HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumAir washing can be effective in removing dust and those fumesand smoke that are soluble in water, but carbons, soot, and similar substancescannot be removed by this type of cleaning. It is possible tocleanse the air of these by substances using either the dry and viscousfilters that have been developed.Heat TransferWhen bodies of unequal temperatures are placed near each other,heat leaves the hotter body and is absorbed by the colder body until thetemperature of each is equal. The rate at which the heat is absorbed bythe colder body is proportional to the difference of temperature betweenthe two bodies, the greater the difference of temperature the greater therate of flow of the heat.Heat is an active form of energy, much the same as mechanical andelectrical energy. Heat can be transferred by three methods, conduction,convection, and radiation.Conduction and ConvectionConduction refers to heat transfer that takes place mainly in solidswhere the heat is passed from one molecule to another without anynoticeable movement of the molecules.Conduction is the transfer of heat through a substance. Conductivitymay be defined as the relative value of a material as compared witha standard, which affords a passage for heat. A poor conductor is knownas a nonconductor or insulator. Copper is a good conductor, while thevarious materials used to insulate buildings are poor conductors. Anysubstance, which is a good conductor of electricity is also a good conductorof heat.Convection is a heat transfer that takes place in liquids and gaseswhere the molecules carry the heat from one point to another. Convectioninvolves the transfer of heat due to the motion of the heated matter.Since motion is a requirement for convection, it can only take place inliquids and gases.RadiationRadiation is heat transfer in a wave motion, such as light or radiowaves. It takes place through a transparent medium without affecting©2001 by The Fairmont Press, Inc. All rights reserved.