^<5^ JAOQGS Tjd^iS: 77 



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

 estimated. To secure good ventilation we have arbitrarily assumed the 

 following: 



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 that derived from the animals in the space to be 

 ventilated. 



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

 four parts carbon dioxide in 1 0,000, and that the standard of purity which 

 is to be preserved in the space to be ventilated be not over 1 7 parts of carbon 

 dioxide in 10,000. 



3. It is also assumed that the average relative humidity of fresh country 

 air is 65 per cent 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 3,953 1,100 pounds 



For Swine 1,510 1 60 pounds 



For Sheep 929 1 00 pounds 



For Hens 37 3 pounds 



With different weights per head, the amounts of air would change in 

 proportion. 



How to Figure Sizes of Flues 



For example, an outtake ventilating flue for thirty cows \vould require 

 30 X 3953 =1 18,590 cu. ft. of air per hour. 



We will assume an air movement of 250 feet per minute, which equals 

 15,000 feet per hour. 



To ascertain the cross section area of the outtake flue required for the 

 cows, it is only necessary to divide the number of cubic feet of air required for 

 30 cows, by i 5,000, thus, 



1 18,590 cu. ft.- 15,000 equals 7.906 sq. ft., 

 requiring a flue 34 inches by 34 inches, or two flues 24 inches by 24 inches 

 each. 



For every outtake flue there should be a number of intake flues whose 

 combined area exceeds that of the outtake flue by 10 per cent, even in view 

 of the unavoidable leakage of air through the walls and around the windows 

 and doors. 



Thirty cows require an outtake flue of 1 1 38.5 sq. in. area; then these cows 

 should have an intake of 1138.5 sq. in. plus 10 per cent which would be 



