Book - School of Science and Technology

Kitchens 365manufactured in stainless steel, to serve as terminals, some to exhaust contaminated airfrom appliances sited belowthem and others to introduce replacement supply air. Asshown in Figure 13.17(a), the former have two shells, an inner and an outer, each with aparabolic profile and holes, which are offset in one shell with respect to those in the other.The latter, as is shown in Figure 13.17(b), has a single shell only.The twin shell arrangement of the exhaust module serves to separate out grease,moisture and suspended particles from the exhaust air, as a result of passage throughthe offset holes and the change of direction thus induced, and allows either deposition on theshell surface or flowto collection troughs mounted beloweach module: in either case, theprofile of the shell is such that drips are avoided.As might be expected, a number of relatively critical design parameters are inherent insuch a system which include the following:. The exhaust air volume must be within the limits of 55 litre/s minimum and 130 litre/smaximum per m 2 .. The number of supply air modules must be determined according to room height andthe kitchen space/supply air temperature differential, typically within the range of 30 to90 litre/s per module.. A minimum clearance space of 350 mm above the modules and belowthe structure isrequired in order to provide for easy removal of the shells.As in the case of ventilation by canopy, cleanliness is a prime requirement. Themanufacturers state that the shells and collection troughs may be dismounted withouttools and then cleaned as required in a catering type dishwasher. It would seem sensiblefor the cleaning staff to carry out preventative maintenance using a rotating stock of sparecomponents, say, 50%.Energy saving ceilingsAn alternative form of `ventilating ceiling' is available which offers the advantage ofenergy economy in that it makes use of venturi slots within a series of shallow concavitiesin the ceiling profile to echo the performance of the previously described energy savingcanopies. Figure 13.18 shows this arrangement. The whole of the ceiling is manufacturedin stainless steel or anodised aluminium and is insulated to avoid condensation. It should30 % air supply(warmed or cooled)ExhaustGrease filtersSupplyplenum30 % air supply(untreated)ExhaustchamberExhaustInducedfumesLuminairesInductionslotsInducedfumesCeiling levelFigure 13.18 Typical energy-saving ceilings