AIR CONDITIONING PRINCIPLES & CONCEPTS.pdf

AIR CONDITIONING PRINCIPLES & CONCEPTS

1. AbhishekK. VenkitaramanIyer
Assistant Professor
Faculty of Architecture, MIT
AIR-CONDITIONING
PRINCIPLES & CONCEPTS

4. References:
1.Egan, David. (1988). Architectural Acoustics. McGraw Hill Book Co., NY.
2. Kinsleter, Lawrence E. and Frey Austin R. (1989). Fundamentals of Acoustics (edition
2). Wiley Eastern Ltd., New Delhi.
3. Templeton ans Saunders. (1987). Acoustic Design. Architectural Press, London.
4. Blue Star. (1996). The Blue Star Guide to Comfort Air Conditioning, Blue Star
Packaged Air Conditioner Devision.
5. Flynn, J.E. et al. (1992). Architectural Interior Systems: Lighting, Acoustics and Air
conditioning. Van Nostrand Reinhold Co.
6. Jones, W.P. (1985). Air Conditioning Engineering. ELBS (Edward Arnold).
7. National Building Code

5. Human comfort
Inevitably 'comfort' is a very subjective matter. The Engineer aims to ensure
'comfort' for most people found from statistical surveys .Most people (90%) are
comfortable when the air temperature is between 18-22°C and the %sat is
between 40-65%. This zone can be shown on the psychometric chart. And is
known as the comfort zone.
Outside air is quite likely to be at a
different condition from the required
comfort zone condition. In order to bring
its condition to within the comfort zone
we may need to do one or more of the
following:-heat it; cool it; dehumidify it;
humidify it; or mix it.

7. •HUMAN COMFORT CONTROL
•A human being is sensitive to impurities such as dust, smoke, & pollen that cause
irritation to the nose, lungs, & eyes, Thus there is a need for clean air.
•A human being also requires fresh air to renew oxygen supply as well as to
dilute undesirable odors.
•Due to these reasons some properties of the air must be adjusted which are
essential to provide a comfortable & healthful environment.
•Temperature- by cooling or heating.
•Moisture content -by humidifying or dehumidifying.
•Movement -by circulation
•Cleanliness -by filtration
•Ventilation- by recalculating fresh air to replace stale air.

8. •COMFORTABLE ENVIRONMENT FOR HUMANS :
•Comfortable environment for humans Human body adjusts to the temperature
changes of its surrounding .Inside temperature of human body, known as
subsurface temperature is 37 degree c.(98.6 F) Temperature at the skin
surface is about 21 degree c.(70 F.)
•If surrounding temperature adjacent to skin, Is more than skin surface
temperature we fill hot, If less we fill cold.
•When cold, nerve send the signal to brain to close the pores tightly, When hot,
nerve send the signal to brain to open the pores causing to release the liquid
from skin, which in turn maintains the temperature of skin surface by
evaporation, to feel comfortable.
•A balance is thus maintained so that deep tissue heat should not deviate more
than one degree Fahrenheit, However this does not means one is always
comfortable, as out side tissues always come across these variable conditions
which results in discomfortable feelings to human being.

9. •WHAT IS AIR CONDITIONING :
•Air conditioning is the process by which
•AIR IS COOLED OR HEATED.
•CLEANED OR FILTERED.
•CIRCULATED OR RECIRCULATED.
•CONTROL THE QUALITY & QUANTITY
•This means by air conditioning system the temperature, humidity & volume of
air can be controlled at any time in any situation.

10. FUNCTIONS OF HVAC
•CONTROL OF AIR TEMPERATURE.
•CONTROL OF MOISTURE CONTENT IN THE AIR.
•PROPER AIR MOVEMENT.
•TO HOLD THE AIR CONTAMINATION WITHIN ACCEPTABLE
LIMITS.

11. •AIR CONDITIONING IS RESORTED FOR THE FOLLOWING PURPOSES:
•It helps in preserving or maintaining health, comfort and convenience.
•It helps in improving the quality of products in certain industrial processes such as
artificial silk, cotton cloth ,etc. In other cases of industries, it provides comfortable
working conditions for the workers, resulting in the increase of the production.
•It helps in making the commercial premises, such as shops, banks, restaurants etc.
more active and efficient.
•It provides more comfortable entertainment in theaters etc.
•In the case of air conditioned railway/roadways coaches or air travel, journey
becomes more comfortable.

