Document X8bZb9NXq6BVyGbYD1LB3Qejx

62 CHAPTER 5 1962 Guide And Data Book Warm Air Heating Systems 63 ftegixtorx xef to direct atr upward along ft* wall af ex wide an angle ax poxxrbto. Fjg. I.... Fhor or Low Side-waU Perimeter Outlets* cold air which usually descends along a cold surface. Furthermore, since delivery of the air outward into the room, rather than upward, is likely to impinge upon the occupants it should be avoided. With certain types*of perimeter dif fusers, the air velocity at the diffuser face is limited only by the pressure available at the diffuser and the noise charac teristics of the outlet. Tests with inside wall supply systems conducted in Warm Air Heating Research Residence No. 1 have indicated that results obtainable with either high side-wall or baseboard registers are comparable if proper registers and air velocities are selected. Baseboard registers should be of a deflecting-diffuser type that will direct the air downward toward the' floor and dif fuse it at the same time. For baseboard registers, air veloci ties over 500 fpm should be avoided as they may cause dis comfort. High side-wall registers should be of a type that will de- * Horizonte! rwmt, back or frooi, to gtoa downward deAecftoox oot to exceed ham IS to 22 dog. . Fig. 2.... Recommended Type of High Side-wall In stallation on Warm Wall*' Vortical bars wrtfi adprttoble deflection, or fixed vertical barx with doflection to rigid and left not exceeding aboot 22 dog. For low udo-watt location, (be deflection for borirantcd, sxdtiple vane rogixton xhoidd oof exceed 22 dog. For boaboard location*, the deflection for horizontal, amitipie vane register* dtoidd oof exceed aboef 10 deg. Fig. 3 .... Recommended Type of Baseboard and Low Side-wall Installation on Warm Wall* liver the air horizontally or in a slightly downward direc tion, and should be so located as to avoid impingement of air on ceiling or wall. Directional flow diffusing type regis ters should be used to insure best results. Register air veloci ties should be such that the air velocity will be about 50 fpm three-quarters of the distance from the register to the opposite wall. Velocities through registers may be reduced by the use of registers larger than the connecting ducts. Diffusers should be used to spread the air uniformly over the register face. Basic rules for the location and selection, of registers, to gether with explanations of factors affecting operation, are given in Section of Manual 4, Sections 3 and 4 of Manual 10, or Section B of Manual 7, published by the National Warm Air Heating and Air Conditioning Association.*- * * Registers should be well proportioned and decorated to harmonize with the trim. Air supply registers should be equipped with dampers, and all registers should be sealed against leakage around edges. The register types shown in Figs. 1, 2, and 3 have been recommended as standard by the National Warm Air Heating and Air Conditioning Associa tion. Return-air grilles may be located in hallways, near en trance .doors, under windows, in exposed corners, or inside walls, depending on location of supply outlets. Baseboard re turns are preferable to floor grilles. It is usually considered' desirable to have them located in or near outside walls when supply outlets are located on inside walls. With this type of system, it is desirable to locate return grilles in as many rooms as possible. When perimeter systems are used, returns may be centrally located, provided means for permitting air to flow from rooms without returns are included. Never- theless, the use of individual room return intakes is desirable. In basementless structures, it is usually convenient to locate the return openings either high in the wall or in the ceiling. So far as the heating is concerned, however, this is merely a matter of convenience because low returns have been found to work equally well. It is usually not recommended in residential systems that any one return serve an area having a heat loss of more than 60,000 Btuh. fig. 5____Cross-Section of Slab Construction Contain ing Perimeter. Duct Made of One Type of Material.4 Dampers Suitable dampers for air direction or volume control are to any duct system. Special care must be used in the of any system, to minimize resistance. Sharp elbows, angles, and offsets should be avoided. Three types of damp ers are -commonly used. Volume dampers are used to com pletely' cut off or reduce the flow through ducts. SpUtter dampers are used where a branch is taken off a main trunk. Squeeze dampers are used for adjusting the volume of air flow and resistance through a given duct. A damper with positive locking device should be provided for each main or duct branch. Labels placed on ducts should indicate the room being served. Damper positions should be marked to indicate proper summer and winter settings, and to reveal tampering. DUCT CONSTRUCTION The ducts may be either round or rectangular in cross section. The centerline radii of elbows should preferably be not less than one and one-half times the pipe diameter for round pipes. The throat radius of a turn in a rectangular duct should be at least one-half the duct dimension in the plane of the turn. Warm air ducts passing through cold spaces or located in exposed walls, should have 1 to 2 in. of insulation. Ductwork must be permanent, rigid, non-buckling, and non-rattling. Joints in ductwork should be airtight. Galvacized-iron or aluminum sheet are usually used in the construction of ducts, but other materials may be used under the proper circumstances. Standard' 90B' of the Na tional Board of Fire Underwriters specifies the type of duct materials that may be used. In general, supply ducts should be constructed entirely of noncombustible material equiva lent in strength and durability to those recommended in Table 1. Supply ducts serving a single-family dwelling need not meet this requirement, except for the first three feet from the unit, provided they are used in conjunction with listed heating units, are properly constructed from a base material of metal or mineral, and are property applied. Furthermore, combustible material which is otherwise suit able for the application* can be used as supply ducts which completely encased in concrete. Ducts for separate air cooling systems and return air ducts need not meet these requirements, except within two feet of a furnace or other kat producing equipment. Supply ducts must be securely supported by metal hangersj straps, lugs, or brackets. No nails should be driven through duct-walls and no unnecessary holes should be cut in then. Supply air stacks should not be installed in outside, walls unless it is .impracticable to do otherwise. If it is necessary to do this, the stack must be effectively insulated against exposure. Failure to do this will materially reduce the heat ing or cooling capacity of the branch duct and will probably result in unsatisfactory conditions in the room with regard to comfort. No supply air duct should come in contact with masonry walls. All supply, ducts which pass through a masonry wall should be covered with at least Vi in. of insulation where they pass through the wall. All supply ducts or outlets should be equipped with an adjustable, locking type damper for air volume control. The damper should be installed in the branch duct whenever it is accessible. SpUtter dampers for volume control are not recommended. Return systems having more than one return intake may be equipped with balancing dampers. This is particularly desirable with systems having the supply outlets on the in ride wall or in the ceiling of the conditioned rooms. Special attention should be given to the problem of noise Table 1 .... Recommended Thickness for Dud Materials ttormd Ouch Otemotor. h. MMorna Tfiidcrtexx US. Cog* Afomowta its Gago Miniawn> Weight of Tin-ote Less than 12 12 or more 30 28 26 IC (107 lb) 28 IX (135 lb) Width, la. 14 or less Over 14 AUntaan Thrcfcwcx Goto, froo, (U. Gage Ahnaimtm StS Gago Miatmna Weight of Ttfl-Ploto Ducts Enclosed in Partitions I 30 I 28 { IC (107 lb) 28 26 IX (135 lb) Duets Not Enclosed in Partitions Less than 14 | 28 ] 14 or more I 26 I 26 I 24 I . Note: The table ia ta accordance with Standard SOB f the National Board * Fb UnderwriteTM.* laduatzy practice ia^to aee^hecTjg octal* where maximum drat width* w--* S4 La. (See aleo NtjrU No. 9