Page:Architectural Review and American Builders' Journal, Volume 1, 1869.djvu/706

 566 The Architectural Review and American Builders' Journal. [Mar., can be kept to about the temperature of the body, 98° ; and if the excessive cold of the windows is counteracted, by steam radiators under them, then the transoms, over the doors, may be left always open, and even the doors them- selves could be safely left open, much of the time, forming a liberal and excel- lent ventilation. If, however, we should allow the main hall to become the ventilator for the water-closets, the boiler-room, &c, it would be an offence to the whole build- ing Separate ventilating shafts must, therefore, be provided for these ; and it is also necessary, to have a separate arrangement, for the ventilation of each room, in case it is desirable to close it entirely ; and thus disconnect it from the main hall. For this purpose, two large shafts have been provided, by the architect, communicating most directly with the water-closets, and by direct or lateral ducts, with exits in the floors of every room in the building, as well as with exits directly over the chandeliers in the ceilings in the principal rooms. There is another advantage to be gained by the. use of these shafts : In spring and autumn, when the external at- mosphere is too warm to require sufficient additional heat to cause the necessary motion of the air ; and j r et too cold to allow of the windows being open : — then, by heating the air, in these shafts, by steam-coils, if the boilers are in use, and, if not, by an ordinary stove, or furnace, that will be placed there for that pur- pose, the air will be set in motion over the whole building. It is just at this point, when the closest comparison should be made, be- tween the values of the fan and the heated shaft, for moving the air, because in winter — when there is a considerable difference of temperature between the external air and that in the building — all the flues draw freely, and it is very easy to keep up sufficient circulation ; and in summer — when the windows are all open — a fan would tie perfectly use- less. The Ventilating Shafts, as shown on the plans and section, commence at the foundation, four feet by seven, in the clear each, the two giving an area of fifty-six feet. Their capacity is increased, thirteen square feet each, where the additional foul air ducts enter, above the fourth story, thus giving au aggregate of eighty-two square feet of ventilating flue. Now, we want to know how much air these shafts will move ; and how much coal will be required for the purpose. Of course, in making these estimates, we lay aside ail other sources of motion, such as the artificial heating, external currents, &c. ; and suppose the air in the building to be perfectly stagnant. Such conditions would scarcely occur six days in a whole year ; but then those six days must be fully provided for. One pound of coal will heat from thirty to forty thousand cubic feet of air 10°. Now we find, theoretically, that a temperature of 10°, in excess of surrounding atmosphere, will give, in a chimney one hundred feet high, a velo- city of more than eleven feet per second. Suppose then we allow the six feet for friction, (which would be larger than necessary, in a flue of that size, made perfectly smooth,) we still have five feet per second for the velocity of the moving current; and this, I believe, will be generally exceeded in practice. Eighty square feet, for size of shaft, with a velocity of five feet per second, gives 24,000 cubic feet a minute, or f7, 000, 000 (omitting the fractions) in a day of twelve hours. This would be an abun- dant ventilation for this building. Now, to warm these 17,000,000 cubic feet 10° in the shaft, for the purpose of giving it this motion, would require only 566 pounds of coal, supposing 30,000 cubic feet to be heated by one pound, which is a small allowance. Let us compare this result with that