Air conditioning involves simultaneously controlling the temperature, humidity, cleanliness, and distribution of air. It conditions and transports air to a conditioned space while maintaining predetermined environmental limits for occupant comfort. There are two main types of air conditioning systems: comfort systems that provide a comfortable indoor environment, and process systems that control the environment for manufacturing or other processes. Common comfort applications include commercial buildings, residences, healthcare facilities, and transportation. Process systems are used in textile mills, clean rooms, precision manufacturing, pharmaceutical facilities, and refrigerated storage. Refrigeration methods include non-cyclic techniques using ice or dry ice and cyclic vapor-compression or vapor-absorption refrigeration cycles.

1. Air Conditioning:
Maintaining a living space or an industrial facility at the desired temperature and humidity requires some
processes called Air Conditioning processes. These processes include simple heating (raising the temperature),
simple cooling (lowering the temperature), humidifying (adding moisture) and dehumidifying (removing moisture).
Some times two or more of these processes are needed to bring the air to a desired temperature and humidity
level. The process of Air Conditioning can simply be defined as:
“Air Conditioning is the process of treating air to control simultaneously its temperature, humidity, cleanliness,
and distribution to meet the comfort requirements of occupants of the conditioned space”.
But a more complete and updated definition of Air Conditioning which fits more on current application of Air
Conditioning is as follows:
“Air Conditioning is a process that performs many functions simultaneously. It conditions the Air, transports it and
introduces it to the conditioned space. It also controls and maintains the temperature, humidity, air movement, air
cleanliness, sound level and pressure differential in a space within predetermined limits for the comfort and health
of the occupants of the conditioned space or for the purpose of product processing”.

2. Refrigeration:
Refrigeration is the transfer of heat from a lower
temperature region to a higher temperature region.
Devices that produce refrigeration are called refrigerators
and the cycles on which they operate are called the
refrigeration cycles.
“Refrigeration is the process of removing heat from an
enclosed space (or from a substance) and moving it to a
place where it is unobjectionable”.
The primary purpose of refrigeration is lowering the
temperature of the enclosed space or substance and then
maintaining that lower temperature. The term “cooling”
refers generally to any natural or artificial process by
which heat is dissipated.
Cold is the absence of heat, hence in order to decrease a
temperature, one removes the heat rather than adding the
cold. Some form of work must be performed to accomplish
this in order to satisfy the Second Law of
Thermodynamics. This work is usually done by
mechanical work.

3. HVAC&R:
HVAC&R is an abbreviation of Heating, Ventilating, Air
Conditioning and Refrigerating. The combination of
processes in this commonly adopted term is equivalent to
the current definition of Air Conditioning. Because all
these component processes were developed prior to the
more complete concept of Air Conditioning, the term
HVAC&R is often used by the industry.

4. Cryogenics:
The point on the temperature scale at which conventional refrigeration ends and
cryogenics begins is somewhat arbitrary. In 1950, engineers and scientists at the National
Bureau of Standards (now called NIST) suggested that the field of Cryogenics be defines
as that temperature region below -1500 C (-2400 F). This point was selected because the
refrigerants used in the air conditioning systems and domestic refrigerators boil at
temperatures above -1500 C, whereas the gases utilized for Cryogenic applications (such
as Oxygen, Nitrogen and Helium boils at temperatures below -1500 C). Application of
Cryogenics includes the industrial gas industry (separation of air into nitrogen and oxygen),
liquefied natural gas and the pursuit of temperatures approaching absolute zero.
Heat transfer in Cryogenic systems is an important factor in design of all low-temperature
systems. The cost of removing energy from a low temperature region is significant. A
power input of approx. 14 KW (19 hp) would be required to drive a refrigerator (Cryocooler)
removing 1 KW (3412 Btu/hr) from a space at 90 0K (-298 0F) and rejecting the energy to
the ambient surroundings. The cost of Cryocoolers is also extremely high and because of
these high costs, heat transfer is examined closely in the design of these systems

