WARMING AND VENTILATING OCCUPIED BUILDINGS. 317 



of air, and does not at all prevent an excessive increase of temperature. 

 Examples of this kind are very numerous. 



49. Position of openings for the admission and discliarge of air. — oSTone of 

 these openings should be placed at the level of the floors as builders 

 usually, but improperly place them, because the sweepings fall in them, 

 and soon choke the corresponding flues. 



Openings arranged to admit warm or cold air should be placed near 

 the ceiling, or at such a distance from the occupants of the room that 

 they may not perceive any current of air. 



When, on the contrary, the openings are placed near the floor the 

 warm air in winter ascends rapidly to the ceiling, while in summer the 

 fresh air, which is heavier, remains at the lower j)art. In both these 

 cases it is unpleasant to stay near these openings. In public halls and 

 lecture-rooms especially, the admission of air under the seats and between 

 the feet of the audience is improper. In the Palace of Luxembourg and 

 the Chamber of Deputies this mode of introducing air has had to be 

 given up entirely. 



Discharge-openings, on the contrary, should, iti general, be arranged 

 near the floor, and also in the vertical walls. Some special cases, in 

 which this latter rule must be violated, will be mentioned further on, 



50. Proper velocities of the air in the discharge openings. — These veloci- 

 ties should increase from the first openings in the room to the chimney, 

 which it is well to make common to all the ventilating-flues of the same 

 house. They should be governed as far as possible by the following: 



First ventilating-openings, velocity in one second. 1 ft. 4 in. to 2 ft. 4 in., 



First collecting-passages 3 3 3 11 



Second collecting-passages 4 3 4 7 



General discharge-chimney 5 6 6 6 



These velocities are easily obtained in most cases by means of an 

 excess of 36° to 45° in the chimney over that of the external air. 



51. Sectional area to be given to openings and flues. — The total volume of 

 air to be discharged in a second, being calculated in advance according 

 to the number of occupants and the conditions of change of air, dividing 

 this volume by the proper velocity for each passage will give in square 

 feet the free sectional area. By free sectional area is meant the actual 

 passage-way, the gratings which often obstruct it being deducted. 



Example. — Take the case of a hospital-ward of twelve beds, to each 

 of which is allowed 2,825 cubic feet of air an hour, making in all 33,900 

 cubic feet an hour, or 9.42 cubic feet a second, the mean velocity in 



9 42 

 the channels being 2.3 feet a secoud,their total section would be — ^ =4.1 



square feet. If it be necessary to have one to each bed, the pipe behind 



4.1 



each bed should have a section equal to yi)= 0.34 square feet, and its 



dimensions should be 7 by 7 inches. The collecting-pipes, which receive 



