The document provides an in-depth overview of refrigeration and air conditioning cycles, detailing the properties and types of refrigerants used, including ammonia, carbon dioxide, and freon. It explains various cooling methods such as evaporative refrigeration, ice refrigeration, and discusses the components and functioning of vapor compression and vapor absorption systems. Additionally, it covers domestic refrigeration systems and air conditioning units, including their operation and the importance of humidity control using humidifiers and dehumidifiers.

1. Unit 5: Refrigeration and air conditioning cycle
5.1 Refrigerant: types and properties
*Introduction
The refrigerant is a heat carrying medium which during their cycles (i.e.
compression, condensation, expansion, evaporation) inthe refrigerationsystem
absorb heat from a low temperature systemanddiscardthe heat so absorbedto
a higher temperature system. It readily absorbs heat from the environment and
can provide refrigeration or air conditioning when combined with other
components such as compressors and evaporators. It is typically found in either
a fluid or gaseous state.
*Properties of refrigerant
A substance which absorbs heat through expansionor vaporizationis termedas
a refrigerant. An ideal refrigerant should possess chemical, physical and
thermodynamic properties which permits its efficient application in the
refrigerating system. An ideal refrigerant should have the following properties:
 Low boiling Point
 High Critical Temperature
 High latent heat of vaporization
 Low specific heat of liquid
 Low specific volume of vapour
 Non-corrosive to metal
 Non-flammable
 Non-explosive
 Non-toxic
 Low cost
 Easy to liquify at moderate pressure and temperature
 Easy to locating leaks by odour or suitable indicator

2.  Mixes well with oil.
 Ozone friendly.
Refrigerants commonly used in practice
Throughthereare many refrigerantswhicharecommonly used,yetthe following
are important from the subject point of view :
1 . Ammonia(NH3). It is one of the oldest and the most commonly usedof all the
refrigerants. It is highly toxic and flammable. It has a boiling point of — 333° C
and a liquidspecific gravity of 0.684 at atmospheric pressure. It is widely usedin
larger industrial andcommercial reciprocating compressionsystems, where high
toxicating is of secondary importance. it is also widely used as a refrigerant in
absorption systems.
2. Carbon dioxide (CO2). It is a colorless and odorless gas, and is heavier than
atmospheric air. It has a boiling point of — 77.6° C and a liquidspecific gravity of
1.56 at atmospheric pressure. It 11 is nontoxic and non-flammable, but has
extremely highoperating pressure (70 bar). It is not widely used, because of its
high power requirements per ton of refrigeration and high operating pressure.
3. Sulphur dioxide (SO2), It is a colorless gas or liquid. It is a extremely toxic and
has a pungent irritating odour. It is non-explosive and non-flammable. It has a
boiling point of - 10.5° C and a liquid specific gravity of 1.36. It is used in small-
tonnage commercial machines (hermetically sealed units).
4. Freon-12*. The entire Freongroup is white in color and odorless. They are all
non-flammable and non-toxic. Freon-12is mostly usedout of all the Freongroup.
It has a boiling point of -30° C and operating pressure of 8 bar. It is widely used
for domestic refrigerators.
5.2 Introduction to evaporative refrigeration and ice refrigeration
Evaporative Refrigeration / Evaporative cooling
Evaporative cooling uses evaporation to cool the air. Based on the principle of
evaporation,hot and dry outsideair isdrawn throughwatersoakedcooling pads.
Asthe air is pushedthroughthesepads, thewater evaporatesandtheheat inthe

3. air is absorbed, which lower the air temperature. A fan then pushes the cool air
throughout the house via a network of ducts.
The heat used to evaporate water into water vapour is called latent heat of
evaporation. As the liquid water changes it's state into vapour, it absorbs heat
fromit's surrounding.EvaporativeCooling is only possiblebecauseof thisnatural
phenomenon of latent heat.
Figure 1: working principle diagram of evaporative refrigerator
Ice Refrigeration
In this method, the ordinary ice is used for keeping the space at temperature
below the surrounding temperature. The temperature of ice is consideredto be
0°C( degree Celsius). Hence, it canbe usedto maintainthe temperature of about
5-10°C (degree celsius).To use the ice refrigerating effect aclosed and insulated
chamber is requiredon one side of chamber ice is kept while on the other side
thereisa space whichistobe cooledwheresome materialtobe cooledisplaced.
If the temperature belowo°C is required, thenthe mixture of ice andsalt is used.
This method of cooling is being used for cooling the cold drinks, food items.
vaccine etc.

