Document V3rONn88YBR4Jj7EEYb6wmpJq

HEATING VENTILATING AIR CONDITIONING GUIDE 1943 the return air may be brought through door grilles or door undercuts into the corridors and then to a common return or exhaust.; The pressure drop through door returns should not be excessive (50 per cent of: supply grille pressure); otherwise.the air distribution to the room may be:seriously unbalanced with the opening or closing of the doors. Outward leakage through doors or windows cannot be counted upon for dependable results. In many cases, particularly in buildings with double glass or hollow glass block walls, forced return and. relief systems are essential. SPECIFIC APPLICATIONS The two methods shown in Fig. 7 \are. suitable for application, to theaters, churches, and auditoriums. In small or medium size theaters, it is sometimes practical to use sidewall or front wall distribution. For the satisfactory operation of such a system during the winter heating period, the returns should be preferably located at the floor level and near J Floor. -o*" Winter convection current Fig. 8. Distribution Methods for Small Rooms A. Satisfactory for cooling. Unsatisfactory.for heating in severe climates where the outside temperature is consistently below 40 F, and single glass and uninsulated walls are. prevalent. B. Performance slightly poorer.than A, unless supplemented by circular diffusers in bottom of the duct. C. Satisfactory for cooling. ' Satisfactory for heating if direct radiation is properly controlled. D. Satisfactory for both cooling and heating. The air should be discharged in a vertical plane parallel to the wall, and should be fanned out' in this plane* at an angle of 10 to 20 deg-with the vertical. *; - the front of the theater to prevent cold spots which may result, from exposed wall convection or infiltration from exits: Return grilles may be located higher where' the1 exits and stage have separate means of heating. . Diagrams -shown in Fig. 8 illustrate distribution methods, for small rooms, with exposed walls, such as for offices, hospital rooms, hotel rooms, apartments, etc. The cooling performance of various distributionmethods as applied to a small store are shown in Fig. 9- BALANCING SYSTEM In designing an air conditioning system, it should be the aim-of theengineer to so proportion the duct system.that proper distribution: of air to every supply opening will be obtained. Since this is almo.st impossible to accomplish in practice, it becomes necessary to have^eans of balancing the systeiii to secure the desired amount of air in each space.: There'are a number of ways in which this may be accomplished, some of'which are; 602 CHAPTER 31. AIR DISTRIBUTION 1. Dampers on the supply and return grilles. 2. Dampers in the supply and return ducts. 3. Reducing the effective area of some supply openings by blank-offs. 4. Combinations of dampers in both supply and return air. . Dampers on the supply grilles themselves are objectionable unless of special design (see Fig. 5), because of their effect on the air stream and noise. Dampers on the return grilles are frequently objectionable because, of noise. A damper in the supply duct some distance back of the supply opening forms a very satisfactory means of regulating the flow without disturbing distribution across the supply opening face. A damper in the return air duct has the advantage over one immediately behind the grille 1=-j JLr--------------' t t t \0 o o o\ \ y \ y \ Fig. 9. Small Store Cooling Distribution A'. Rear Wall. High outlet velocity, possibility of excessive air motion and drafts. B. Front Wall. High outlet velocity, possibility of excessive air motion and drafts. May cause excessive infiltration of outside air. C. Front and Rear Walls. Moderate' room air motion, outlet blows should not Impinge giving rise to down drafts in center of store. D. Center. Moderate air motion, no impingement of air streams. Good results. E. One Side. Moderate room air motion, should blow toward exposed wall. Good results. F. Ceilings Low room air motion. Good results. in that it does not tend to create high localized velocities through the'grille as the latter might do if nearly closed. Blank-offs consisting of pieces of sheet metal covering a portion of the supply opening face can frequently ' be used satisfactorily, although determination of just what is required is a matter of experiment, and the balancing of the system is not nearly so conveniently accomplished as with dampers. Blank-offs have the further objection that as the area is reduced, pressure builds up and. air motion tends' to remain constant.. Dampers in both' supply and return air form the most flexible means of controlling the supply to the room and the static pressure within the room. When feasible, these dampers, particularly those in the supply .ducts, should be a substantial distance from the. supply opening, aiftbahead of the acoustic duct lining if used- Due con sideration should also be given to the use of the several volume control and uniform distribution devices now available. See Catalog Data Section. ^ 603