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810 CHAPTER 51 1965 Guide-Arid Data Book the oil piping b enclosed with steam lines in the nanTM thermal insulation. The economy of the steam preheating method is have a opacity greater than'the burner requirement and return ing the excess heated oil continually to the.fue) oil tank also dependent on the availability of steam at the pressure and quantity required, and on the distance from boiler to storage tank. The hot water preheating method utilizes equipment simi lar to that used for steam. Because of the possibility that oil may penetrate into the boiler through a faulty heat ex changer, some devices have been developed to prevent this condition. Double-transfer.heaters and fuel-oil detectors are those most frequently- used. Similarly, as with steam, con tinuity of burner operation,- or cycling burner operation, b needed to maintain the temperature of the heating medium Since oil heating b limited by the water temperature in' the All the oil in the tank, or a portion of it, may be heated by one of the following methods: 1. By steam coils in the bottom of the tank. 2. By hot water,coils in the bottom of the tank. 3. By a suction-belL which is provided with either steam or hot water coils, in the bottom of the tank. 4. By providing a hot-well that extends from the top to the bottom.or the tank, and provides enough heated oil to supply the . burner under a full load.. 5. By submerging ah electric preheater in the wall or bottom of the tank. Pipe Sizes for Heavy Oil boiler, less transmission and transfer losses, such losses must be taken into account, particularly on installations having a considerable length of oil piping. Table 1 gives recommended good practice pipe sizes, for handling No. 5 and No. 6 oils. The indirect gas-fired preheating method b a package ar rangement that uses gas as the primary energy source'. It generates its own supply of low-pressure steam in a,Jclosed vapor-condensate cycle- The oil b pumped through the steam oil heater as required to compensate for radiation losses in the oil-circuit lines, whenever pumping action stops. During the layover period, the main boilers and oil burners are entirely inactive. If separate oil transfer pumps are not available, a small circulating-oil pump b added to the pack age to provide circulation in the oil lines during the gas firing periods. The electrical preheating method involves use of-immer sion heaters, plus a special arrangement for hPAiing the fuel oil piping. Ode special arrangement is a heating cable-(soil, cable or plastic covered-wire), wrapped around the supply fine or all oil piping, and a vertical-clement immersion heater in the suction pipe inside the' oil tank. The closeness and evenness of the spiral winding of the cable determine;the heat input. The on-off periods ore thermostatically,controlled. For protection of the heating cable, the .temperature .of the- oil piping has to be limited, and usually must not.-exceed 170 F. Where pipe and oil-temperatures permit wrapping of all oil piping, constant oil circulation- b cot required. The efficiency of this preheating method is lower than for element- immersion or electric-impedance heating, because of transfer' losses between the heating element and the pipe. ' .. - ;> Oil burners designed for automatic operation on No;> 5 or No. 6 oil are generally equipped with thermostatically con trolled electric immersion heaters. In an-emergency,' the burner-immersion heater may be used alone to heat a modu lated, very low quantity of oil for combustion. However, in a norma! operation, it functions in conjunction with the primary, preheating system. ,. Maintaining Piping and Tank Temperature Oil Storage Tarildi arid. Piping Storage tanks, and the piping and pumping facilities for delivering.the oil-from the tank-to the burner, are very im portant considerations 'in' the"design of an industrial'oil- burning system. The construction and location-of the.tank and oil piping arc usually subject to local regulations, which should always be consulted, and to the standards of the Na tional Board of Fire Underwriters, such as NBFU Pamphlet No. 31.* . :4 The size of the* storage tank is usually based' on the" rate- at which oil is io He consumed; the spriie available, the method! of oil defiveiy'(thick or'tank car); and the ease with whicli deliveries can (re made' underfill weather conditions; A 'mini mum capacity of'at' least the maximum weekly usage is dfef arable. If deliveries are'to be made by tank car, the capacity should not be less than 15,000 gah Controls The control of oil-fired equipment is discussed in the sec tion Automatic Control of Fuel-Burning Equipment GAS-RRED. HEATING. EQUIPMENT A* gas'burner is defined by the American Gas Association as "a device for the final conveyance of the gas, or a mixture of gas and air, to the combustion zone." Burners used for do mestic heating are of the atmospheric injection, luminous flame, or ptiwer burner. types. ' ` . DOMESTIC Domestic gas burners may be classified as either those types designed for central heating plants or those designed for unit application.' Gas-designed units and conversion burners are available for^he several kihds'of central systems'in'`which When using-No.' 5 and No. 6 oils, special'arrangements must be made to keep the oil fluid in the piping at'all and to keep a portion of the oil in the storage tank'around the suction draw-off fluid. gravity andforeedwarm air furnaces or-steam and hot Water boilers are used,' and for other applications where warm'air floor fumaces'and' room heaters-are installed in' the space being Heated.- - The piping may be'heated by one or more of the following methods: Central Heating Systems 1. Wrapping the supply line with electrically heated tape. ; 2. Passing's current through the supply line itself. 3. Enclosing the supply line with a steam'or hot'water fine in' the same envelope, -. 