318 WARMING AND VENTILATING OCCUPIED BUILDINGS. 



the foul air from the six beds on each side, should discharge 4.715 cubic 

 feet in a second, at the velocity of 3^ feet a second. Their greatest sec- 

 tional area should be 1.437 square feet, and their dimensions 1 foot by 

 1 foot 5 inches; but they should be made smaller at first, and propor- 

 tioned at every point to the amount of air to be removed. The sizes of 

 the other air-passages should be determined in the same way. If there 

 are three stories to each wing, or thirty-six beds in all, the amount of 

 air to be removed will be 101.710 cubic feet an hour, or 28 feet a second. 

 The velocity in the chimney being given at about 7 feet, the area should 

 be 4.3 square feet, and the dimensions 2 feet 1 inch by 2 feet 1 inch. 



52. Proper velocities for tlie air in fresh-air openings. — When the open- 

 ings are placed in the ceiling of the places ventilated, and when the air 

 descends vertically, the velocity of the fresh air should not exceed If 

 feet a second. 



When the air is distributed laterally, and almost parallel with the ceil- 

 ing, or at 16 to 20 feet above the heads of the occupants, the velocity 

 of the entering air may be 3|- feet without inconvenience. Such enter- 

 ing velocities are usually easily produced by the simple effect of the 

 draught, which causes the removal of the air. Thus, in the large 

 lecture-hall of the Conservatory of Arts and Trades, which often con- 

 tains 750 auditors, to each of whom is allowed 1,059 cubic feet of air an 

 hour, which requires a change of 794,010 cubic feet an hour, or 227 

 cubic feet a second, the total free section of fresh-air openings is about 

 129 square feet, and the admission of this large volume of air is scarcely 

 perceptible. 



53. Proper area of fresh-air openings. — Although in every case a part 

 of the air carried off will be naturally replaced by that which enters 

 through the joints of the doors and windows, it will be well to calculate 

 the free area of the openings for the admission of fresh air by dividing 

 the total amount to be introduced in one second by the fixed velocity 

 of entrance. Thus, the currents of air from the doors and windows will 

 be diminished. 



54. Means of overcoming the ef-ects of currents of air produced by the 

 draught — The system of ventilation by direct draught is rightly charged 

 Avith producing currents of air, often very unpleasant, when the out- 

 side doors are open; but the effect of these currents may be rendered 

 less unpleasant by following the preceding rules, and, besides, they 

 may be rendered almost entirely imperceptible by taking care to warm 

 the entrances to ventilated buildings, such as corridors, vestibules, 

 waiting-rooms, &c., so that the opening of doors will only cause the 

 admission of warm air at a temperature at least equal to that of the 

 places to be ventilated. We will specify in each case the particular 

 arrangements to be adopted for this purpose. 



[To be continued in the next volume.] 



