Document R27X5LjGLm34jN8YxjRBYvZXE

376 CHAPTER 15 . 1954 Guide is utilized. This design produces a horizontal flame which strikes a curved baffle.that spreads the flame in a fan shape. ; : Several power burners in domestic sizes are available. These are of gun burner design and feature small mechanical blowers for supplying all the air required for combustion. These are particularly desirable for handling restricted flue boilers or furnaces where an atmospheric burner cannot obtain the desired output. Conversion burners for domestic application are available in sizes ranging from 50,000 to 400,000 Btu per hr capacity. It should be noted that the American Standard Approval Requirements are limited at present to con version burners of capacities up to 400,000 Btu per input hr. Burners of larger capacity, for use in large steel boilers, are usually engineered by a contractor specializing in this type of work, or by the local utility company. They are available in a large number of sizes and types. In some cases the burner may be an assembly of multiple burner heads filling the entire firebox. For conversion burner installation in boilers requiring more than 400,000 Btii per hr input, reference should be made to the American Standard Requirements for Installation of Gas Equipment in Large Boilers, ASA Z21.33-1950. Domestic sizes of conversion burners should conform to American Stand ard Listing Requirements of Conversion Burners, ASA Z21.17-1948. As the successful and safe performance of a gas conversion burner depends on numerous factors other than those incorporated in such equipment, instal lations of this kind must be made in strict accordance with American Standard Requirements for Installation of Domestic Gas Conversion Burn ers, ASA Z21.8-1948. Also, draft hoods conforming to American Standard Listing Requirements for Draft Hoods, ASA Z21.12-1937, R 1950, should be installed (in place of the dampers used with a solid fuel) on all boilers: and furnaces intended to operate without chimney draft. The A .G.A. lists the output efficiency of conversion burners at 72 percent. This valuer is based on average installations and average heating equipment perform-- ancOen. e form of central heating system is the warm------- a-1ir- Aflonronrt ffiunrmnaoc/teo.&5 TThhefi use of these furnaces is adaptable to mild climates, or for auxiliary heating: or heating of single rooms in colder climates. They are used for heating:, first floors, or where heat is required in only one or two rooms. A numbej may be used to provide heat for the entire building where all rooms are on the ground floor, thus giving the heating system flexibility. . .( In floor-furnace applications, the heating element, gas piping, and flue, vent piping are suspended below the floor, and the only part in the roomt; being heated is the circulating air register which may be of the single-typL installed in the floor, or of the dual-type installed in a partition, and heating; two rooms. The A.<7.A. rating of floor furnaces is based on an efficiency^ of A70repceercnetntty.pe of central heating, used in mild climates, is the recess|*: heater which is either a gravity or forced-air furnace designed for installs^: tion in the interior partition of a building, and having stub ducts conduct; ' ing air to two or more rooms. This type of heater is usually installed a?) new homes, and is plastered into the wall, becoming a permanent part.^b the building. yK Space Heaters Space heaters are defined as heating units that take the air for cofflU bustion from the space being heated. They may be broadly classified* as room heaters and unit heaters. " Automatic Fuel Burning Equipment 377 Room healers are used for heating single rooms or connecting rooms with good circulation between them and, except for wall-type heaters, they are semi-portable. Unvented-type room heaters should not be used unless space is properly ventilated to prevent excess moisture and to provide sufficient combustion air to prevent formation of carbon monoxide. All types of room heaters are capable of automatic control, although they are generally controlled manually. When equipped for automatic control, they must have an automatic pilot as part of the control equipment. Room heatera may be classified as follows: Circulators, vented and unvented, are small warm air furnaces that heat the room mainly by convection, although some have radiants over the burner, with windows in the front to allow some heat by radiation. Radiant heaters, usually unvented, although some vented types are avail able, have a refractory directly above the burners which is heated to in candescence, and gives off at least 30 percent of its heat in the form of radiant energy. Gas-fired steam, and hot water radiators, vented and unvented, are similar in appearance to an ordinary steam or hot water radiator, but are self- contained, and the gas input is controlled by steam pressure or water tem perature within the radiator. W"Waarrmm air radiators are vented-------------------- ' 1 or unvented circulators whose heating elements are c_o_n__s_tr_u_c_t_e_d in the fiuoirtmu voif aa sstteeaamm rraaddiiaattoorr.. Wall herders, vented or unvented, are usually a type of radiant heater constructed with sufficient insulation (either solid or circulating air) to prevent overheating of the casing, and are built into a wall with the front flush with the wall surface. The A.G.A. rating of room-type heaters is based on an efficiency of 70 percent. Unit heaters are used extensively for heating large spaces such as stores, garages, and factories. These heaters'consist of a burner, heat exchanger, fan for distributing the air, draft hood, automatic pilot, and controls for burners and fan. They are usually mounted in an elevated position from which the heated air is directed downward by louvers. Some unit heaters are suspended from the ceiling, and others are free-standing floor units of the heat tower type. Unit heaters are classified for use with, or without, ducts depending on specific A.G.A. approval. "When connected to ducts they must have sufficient blower capacity to deliver an adequate air quan tity against the duct resistance. Duct furnaces are usually of the unit heater type without the fan, and are used for heating air in existing duct systems where blowers are pro vided for moving the air through the system. Duct furnaces are tested for operation at much higher sta_ tic pre_s.rs..u.r.e..s. than are obtained in unit heaters. VUUEMlittVi ill VlOYVr II6&I16IS. Combustion Process and Adjustments Most domestic gas burners are of the atmospheric injection (Bunsen) type in which primary air is introduced and mixed with the gas in the throat of the mixing tube. For normal operation of most atmospheric ^Pe burners, 40 to 60 percent of the theoretical air as primary air will I've best operation. Slotted port and ribbon burners may require from . to 80 percent primary air for proper operation. The amount of excess ai,r Required in practice depends upon several factors, notably: uniformity ? .aw distribution and mixing, direction of gas travel from burner, and the Snt and temperature of combustion chamber. With power type burners 'Sizing motor driven blowers to provide both primary and secondary air, - "e excess air can be closely controlled while securing proper combustion.