12. VARIOUS APPLICATIONS OF AIR CONDITIONING

•SHOPPING MALLS
•AUDITORIUMS & THEATRES
•HOSPITALS
•HOTELS AND RESTAURENTS
•OFFICES
•COMMERCIAL COMPLEX
•LUXURY APPARTMENTS
•INFOTECH PARKS
•PHARMA INDUSTRY
•TELECOM INDUSTRY AND MANY MORE………!!

13. • ENVIRONMENTAL CRITERIA FOR BUILDINGS
•A building or a space within a building may be used in many different ways.

For each of these applications the HVAC designer must determine the general
criteria from personal experience or study and then add the special
requirements of the user of the facility.
•In every environment there are concerns for temperature, relative humidity,
sound level, air quality, and noise. In general, the higher the standard to be met,
the more expensive the system will be to install and, probably, to operate.

14. •Residences
•Two essential residential criteria are comfort and the need of occupants to
adjust the controller set point. In larger residences (over 2400 square feet) the
use of multiple or zoned systems should be considered. First, cost and operating
cost are always concerns, as are simplicity and an acceptable sound level.
•Offices
•Basic needs are comfort and an adequate ventilation rate, especially if
smoking is allowed. Controls are usually designed to be nonadjustable by
occupants. Zoning must be provided to compensate for use, occupancy, and
exterior exposure. The ideal HVAC system should be flexible enough to allow for
adding or rearranging zones as use changes. Background noise level should be
in the range of 30 to 40 decibels (DB).

15. •HOTELS AND MOTELS
•A large resort or conference hotel has many varying needs. The building may
include public areas, such as lobbies, restaurants, health and recreation
facilities, meeting rooms, retail shops and ballrooms, as well as “behind the
scenes” facilities—kitchens, laundry, repair shops, offices, storage, HVAC and
electrical equipment, employee lounge, etc. Each area has different HVAC
requirements.
•Kitchens are often cooled indirectly by transferring air from adjacent areas.
Transferred air should be filtered.
•Laundries and pool areas have high humidity problems that must be
addressed, usually by high exhaust air rates.
•Meeting rooms have high occupancy rates; cross radiation from people usually
suggests lower design temperatures for comfort.
• Zoning and individual guest room control are essential. Auxiliary heat at
entrances may be needed even in mild climates.
•Through-the-wall independent HVAC units are popular in motels and some
hotels. They have a low first cost but are often noisy.

16. •EDUCATIONAL FACILITIES
•A school is more than classrooms and offices, though these constitute the major
portion of most schools.
•Comfort criteria apply in classrooms and offices, including special-purpose
rooms for music, laboratories, practice rooms, study halls, and lunchrooms.
•Auditoriums, with or without stages, have criteria peculiar to theaters—a need
for somewhat lower temperatures due to high occupant density, a low
background noise level, and avoidance of drafts in what is typically a high
airflow rate situation.
•Many elementary and high schools have smaller, distributed AHUs, single
or multizone, with a central plant source of heating and cooling.
•In single-story schools, rooftop self-contained units are sometimes used. At the
college or university level the facility takes on an institutional character, with
emphasis on higher-quality equipment and systems, with longer life and lower
maintenance costs.
•There are many special-purpose buildings with widely varying HVAC
requirements. Central HVAC plants are often used with elaborate distribution
systems.

17. •THEATERS AND CONCERT HALLS
•The acoustic design of a good theater or concert hall should be such that
electronic amplification is not needed.
•The HVAC system must not produce a noise that will interfere with the
audience’s enjoyment of the performance.
•This is not easy to achieve; it requires careful design and construction of the
building and the HVAC and electrical systems. The HVAC designer will profit
from earnest discussion with the acoustical consultant for this type of facility.
•LABORATORIES
•Laboratory facilities associated with education, public health, or industry can
have very complex requirements, including humidity control and high levels of
cleanliness. Most laboratories require high rates of exhaust and makeup air.

18. •HOSPITALS
•Hospitals are always interesting and challenging for the HVAC designer
because of the wide variety of environmental conditions required in various
departments.
•The operating suite, with heavily clothed staff working under hot lights,
requires a design temperature of 65 to 70°F with a relative humidity of 50
to 60 percent and a high percentage of outside air when in use. This
requires at least high-efficiency filters and high airflow rates.
•Nurseries do not require high airflow rates but do require about 55 percent
relative humidity.
•Patient room requirements vary depending on usage—i.e., isolation rooms
require exhaust with no recirculation to other parts of the hospital.
•Public areas and offices may be treated as in any other building.
•Laboratories and treatment rooms require special treatment with no
recirculation. There may be requirements for air pressure relationships to keep
air moving from higher-quality to lower-quality environments. Exhaust air from
contaminated spaces must be scrubbed.