4. Figure 2: Working principle of Ice Refrigeration
5.3: Vapour compression system:
Figure3:Vapour Compression Refrigeration System

5. 1. Compressor: The vapour at low pressure and low temperature
enters the compressor from the evaporator where it is compressed
to high pressure and high temperature. This high pressure and
temperature vapour refrigerant are discharged into the condenser
through the discharge valve.
2. Condenser: The condenser or cooler consists of coils of pipe in
which the high pressure and temperature vapour refrigerant are cooled and
condensed. The refrigerant while passing through the condenser gives up its
latent heat to the surroundings condensing medium which is normally air or
3. Receiver:The condensedliquid refrigerant fromthe condenser is storedin
a vessel known as a receiver from where it is supplied to the evaporator
through the expansion valve.
4. ExpansionValve:It is alsocalleda throttle valve. Its functionis toallowthe
liquid refrigerant under high pressure and temperature to pass through it
where it reduces its temperature and pressure
5. Evaporator: It alsoconsistsofcoilsof pipeinwhichliquid-vapourrefrigerant
at low pressure and temperature is evaporated and converted into vapour
refrigerantatlowpressureandtemperature.Thecondensedliquidrefrigerant
from the condenser is storedin a vessel known as a receiver fromwhere it is
supplied to the evaporator through the expansion valve.
5.4: VAPOUR ABSORPTION SYSTEM:

6. Figure4:Vapour Absorption Refrigeration System
Vapour absorptionrefrigerationsystem(VARS) is mainly usedwhere highpower
is not easily available.
It is different from vapour compression refrigeration system because in this
system compressor is replaced with an absorber, pump, and generator.
Vapour absorptionrefrigerationsystemuses heat energy for refrigerationwhile
theVapour CompressionSystemusesworkenergyforrefrigerationwhichismuch
more expensive to produce.
Vapour absorption refrigeration system is best for places where heat energy is
available easily at a low price.
This process is best for Steam Power Plants. Steam Power Plants can easily run
this refrigeration system using the waste heat produced in the power plant.
Components in Vapour Absorption Refrigeration System:

7. 1.Evaporator: The main function of the evaporator is to provide cooling to the
area with which it is in contact.
The chilledliquidwill enter inside this evaporator and will receive heat fromthe
evaporator and will convert into vapour. This vapour will be at low pressure.
From this evaporator, the ammonia vapour comes out at low pressure and will
go towards absorber.
2. Absorber:
The absorber is used to absorb the refrigerant. At the absorber, there will be a
weak solution of water and ammonia. When the ammonia vapour from
evaporator will reach the absorber, water present in the absorber will absorb it.
As water will absorb ammonia, strong solutionof ammonia and water will start
getting created.
When the water will absorbammonia water will liberate heat andthe absorbing
capacity of water reduces. So, cool water is suppliedin the absorber so that the
absorbing capacity stays high so that it continuously absorbs the ammonia
vapour.
3. Pump:
The pumpwillpump thestrongsolutionofammonia andwaterfromtheabsorber
to the generator.
4. Generator:
Ammonia and water solution is used inside this system. Ammonia is used as a
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refrigerant and water is used as an absorbent. A solutionof these two is made
because water has a strong affinity towards ammonia. Water plus ammonia
solution is present inside the absorber.
The generator is provided with auxiliary heat from outside. For providing this
auxiliary heat steamor hot water or any type of heater can be used. The heat is
provided so that the ammonia and water solution converts to vapour.
5.Analyzer:
Analyzer is placedat the topof the generator. Ammoniawill convert intovapour
before the water but some water particles convert into vapour with ammonia.
This analyzer is usedtoseparate the water particlesfromammonia vapour.If the
water particles move forward from the generator, it will decrease the efficiency
of the whole system. If the water particle passes forwardinlarge quantity, it can
damage the systemalso. So, the analyzer condenses the water particles but the

