased on the olour of a fla"ethat surrounds a glowing opper ele"ent. -he fla"e turns (lue green if

the air (eing onsu"ed ontains the refrigerant.

'ulphur candlesA-he lit andles indiate the presene of a""onia gas

(y gi'ing off a loud of dense white s"o*e.itmus or other indicating papersA-he paper when wet indiates the

presene of a""onia gas (y hange in olour eg red lit"us paper turns

(lue. 190

Refrigerant chargingRefri

gerant charging!yste" whih ha'e (een opened to the at"osphere during

repair should (e flushed through to re"o'e solid partiles and

d i d d (l


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e'auated to re"o'e "oisture and non ondensa(le gases.

+lushingA fit a fine "esh filter or sto* in the strainer in the

o"pressor sution inlet

2. harge the syste" with the pressure test "ediu" and runthe o"pressor to irulate the gas thro the syste".

-o pre'ent (lo*age the epansion 'al'e and other regulating

ontrols with s"all orifie "ust (e (ypassed.

3.stop the o"pressor at inter'als and lean the filter repeating

this proedure until no partiles are found.191


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Refrigerant charging!Refri

gerant charging!

1 onnet the ylinder to the harging 'al'e and purge the line of air


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1.onnet the ylinder to the harging 'al'e and purge the line of air.

2. #pen the harging and ylinder 'al'es and run the o"pressor.

3.llow the liquid to flow in to the syste".

/f the liquid is harged with out a o"pressor running the "ust (e

slightly war"er than the syste".

=reautionsA1. liquid refrigerant "ust ne'er (e harged diretly into the

o"pressor sution.

2. =roperly tested harging hoses are used) and that non return 'al'es arefitted when harging into the high pressure side of the syste".

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%top +al+e :ith gauge or charging connection%t

op +al+e :ith gauge or charging connection..


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194


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+ervice valves are, used when the refrigeration unit needmaintenance or repair.

The purpose of the service valves is to isolate parts of therefrigerant system in a way that ma#es it possible to service the


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system.

The service could either be refilling of refrigerant, measuring ofpressures in the system or replacement of a compressor or othercomponents.

There are different positions on the service valves

Front seated position7 isolate the system and ma#es it possibleto change components e.g. compressor.

Service position8 ma#es it possible to empty and fill in refrigerant

or connect a pressure gauge via the service port for measuringthe pressure inside the system.

&ac* seated position8 is the normal operation position196


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ContaminantsContaminants


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'olid particlesA -he presene of solid partiles an ause pro(le"s (y (lo*ing the ontrol 'al'es) da"aging o"pressor (earings and other

ru((ing surfaes.

-o a'oid these pro(le"s ta*e preautions when arrying out repair.

+it loth filter in the o"pressor sution strainer.

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Classification society re@uirementsClassification societ

y re@uirements..).to show that the installation was built and installed tothe satisfaction of 2loyds @egister of shipping @&$@efrigerated machinery ertificate % was assigned in the


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register boo'.In order to maintain its @& 5otation any classedrefrigerated cargo installation must undergo satisfactoryperiodical suey as folows.

Annual surveyF Intereals )4 month.Burpose is toestablish that the condition of the installation as a wholeis satisfactory and the machinery is operating reliably andmay be expacted to continue to do so for ensuing )4months.

-ith a iew to minimising interference with operationalcommitments, the surey requirements hae been framedto aoid any opening up or dismantling unless the shipsrecords or external examination indicate the presence ofsome fault requiring attention. 202

pecial surveyF This is to confirm the findings ofexaminations at the annual sureys by openingup plant and machinery eery fie years for thep pose of establishing that no cocealed defects


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purpose of establishing that no cocealed defectshae dealoped.The following equipements areopened up ). ompressors 4.shell and tubecondensers and eaporators, :. Bressure esselsand piping and some insulation from therefrigerated pipes to erify it has not beeneffected by corrosion.;. The cargo chamberslining and insulation.

ondition of class may be recommended whenobjects are found which can not receieimmediate attention, but which do not jeopardi


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!oading surveyF arried out at any time on one or

more chambers to certify their condition prior to loading

of refrigerated cargo.The chambers must be clean and

fitted with thermometers in wor'ing order. The electrical

generating plant is inspected and refrigerated macinery

seen in operation. The temperature of each chamber

subjected to surey is noted and enterd in the certificate

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-ir conditioning -ir conditioni

ng (ir conditioning is the control of humidity, temperature,cleanliness and air motion.

-inter conditioning relates to increasing temperature and


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-inter condition

03.BE REFRIGERATION AND AIR CONDIONING,(Class Room).ppt

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Transcript of 03.BE REFRIGERATION AND AIR CONDIONING,(Class Room).ppt