Book - School of Science and Technology

426 Air distributionAir supplyPerforatedfaceSupply ductPerforatedplateLow leveldischargeAir deflectorsFront panelRecessed type (section)Figure 15.25 Low-level, low velocity side-wall outlets. The velocity of inlet must not be so high that the air will impinge on the wall opposite,thereby causing undue turbulence. The throw should be about three quarters of thedistance to the point of impingement with a wall, or opposing air stream.. The distance apart of inlets, particularly in the case of ceiling diffusers, must be suchthat the streams from two adjacent units do not collide at such a velocity that a strongdownward current results.. The velocity selected for the grille or diffuser must be such that the sound levelproduced therefrom is below the design standard for the room.. Appearance, layout and pattern are all architectural matters, which must also as a rulebe taken into account and this sometimes creates a difficulty where the desired spacingor size is not acceptable on these grounds: system performance must take priority.. The throw must not be directed towards projections that will deflect the air stream fromthe intended direction.. The distribution should be arranged to deal with loads at source.Primary selection should be by use of the design guides published by BSRIA* orthe 2001 edition of Guide Section B2 prior to reference to manufacturers' data. Theselatter are now freely available for all types of equipment and, from a study of them,a variety of alternative solutions to a particular problem may be put down with theobject of a final selection being made best suited to meet all the other conditions.The reader is referred to such data for precise information, but a few sample sizesare given in Table 15.1. It will be clear that, with the large number of variables, airdistribution design is perhaps more an art than a science but on it to a largemeasure, as has previously been emphasised, depends the success or otherwise ofany air handling installation, particularly in the case of air-conditioning. It is worthnoting again here that particular attention must be given to the selection of terminalsfor variable air volume applications to ensure that satisfactory distribution will beachieved through the full range of operating volumes.* Laboratory Reports 65, 71, 79, 81 and 83. Application Guides AG 1/74 and 2/75, and Technical NotesTN 3/76, 4/86 and 3/90. The principal authors are P. J. Jackman and M. J. Holmes.