AIR AND VENTILATION 



93 



to make this full allowance when the building is situated in a 

 sheltered position or is shut in by other buildings. For buildings 

 on exposed sites and not sheltered from prevailing winds the size 

 of both inlets and outlets may be less, especially if they are of a 

 fixed type and not controllable. 



As it is desirable to introduce into a stable for heavy horses, 

 or into a byre for large milking cows, between 10,000 and 30,000 

 cubic feet of 'air per hour per head, the amount of actual inlet 

 area per head will need to be 270 square inches for the higher and 

 90 square inches for the lower standard. For cab horses, light 

 vanners and small dairy cattle the inlet per animal should be 136 

 square inches if the total CO 2 content is not to exceed 0-05 per cent, 

 of the air, and 45 square inches if the lower standard or 0-09 per 

 cent, of CO 2 is allowed. 



The minimum inlet area to be allowed for any of the domestic 

 animals can be readily ascertained by dividing the volume of air 

 to be supplied hourly by the volume of air passing through each 

 square inch of inlet when the wind is blowing at 3 miles per hour, 

 i.e., 110 cubic feet. 



It is advisable that both inlets and outlets are made so that 

 they can at least be partially closed when the wind is very strong and 

 cold. It is, however, undeniable that excellent ventilating systems 

 exist where neither inlets nor outlets can be altered, or where the 

 outlets can be controlled and the inlets are fixed or vice versa. 



In view of the greater tendency there is to close ventilators than 

 to open them, it is strongly to be advised that at least a proportion of 

 both inlets and outlets be of a fixed type. If the inlets and outlets 

 are controllable they may be adjusted according to the force of the 

 wind ; thus with a wind blowing at 12 miles per hour the inlet area 

 need only be one-quarter of that prescribed for the minimum 

 provision. 



A table is given on page 94 showing the inlet and outlet area that 

 should be supplied for the various domesticated animals. 



Relative Size of Inlets and Outlets. Some are of the opinion 

 that the total outlet area should be larger than the total inlet area 

 on the supposition that heated and therefore expanded air occupies 

 a greater volume than the colder incoming air, while others hold that 

 the outlet area should be smaller than the inlet so as to prevent down- 

 draught. 



In practice it is found that if the total inlet and total outlet 

 area are the same the result is quite satisfactory. 



The table is therefore applicable for both inlets and outlets, 

 i.e., a large cow may be said to require a minimum inlet area of 