5. Heat pump Systems:
The term Heat Pump is used for a type of Air Conditioner
in which the refrigeration cycle is able to be reversed i.e
producing heat instead of cold in the conditioned space.
Heat pump is also commonly referred to as a reverse
cycle Air Conditioner.
The most common energy source for heat pumps is
atmospheric air (air-to-air systems), although water and
soil are also used. The major problem with air-to-air
systems is frosting which occur in humid climates when
the temperature falls below 2 0C to 5 0C. The frost
accomolation on the evaporator coils is highly undesirable
since it seriously disturbs the heat transfer. The coil can
be defrosted, however, by reversing the heat pump cycle
(running it as an air conditioner). Water-source systems
usually use Well water from depths of upto 80 m in the
temperature range of 5 0C to 18 0C and they do not have
frosting problem, they have higher COP but are more
complex. Ground-source systems are also rather involved
since they require long tubing placed deep in the ground
where the soil temperature is relatively constant.

6. Some home-owners elect to have a heat pump system
installed, which is actually simply a central Air Conditioner
with heat pump functionality (the refrigeration cycle is
reversed in the winter). When the heat pump is enabled,
the indoor evaporator coil switches roles and becomes the
condensor coil, producing heat. The outdoor condensor
unit also switches roles to serve as the evaporator, and
produces cold air (colder than the ambient outdoor air).
Heat pumps are most competitive in the areas that have a
large cooling load during the cooling season and a
relatively small heating load during the heating season. In
these areas, the heat pump can meet the entire cooling
and heating needs of residential or commercial buildings.

7. Professional bodies:
American Society of Heating,
Refrigerating, and Air-Conditioning
Engineers (ASHRAE):
ASHRAE headquarters in Atlanta, GA, is an organization
devoted to the advancement of indoor-environment-
control technology in the HVAC industry. ASHRAE was
founded in 1894 to serve as a source of technical
standards and guidelines. Since that time, it has grown
into an international society that offers educational
information, courses, seminars, career guidance, and
publications. The organization also promotes a code of
ethics for HVAC professionals and provides for liaison with
the general public.

8. Australian Institute of Refrigeration Air Conditioning and Heating (AIRAH):
AIRAH was founded in 1920 and currently has around 10,000 members. AIRAH is the official Australian
secretariat of the International Institute of Refrigeration (IIR) and collaborates closely with the American Society of
Heating, Refrigeration and Air Conditioning Engineers (ASHRAE).
Air Conditioning Contractors of America (ACCA):
The ACCA is a large organization of American HVACR professionals. They have over four thousand members
and have individual charters in each state.
Air Conditioning and Mechanical Contractors Association of Australia (AMCA):
AMCA is a nation wide industry association dedicated to represent and service the air conditioning and
mechanical services industry in Australia. Members of AMCA design, install and provide ongoing service of air
conditioning and mechanical ventilation systems.
Pakistan HVACR Society & ASHRAE Pakistan Chapter:
Pakistan HVACR Society and ASHRAE Pakistan Chapter are the two main local bodies working for the upliftment
and development of HVACR Industry in Pakistan. Pakistan HVACR Society was founded in 1993-94 under the
Chairmanship of Mr. Anwar Saadat.

9. Air Conditioning Systems:
Most Air Conditioning Systems have the following
functions:
1. Providing the cooling and heating energy required.
2. Conditioning the supply air i.e cooling or heating,
humidifying or de humidifying, cleaning and purifying
and attenuating any objectionable noise produced by
the HVAC&R equipment.
3. Distributing the conditioned air, containing sufficient
outdoor air, to the conditioned space.
4. Controlling and maintaining environmental parameters
(such as temperature, humidity, cleanliness, air
movement, sound level and pressure differential
between the conditioned space and surroundings)
within predetermined limits.
We can classify Air Conditioning Systems into following
two main categories:
(1) Comfort Air Conditioning Systems (2)
Process Air Conditioning Systems

