• F 278 PHYSICAL LIMITATIONS HAVE BEEN OVERCOME erally suggested that 68° F. is the ideal temperature. Many people have found that they feel cold at temperatures considerably higher than this in the winter because the humidity is so low. It is therefore desirable to add moisture to the indoor air in winter. The humidity of the air is usually controlled by passing it through a spray of water, thus adding water to dry air and removing excess water from moist air. Many people do not realize that the humidity of hot moist air can be decreased by passing it through a spray of cold water. Moist room Hot dry Air to rooms air 85 Silica -Gel dchumidlficr air 130 Air cooler 80° Sili'cdt Gal Outdoor "air 95°F. DehumidiFiad Dehumidified Silica Silica Qel cooler Gel 300' Saturated Silica Qel Silica Gel reactivator '70'f " 78°F In Out Tap water 300 F Hot gases carrying water vapour dischard'ed to atrnospnerc 120 F Air out Hot furnace gases 450° Purnacc Fig. 93. Silica gel air conditioning system. (Courtesy of the General Electric Air Conditioning Company.) Various devices for adding moisture in the winter have been used with rather indifferent effectiveness in the past. These devices include water pans in hot-air furnaces, troughs of water heated by radiators, and steam jets controlled by a humidistat. One ingenious device for the control of humidity depends upon passing air through a spray of a solution of some salt such as lithium chloride. The vapor pressure of this solution can be controlled by controlling the concentration of the salt in the solution, thus making it possible to obtain any desired humidity. Such a solution would take excess moisture from the air and would add the proper amount of moisture to air that is too dry.
Silica gel is AIR CONDITIONING 279 used in another successful method of controlling humidity. Silica gel has very high adsorptive power because it exposes a very large amount of surface relative to its mass. The silica gel is placed in a slowly revolving drum through which humid air is drawn and thus dried. At another location hot air is driven through the drum to remove the moisture. An interesting fact to consider is that the humid air is warmed by the condensation of the water vapor on the silica gel — the Silica gel de- (Courtesy of Pop- a valuable consideration in the wmter, but not desirable in the summer. Control of the humidity not only adds to the bodily comfort, but it also prevents the furniture and windows from drying out and cracking. Dry air robs the throat and nasal passages of moisture and renders them more susceptible to colds, pneumonia, and influenza. The air in many homes in the winter is often drier than that in DRYING CHAMBER FOR AIR STATIONARY PARTITION WITH SEALS SEPARATES CHAMBERS DRUM MAKES ONE REVOLUTION IN 7 TO 9 MINUTES ^ .silica ceu jk having a moisture Adriven off ir Ij- J /HOT AIR ^//FROMQAS T* HEATER > HOT AIR TO OUTDOORS RECONDITIONING CHAMBER FOR SILICA GEL the Sahara Desert. It is the drying of the skin that produces the winter itch that is so annoying to many people. (This itch may also be due to an unusual sensitiveness to cold.) It has been generally argued that this increase in humidity will lower the fuel bill, but such arguments overlook the fact that the amount of heat required for vaporization of the water to provide this humidity the amount of heat saved by maintaining a lower practically offsets temperature. The amount of water that must be added to the dry atmosphere in the winter to bring the humidity within desired limits is surprisingly large. In an average home it involves the evaporation of gallons of water daily. Fig. 94. How humidifier works. ular Science.) The Air Must Be Filtered. One of the most difficult phases of air conditioning is that of dust and dirt removal. Very small particles are very difficult to remove, although human beings remove nearly 100 per cent of the dust from the air that they breathe. Unfortunately this dust often contains materials which are harmful to the lungs where it accumulates. As much as two quarts of dirt have been filtered from the air in an average home in one month. The removal of dirt from the air materially reduces the amount of housecleaning and dusting required.