Air-conditioning systems

Office buildings, banks, large theatres, stores are usually air -condi­tioned by a central station system in the basement and serving all the rooms by means if air ducts.

In smaller stores, theatres, hotels and residencies the direct expansion type of the system is commonly used. By this method the refrigerant is ex­panded in a finned tube evaporator and the air blown over it comes in contact with the cold surfaces of the fins and pipes. The cooled dehumidi­fied air is then blown by a fan to the space to be air-conditioned. Most systems have filters to remove dust.

The air-conditioning system also contains a small compressor and condenser for liquefying gas as rapidly as it expands in the evaporator unit. The conversion of the refrigerant from a liquid to a gaseous state requires heal and this is secured from the atmosphere. Thus, the air is cooled and the gas is heated.

Direct expansion systems are cheaper to construct and installed than central station systems. They are usually designed so that no long duel, work is required. Units capable of air-conditioning one room or several rooms arc now available. Some of them arc portable requiring only an electric connection to a light socket to place them in operations. Many of them provide for the introduction of fresh air into the air- conditioned space, having a short duct to a window ventilation for this purpose.

As direct expansion systems are usually placed in the room or rooms which are air-conditioned it is necessary that they employ a refrigerant which is harmless in character.

4. The text is headlined "Air -conditioning Systems". Define what systems are dwelt on by reading the text.