Book - School of Science and Technology

Kitchens 361Table 13.8 Nominal exhaust rates for kitchen appliancesAir extraction rates (litre/s)EquipmentUnitPer m 2 net areaof appliancesRoasting and grillingranges, unit type, (approximately 1 m 2 ) 300 300pastry ovens 300 300fish fryers 450 600grills 250±300 450steak grills 450 900speciality grills 450 900Steaming and vapour producingboiling pans (140±180 litre) 300 600steamers 300 600sterilising sinks 250 600bains-marie 200 300tea sets 150±250 300unusual. In order to prevent the spread of odours from the kitchen, the replacement airdelivered by a supply plant should generally be 15±20% less than the volume extracted,the balance being drawn either from the restaurant or some other intervening areathrough serving hatches and transfer grilles associated with them. Air velocities throughhatches should not be allowed to exceed about 0.2 m/s if complaints are to be avoided.Table 13.8, taken from the 1986 edition of Guide Section B2, lists the more commonappliances and the notional exhaust air requirement per unit and per m 2 area of appliance.Ventilation by canopyAn extract ventilation system, using collecting hoods, or more properly canopies, over allthe principal items of equipment is the method most commonly adopted, as shown inFigure 13.14, which illustrates a large institutional kitchen. The design and constructionof canopies, commonly finished in polished aluminium or stainless steel, is nowusuallydealt with by specialist manufacturers but was, in the recent past, in the hands ofcontractors fabricating and installing ductwork.If canopies are to be effective, their size in plan should be such that they overlap thearea of the block of appliances which they serve by about 300 mm to 400 mm on all opensides. The capture velocity of the air extracted over this plan area should be not much lessthan 0.4 m/s. Provision must be made for drainage of the condensate which will form onthe inside surfaces, by means of a perimeter channel, and grease filters must be fitted, atthe point of air exit into ductwork, from any canopy which collects fumes from a processgenerating oily vapours. Cleanliness in a kitchen is a prime requirement and all exposedsurfaces, including the not inconsiderable internals and vertical outside enclosuresof canopies, need regular cleaning in situ with detergents.Energy recoveryBearing in mind the large volume of air extracted from a kitchen through conventionalcanopies and the consequent need to supply replacement air which must not be muchbelow kitchen temperature which, inevitably, is high, it follows that an appreciable wasteof energy will occur. An energy recovery system of conventional plate type may be used