Document QgrK1dZpZJQxq7B0r7xzZLj58

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 Report 2204, The Crater Method of Firing. Report 2403, Anthracite Industries Manual. An Experimental Investigation of the Use of Oil for the Treatment of Coal, by Ralph A. Sherman and J. M. Pilcher (A.S.M.E. Transactions, February, 1938). Handbook of Oil Burning, by Harry F. Tapp, American Oil Burner Association. Industrial Gas Series, Combustion, American Gas Association. Comfort Heating, American Gas Association. Tests of Gas Home-Heating Equipment, by R. B. Leckie and C. H. B. Hotchkiss (Purdue University, Engineering Bulletin Research Series No. 36). 164 Chapter 8 CHIMNEYS AND DRAFT CALCULATIONS Natural Draft, Mechanical Draft, Draft Control, Characteristics of Natural Draft Chimneys, Determining Chimney Sizes, General Equation, Domestic Chimneys, Construction Details, Chimneys for Gas Heating DRAFT, in general, may be defined as the pressure difference between the atmospheric pressure and that at any part of an installation through which the gases flow. Since a pressure difference implies a head, draft is a static force. While no element of motion is inferred, yet motion in the form of circulation of gases throughout an entire boiler plant installation is the direct- result of draft. This motion is due to the pressure difference, or unbalanced pressure, which compels the gases to flow. Draft is often classified into two kinds according to whether it is created thermally or artificially, such as, (1) natural or thermal draft, and (2) artificial or mechanical draft. Natural Draft Natural draft is the difference in pressure produced by the difference in weight between the relatively hot gases inside a natural draft chimney and an equivalent column of the cooler outside air, or atmosphere. Natural draft, in other words, is an unbalanced pressure produced thermally by a natural draft chimney as the pressure transformer and a temperature difference. The intensity of natural draft depends, for the most part, upon the height of the chimney above the grate bar level and also the temperature difference between the chimney gases and the atmosphere. A. typical natural draft system consists essentially of a relatively tall chimney built of steel, brick, or reinforced concrete, operating with tfie relatively hot gases which have passed through the boilers and accessories and from which all the heat has not been extracted. Hot gases are an essential element in the operation of a natural draft system, although inherently a heat balance loss. A natural draft chimney performs the two-fold service of assisting in the creation of draft by aspiration and also of discharging the gases at an elevation sufficient to prevent them from becoming a nuisance. Natural draft is quite advantageous in installations where the total loss of draft due to resistances is relatively low and also in plants which have practically a constant load and whose boilers are seldom operated above their normal rating. Natural draft systems have been, and are still being, 165