THE MECHANICS OF VENTILATION. 549' 



Taking formula (18) we have for the loss through walls exclusive of 

 windows: 



a =z 6306 square feet, 



^=32°, 

 li = 0.09O, 



d = thickness of wall =2 feet, 

 then 



71—32 



Qz=:0.095 x6306 =11487=nuniber of heat-units conducted away 



2 



through walls per hour. 

 For windows we have 



a = 1696, 

 . t'= 71°, 

 ^=32°. 

 Exi^eriments have been made in the case of window glass, showing that, 

 neglecting d the value of k varies from 1 to 3. We will take it for this cal- 

 culation at a mean value, namel}^, 2. We have therefore 



Q=2x 1696(71— 32)z=132288. 

 hence the total loss by conduction per hour under the conditions of temper- 

 ature assumed is 



11487+182288=143775 heat-units. 

 Suppose, however, instead of allowing 2000 cubic feet per hour for eacfe, 

 person, we take what is more nearly the actual supply, that is 850 cubic 

 feet. With that assumption we have a total supply per hour of 1,360,000 

 cubic feet. The amount of heat from people and lights will be the same a^- 

 befbre. Assume temperature of air supply at 62° as previously. Amount 

 of air in pounds 



1360000 



=104615 



13 

 Number of heat-units per pound of air is 

 1096000 



=10.4, 



104615 

 making an increase of actual temperature of 

 10.4x4.2=43°. 68. 

 Assuming no loss by conduction and radiation, and the temperature of' 

 the outflowing air is 



62°+43°.68=105°.68. 

 In fact loss by conduction, &c., increases in proportion as inside temper- 

 ature increases, consequently the amount conducted aAvay Avill be corre- 

 spondingly greater than in the preceding case. Observation will show air- 

 in upper part of room to range from 85° to 95°. The writer has on several 

 occasions observed it higher than 80° in lower part of room, and this too 

 with windows open, and outside temperature at from 35° to 40°. 



A partial exhibit has now been made of the main principles underlying 



