<^7^ JAOaGS XjJA'Y 77 



The need of a continuous and sufficient supply of fresh air cannot be over- 

 estimated. To secure good ventilation we have arbitrarily assumed: 



1 . That the flow of air in a square outtake flue will have at least an 

 average velocity in the flue of 250 feet per minute, without mechanical forcing 

 or the aid of heat other than from the animals in the space ventilated. 



2. That the standard of purity of fresh country air contains no more than 

 four parts carbon dioxide in 10,000, and the standard of purity to be preserved 

 in the space ventilated be not over 1 7 parts of carbon dioxide in 1 0,000. 



3. That average relative humidity of fresh country air is 65 ^r or less. 

 To secure this air movement, the number of cubic feet of air required per 



head per hour would be as follows: 



TABLE 1: 



Cu. Ft. Per Hour Assumed Weights 



Per Head Per Head 



For Horses 4,924 1 ,200 pounds 



For Cows 3,95 3 1 , 1 00 pounds With different weights 



1- c ■ 1 c I n 1 z' n J per head, the amounts 



For bwme 1,510 60 pounds ^j ^j^ ^^.^^,j ^.^^^^^ j^ 



For Sheep 929 1 00 pounds proportion. 



For Hens 37 3 pounds 



How to Figure Sizes of Flues 



To ascertain cross section area of outtake flue required to supply this 

 amount, it is necessary to consider speed of air movement through the flue. 

 The area of cross section depends in great degree upon height of the outtake. 

 If outtake is short, it must have a sufficiently larger cross section to compensate 

 for less velocity of air current in the flue, always associated with short flues. 



The air movement in outtake flues is also directly affected bv difference in 

 temperature and wind velocity; and therefore may vary from 250 to 500 feet 

 per minute. 



A ventilating system should be designed of ample capacity to supply the 

 required change of air under most adverse conditions, and provisions made for 

 throttling when the air is moving too rapidly. 



Assuming a velocity of 295 ft. per minute for flues 30 ft. high, and 250 ft. 

 for flues 20 ft. high, the size outtake for one cow is arrived at as follows: 



Table 1 gives 3953 cu. ft. as amount of air for one cow per hour. Assum- 

 ing an air movement of 295 feet per minute or I 7,700 cu. ft. per hour, the cross 

 section area of outtake to supply one cow per hour is 3953 -^ 1 5,000 = .22.3 

 sq. ft., or 32.1 I sq. in. 



Assuming a short outtake with velocity of 250 feet per m.inute or 15,000 

 feet per hour, the cross section area for one cow will be 3953 -^ 1 5,000 = .263 

 sq. ft., or 37.87 sq. in. 



For 20 cows, the cross section area of 20 ft. outtake flue would be 

 37.87 ^ 20 =757.4 sq. in. or a flue about 20 in. x 38 in. For 30-ft. flue 

 32. 11 ^ ' 20 = 642 sq. in., or a flue 20 m. x 32 in. 



