HVAC is a combined process that performs many functions simultaneously

1-HVAC:

HVAC is a combined process that performs many functions simultaneously. It conditions
the air, transports it it, and introduces it to the space . It provides combined processes such as 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 acceptablelimits for the comfort and health of the occupants of the conditioned space or for the purpose of product processing.

a common 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 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 HVACSYSTEMS:

2.1-Air Conditioning Systems:

An air conditioning, or H.V.A.C&R, system consist of components and equipment designedin sequence to condition the air, to transport it to the conditioned space, and to control the indoor Comfort Requirements of a specific space within acceptable limits.Most HVAC 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 dilation of any objectionable noise produced by the H.V.A.C&R equipment

C- Distribute the conditioned air, containing outdoor air, to the conditioned space

D- Control and maintain the Comfort Requirements:-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 people in) 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.

HVAC 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 of the conditioned space 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 achieve 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.

E. 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