8. ammonia vapour willpassthroughthe analyzerandwillgoforwardinthe system.
Some ammonia vapour will also condense in the analyzer but most of the
ammonia vapour will pass through the analyzer.
6.Pressure Reducing Valve:
After the ammonia vapour passes through the analyzer, the weak solution
present in the generator will pass through the pressure reducing valve and will
reach the absorber again.
7.Condenser:
Condenser is used to convert the ammonia vapour into liquid phase. This
condenser can be either water-cooled or air-cooled.
8.Expansion Valve:
Its main function is to convert the liquid into chilled liquid and give it to the
evaporator. At the expansion valve, the ammonia liquid will come from the
condenser and the temperature andpressure of this liquid ammonia will reduce
and this ammonia liquid will become chilled liquid ammonia temperature of
which will be very low.
5.6: DOMESTIC REFRIGERATION SYSTEM:
Domestic refrigerator is anelectrical appliance usedinmany households for
keeping foods cool enoughso that they won’t spoil. There are other types of
refrigerators that donot operate using electricity, suchas gas- or oil-powered
refrigerators.
The principal parts of any domestic refrigerator are evaporator, compressor,
condenser, andcapillary tube. A domestic refrigerator works onvapor
compressionrefrigerationcycle.
To preserve foods/vegetables andfor drinking cold water, we normally rely on
the domestic refrigerator but doyou know how this machine works? Actually,
the domestic refrigerator is aheat pump that throws the heat of the foods or
stuff to be cool to the atmosphere by taking the power of a compressor. The
secondlaw of thermodynamics withits Clausius statement suggests, to throw
heat from low temperature tohightemperature, one must put extraeffort in
the form of work. The same is done by the compressor inthe domestic
refrigerator.
Working principle of domestic refrigerator:

9. Figure5:Working of domestic refrigerator
The functionof the compressor is toraise the pressure of gaseous refrigerant
coming from the evaporator. By raising the pressure, the boiling point of the
refrigerant increases. This highpressure andhigh-temperaturerefrigerantwhile
passing throughthe condenser changes the phase and condenses inhigh
pressure andtemperature liquidrefrigerant. The roomair is at a lower
temperature thanthe refrigerant passing throughthe condenser, hence
condensationtakes place and vapor refrigerant is convertedtoliquid
refrigerant. Thus heat is thrownintothe air at this point in the refrigerator. Now
resultant liquidrefrigerant whichis at highpressure andtemperature passes
throughthe capillary tube which is made up of copper material and has a very
small diameter and longer length. As the high-pressure liquidrefrigerant passes
throughthe capillary tube, due to the throttling effect, the temperatureand
pressure of the refrigerant decrease. The majority of the cooling is producedat

10. this point in a refrigerator. This lowtemperatureandlow-pressurerefrigerant
now pass throughthe evaporator where refrigerant inliquidphase takes heat
from foods and stuff. At this point, the boiling point of liquidrefrigerant is very
low (because of low pressure) interms of -20 degrees C. Thus anything above
this temperature makes refrigerant toboil. This low-pressure vapor again
circulatedtothe compressor andthe cycle continues as long as the compressor
is in running condition.
Note:The boiling point of the refrigerant is afunctionof pressure. Thus the
change inpressure inthe compressor andcapillary makes it to be able to
change the phase.
5.9 Air conditioning system
Working of air conditioning system
Air conditioningunitswork by removingthe warm air from inside yourhome and pumpingit outside,
while releasingthe cool air back intothe room, reducingthe temperature.Whenliquidbecomesgas,
it absorbs heat, this is how theyfunction. Air conditioningsystemswork very much in the same way
as your standard refrigerator,in that heat isabsorbed inside the system and thenremovedfrom the
room. Here’sthe process:
• Firstly,the warm air from the room is drawn into the system. This air flowsover the cold
evaporator pipesinside,whichcools the air down while a dehumidifierremovesexcess
moisture.
• Meanwhile,the coolant flowingthroughthe chillerpipesabsorbs the heatfrom the air blowing
past and evaporates,turning from a cool liquidto a warm gas.
• This warm air is pumpedoutside while the coolant flowsthrough a compressor unitand a
condenser,whichturn it back into a cool liquid.
Cold air is then re-circulated intothe room where it mixes with the existing air and
reduces the temperature and humidity.

11. What do the separate air conditioning components do?
• We know that air conditioning units require a coolant liquid that is pumped through the
coils to cool down the air. For the air conditioning process to work, this refrigerant
circuit has to have three key components. The air conditioning evaporator.
• The warm air from inside your home is drawn in and passed through an expansion valve
which regulates the flow. It is then blown over the cold evaporator coil, which absorbs
the heat from the air. As the refrigerant inside the coils absorbs the heat, it changes
back into a gas and moves towards the compressor. The air conditioning compressor.
• The compressor in an air conditioning system acts as a pump, decreasing the volume of
the gas and raising its pressure and temperature for the condensing process. The air
conditioning condenser.
• The air conditioning condenser takes the heat collected from inside the room by the
refrigerant, now in vapourform, and pumps it outside where the outside air absorbs
the heat and changes the state from a gas back to a liquid.
Once the heat has moved outdoors, the cold refrigerant travels back indoors to the
evaporator to repeat the process.
Function of different Components
Humidifier:A humidifierisan appliance that increasesthe amount of moisture in the air. This device
ensuresthat the air around you is not completelydry,which can lead to various bodilyirritations.
There are various signsthat you may needa humidifierinyourhome, especiallyifyou’re suffering

