VENTILATION 



115 



and the air is brought in cold, the inlet should be high ; the out- 

 let may be either low or high, and controlled by a damper for 

 cold weather. 



Outlets and inlets. — In cases where suitable outlets are pro- 

 vided above, and the conditions are favorable, warmed air passes 

 upward and out of the room or building ; but if such outlets are 

 not provided, then heated air merely rises to the ceiling, cools, 

 spreads out and descends, and no pure air can come in to take 

 its place. Circular, straight tubes are preferable. It is esti- 

 mated that a right-angle bend in 

 an outlet diminishes the velocity 

 of the outgoing air about one 

 half. Where it is absolutely nec- 

 essary that an outlet tube should 

 change its course, it should be 

 done in a curve or slight bend 

 rather than at a right-angle. All 

 parts of ventilator, shafts and 

 tubes should be accessible for 

 cleaning purposes, as it is not un- 

 common for them to become so 

 obstructed by cobwebs and dust 

 as to be useless. In a general way, 

 the outlet tube, if it must be near 

 an outside wall, should be placed 

 on the south side of the building 

 in order to economize the heat of the sun in rendering it more 

 effective. Central outlet tubes are generally more efficient, be- 

 cause they cool the column of air less, and maintain the current 

 velocity better. One or two outlet tubes are more efficient than a 

 larger number and should be preferred whenever construction 

 permits. 



Many small inlets are always better than a few large ones, as 

 they admit the same volume of air, and give it better distribu- 

 tion, without direct currents. 



"Wing describes a form of cupola ventilation which has been 

 found quite satisfactory in providing air outlet for some barns 

 (see Fig. 40). This cupola outlet seems always in operation. 

 There is no chance for wind to blow in and force strong down 

 drafts. When in working order, it serves always as an outlet. 

 It is easily closed by a rope from the ground floor. 



1 2 



Pig. 39. — Ventilation. (Paige.) 



1. Air duct obstructed by cob- 

 webs and dust. 



2. Stationary outlet cowl to 

 utilize the force of the wind for 

 producing upward suction, and to 

 prevent down draft. 



