Book - School of Science and Technology

Air supply to boiler houses 337This terminal locationis only suitable forbalanced compartmentapplicationsTerminal600 mmWeathering toair intakesAir intakes protectedby bird wire guards300 mmInsulatedflues usedinternallyto boilercompartmentNo otherholes oropeningsintocompartmentSelf-closingdoor withnotice affixedSelf closingdoor withnotice affixedOpen flued applianceFigure 12.15 Balanced compartment installations (reference BS 5440 Part 1) (a) adjacent termination,(b) roof terminationwith than oil ± there is no delivery pumping and negligible fire risk. Thus, in manyexamples of multi-storey buildings, the use of gas in this location for boilers has muchto commend it.Air supply to boiler housesThe manner in which calculations are made in order to determine the quantity of airwhich is required theoretically for combustion has been set out earlier in this chapter. Inthe design of a boiler house, provision must be made for this air to enter, together withany excess which may be necessary. Where atmospheric burners are used with gaseousfuels, the associated boiler fuel must be equipped with draught diverters and further airwill be necessary to replace that which is used as the dilutant (see p. 334).Table 12.4 sets out, in round figures, the air quantities required for various fuels andsituations. The last column of this table makes use of the respective calorific values of thefuels and expresses the requirements as a function of boiler rating in kW. It will be notedthat, with the exception of those associated with atmospheric gas burners, the figures inthat last column all fall in the range 0.44±0.56 litre/s per kW.As far as is possible, air should be supplied to the boiler house by natural inductionthrough door or wall louvres and other openings. A velocity of between 1 and 2 m/s iscommonly used in calculating the free area of opening needed. Taking the higher figure of0.56 litre/s per kW ( ˆ 0:56 m 3 /s per MW), and a face velocity of 1 m/s, we arrive at a freearea for inlet louvres of, say, 0:6m 2 /MW of boiler rating.