428 



SCIENCE OF HOME AND COMMUNITY 



\Jn/et _^ 



Breathing Line 



Ovt/et 



Air admitted on side. 

 Discharged near bottom. 



f Breathing Line 



Outlet 



In securing this supply of fresh air, a motion of air is pro- 

 vided for at the same time. 



Gravity system. Various methods are used to produce 

 this circulation of air. One system is called the gravity 



system. In this system the mo- 

 tion is brought about through 

 a difference in the weight of 

 the air due to a difference in 

 temperature. The foul air 

 duct is connected with the 

 chimney, and the air here be- 

 ing much warmer than the air 

 outdoors rises, while the cold 

 air is taken in at the basement 

 and after being heated is led 

 into the various rooms. This 

 may work fairly well in cold 

 climates during the winter 

 where the air outdoors is much 

 colder than that in the school- 

 room. But in the fall and 

 spring, when the difference in 

 temperature is small, the sys- 

 tem is not satisfactory. 



Fans. In order to obtain 

 the best circulation, fans are 

 generally used. Two systems 

 are used, the pressure and the 

 exhaust. In the pressure system, the air is forced into the 

 room by means of a fan located in the basement. In th( 

 exhaust system, the air is drawn out of the room by m< 

 of a fan which rotates in such a way as to suck the air out 

 If only one of these systems is used, it should be the pressui 

 as that is generally found to be better. Sometimes bot 

 systems are used. 



Air admitted at bottom. 

 Discharged near bottom. 



fntet near top. 

 Discharge near bottom. 



FIG. 169. Inlets and outlets. 



