Document 4a7VbqLNY8VwoLmmem09nyXJG

806 CHAPTER 40 1949 Guide methods for small rooms with exposed wall, such as offices, hotel (guest) rooms, hospital (patients) rooms,'apartments, etc. For o small store the cooling performance of various distribution methods is illustrated in Fig. 10. Marine applications of air distribution systems are given in Chapter 49. REFERENCES 1 Control of Air Streams in Large Spaces, by G. L. Tuve and G. B. Priester (A.S.H.V.E.TRANBAcrri6Ns,Vol.50,1944, p. 153). ' 1 Air Conditioning Principles, by C. 0. Mackey, (International Textbook Com pany, Scranton, Pa.; 1941) p. 187. * Throw of Air from Slots and Jets, by R. D. Madison and W. R. Elliot (A.S.H.V.E. Journal Section, Heating, Piping and Air Conditioning, Nov. 1946, p. 108). ' * Modern Air Conditioning, Heating and Ventilating, by W. H. Carrier, R. E. Cheme, and W. A. Grant (Pitman Publishing Corp., New York, N. Y., 1940). * A.S.H.V.E. Research Repobt No. 1155--The Performance of Stack Heads, by D. W. Nelson, D. H. Krans and A. F. Tuthill (A.S.H.V.E. Transactions Vol. 46 1940, p.205). ' A-S.H.V.E. Research Report No. 1226--Performance of Side Outlets on Hori zontal Ducts, by D. W. Nelson and G. E. Smedberg (A.S.H.V.E. Transactions Vol. 49,1943, p. 58). ' BIBLIOGRAPHY A.S.H.V.E. Research Report No. 1076--Air Distribution from Side Wall Outlets by D. W. Nelson and D. J. Stewart (A.S.H.V.E. Transactions, Vol. 44,1938, p. 77)' AB.H.V.E. Research Report No. 1140--The Use of Air Velocity Meters, by G. L. Tuve, D. K. Wright, Jr. and L. J. Seigel (A.S.H.V.E. Transactions, Vol. 45. 1939,p.645). ' A.S.H.V.E. Research Report No. 1162--Air Flow Measurements at Intake and Discharge Openings and Grilles, by G. L. Tuve and D. K. Wright, Jr. (A.S.H.V E Transactions, Vol. 46,1940, p. 313). A.S;H.V.E. Research Report No. 1165--Development of Instruments for the Study of Air Distribution in Rooms, by A. P. Kratz, A. E. Hershey and R. B. Enedahl (A.S.H.V.E. Transactions, Vol. 46,1940, p. 351). A.S.H.V.E. Research Report No. 1204--Entrainment and Jet-Pump Action of Air Streams, by G. L. Tuve, G. B. Priester and D. K. Wright, Jr. (A.S.H.V.E. Trans actions, Vol. 48,1942; p. 241). Air Flow at Discharge of Fan Pipe Lines in Mines, by G. E. McElroy, (Bureau of Mines, Report of Investigations--No. 3730, November, 1943). The Rationale of Air Distribution and Grille Performance, by C. O. Mackey (Re frigerating Engineering, Vol. 35, No. 6, June 1938, p. 417). CHAPTER 41 AIR DUCT DESIGN Pressure Losses, Friction Losses, Circular Equivalents of Rectangular Ducts, Dynamio or Shock Losses, Pressure Loss in Elbows, Losses Due to Area Changes, Pressure Changes, Duct Design,'Duct Construction Details, Heat Losses from Ducts, Maintenance AIR ducts for the transmission of the air in forced air heating, ventilat ing, cooling or air conditioning systems must be carefully designed for functional as well as economical reasons. The design should.be based upon the fundamental laws of fluid flow in pipes and should take into ac count recent analytical and experimental studies which complement and substantiate the fundamental laws. The basic equations of the flow of fluids will be found in Chapter 4, Fluid Flow. PRESSURE LOSSES Air ducts impose resistances to air- flow which must be overcome by pressure differences resulting from the expenditure of energy in maintaining the flow. In ventilating and air conditioning work the flow of air takes place under very small pressure, differences, and the assumption that the -> gas density remains constant throughout the flow will cause only a negligible error. It is therefore possible to use the equation for incompressible fluids . (liquids) for the flow of air in a duct, instead of the complicated thermo- . dynamic formulas for air discharge under conditions of adiabatic flow which would be necessary for .large pressure differences. . A reasonably accurate estimate of the flow resistances offered by the system is essential for satisfactory duct design. The theoretical resistance of an air handling system can be computed from the methods and data given in this chapter. The actual resistance for any given installation, however, may vary considerably from the calculated resistance because of variation in the smoothness of materials, the type of joints used and the ability of the workmen to manufacture the system in accordance with the design. It is best to. select fans and motors of sufficient size to allow a factor of safety. Dampers should be installed in each branch outlet to balance the system, and. the necessary allowance for this balancing should be made in calculating the pressure loss in the system. . . The drop in pressure in air transmission systems is due to friction losses and dynamic (shock) losses; Pressure increases and decreases may also be effected by changes in duct areas resulting in the conversion of velocity pressure to static pressure, and vice versa. The friction losses for turbulent flow (which occur in all practical air flow problems) are due to the friction of air against the sides of the duct and to internal friction between the molecules. The dynamic losses are caused by changes, in the direction or in the velocity of air flow, such as caused by changes in size and shape bf the cross-section of the duct, bends (elbows) and to obstructions to flow offered by dampers. FRICTION LOSSES Pressure drop in a straight duct is caused by surface friction and this friction loss is most readily calculated by means of the Air Friction Chart / 807