Document mpz6d9orpVv6mX6Q3g4eYXGyO

American Society of Heating and Ventilating Engineers Guide, 1937 ' 1 | ' ' ' ?f When the estimated heat emission of the piping (connecting radiation ; j and other apparatus to the boiler) is not known the net load to be con sidered for the boiler may be determined from Table 4. j| Selection of Gas-Fired Boilers al Gas-heating appliances should be selected in accordance with factors given in Table 2, Chapter 28, which include an allowance for heating up cold radiation, and for the piping tax. These factors are for thermo statically-controlled systems; in case manual operation is desired, a warming-up allowance of 100 per cent is recommended by the A.G.A A gas boiler selected by the use of the A.G.A. factors will be the minimum size boiler which can carry the load. From a fuel economy standpoint, it may be advisable to select a somewhat larger boiler and then throttle the gas and air adjustments as required. This will tend to give a low stack temperature with high efficiency and at the same time provide reserve capacity in case the load is underestimated or more is added in the future. Conversions 1 si ;$ The conversion of a coal or oil boiler to gas burning is simpler than the reverse since little furnace volume need be provided for the proper com bustion of gas. When a solid fuel boiler of 500 sq ft or less capacity is converted to gas burning, the necessary gas heat units should be approxi mately double the connected load. The presumption for a conversion job is that the boiler is installed and probably will not be made larger; therefore, it is a matter of setting a gas-burning rate to obtain best results with the available surface. Assuming a combustion efficiency of 75 per cent for a conversion installation the boiler output would be 2 X 0.75 = 1.5 times the connected load, which allows 50 per cent for piping tax and pickup. In converting large boilers, the determination of the re quired Btu input should not be done by an arbitrary figure or factor but should be based on a detailed consideration of the requirements and characteristics of the connected load. m m An efficient conversion installation depends upon the proper size of flue connection. Often the original smoke breeching between the boiler and chimney is too large for gas firing, and in this case, flue orifices can be used, which are discs provided with an opening of the size for the gas input used in this boiler. The size should be based on 1 sq in. of flue area for each 7500 hourly Btu input. If dampers are found in the breeching they should be locked in position so that they will not interfere with the normal operation of the gas burners at maximum flow. In the case of large boiler conversions, automatic damper regulators proportion the position of the flue dampers to the amount of gas flowing and may be substituted for existing dampers. Generally in residence conversions automatic dampers are not of the proportioning type but close the flue during the off periods of the gas burners. Automatic shutoff dampers should be located between the backdraft diverter and the chimney flue. Automatic dampers are usually designed to operate with electric contact mechanism, but frequently an arrangement is utilized which functions with, mechanical fluid or gas pressure. As it will usually be found that several boilers will meet the speci 456 Chapter 25--Boilers fications, the final selection of the boiler may be influenced by other, con siderations, some of which are: j. Dimensions of boiler. 2. Durability under service. 3 Convenience in firing and cleaning. 4 Adaptability to changes in fuel and kind of attention. 5. Height of water line. ' In large installations, the' use of several smaller boiler, units instead of one larger one will obtain greater flexibility and economy by permitting the operation, at the best efficiency, of the required number of units according to the heat requirements. Boiler rooms should, if possible, be situated at a central point with' respect to the building and should be designed for a maximum of natural light. The space in front of the boilers should be sufficient for firing, stoking, ash removal and cleaning or renewal of flues, and should be at least 3 ft greater than the length of the boiler firebox. A space of at least 3 ft should be allowed on at least one side of every boiler for convenience of erection and for accessibility to the various dampers, cleanouts and trimmings. The space at the rear of the boiler should be ample for the chimney connection and for cleanouts, and with large boilers the rear, clearance should be at least 3 ft in width. The boiler room height should'be sufficient for the location of boiler accessories and for proper installation of piping. In general the ceiling height for small steam boilers should be at least 3 ft above the normal boiler water line. With vapor heating, especially, the.height above the boiler water line is of vital importance. When steel boilers are used, space should be provided for the removal and replacement of tubes. CONNECTIONS AND FITTINGS The velocity of flow through the outlets of low pressure steam heating boilers should not exceed 15 to 25 fps if fluctuation of the water line and undue entrainment of moisture are to be avoided. Steam or water outlet connections preferably should be the. full size of the manufacturers' tapping and should extend vertically to the maximum height available above the boiler. For gravity circulating steam heating systems, , it is recommended that a Hartford Loop, described in Chapter 32, be utilized in making the return connection. Particular attention should be given to fitting connections to secure .con formity with the A.S.M.E. Boiler Construction Code for Low Pressure Heating Boilers. Attention is called in particular to pressure gage piping, water gage connections and safety valve capacity. Steam gages should be fitted with a water seal and a shut-off,consistingof a cock with either a tee or lever handle which is parallel to the pipe when the cock is open. Steam gage connections should1 be of copper or brass when smaller than 1 in. J.P.5.9 if the gage is more than 5 ft from the A-S.Ai.E. Code, Identification of Piping Systems. 457