19. •MANUFACTURING FACILITIES
•Process environments dominate in manufacturing applications of HVAC. Typical
applications include close control of temperature (plus or minus 1°F is not unusual)
and humidity (plus or minus 5 percent RH is typical). These criteria can be met only
by the use of carefully designed HVAC systems with high-quality controls.
•Clean rooms require high flow rates but have normal or low heating and cooling
loads. The typical solution is to provide a small HVAC system with a supplemental
high flow rate fan system.
•Electroplating and painting facilities require high rates of exhaust air flow, usually
with filtering.
•Machining operations generate an oil mist, which is carried in the air and
deposited everywhere. The HVAC system can be designed to control this problem
to some degree.
•Flammable vapors are often of concern; some processes generate heat and
combustion products. Many processes offer opportunities for heat reclaim.
Industrial hygiene criteria complement HVAC criteria in these environments.

20. •DESIGNING FOR Hospital operating room.
•This is a critical environment, often served
•by a dedicated air-conditioning system. The design objectives include:
• Heating, to avoid the patient from becoming too cold.
• Cooling, to prevent the members of the operating team from becoming too
•hot.
• Control adjustment by the operating team for temperatures between 65°F
•(Fahrenheit) and 80°F.
• Humidifying, to avoid low humidity and the possibility of static electricity
•sparks.
• Dehumidifying, to minimize any possibility of mold and to minimize
•operating team discomfort.
• Cleaning the incoming air with very high efficiency filters, to remove any
•airborne organisms that could infect the patient.
• Ventilating, to remove airborne contaminants and to keep the theatre
•fresh.
• Providing steady air movement from ceiling supply air outlets down over
•the patient for exhaust near the floor, to minimize contamination of the
•operating site.

21. WORKING OF AIR CONDITIONERS
•The main principle at work in air-conditioners is evaporation.
•In the refrigeration cycle this principle is put to work by causing a liquid
refrigerant to evaporate in a cooling coil(evaporator).
•The refrigerant is a specially chosen substance which has the property of
evaporation at very low temperatures.
•The cooling coil in which the refrigerant evaporates ,is in contact with the air
(or water in chilled water systems)surrounding it , thereby cooling that as
well.
•Once cooled this air (or water)is then directed to spaces which require cooling.

22. •Equipment used to produce cooling
•COMPRESSOR: the equipment that increases the
pressure of the gas by compressing it ,is called the
compressor.
•under atmospheric temperature and pressure the
refrigerant is in gaseous form.
•Cooling takes place when liquids evaporate to become
gas therefore the refrigerant gas must be transformed
to liquid form.
•Most gases can be made into liquid form by raising its
pressure which is done in the compressor.
•CONDENSER: the equipment that removes heat is called
the condenser.
•During compression the refrigerant becomes hot
because of the work done on it and because the
refrigerant is converted from gas to liquid releasing its
latent heat.
•This heat has to be removed to enable the gas to
condense into liquid easily .this is done by the condenser.

23. •EVAPORATER(cooling coil):
•The liquid refrigerant from the condenser is injected through a metering
device called the capillary or the expansion valve into the cooling coil which
is a bundle of tubes.
•When the refrigerant evaporates in the evaporator, it absorbs heat from the
surrounding air and produces cooled air.
•END OF CYCLE AND BEGINNING OF THE NEXT ONE:
•The refrigerant is back to gaseous form .It is sucked into the compressor where it
will be compressed again for the next refrigeration cycle.

24. REFRIGERATION CYCLE
Refrigerant
Refrigerants are substances used by air conditioners to transfer heat
and create a cooling effect. Air-conditioning systems use specially
formulated refrigerants designed to change state at specific
temperatures providing optimum cooling.
Portables use a refrigerant called R-22 or HCFC-22. HCFC stands for
hydrochlorofluorocarbon. This is currently the most common
refrigerant used by air-conditioning systems.
In the refrigeration cycle, a heat pump transfers heat from a
lower temperature heat source into a higher temperature heat sink.
Heat would naturally flow in the opposite direction.
A refrigerator works in much the same way, as it pumps the heat
out of the interior into the room in which it stands. This cycle takes
advantage of the universal gas law PV = Nrt.

