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PRINCIPLES OF AIR-CONDITIONING

The term air conditioning has been so widely and loosely used that the student should be careful in trying to understand its true meaning. For many years we have introduced air into buildings after heating, dehumidifying and in some cases, cooling it, and we have called that process ventilation. In recent years much greater stress has been laid on the treatment of air as compared with circulating it merely through the building, and we now call the process air-conditioning. Air-conditioning, then, may be said to the treatment of the air in the building so as to make it more comfortable or healthful for human beings or more suitable for manufacturing processes.

The factors which are of importance in air-conditioning are many, and unfortunately the term is sometimes used to refer only to minor factors such as cleaning and circulating of air. It is important that the engineer should exactly realize what an air-conditioning system does and what it does not do, and that he should make clear to others what results can be expected from the system.

Complete air-conditioning is known to involve the simultaneous control of the following factors temperature, humidity, air motion, air distribution dust, bacteria, odors, toxic gases. Of these the first three, temperature, humidity and air motion, are the most important, and no air-conditioning system deserves the name unless it satisfactory controls those three factors. Thus it follows that air-conditioning involves heating as well as cooling.

The general problem of maintaining comfortable conditions in an occupied room has been the subject of study for many years. Early investigations believed the atmosphere of a crowded room to cause discomfort through its effect on the lungs, and carbon dioxide, being the principal product of respiration, was looked upon as the harmful element. Air-conditioning or ventilation, as it was formerly called, was therefore considered for many years to be a problem of supplying sufficient fresh air to dilute the carbon dioxide content.

Experiments led engineers to give up this theory. Several men were placed in an airtight chamber until the carbon dioxide content increased and oxygen content decreased considerably. They suffered great discomfort, but when their was set in motion by fans, the discomfort at once disappeared. Other men outside the chamber experienced no discomfort from breathing the air from the chamber through tubes, but those within the chamber experienced no relief from breathing outside air. This experiment demonstrated the modern concept of air-conditioning, namely that the cooling effect of the atmosphere upon the skin is of great importance and comfort depends upon maintaining the proper thermal environment. The men within the test chamber were uncomfortable because their body heat was not being properly removed, and they became more comfortable as the fans increased the rate of heat removal.

 


Date: 2015-12-24; view: 1118


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