12. from various symptoms such as dry skin, strainedvocal chords,chapped lips,nose irritation, and
headaches.Humidifierscan helprelieve these symptoms;however,overusinga humidifiercan
worsenany current respiratory issuesyou may have.
The benefitsofaddingmore moisture in the air are numerous,but there are a fewdrawbacks to the
process ifyou overuse your humidifier.Aswith everythinginlife,balance is required – too little isn’t
enough,but too much could cause your home to become damp. Dampness may cause bacteria, mold,
mildew,and evendust mitesto spawn in your home. Researchshows that by keepingthe humidity
levelsinyour home betweenapproximately30% and 50%, you can avoid excessive dampnessand
ensure that your home remains free ofmold and mildew.
Dehumidifier:Adehumidifierisan air conditioningdevice whichreducesand maintainsthe level of
humidityin the air. This is done usuallyfor health or comfort reasons, or to eliminate mustyodor and
to preventthe growth of mildewby extracting water from the air. It can be used for household,
commercial,or industrial applications.Large dehumidifiersare usedin commercial buildingssuchas
indoor ice rinks and swimmingpools, as well as manufacturing plants or storage warehouses.
The benefitsofhaving a dehumidifierina home or office space are many. Here are several reasons to
consider:
1. A dehumidifierhelpsreduce mustyodors that can accompany mold and mildew.
2. Reducingthe potential developmentofmoldon furniture,curtains, bedsheetsand clothing.
3. Running a dehumidifierreducesdust.Dust can trigger allergies;and thisdevice will helpto reduce
allergenssuch as dust mites,mold and mildew.Plus,cleaningtime is reduced.
4. A dehumidifiercanalso lowerenergycosts because it helpsthe HVAC units run more efficiently.If
a home is locatedin a humidclimate,an air conditionermust work harder to not onlycool the air,
but also remove moisture.Plus,if the air conditionerworks harder, it could wear out soonerand
may needto be replaced.As we all know,HVAC systems can be quite expensive
Diffusers:Adiffuserimprovesairflowthrough the condensingunit. Made out of sheetmetal
shapedlike an upside-downcone,the diffuserattachesto the top of the condensingunit.The shape
of the diffusermakesairflowout of the condensingunitaerodynamic.
A diffuser also helps to push heated air up and away from the condensing unit, ratherthan
ejecting it in close proximity. Ultimately, a diffuser makes the condensing unit's job easier to
reject heat. As a result, the heat transfer from the refrigerant tothe air can occur at a greater
rate, leading to efficiency increases of between 7 and 18 percent.

13. Air Handling Unit :Air handling units’ condition and distribute air within a building. They take
fresh ambient air from outside, clean it, heat it or cool it, maybe humidify it and then force it
through some ductwork around to the designed areas within a building. Most units will have
an additional duct run to then pull the used dirty air out of the rooms, back to the AHU,
where a fan will discharge it back to atmosphere. Some of this return air might be
recirculated back intothe fresh air supply to save energy.
Ducts: Ducts are conduits or passages used in heating, ventilation, and air conditioning
(HVAC) to deliver and remove air. The needed airflows include, for example, supply air,
return air, and exhaust air. Ducts commonly also deliver ventilation air as part of the supply
air. As such, air ducts are one method of ensuring acceptable indoor air quality as well as
thermal comfort.
Fan: The fan of an AC unit connects to indoor air handler. The fan will return the warm air in
home to the condenser. The re-circulated air will come back to the air handler where it’s
converted to cool air and dispersed throughout system of ducts and vents into home. While
it doesn’t work the same way a traditional fan, we can use it to help circulate the air in our
home. It doesn’t produce cool air, though.
Comfort zone : The ranges of indoor temperature, humidity, and air movement, underwhich
most persons enjoy mental and physical well-being is called comfort zone . The limiting
conditions vary somewhat according to season and to the native climate of the person or
group. In the United States the comfort zone with normal ventilation lies between air
temperatures of about 17° and 24°C (63° and 75°F) at a relative humidity of 70%, and 19°C
(67°F) at a relative humidity of 30%, giving an effective temperature within a few degrees of
19°C (67°F). The limits, however, vary with the season, being higher in summer than in
winter.
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