The American Society of Heating, Refrigerating
and Air-conditioning Engineers (ASHRAE) defines
air-conditioning as “the process of treating air so
as to control simultaneously its temperature,
humidity, cleanliness and distribution to meet the
requirements of the conditioned space”.
From the definition, the important actions involved in the
operation of an air-conditioning system are:
• Temperature control
• Humidity control
• Air filtering, cleaning and purification
• Air movement and circulation
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
An air-conditioning system is for:
• Temperature control
• Humidity control
• Air filtering, cleaning and purification
• Air movement and circulation
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
The Cardinal Principle of Air-conditioning /
Refrigeration is Heat Transfer…….
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Air-conditioning / Refrigeration means the
reduction of the temperature of a particular space
or of any substance. This is achieved by removing
heat from the space where air-conditioning is
required, or from the substance to be refrigerated.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
• Any change of state transfers a large amount of
energy.
• At saturation temperature, materials are sensitive
to addition or removal of heat.
• Refrigerants use the same principles as ice. For
any given pressure, all refrigerants have a
saturation temperature.
• If the pressure is low, the saturation temperature
is low. If pressure is high, saturation temperature
is high.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
• Heat is a form of energy that is transferred from
one object to another object by a difference in
temperature. Heat transfer can occur, when there
is a temperature difference between two or more
objects. Greater the temp. difference, greater the
heat transfer.
• Heat will only flow from a warm object to a colder
object.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
1 – 2 : Low Pressure Refrigerant (Gas) is
Compressed to (relatively) high
temperature & pressure Superheated
vapour & sent via Discharge Line.
2 – 3 : Compressed Refrigerant (Gas)
Condenses to low temperature & high
pressure liquid by losing heat to air/water in
the Condenser & sent via Liquid Line.
3 – 4 : Liquid Refrigerant Expands in
volume through Expansion valve and enters
Evaporator as low pressure, low temperature
2 phase saturated Liquid/Gas.
Two-phase
liquid-vapor
mixture
4 – 1 : 2 phase Liquid/Gas Evaporates drawing heat from
the Refrigerated space/object & returns via Suction Line.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Expansion
Valve
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 Piston compressors are also called as
reciprocating compressors and use a
piston and cylinder arrangement to
provide compressive force .
 The reciprocating motion of the piston
due to external power compresses the
refrigerant inside the cylinder.
 Piston compressors have a low initial
cost and a simple, easy to install design.
They have a large power output
range and can reach extremely high
pressures.
 However, they have high maintenance costs, potential vibrational issues,
and are not typically designed to run continuously at full capacity.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 TYPICAL USAGE: (a) Weld –sealed = up to 20 Tons (b) Semi-hermetic = 2
to 50 tons & (c) Open type = 5 to 150 Tons.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 Rotary compressors have two rotating
elements or vanes ( like gears) , between
which the refrigerant is compressed..
 These compressors are very efficient
because the actions of taking in the
refrigerant & compressing it occur
simultaneously.
 They have very few moving parts, low
rotational speeds, low initial and
maintenance costs, and can work even in
very dirty environments.
 However, they are limited to smaller volumes of the gas and produce
less pressure than other types of compressors.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 TYPICAL USAGE: Rotary Compressors are most often used in
appliances, such as refrigerators, freezers, water coolers, but it is also
used for residential air conditioning and heat pump products up to 5
tons.(Nowadays upto even 7.5 tons).
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 Screw compressors use a pair of helical
rotors or screws which mesh together to
compress the refrigerant between them.
 They can produce high pressure for a
small quantity of gas and consume less
power than reciprocating compressors..
 They have low to medium initial and
maintenance costs and few moving parts.
 However, they are difficult to operate in dirty environments, have high
rotational speeds, and have shorter life expectancies than other designs.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 TYPICAL USAGE: Screw type compressors compete with open
reciprocating compressors in large commercial and industrial market,
and have a wider range of capacities from 20 to 750 tons.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 Scroll compressors use two offset spiral
disks nested together to compress the
refrigerant.
 The upper disk is stationary while the
lower disk moves in orbital fashion.
 Scroll compressors are quiet, smoothoperating units with few moving parts
and the highest efficiency ratio of all
compressor types.
 They also are more flexible for handling
refrigerants in the liquid form.
 However, as fully hermetic designs, scroll compressors cannot be easily
repaired. They also typically cannot rotate in both directions. \.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 TYPICAL USAGE: Scroll Compressors are used from 5 to 10 tons and are
popular for cooling, and for large residential and light commercial
Central systems. The range is increasing nowadays up to 20 tons.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 Centrifugal compressors use the rotating
action of an impeller wheel to exert
centrifugal force on refrigerant inside a
round chamber (volute).
 Unlike other designs, centrifugal
compressors do not operate on the
positive displacement principle, but have
fixed volume chambers.
 They are well suited to compressing large volumes
of refrigerant to relatively low pressures.
 The compressive force generated by an impeller wheel is small, so
systems that use centrifugal compressors usually employ two or more
stages (impellers) in series to generate high compressive forces.
Centrifugal compressors are desirable for their simple design, few
moving parts, and energy efficiency when operating multiple stages.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
 TYPICAL USAGE: Centrifugal compressors are used in systems
requiring capacities of more than 150 tons and are usually available upto
10,000 tons capacity while several custom built compressors of even
greater than 20,000 tons are in use.
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
• Based on flow , Evaporators
can be:
a. Natural Convection
b. Forced Convection
• Based on construction, it
can be:
a. Tube and Plate
b. Finned type
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS
Senthil Kumar, AGM(CEM)
AIR-CONDITIONING BASICS