Document Z4p5q0m5rpwGQ58bOJKq3kJXY

American Society of Heating and Ventilating Engineers Guide, 1936 Referring to Table 2: a = (4 X 12 X 30 X 0.031) + (2 X 30 X 30 X 0.016) = 73.4 o' = (2 X 12 X 30 X 0:031) + (30 X 30 X 0.016) + (2 X 12 X 30 X 0.6) + (30 X 30 X 0.6) = 1008.7 / o'. . 1008.7 h ~ a 73.4 13-7 Noise level reduction = 10 logu. -jj- = 10 Iogio 13.7 = 11.4 db. 14 # What relation does the movement for the suppression of noise bear to the' trend toward air conditioning of offices and other places in cities where people work or congregate? Very important sources of disturbing sounds are the various street noises that gain entrance, not only through open windows but to a certain extent even through closed windows. If windows are to be kept closed to exclude noise, air conditioning is a practical necessity, especially ` in summertime. Summertime air conditioning makes use. of awnings, which are not only desirable but economical in that they keep down, cooling loads. To obviate condensation and frost on windows, wintertime air conditioning calls for storm sash or double glazing which in turn reduces the transmission of street noises. \ 342 Chapter 19 AIR DISTRIBUTION Opening Characteristics, Residences, Stores and Offices, Auditoriums, Railroad Cars TO produce proper air distribution in an enclosed space to be venti lated, heated, or cooled by air, the design and location of the air inlet and exhaust openings must be carefully considered. A system may fail, though it handles the proper amount of air at the required temperature, if such important design principles of air distribution are ignored.. Since air temperature and quantity are now moderately easy to control and vary, air distribution becomes the prime factor, particularly when comfort air conditioning is involved. ) Owing to the lack of practical and satisfactory instruments for measur ing accurately air movement all air distribution information available may be justly criticized, but for practical design purposes this infor mation is sufficiently accurate. >, OPENING CHARACTERISTICS Any temperature differential between an occupied space air and inlet air causes the air to rise or fall a given vertical distance in a given time. This vertical rise or fall of the air' stream can be moved horizontally by velocity, and if the mass of supply air is not diffused, the horizontal movement may be accomplished without changing the given vertical distance or the given time. This horizontal movement at a constant velocity may be reduced by expanding the air stream either by deflection, changing the dimensional ratio of the stream, or breaking the air into a series of streams in close proximity. With a few exceptions a high velocity should be used, with a large compact mass of air for a long air throw (Fig. 1), so that the periphery of the air stream will be reduced as much as is consistant with good practice. A grille used for a long air throw should have a large free area, and should have a number of fins, bars, or tubes with sufficient depth so that the width of each slot is approximately one-half the depth of the fins or bars. The grille opening should be as near square as possible and should' be expanded only slightly between the riser or duct and opening. When using grilles with a large free area, if the supply-air makes an abrupt turn before being introduced into the occupied space, turning blades (Fig. 2) may be used to equalize the velocity and volume over the entire grille area and assist in controlling the direction of the air stream. 343