Document 7OB11JajYELDDKwxBEdbB9YpE

American Society of Heating and Ventilating Engineers Guide, 1928 Chapter XIII--Heating with Gas appliance enjoys uninterrupted and efficient service from it. It is common practice among gas companies to make periodical inspections of the heating appliances on their lines and some even go so far as to light the pilots when the heating season approaches so that the appliance stands ready to respond to the thermostat's call for heat when cool weather comes. A notable development of comparatively recent date is the.offering., of gets burning boilers designed with the object of meeting the require ments peculiar to large scale heating. Compact, automatic in operation, and with large steam releasing area and storage space; these large unit boilers are adaptable to the heating requirements of office buildings, college buildings, and hospitals; as well as to the production of large amounts of low pressure steam for industrial and process work. j ! . i j 1 I blue as in the familiar Bunsen burner. A blue flame has very little radiating power. The combustion is complete within a few inches of the burner. After combustion is complete, the hot gases must im mediately be brought into close contact with the heat-absorbing surfaces and kept in contact with them until the maximum possible amount of heat has been absorbed. A gas burning appliance is therefore designed with a small combustion chamber and with many thin passages for the hot gases to pass through so that they can be brought into intimate contact with the heat absorbing surfaces. In order for gas to be burned with reasonable economy in an appliance designed for coal, an intricate baffling arrangement must be built up within the combustion chamber so that the products of combustion will be caused to wipe over the walls of the combustion chamber. Even when this is done, the appliance will not generally develop its full rated TYPES OF GAS HEATING APPLIANCES ! output with economy because it will not have sufficient indirect heating ` surface beyond the combustion chamber so arranged that it will break Gas burning heating appliances in general use may be classified as follows: ; j the gas up into the fine streams necessary to insure complete heat absorption. Appliances for gas burning must be so designed that each particle 1. Central heating plants: i of hot gas is brought very, close to a heat absorbing surface. The general a. Steam heating boilers j practice of gas companies interested in heating is to discourage conversions. b. Water heating boilers c. Warm air furnaces GAS BOILERS 2. Room (or space) heaters: a. Radiant heaters (blue flame) . b. Reflector heaters (luminous flame) c. Convection type unit heaters. Gas boilers have taken on a well defined form just as coal boilers have. The usual boiler is sectional in construction with a number of independent burners placed beneath the sections. In most boilers each section has its own burner. Some makers fashion their sections so as to give the CONVERSIONS VERSUS ORIGINAL INSTALLATIONS (for central heating plants) effect of a horizontal tubular boiler so as to accelerate water circulation. :i. Other makers either do not incorporate the tubular feature in their designs or depend on internal baffling to give the tubular effect. In all During the years when gas heating was limited to those localities where a cheap supply of natural gas was available, practically all installations were what are termed conversions. By conversion is meant an appliance designed to burn coal, with gas burners inserted. This practice, however, cases the sections are placed very close together, much closer than would be possible with any soot forming fuel. Extended heating surfaces, such as lugs, pins, or fins are features of some designs. In all cases, the effort of the designer is to break the hot gas up into thin streams. has not been followed in manufactured gas territory, for certain definite Because there is no fuel bed resistance and because the gas company and scientific reasons; and the increasing price of natural gas eventually supplies the motive power to draw in the air necessary for combustion will bring it to an end in that territory. (in the form of the initial gas pressure) draft losses through gas boilers No two fuels burn and give off heat in exactly the same manner; and no two fuels differ so widely in this respect as do coal and gas. In coal boilers or furnaces, the path traveled by the hot gases is relatively short. are low. A gas boiler will therefore operate with a very slight draft, thus making it possible to operate at very low stack temperatures. Terminal temperature differences as low as 50 deg. are not uncommon. Most of the heat made available by the combustion of coal is given off All gas boiler designers strive to make their product as light as is . as radiant energy by the incandescent coke and flame. This radiant compatible with strength and to render all heating surfaces easily energy is absorbed very rapidly by the heating surfaces which are so accessible for cleaning. placed that they can see the fuel bed and flame. Very little remains to be absorbed by the heating surfaces that are placed farther on in the boiler or furnace. A coal burning appliance is therefore designed with INSTALLATION AND CONTROL OF BOILERS a large combustion chamber with heat-absorbing walls so placed that One feature of the piping installation that adds to the satisfactory they will see the heat radiating flame. Close confinement of the products service rendered by gas boilers is provision for adequate and rapid venting of' combustion is not necessary except in the last passes of the appliance. of the air from steam heating systems. It is particularly necessary that Gas, on the other hand, burns most satisfactorily and most completely when air is mixed with it previous to ignition. The resultant flame is the air vent out freely when a gas control that either permits the gas to burn at full rated amount, or shuts it off completely, is used. This 230 231