26. The Refrigeration Cycle
A=Inside the refrigerator

B=Compressor

C=Expansion Valve
•The high-pressure ammonia liquid flows through the
expansion valve. Expansion valve can be considered as a
small hole. On one side of the hole is high-pressure
ammonia liquid. On the other side of the hole is a low-
pressure area (because the compressor immix sucking gas
out of that side).
•The liquid ammonia vaporizes (light blue), its
temperature dropping to -27 F. This makes the inside of
the refrigerator cold.
•The cold ammonia gas is sucked up by the compressor,
and the cycle repeats.
In the refrigerator, the cycle is continuous. In the following
example, provided that the refrigerant being used is pure
ammonia, which boils at -27 degrees F. This is what happens
to keep the refrigerator cool:
•The compressor compresses the ammonia gas. The
compressed gas heats up as it is pressurized (orange).
•Coils on the back of the refrigerator let the hot ammonia gas
dissipate its heat. The ammonia gas condenses into ammonia
liquid (dark blue) at high pressure.

27. Heat pump and refrigeration cycle
A heat pump is when heat is removed from a low-temperature space
or source and rejected to a high-temperature sink with the help of
external mechanical work.
Heat pump can be classified as:
•Vapor cycle,
•Gas cycle, and
•Sterling cycle

28. Vapor cycle refrigeration can be classified as:
•Vapor compression refrigeration
•Gas absorption refrigeration
Vapor-compression cycle
In this cycle, a circulating refrigerant such as Freon enters the
compressor as a vapor. From point 1 to point 2, the vapor is
compressed at constant entropy and exits the compressor
superheated. From point 2 to point 3 and on to point 4, the
superheated vapor travels through the condenser which first
cools and removes the superheat and then condenses the
vapor into a liquid by removing additional heat at constant
pressure and temperature. Between points 4 and 5, the liquid
refrigerant goes through the expansion valve (also called a
throttle valve) where its pressure abruptly decreases,
causing flash evaporation and auto-refrigeration of,
typically, less than half of the liquid.

30. •That results in a mixture of liquid
and vapor at a lower temperature
and pressure as shown at point 5.
The cold liquid-vapor mixture then
travels through the evaporator coil
or tubes and is completely
vaporized by cooling the warm air
(from the space being refrigerated)
being blown by a fan across the
evaporator coil or tubes. The
resulting refrigerant vapor returns to
the compressor inlet at point 1 to
complete the thermodynamic cycle.

31. Vapor absorption cycle
•Nowadays, the vapor absorption cycle is used
only where waste heat is available or where
heat is derived from solar collectors.
•The absorption cycle is similar to the
compression cycle, except for the method of
raising the pressure of the refrigerant vapor.

32. •In the absorption system, the compressor is replaced
by an absorber which dissolves the refrigerant in a
suitable liquid, a liquid pump which raises the
pressure and a generator which, on heat addition,
drives off the refrigerant vapor from the high-
pressure liquid.
•Some work is required by the liquid pump for a given
quantity of refrigerant but smaller than that needed
by compressor in the vapor compression cycle.
•A suitable combination of refrigerant and absorbent
is used .
•The most common combinations are ammonia
(refrigerant) and water (absorbent), and water
(refrigerant) and lithium bromide (absorbent).

33. How Air –Conditioners work ?
Air conditioners and refrigerators work the same way. Instead of cooling
just the small, insulated space inside of a refrigerator, an air conditioner
cools a room, a whole house, or an entire business. Air conditioners use
chemicals that easily convert from a gas to a liquid and back again. This
chemical is used to transfer heat from the air inside of a home to the outside
air.
The machine has three main parts. They are a compressor, a condenser and
an evaporator. The compressor and condenser are usually located on
the outside air portion of the air conditioner. The evaporator is located
on the inside the house, sometimes as part of a furnace.

34. ❖The working fluid arrives at the compressor as a cool, low-pressure gas called
Freon. The compressor squeezes the fluid. This packs the molecule of the fluid closer
together. The closer the molecules are together, the higher its energy and its
temperature.
❖The working fluid leaves the compressor as a hot, high pressure gas and flows
into the condenser. If you looked at the air conditioner part outside a house, look for
the part that has metal fins all around. The fins act just like a radiator in a car and help
the heat go away, or dissipate, more quickly.
❖When the working fluid leaves the condenser, its temperature is much cooler and
it has changed from a gas to a liquid under high pressure. The liquid goes into the
evaporator through a very tiny, narrow hole. On the other side, the liquid's pressure
drops. When it does it begins to evaporate into a gas.
❖As the liquid changes to gas and evaporates, it extracts heat from the air around it.
The heat in the air is needed to separate the molecules of the fluid from a liquid to a
gas.
❖The evaporator also has metal fins to help in exchange the thermal energy with the
surrounding air.

