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1-AIR CONDITIONING:
Air conditioning is a combined process that performs many functions simultaneously. It conditions
the air, transports it, and introduces it to the conditioned space. It provides heating and cooling from
its central plant or rooftop units.
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.
The
term H.V.A.C&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 individual component processes were
developed prior to the more complete concept of air conditioning, the
term H.V.A.C&R is often used by the industry.
2-COMFORT AND PROCESSING AIR CONDITIONING SYSTEMS:
2.1-Air Conditioning Systems:
An
air conditioning, or H.V.A.C&R, system is composed of components
and equipment arranged in sequence to condition the air, to transport
it to the conditioned space, and to control the indoor environmental
parameters of a specific space within required limits.Most air
conditioning systems perform the following functions:
A- Provide the cooling and heating energy required
B-
Condition the supply air, that is, heat or cool, humidify or
dehumidify, clean and purify, and attenuate any objectionable noise
produced by the H.V.A.C&R equipment
C- Distribute the conditioned air, containing sufficient outdoor air, to the conditioned space
D-
Control and maintain the indoor environmental parameters–such as
temperature,humidity,cleanliness, air movement, sound level, and
pressure differential between the conditioned space and
surroundings-within predetermined limits.
Parameters such as the
size and the occupancy of the conditioned space, the indoor
environmental parameters to be controlled, the quality and the
effectiveness of control, and the cost involved determine the various
types and arrangements of components used to provide appropriate
characteristics.
Air conditioning systems can be classified
according to their applications as (1) comfort air conditioning systems
and (2) process air conditioning systems.
2.2-Comfort Air Conditioning Systems:
Comfort air conditioning systems provide occupants with a comfortable and healthy indoor environment
in
which to carry out their activities. The various sectors of the economy
using comfort air conditioning systems are as follows:
A- The
commercial sector includes office buildings, supermarkets, department
stores, shopping centers, restaurants, and others. Many high-rise
office buildings, including such structures as the World Trade Center
in New York City and the Sears Tower in Chicago, use complicated air
conditioning systems to satisfy multiple-tenant requirements. In light
commercial buildings, the air conditioning system serves the
conditioned space of only a single-zone or comparatively smaller
area.For shopping malls and restaurants, air conditioning is necessary
to attract customers.
B- The institutional sector includes such
applications as schools, colleges, universities, libraries,museums,
indoor stadiums, cinemas, theaters, concert halls, and recreation
centers. For example,one of the large indoor stadiums, the Super dome
in New Orleans, Louisiana, can seat 78,000 people.
C- 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-day-a-week schedule, since they can be occupied at any time.
D.
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 micrometer size
from areas such as operating rooms, nurseries, and intensive care
units. The relative humidity in a general clinical area is often
maintained at a minimum of 30 percent in winter.
D. The
transportation sector includes aircraft, automobiles, railroad cars,
buses, and cruising ships. 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. According
to the Commercial Buildings Characteristics (1994), in 1992 in the
United States, among 4,806,000 commercial buildings having 67.876
billion ft2 (6.31 billion m2) of floor area, 84.0 percent were cooled,
and 91.3 percent were heated.
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