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Abstract
High technology and fast scientific progress lend our era different from any other era. Scientists set their goals to provide luxury, health and comfort conditions for human beings. Thus appears the important role-played by the air conditioning engineering science, seeking for creating an artificial climate suitable for human comfort and industrial processes. The latest interest, which has a great importance, is the indoor air quality. As the impurities as well as high or low relative humidity, with high or low air velocity, when existing for long periods, has a bad effect on human health and it may leads to death, as in clinical applications (intensive care and similar).
Proper design also considers controlling noise and minimizing pollution of the atmosphere and water systems around the building.
As the sources of energy are decreasing and the high energy requirements lead to importance of reducing the total energy consumption. In the same time, retrofitting existing buildings is also an important part of the construction industry because of increased costs of construction and the necessity of reducing energy consumption. The selection is often made by the owner and may not be based on an engineering study. To a great degree, system selection is based on the engineer’s ability to relate those factors involving higher first cost or lower life-cycle cost and benefits that have no calculable monetary value.
1.2 Human Comfort
It is logical to ask what is the desired temperature and humidity relationship?. The answer is that there is one specific condition. People react differently to different conditions. ASHRAE conducted a research Study over many years checking the reactions of large numbers of people to establish a range of combined temperatures, humidity and air movement that provided the most comfort. This is known as the comfort zone. The combined effect of Dry Bulb Temperature (DBT) and Wet Bulb Temperature (WBT) is known as effective temperature (ET). And when the effect of air movement is taken into consideration, the combination of (ET) and air movement is known as equivalent effective temperature (EET). There is another factor affects on the comfort zone (radiation) this factor involves the amount of radiant exchange between a person and the surroundings.