35. ❖By the time the working fluid leaves the evaporator, it is a cool, low pressure gas. It
then returns to the compressor to begin its trip all over again.
❖Connected to the evaporator is a fan that circulates the air inside the house to blow
across the evaporator fins. Hot air is lighter than cold air, so the hot air in the room
rises to the top of a room.
❖There is a vent there where air is sucked into the air conditioner and goes down
ducts. The hot air is used to cool the gas in the evaporator. As the heat is removed
from the air, the air is cooled. It is then blown into the house through other ducts
usually at the floor level.
❖This continues over and over and over until the room reaches the temperature you
want the room cooled to. The thermostat senses that the temperature has reached the
right setting and turns off the air conditioner. As the room warms up, the thermostat turns
the air conditioner back on until the room reaches the temperature.

41. NON DUCTED PRODUCTS

42. •Window Air Conditioning System
•Window air conditioners are one of the most
commonly used and cheapest type of air
conditioners.
•To install one of these units, you need the
space to make a slot in the wall, and there
should also be some open space behind the
wall.
•These air conditioners come in cooling capacities
from 0.5 to 2 tons, adequate for a room
between 5 to 20 msq in size. Larger spaces may
be handled by using multiple units of this type.
•Window air-conditioner units are a reliable and
simple-to-install solution to keep a room cool
while avoiding the costly construction of a central
air system.
•While window air conditioners are economical
and most convenient to install, they could be
noisy for some applications.
•Better yet, when the summer heat dies down,
these units can be easily removed for storage,
and you can use the windowsill for other
purposes.

43. ADVANTAGES DISADVANTAGES AREAS WINDOW
A.C’S ARE USED
REASONS WHY THEY
ARE USED
Inexpensive Tonnages are limited
(1 to 2 TR typically)
homes Homes and small
offices generally use
ACs as unitary
(independent)
products to cool
separate rooms.
Easy to installNoisier than other
types of Acs.
Small office
executive cabins
Each room can
operate its AC
independently
A window is required
which is blocked by
the AC.
Small shops Tonnage
requirements per
room is limited
typically to 1-2 TR
Simple,low-
cost,service and
maintenance
No constant fresh air
circulation
Budgets are usually
tight.
Running costs are
low

44. •SPLIT AIR CONDITIONER SYSTEM
•The split air conditioner comprises of two
parts: the outdoor unit and the indoor
unit.
•The outdoor unit, fitted outside the
room, houses components like the
compressor, condenser and expansion
valve.
•The indoor unit comprises the evaporator
or cooling coil and the cooling fan.
•These two units are connected by
refrigeration tubing and electrical wires
that can pass through a hole in the wall
barely 10cms in diameter.
•Since the noisier components are outside
the building , the conditioned space is
much quieter.
•Further, the present day split units have
aesthetic looks and add to the beauty of
the room. The split air conditioner can be
used to cool one or two rooms.

46. ADVANTAGES DISADVANTAGES AREAS SPLIT A.C’S
ARE USED
REASONS WHY
THEY ARE USED
Quieter than
window ACs
Costlier than
window ACs
Senior executive
cabins
Such applications
place a primium on
‘quiet’ cooling.
Available in large
tonnages(even upto
5TR in turbo splits)
Require space
outside the room for
the outdoor unit
Professionally
positioned small or
mid-sized
showrooms
Budgets allow mini
split purchase.
Do not require or
block a window
Some piping and
cabling is required
Up-market homes Windows unlikely to
be available for
window ACs
May be used as
‘multiple’units to
cool 2 or 3 adjacent
rooms.
Do not provide fresh
air intake
Small clinics,ATMs
etc.
Fresh air may not be
a problem due to
constant opening
and closing of doors.
Asthetically suit the
interiors better
May suit
aesthetics/interiors/
status better than
window Acs.