4. Insulating the supply line so as-to decrease the thermal) losses. . - ,- y ...... 5. Setting up a dual'syitem in'which the. primary preheaters Ga&desigried tellers' for hot water or steam' heating- are available in cast-iron!, steel, and non-ferrous metals (Fig`..9). The burners''are' located'beneath the sections^ ancTti&fiu* gases pass.upwards' between the sectioas'to the flue .collector! Some boilers' 'are' designed to proylde'domesuc hot waier, using tankless or inctantaninis hipsters.' Automatic Fuel-Burning Equipment 811 afSoctba Una Poof - Table 1.... Recommended Minimum Suction and Return Pipe Sizes for Fuel Oil lines* (for No*. S and 6 Fuel Oil)* Pump Capacity, GaOons par Hour 50 100 | 150 | 200 | 300 600 3 1. 6 Grade of Oil (Numbed 5 | 6 | 5 | .. 5 | 5 | 6 | 5 | 5 5 |6 900 5 |5 Ofooefer of Pipe, tadms . 10-60. 60-100 110-1S0 .St IX ix -2 2 2 2 2 2 2 2X 3 3 4 IX 2 IK 2 2 2 2 2. 2 2X 2H 2X 3 2 2 -2H 2M 2X 2X 3- 3 334 -4 4 4 Pipe riswabowa art baaed on vertical euctiofi lift not to exceed 10ft from bottom of stone* task to oil pump. . ' b A'mtioo Use leoctu in erceea of 100 linear feet b sot recommended for system* smt No. 5 or No. 0 oil. Where the length is (roster s.separate pump should be intailed oees.the atone* tank. .. * Equivalent length of pipe metades ell horisoatal aod vertical measured piping plus proper allowance for tbIto sod fitting* ae follows: Multiply pipe diameter in by factor below to obtain equivalent pipe length in feet- Qbow -- Factor S; Tee " Factor l;'Gate Valve m Factor 1H; Globe Valve -- Factor 9. Warm air furnaces are of two types, gravity and forced air.. Forced .warm air furnaces utilize a motor-driven blower to' circulate air over the heat exchanger and through the ducts. One common type is quite similar to Fig. 7, except that gas burners, pilots, controls, and the gas pressure regulator are substituted for the oil burner, its blower, ignition system, and controls. A draft hood is attached, to the outlet of the `furnace and replaces the barometric damper. Heat exchangers 'are available with upflow of air as shown, or with crossflow or downflow of air to be heated. Some gas furnaces and boilers are available with sealed comimstitm chambers. These units have'no draft hood. Com bustion air is piped, usually through a ride wall from out- . doors, directly to' the combustion chamber. . .... . The air intake pipe terminates in the same location as* the flue gas vent, sometimes as concentric pipes, with an ap propriate terminal covering or cowl. No chimney or vertical flue is heeded with such units. ` " -`-The A.G.A; listed output at the boiler nozzle, or at the bonnet for forced air furnaces, is 80 percent of the approved input to the burners, as set by the American Standards Association (ASA) requirements. The corresponding output for gravity furnaces is 75 percent. Conversion Burners Conversion burners are complete burner and control unite designed for installation in existing boilers and furnaces. A typical gas conversion burner is shown in fig. 10. Atmospheric conversion burners may have drilled-port, slotted-port, or single-port1humer heads. Several power burners in domestic rises are available. These are of gun-burner design and are-particularly desirable for-accommodating furnaces or boilers with restricted flue passages. Conversion burners for domestic application are available in bum ranging' from 40,000 to 400,000 Btuh capacity. It should be noted that the American Standard listing Require ments are-limited at present to conversion burners having in put capacities up to 400,000 Btuh. Burners of larger capacity, for use in large steel boilers, are usually engineered by a con tractor 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 conver sion burner installation in boilers requiring more than 400,000 Btuh input, reference Bhould be made to the current American Standard Requirements for Installation of Gas Equipment in Large Boilers, ASA Z21.33. Domestic sizes of conversion burners should conform to current American Standard Listing Requirements for Domestic Gas Conversion Burners, ASK Z21.17. As the successful and safe performance of a gas conversion burner depends on nu merous factors other than those incorporated in such equip ment, installations of this kind must be made in strict accord ance with current American Standard Requirements for Installation of Domestic Gas Conversion Burners, ASA Z21.8. Draft hoods conforming to current American Standard Listing Requirements for Draft Hoods, ASA Z21.12, should also be installed (in place of the dampers used with a solid fuel) on all boilers and furnaces converted to burn gas. Floor Furnace The floor furnace is used to supply central heating in mild climates, or for auriliary heating or heating of single rooms in colder climates. It is used for heating first floors, or where heat is required in only one or two rooms. However, upper floor installations are possible. A number may be used to provide heat for the entire building where all rooms are on the ground floor, thus giving flexibility to the heating system. In floor-furnace applications, the heating element, gas pip ing, and flue vent piping are suspended below the floor, and the only part visible in the room being heated is the circulating air register, which may be of the single type, inst-allaH in the floor, or of the dual type, installed in a partition and heating two rooms. The A.G.A. output rating of floor furnaces is x based on an efficiency of 70 percent for the gravity-type and 75 percent for the fan-type unit. Vented Wall Furnace . -.Another type of heating appliance is the vented.recessed heater .which is either a gravity or fan-type appliance de signed for installation in or permanent attachment to a wall, floor, celling, or.partition. Such heaters may have short stub ducts io conduct heated air to adjacent rooms. They aie instailed primarily in new homes,, usually being plastered into the wall as a permanent part of the building. The A.G.A.