550 THE MECHANICS OF VENTILATION. 



the Mechanics of Ventilation. In conclusion it will be well to collate px-in- 

 ciples and facts for convenience of reference. 



1. Perfect ventilation is hardly automatic. A certain amount of atten- 

 tion is necessary to keep any system in working order, 



2. Ventilation by draught is preferable to ventilation by forcing air in, 

 it having the advantage of supplying fresh air as fast as foul air is removed, 

 provided of course the design is properly carried out. 



3. The vacuum ma}' be produced in case of rooms or suites of apart- 

 Kients by fire places or by small flues properly connected with the rooms at 

 or near the floor, in which gas jets are kept burning vvhenevcr ventilation 

 is needed. In large buildings, however, the vacuum will of necessity be 

 produced by vertical shafts designed in accordance with the principles 

 herein contained. 



Corollary. — Where gas jets are used the amount of heat from one cubic 

 foot of gas may be taken as given in the beginning of this paper. Knowing 

 the amount of air to be carried away per hour, the size and number of 

 burners is easily found. 



4. Perfect ventilation will cost something. To lift a thousand pounds 

 •of air 50 feet, requires exactly the same expenditure of force as to lift a 

 thousand pounds of iron, or any other substance 50 feet. 



Corollary 1. — Since to ventilate a building means there is work to be 

 done, and consequently an expenditure of force necessary, any system j)ro- 

 fessing to ventilate without such expenditure of force can hardly be other 

 than a failure. 



Corollary 2. — Careful study of the matter shows the importance of re- 

 ducing friction in flues, ducts, elbows, etc., to a minimum; otherwise a 

 large percentage ot force will be expended for that purpose only. 



5. Ventilation is a branch of mathematical investigation, actual con- 

 struction should, therefore, be preceded by careful calculation. 



6. Heating is a branch of ventilation, and should always be considered 

 in connection with it. 



Corollary 1. — In warming by heated air the current should be intro- 

 duced at or near the ceiling. It is a violation of first principles to introduce 

 it near the floor. 



Corollary 2. — In designing a system of warming by heated air, 2)rovision 

 should be made for introducing cold air in connection with the warm cur- 

 rent, in order that the air may not enter the room at too high a temperature. 



Corollary 3. — The cold air currents as per Corollary 2 should be under 

 perfect control as well as the heated currents, in order that the proper tem- 

 perature inside may be maintained under everj' variation of outside tem- 

 perature. 



Corollary 4. — Warming by steam or hot water, by a combination of the 

 two, or by steam and hot air combined may all be exceedingly healthful, 

 pi'ovided adequate ventilation accompanies them. These methods are all 

 reasonably economical as regards consumption of fuel. 