47. •THERE ARE a variety of indoor units
available. The choice of indoor unit
(IDU)depends on the application and
available space.
•WALL MOUNTED SPLITS.
•Homes that use mini-splits to cool large
living rooms or bedrooms may prefer high
wall units .
•Such units are fixed on the wall,at a height
of about 2.5 metres from the floor.
•The controls are generally operated by a
corded or cordless remote control unit.
•Because it is mounted on the wall it is
preferred for rooms having less floor space.
•Advantages of wall mounted or floor
mounted splits.
•They are easy to install and maintain.
•Do not require false ceiling work.

48. •Showrooms may prefer the semi
concealed(cassette) or concealed(hideaway)
ceiling mounted IDU’s
•Advantages of ceiling mounted split ACs
are:
•They are tucked away on the ceiling and not
eat up precious showroom wall space.
•Neither IDU demands too much by way of false
ceiling work, just the space around the unit
really needs aesthetic cover.
•Both the AC units are slim in height and require
just a little space between false and real
ceiling.

49. •Larger single hall showrooms may find the turbo split ceiling mounted IDU most
suitable.
•Advantages of ceiling mounted split ACs are:
•In larger spaces where ceiling is criss-crossed by beams and ducts are difficult
to run turbo splits can be installed.
•Where the ceiling height is low , cassettes can be installed as they are slim in
height.
•When air throw must be directed over specific areas of the room that wall-
mounted or floor mounted units may not reach.
•Cassettes are also available in ‘multiple’ units , so larger areas may be cooled
using multi cassette system.

50. ADVANTAGES DISADVANTAGES AREAS SPLIT A.C’S
ARE USED
REASONS WHY
THEY ARE USED
Quieter than
window ACs
Costlier than
window ACs
Senior executive
cabins
Such applications
place a primium on
‘quiet’ cooling.
Available in large
tonnages(even upto
5TR in turbo splits)
Require space
outside the room for
the outdoor unit
Professionally
positioned small or
mid-sized
showrooms
Budgets allow mini
split purchase.
Do not require or
block a window
Some piping and
cabling is required
Up-market homes Windows unlikely to
be available for
window ACs
May be used as
‘multiple’units to
cool 2 or 3 adjacent
rooms.
Do not provide fresh
air intake
Small clinics,ATMs
etc.
Fresh air may not be
a problem due to
constant opening
and closing of doors.
Asthetically suit the
interiors better
May suit
aesthetics/interiors/
status better than
window Acs.

51. Central air conditioning
Central air conditioning, commonly referred to as central air (US) or air-con (UK), is an air
conditioning system which uses ducts to distribute cooled and/or dehumidified air to
more than one room, or uses pipes to distribute chilled water to heat exchangers in
more than one room, and which is not plugged into a standard electrical outlet.
With a typical split system, the condenser and compressor are located in an outdoor unit;
the evaporator is mounted in the air handling unit (which is often a forced air furnace). With
a package system, all components are located in a single outdoor unit that may be
located on the ground or roof.
Central air conditioning performs like a regular air conditioner but has several added
benefits:
When the air handling unit turns on, room air is drawn in from various parts of the house
through return-air ducts. This air is pulled through a filter where airborne particles such as
dust and lint are removed. Sophisticated filters may remove microscopic pollutants as well.
The filtered air is routed to air supply ductwork that carries it back to rooms. Whenever the
air conditioner is running, this cycle repeats continually.
Because the central air conditioning unit is located outside the home, it offers a lower
level of noise indoors than a free-standing air conditioning unit.

53. •CENTRAL AIR CONDITIONING PLANTS
•The central air conditioning plants are the systems used when large buildings,
hotels, theaters, airports, shopping malls etc are to be air conditioned completely
which require very high cooling loads.
•In the central air conditioning systems there is a plant room where large
compressor, condenser, thermostatic expansion valve and the evaporator are kept
in the large plant room. They perform all the functions similar to a typical
refrigeration system.
• However, all these parts are larger in size and have higher capacities. The
compressor is of open reciprocating type with multiple cylinders and is cooled by
the water . The compressor and the condenser are of shell and tube type and a
thermostatic expansion valve is used.
• The chilled air is passed via the ducts to all the rooms, halls and other spaces
that are to be air conditioned. Thus in all the rooms there is only the duct passing
the chilled air and there are no individual cooling coils and other parts of the
refrigeration system in the rooms.
•in each room we get a completely silent and highly effective air condition system .
In this system the amount of chilled air that is needed in the room can be controlled
by the openings depending on the total heat load inside the room.

54. The central air conditioning systems are highly sophisticated applications of the air
conditioning systems and many a times they tend to be complicated.