Document dDRV2w5rq9MmX35rbjGj11d86

788 ,<CHAPTER 42 1948 Guide --Sound Propagation in Ducts Lined with Absorbing Materials, by L.J. Sivian {Journal.Acoustical Society cj America, Vol. 9, 1937-38, pp.' 135-140). ;, .. 7--Specific Normal Impedance and Sound Absorption Coefficients of Material, by P. E. Sabine {Journal AcousticalSocicty of Amcrica,~Vo\.'12, pp. 317-323, January, 1941). Application of Wave Theory of Room. Acoustics to the Measurement of Acoustic. Impedance, by C. M.Harris {Journal Acouslical_Spciety oj America, voL'17, pp. 3W6, July, 195). "Sound Absorption in Rectangular Ducts, by L. L. Beranek (Journal Acoustical Society of America, VoL 12, pp. 228-237, October. 1940). ' The Transmission of Sound Inside-Pipes, by. Philip M. Morse {Journal Acoustical Society of America, VoL 11. pp. 205-210; October, 1939). \ .' "Precision Measurements of Acoustic Impedance by L. L. Beranek {Journal Acoustical Society of America, Vol. 12, pp. 3-14, July, 1940). ,, Notes oh Acoustic Impedance Measurement, by H. j. Sabine {Journal Acoustical Society of America, Vol. 13. pp. 143-150, October. 1942). io--The Absorption of Noise in Ventilating Ducts, by Hale J. Sabine {Journal Acoustical Society of America, VoL 12, p. 53, 1940).; ,. . l ("The Prediction of Noise Levels from Mechanical Equipment, by J. S. Parkinson {Heating and Venti lating, March, 1939, pp. 23-26). / .. Methods of Raring the Noise from Air Conditioning Equipment, by J. S. Parkinson (A.S.H.V.Er Journal Section, Heating, Piping and Air Conditioning, July, 1940. p. 447). l*--The Noise Characteristics of Air Supply Outlets, by -D. J. Stewart and-G. F. Drake (A.S.H.V.E. Transactions, VoL 43,1937, p. 81). *v Chapter 43 , CENTRAL SYSTEMS FOR AIR CONDITIONING Features of Systems, Zoning, Apparatus Dew-Point, Cooling Load, Heating Load, Air Quantity and Effective Temperature Difference, Low and High Pressure Induction Convectors, Evaporative Cooling, Precooling, Sensible Cooling with Unwetted Coils, Run-Around System; Selection of Type of System, Location of Apparatus THE term central applied to an air conditioning system implies that the equipment such as fans, coils, filters and their encasement are designed for assembly in the field rather than in a factory as a unit. As a central system usually serves several different rooms, individual con trols are required for each room. FEATURES OF CENTRAL SYSTEMS One advantage of a central air supply system is that one apparatus serving many rooms may involve a lower investment cost than that for a number of self-contained plants, each serving a single room. A central ' system may occupy basement or. attic space that is relatively unimpor tant, whereas individual factory-assembled apparatus placed in each room may occupy otherwise valuable space. Another advantage of a central system is accessibility for servicing, since it is possible to provide doors, in the encasement for. cleaning and inspecting all of the component parts in a manner usually superior to that practicable with compact factory-assembled equipment. Central air conditioning systems usually are connected by ducts with the various rooms served, and preferably have exhaust fans that may effect complete removal and disposal of any desired proportion of the air. The exhaust fan may return air to the supply system for recirculation, as a-measure of economy of fuel or refrigeration. Central air conditioning systems are served by heating and refrig erating equipment which may be located at some distance from the air supply apparatus and which may serve one or more central air supply systems. Year-Round Air Supply System Fig. 1 is a plan of a year-round air supply system. Outside air may enter from the left at A, desirably from an intake on the side of the building least exposed to solar heat and not close to the ground or to a sun-heated, or dust-gathering roof. A damper B for proportioning the volume of outside air, is interlocked with the return air damper C in such manner that as the outside air volume. increases the return air volume decreases. The return air duct D, shown diagrammatically, comes from the exhaust fan. All the air, it will be observed, must pass through the filters E and there is ample room on both the inlet and outlet sides of the filters for servicing them.- The filters may be of mechanically cleaned type, of replaceable cell type, or may be electronic, as described in more detail in Chapter 33. The cleaned air passes to the equipment that changes its temperature and humidity. Except in very warm climates, a heating or tempering 789