Document YMg2Ne6VOR6rojzNq3RZzo1D

American Society of Heating and Ventilating Engineers Guide, 1935 Most large continuously operated theaters are; provided with complete downwa systems of air distribution similar to the one shown in Fig. 9. With this system a U ^ number of inlet openings is provided, each of which discharges air in a thin horizons ' stream at high velocity in order that the cool air will be mixed with the air in the theai before it reaches the patrons. ter 13 t What system of air distribution is frequently used in smaller theate The system used, particularly where artificial cooling is had, brings air in at high velocit through a large number of small horizontal nozzles located in the rear of the auditorTM' near the ceiling. This high -velocity air mixes with a much larger quantity of air anrt causes circulation within the theater before it comes into contact with the occupants With this method care must be exercised not to discharge the air against ceiling beamso projections which may give a downward direction to the cool air before it is thorough!, diluted. ' if Chapter 20 AIR DUCT DESIGN Pressure Losses, Friction Losses, Friction Loss Chart, Proportioning the Losses, Sines of Ducts, General Rules, Procedure for Duct Design, Air Velocities, Proportioning the Size for Friction. Main Trunk Ducts with Branches for Public Buildings, Equal Friction Method, Details of Duct Construction THE flow of air due to large pressure differences is most accurately stated by thermodynamic formulae for air discharge under condi tions of adiabatic flow, but such formulae are complicated, and the error occasioned by the assumption that the gas density remains constant throughout the flow may be considered negligible when only such pressure differences are involved'as occur in ordinary heating and ventilating practice. if In the development of the formulae, diagrams, and tables for the flow I i of air, use is made of the following basic.equation for the flow of fluids:' If Hy be the velocity head in feet of a fluid, and the velocity, V, be expressed in feet per minute, the fundamental equation is ' ' V = 60 ^2g Hy The factor g is the acceleration due to gravity, or 32.16 ft per second per second. v.'; It is usual to express the head in inches of water for ventilating work and, since the heads are inversely proportional to the densities of the fluids, - - Hy 62.4 hy P 12 Hy - 5.2- therefore, / where v;1096.5 (1) V = velocity in feet per minute. hy = velocity head or pressure in inches of water, p = weight of air in pounds per cubic foot. - For standard air (70 F and 29.92 in. barometer) p = 0.07.495 lb per cubic foot, Substituting this value in Equation 1: fVa V = 1096.5 = 4005 .07495 (2) 324 325 3 I M j! I IH4; s>! IJ tit I