10. Comfort Air Conditioning System:
The primary purpose of Comfort Air Conditioning is to provide the occupants a comfortable and healthy indoor
environment in which they can carry out their activities. Various sectors of economy using Comfort Air Conditioning
System are as follows:
(1) The Commercial Sector includes Office Buildings, Super markets, Departmental Stores, shopping centers,
restaurants and others. Mostly Air Conditioning systems used in this sector is simple but many high rise and
other sophisticated buildings use very complicated systems to satisfy multiple tanent requirements.
(2) Public Sector includes such applications as indoor stadiums, libraries, museums, cinemas, theatres, concert
halls and recreation centers. One of the large indoor stadiums, the Superdome in New Orleans, Louisiana, can
seat 78,000 people.
(3) The residential and lodging sector consists of hotels, motels, apartment houses and private homes. Many
systems serving the lodging industry and apartment houses are operated continuously on a 24 hour, 7 days a
week schedule, since they can be occupied at any time.
(4) The health care sector encompasses hospitals, nursing homes and convalescent care facilities. Special air
filters are generally used in hospitals to remove bacteria and particulates of sub micron size from areas such as
operating rooms, nurseries and ICU’s. The Relative Humidity in the general clinical area is often maintained at
a min. of 30% in the winters.
(5) Transportation sector includes automobiles, trains, buses and aircrafts. Passengers increasingly demand ease
and environmental comfort, especially for long distance travel. Modern airplanes flying at high altitudes may
require a pressure differential of about 5 psi between the cabin and the outside atmosphere.

11. Process Air Conditioning Systems:
Process Air Conditioning Systems provide needed indoor environmental control for manufacturing, product storage
or other research and development processes. Following areas are examples of Process Air Conditioning Systems:
(1) In textile mills, natural and many manufactured fibres are hygroscopic. Proper control of humidity increases the
strength of the yarn and fabric during processing. For many textile manufacturing processes, too high a space
Relative Humidity can cause problems in the spinning process. On the other hand, a lower Relative Humidity
may induce static electricity that is harmful to the production process.
(2) Many electronic products require clean rooms for the manufacture of such things as ICs, since their quality is
adversely effected by airborne particles. Relative Humidity control is also needed to prevent corrosion and
condensation and to eliminate the static electricity. Temperature control maintains materials and instruments in a
stable condition and is also required for workers who wear dust-free garments.
(3) Precision manufacturers always need precise temperature control during their production of precision
instruments, tools and equipment.
(4) Pharmaceutical products require temperature, humidity and air cleanness control. For Example liver extracts
require a temperature of 750 F and a Relative Humidity of 35%.
(5) Modern refrigerated warehouses not only store commodities in coolers at temperature of 270 F to 320 F and
frozen foods at -100 F to -200 F, but also provide control for perishable foods of relative humidity between 90%
and 100%. Refrigerated storage is used to prevent deterioration.

12. Methods of Refrigeration:
Non-cyclic refrigeration:
In these methods, refrigeration can be accomplished by melting ice
or by subliming dry ice. These methods are used for small-scale
refrigeration such as in laboratories and workshops, or in portable
coolers.
Ice owes its effectiveness as a cooling agent to its
constant melting point of 0 °C (32 °F). In order to melt, ice
must absorb 333.55 kJ/kg (approx. 144 Btu/lb) of heat.
Foodstuffs maintained at this temperature or slightly
above have an increased storage life

13. Cyclic refrigeration:
This consists of a refrigeration cycle, where heat is
removed from a low-temperature space or source and
rejected to a high-temperature sink with the help of
external work, and its inverse, the thermodynamic power
cycle. In the power cycle, heat is supplied from a high-
temperature source to the engine, part of the heat being
used to produce work and the rest being rejected to a low-
temperature sink.
A refrigeration cycle describes the changes that take place
in the refrigerant as it alternately absorbs and rejects heat
as it circulates through a refrigerator. It is also applied to
HVACR work, when describing the "process" of refrigerant
flow through an HVACR unit, whether it is a packaged or
split system.
Heat naturally flows from hot to cold. Work is applied to
cool a living space or storage volume by pumping heat
from a lower temperature heat source into a higher
temperature heat sink. Insulation is used to reduce the
work and energy required to achieve and maintain a lower
temperature in the cooled space.

14. • Cyclic refrigeration can be classified as:
1. Vapor cycle & 2. Gas cycle
• Vapor cycle refrigeration can further be classified as:
• Vapor compression refrigeration 2. Vapor absorption refrigeration