Document rxe7ZJ1G1mm3B786L8nqJ6gjV

556 CHAPTER 30 1965 Guide.Arid, Data Book; sufficient length, to establish surface effect. Under On*** con-: ditious, air.will travel along the ceiling to the end,of thethrow: i If-the slot diffuseras mounted 1-2 ft below the ceiling, an out-'l let which deflects the air up to the roiling must.be used, and', will then achieve the same result. If the slot is located.more than 2 ft below the ceiling, premature drop into' the occupied' zone of cold air will probably, be the result.', Ceiling Instnllntum. TTm. peTpendiftnlftr-flow tint_ Hiffnaon should not,* in general, be,mounted on the ceiling. In this the discharge pattern is directed downward into, the occupied, zone and causes,localized.areas of: high air motion affecting' human comfort, Outlets of.,this type are sometimes located, in the.ceiling at the perimeter,of. the. building, with air dis-. charge.-towards, the. floor along the perimeter wall. This is a, highly undesirable method, because it results in relatively high velocities on the floor near the walL The parallel-flow 'slot'diffuser' is*ideally suited to ceiling installation. Its discharge pattern is-across the ceiling., .. SiUInstalldtum. The perpendicular-flow slot diffuse? is well suited to sill .installation.; but tha diffuser may-'alsp be in-, stalled in the curb and floor. When the'diffuser is.located within 8 in. of.the, perimeter wall, the discharged air may be directed straight towards, the ceiling, or it may be deflected, slightly towards the walL When the diffuser distance from the wall is greater'than 8. in., the air should generally be deflected towards the wall at an'angle of approximately. 15 deg. In some cases, deflections as great as 30 deg towards the wjfll may be desirable. The air should never be deflected away from the wall intothe occupied .zone. The resulting air motion in the occupied zone will cause discomfort to the occupants.', To perform satisfactorily,,outlets of this type'must only be used in installations with chrefuQy.designed ductand plenum systems. (Refer to section. Discharge from a Long Slot in Chapter 29.) ; Slot diffusers are generally equipped with accessory devices' for uniform discharge of the supply air along the entire length of the slot. While accessory devices help to correct the* air flow pattern, proper approach, conditions for the air stream are also highly'importi^t for satisfMtory.perf6rmanee.~Two' different approaches' are commonly used.' With1a plenum located behind'thfe'entire'length'of'the'outlet, the air must' be introduced into the plenum from the main duct`through d&mpered supply taps spaced approximately 4 ft from each other. The plenum should be sized for a mArimnm velocity of approximately .500 fpm. This low velocity is necessary for satisfactory air discharge. The taps feeding the plenum should be sized for a velocity of. approximately 800 fpm. The use of a multiplicity _of supply taps minimizes static regain. If tapered duds are used for introducing the supply air into the diffuser, ` theyshould be sized to maintain a velocity of Fig. 2 .... Accessory Control Devices for " Slot Diffuser Outlets'' ' approximately. 500 fpm, and they must be tapered to main tain constant static pressure. .- Air-Light Fixtures. Slot diffusers having a single'slot dis. charge and nominal 2,3, and 4 ft lengths, are available for u, in conjunction with recessed-fluorescent light troffere. The, diffuser mates with the light fixture and is entirely concealed' from the room. It discharges air through suitable openings in( the fixture and is available with fixed or adjustable air db>' charge patterns, air distribution plenum, inlet dampers for. balancing, and inlet collars suitable for flexible duct connec tions. light fixtures adapted for slot diffusers are available instyles to fit the common ceiling constructions. Various dotdiffuser and light fixture manufacturers can furnish products compatible with one anothere equipment. , Accessory. Devices, Dampers are available as integral or separate standard- equipment for use with-slot diffusers. Generally the opposed-' blade damper shown'in Flg.'lA is used. However, .in the case' of narrow slot diffusers! it is often impossible to use an- opposed-blade damper. In such cases, a single-'or double-' louver damper as shown in Fig. 2 must-be used. This type of damper can generally be fully opened to 90 deg,'and in this position does not restrict the capacity of the diffuser. Plow equalizing cones-consist of a set of individually ad justable bars, installed behind the slot openings at right angles to'the slot.1 If-designed and ingtAllpd correctly,-they- improve the discharge pattern of the diffuser (see section' Discharge from a'Long Slot in Chapter 29). For slots up to 36 in. in length, these bare may also be used to increase spread of the air stream for greater coverage. Dampers and flow-' equalizing vanes can<generally<be adjusted without removing the diffuser. -- . .. -I Special Construction Features ' Materialt. Slot diffusers - are made of steel or aluminum.' Extruded aluminum1 diffusers conform to' present-day archi-1 tectural concepts, and can be: easily modified to suit special requirements.- : ; Finishes. Standard1 finish**^ such as prime -coat paint,1 lacquer, enamel, as well as electroplated and polished finishes are used in-the manufacture of steel diffusers. Aluminum and extruded aluminum diffusers have polished and anodizedfinighpq Special Features. Hand-hole doors, special friction spring mounting-arrangements, 'specif frames,' hinges, reinforce ments and other modifications to suit installation in various types of surfaces and materials are made to order.' , . CBLiNG DIFFUSER. OUTLETS. Multirpassage round and square ceiling diffusers &re the most common type of nailing diffusers ingeneral use. They consist of a series of flaring rings or louvers which form a series of concentric air passages,' and for easy installation are'usually made in two parts: an outer ishell with duct1 collar! and an eatily'removable inner assembly. Ceiling diffusers are-avail-* able as standard equipment ranging in duct collar sizes from 5 to 36 in. diameter. Flush and eteppcd-down units are also available. In the flush unities the