Document ajE14NQDDKEoq56jE7aZDV8M

American Society of Heating and Ventilating Engineers Gu depends largely on the kind of fuel to be burned. Accordingly manufacturers are making special units for coal, oil and gas' ~ ' of fuel requires a distinct type of furnace for highest efficiency anri omy, substantially as follows: 0 t. Coal Burning: a. Bituminous--Large combustion space with easily accessible secondary or flue travel. b. Anthracite or coke--Large fire box capacity and liberal secondary k surfaces. dry 2. Oil Burning: a. Liberal combustion space. b. Long fire travel and extensive heating surface. 3. Gas Burning: a. Extensive heating surface. b. Close contact between flame and heating surface. A combustion rate of from 5 to 8 lb of coal per square foot of grate oer hour is recommended for residential heaters. A higher combustion rate! Chjinn 23--Mechanical Warm Air Furnace Systems 'th black iron liners, extending from the grate level to the top of ^a0d spaced from 1 in. to 1 Yi in. from the outer casing. Casings forna . , Qr j^yy duty furnaces, if. built of galvanized iron, should ed with fireproof insulating material at least 2-in. thick. It is {Ml Relieved that either brick or sheet metal casing should be baffles to secure impingement of the air to be heated ^ ttbe heating surfaces. Brick furnace casings should be supplied Access doors for inspection. furnace casings sized for gravity flow of air, where a fan is to be BBI many manufacturers recommend the use of special baffles to restrict {>' aTea within the casing and to force impingement of the air against heating surfaces. The method of making these baffles for furnaces lSfiraidthisttooipplluhfsiootrrrsasetce-s-dbhoimieutr.Faigd.ia1to. rs and for furnaces with back crescent radia- luther square or round casings may be used. Where square casings are jsj the comers must be baffled to reduce the net free .area and to force ia^Sinneveemment olf air against thne hneauting surnfaces. Friigg. 2 shows the usual Sgjfd of baffling square furnace casings for fan-furnace work. Fig. 1. Usual Method of Baffling Round Casings for Fan Furnace Woes A. Liner, l in. from casing. B. Hole to vent baffle. C. Baffle, closed top and bottom. D. Outer easing. permissible with larger furnaces for buildings other than residences; depending upon the ratio of grate surface to heating surface, firing period, and available draft. Where oil fuel is used, care must be exercised in selecting the proper size and type of burner for the particular size and type of furnace used. It is recommended that the system be designed for blow-through installations, so that the furnace shall be under external pressure in order to minimize the possibility of leakage of the products of combustion into the air circulating system. In residential furnaces for coal burning, the ratio of heating surface to grate area will average about 20 to 1; in commercial sizes it may run as high as 50 to 1, depending on fuel and draft. Furnaces may be installed singly, each furnace with its own fan, or in batteries of any number of furnaces, using one or more fans. Casings are usually constructed of galvanized iron, 26-gage or heavier, but they may also be constructed of brick. Galvanized iron casings should 376 ijc. 2. Method of Baffling Square Furnace Casing for Fan Furnace Work A. Baffle, dosed top and bottom. B. Liner, 1 in. from casing. C. Outer casing. D. Hole to vent baffle. The hood or bonnet of the casing above the furnace should.be as high ^basement conditions will allow, to form a plenum chamber, over the top jpfthe furnace. This tends to equalize the pressure and temperature of the Ipeaving the bonnet through the various openings. It isgenerally com sdered advisable to take off the warm air pipes from the side of the bonnet near the top, as this method of take-off allows the use of a higher bonnet 258 thus provides a larger plenum chamber. Fig. 3 illustrates a complete rtsidence fan furnace installation showing location of fan, furnace, filters, ffonun chamber and method of take-off of warm air pipe. FANS AND MOTORS jj&trifugal type fans are most commonly used, and these may be quipped with either backward or forward curved blades. Low tip speed jjearable for the elimination of air noise, especially where forward Sffigd blades are used. Motors may be mounted on the fan shaft or ' of the fan with belt connection. Multi-speed motors or pulleys 377