Hospitals and such places, where the vitiation is due to exhalations from diseased or sick people, should be provided with at least twice this amount. VOLUME OF AIR NECESSARY TO MAINTAIN A GIVEN STANDARD OF PURITY. (American Blower Company.) Proportion of Carbon Dioxide in 10,000 Parts of the Cubic Feet of Space in Room per Individual. Cubic Feet of Air, of Composition 4 Parts of Carbon There is a certain minimum space required in buildings for each person, because the carbon dioxide and other exhalations from the body are very slowly diffused through the air. This minimum space, in cubic feet per person, is as follows: In a lodging or tenement house Barracks Ordinary hospital ward Fever or surgical ward. CU. FT. 300 250 600 1,000 1,400 Floor Space must be considered as much as cubic space. Thus, in a schoolroom, there must be at least 15 sq. ft. of floor surface for each pupil; and in hospitals each bed should have 100 sq. ft. of floor space. In stables, each horse or cow should have 100 sq. ft. of floor space. A horse should have 1,600 cu. ft. of air space, and a cow not less than 1,200. As cows are usually kept to furnish milk for food, it is important that they should be kept in a healthy condition, and that the air around them should be clean. In quantity, the toxic, or poisonous, organic impurities exhaled from the lungs and surface of the body bear a definite proportion to the amount of carbon dioxide produced by respiration in the same time. The ratio is found to be so nearly constant that, in testing air to determine its fitness for breathing, the percentage of carbon dioxide is taken as an index of the quantity of organic impurities in the air. Apparatus for testing air, called carbonometers, can be purchased from dealers in chemical supplies, the necessary instructions being furnished with the instruments. NATURAL VENTILATION. In natural-ventilation systems, the drafts in the flues or ducts are caused by the difference in density between the air in the ducts and the outer atmosphere. The higher the temperature in the ducts, the more rapid will the draft become. In the following table, 50 per cent. (a fair average in good work) has been deducted from the theoretical flow to offset all ordinary resistances in the flues, such as friction, change in direction, etc. The difference in temperature given in the table is that existing between the outer atmosphere and the average of the air in the flue. Knowing the velocity per minute, and the cubic feet of air per minute to be removed, the area of the flue in square feet is found by dividing the volume by the velocity. Wind pressure also affects natural ventilation. The movement of air through a building may be accelerated or retarded by the wind, according to the location of the outlets and the kind of cowls used. FLOW OF AIR IN FLUES PER SQUARE FOOT OF SECTION, BY NATURAL DRAFT, IN CUBIC ESTIMATING THE HEAT LOSSES. Heat escapes from buildings in two ways: first, by conduction through the windows, walls, floor, and roof; and second, by ventilation or leakage of warm air. The loss from the latter cause will depend on the tightness of the windows and doors and on the thoroughness of the construction of the walls, especially in wooden buildings. If the outer walls are exposed to the wind, the loss of heat by conduction will be increased from 10 to 30 per cent., while, if they are not windtight, the loss by escape of air will be increased to an unknown amount. The rate at which heat will be lost through walls and windows has been found, by careful experiment, to be proportional to the difference in temperature between the inside and outside air. The rate of loss under ordinary conditions, in B. T. U., and in rooms that have only a moderate exposure to wind, is shown in a diagram, Fig. 1, by Alfred R. Wolff, M. E. The heat losses under various conditions may be read directly from the diagram, the line a showing loss through vault light; b, single window; c, single skylight: d, 4-in. brick wall; e, double window; f, double skylight; g, 8-in. brick wall; h, 1-in. pine board door; i, 12-in. brick wall; j, concrete floor on earth; k, fireproof partition; 7, 2-in. pine board, heavy door; m, 16-in. brick wall; n, 20-in. brick wall; o, concrete floor on brick arch; p, 24-in. brick wall; q, 28-in. brick wall; r, 32-in. brick wall; 8, wood floor on brick arch; t, 36-in. brick wall; u, 40-in. brick wall; v, double wood floor. 25 2.5 25 10 10 15 The requisite allowance for different exposures is indicated by the figures on the diagram given in Fig. 2, which shows that for north and west exposures 25 per cent. should normally be added to the calculated heat loss through walls, while for east and south exposures an allowance of 15 and 5 per cent., respectively, should be made. A further allowance of 10 per cent. is made for heating the air that constantly leaks in through cracks and crevices, and a similar allow 28 10 35 (35) (30 Floor or Roof 10 15 10 W (35 10 20 (25) 25 10 10 10 5 肉 ance is advised for the loss of heat through floors and ceilings. When the rooms are comparatively small, the results given by the use of the diagram in Fig. 1 are increased by the percentage indicated by the figures given inside the circles on the diagram in Fig. 2. If brick walls are made double, with an intervening air space, the loss of heat is less than that of a solid wall having an equal thickness of brick. The saving will be about .07 or .08 B. T. U. per sq. ft. |