implies,- all rings or louvers projectr:to a plane surface, whereas in- the stepped-down unit they project beyond the surface of ' the outer! shell As a general rule; step'ped-down; uruts 'perform better than flush unite, but flush units have a morepleasing appearance. ' Common" variations of this diffuser type are the ad- Air-Diffusing Equipment C f ;-p 557 pattern diffuser and the multipattem diffuser. In-the SttjtoMe pattern diffuser, the air discharge pattern may be Smeedfrom horizontal to a vertical or downbiow pattern: SKsis done either by special construction of the diffuser it self or by the use of separate deflection devices. Multipattem diffusers are square or rectangular in shape, and have special louvers to discharge the air in one or more directions. Other outlets which are available.as standard equipment are half-round diffusers, supply and return diffusers, and Hffht fixture air diffnaw combinations. Complete' information on these outlets is given in manufacturers' catalogs. perforated-face ceiling diffusers meet architectural demands for air outlets which completely blend into perforated ceilings. They have a perforated metal face with an open area from approximately 20 to 50 percent which determines their ca pacity. Units with high capacity are equipped .with a special deflection device to. obtain a horizontal discharge pattern. Units with tow capacity have no deflecting device, and dis charge tow volumes of air at low velocities. Installations using these diffusers must be carefully designed for satisfactory performance. These diffusers should not be used in critical applications. .. perforated-face ceiling diffusers must be distinguished from perforated ceilings and perforated panels. These devices dis charge air through perforations in the ceiling or part of the ftpilmg, and share with slotted outlets the advantage of unob trusive appearance. In addition, sound-absorbing materials may be used for the panels, or the panels may provide a luminous ceiling. Outlet air velocities may be kept tow by using large outlet areas, particularly in spaces with high room, loads, high ventilating requirements, or tow ceilings. Some perforated p>nk have a control plate frame which is inserted in the con ventional duct. Supply air enters the plenum above the distribution through an adjustable air valve which can ^ be set for varying .air quantities and velocities. . Applications Ceiling Installations. Ceiling diffusers should be mounted in the center of the space which they serve, because they dis charge the supply air in all directions. Half-round diffusers are derigned-to be installed adjacent to partitions or.in,similar, locations where round diffusers cannot be installed in the center of the conditioned space. Multipattern diffusers can; be used in. the center of the space, or adjacent to. partitions, depending on the discharge ,pattern. By using different inner, assemblies, their air pattern can be changed to suit particular requirements. This feature mnlrre multipattem diffusers an- excellent choice for modular room layouts with movable par titions. ' , ` Side Wall Installations. Half-round diffusers and multipat*' tern diffusers, when installed high in ride walla, should d& charge the'air towards the ceiling. ' Exposed Dud Installation: Some ceiling diffuser types, par-, ticulariy stepped-down units perform satisfactorily oh exposed ducts. Consult manufacturers' catalogs for diffusers which can. be installed on exposed ducts. ........... '* Adjustable Pattern Diffusers. Surface effect' (see section Supply Air Outlets) b important in the performance of ad justable pattern diffusers. In fact, thte effect b so pronounced, that usuklly only two discharge patterns are possible with' adjustable pattern diffusers directly on the ceiling.* When the diffuser b changed from a horizontal pattern posi tion towards the downbiow pattern position, the surface effect' will maintain the horizontal discharge pattern until a low pressure region is created under the center- of the unit, -which results in: sudden vertical air discharge.- Therefore,' only hori zontal and vertical discharge, but no intermediate discharge. patterh b possible. However, when'adjustable pattern ceiling diffusers are mounted on the exposed duct, there b no surface effect, and the air may assume any pattern between horizontal and vertical discharge. Accessory Devices ' Dampering 'and air straightening accessories 'of various types are available,'as standard equipment.. Multi-louver dampers'consist' of a series of parallel blades mounted inside a round or square frame, and are inktailed in the Hiffwar collar or the take-off. The blades are usually arranged in two groups rotating in opposite directions,(Fig: 3A), are key-operated from the face of the diffuser.,This arrahgemehteiqualizes air flow'in-the diffuser collar.-" ` ,' - Opposed-blade dampers for round ceiling diffusers'- usually consist of a'series of pie-shaped vanes mounted inside a round frame; and they are in the diffuser collar or the take off. The vanes pivot about a horizontal axis, and'are arranged in two'.groups,' with adjacent vanes rotating counter to each other (Fig. 3B).: The vanes are key-operated from the diffuser face.''''`:^'.',"! - ' 1 ' " Another opposed-blade damper b similar in construction to' the'damper shown in'Fig. LA, and has either a round or square frame: -' ' ' Splitter Damper. A'splitter damper b*a tingle blade sheet metal-plate' hinged at one edge, and usually located at the branch connection of a duct or outlet (Fig: 3B). It b easy to operate, but often causes irregular air flow in the duct. When used in-connection with, and.near an outlet, additional direc tional control b required.' -Equalizing devices provide uniform air flow in the diffuser collar, and'consist of individually adjustable parallel blades mounted'withina frame: They are installed in the diffuser collar or the take-off. If used in pairs at right angles to each other; they serve as-both equalizing and directional control devices.' - > 'H air'_ - . 8R>wch FLOW* . DUCT AIR FLOW BRANCH ,s DUCT SXAf, ROUND OUTLET COLLAR C?23s ROUND ` OUTLETCOLLAR ... . .. ; Fig.' 3 . i v Accessory Control Devices for Ceiling Diffuser Outlets - ' v '