Document XO8m6RBX7LDj0a8JNpdQn6m5K

HEATING VENTILATING. AIR CONDITIONING CUIDE 1940 dead or inactive spaces in the combustion chamber. An overhanging arch at the back of the fire pot is sometimes used to increase the flame travel and give more time for mixing and burning and sometimes to pre vent the gases from going too directly into the boiler flues. When good atomization and vigorous mixing are achieved by the burner, combustion chamber design becomes a less critical matter. Where secondary air is used, combustion chamber design is quite important. With some of the vertical rotary burners considerable care must be exercised in definitely following the manufacturers instructions when installing the hearth as in this class successful performance depends upon this factor. Combustion Adjustments Where adjustments of oil and air have been made which give efficient combustion, the problem of maintaining the adjustments constant be comes an important one. Particularly is this true when the change causes the per cent of excess air to decrease below allowable limits of the burner. A decrease in air supply while the oil delivery remains constant or an increase in oil delivery while the air supply remains constant will make the mixture of oil and air too rich for clean combustion. The more efficient the adjustment (i.e., 25 per cent excess air) the more critical it will be of variations. The oil and air supply rates must remain constant. The following factors may influence the oil delivery rate: (a) changes in oil viscosity due to temperature change or variations in grade of oil delivered, (b) erosion of atomizing nozzle, (c) fluctuations in by-pass relief pressures and (d) possible variations in methods 2b (3) and 2b (4) listed in the previous classification table. Note that any change due to partial stoppage of oil delivery will increase the proportion of excess air. This will result in less heat, reduced economy and possibly a complete inter ruption of service but usually no soot will form. The following factors may influence the air supply: (a) changes in combustion draft due to a variety of causes (i.e., changes in chimney draft because of weather changes, seasonal changes, back drafts, failure or inadequacy of automatic draft regulator, use of chimney for other purposes, possible stoppage of the chimney and changes in draft resis tance of boiler due to partial stoppage of the flues), and (b) changes in air inlet adjustments to the fan. It is recognized that a secondary source of air due to leakage in the boiler setting is present in many installations and it is highly desirable that this leakage be reduced to a minimum. Obviously the amount of air leakage will be determined by the draft in the combustion chamber. It is important that this draft should be reduced as low as is consistent with the proper disposal of the gases of combustion. When using mechani cal draft burners with average conditions, the combustion chamber draft should not be allowed to exceed 0.02-0.05 in. water. An automatic draft regulator is very helpful in maintaining such values. Measurement of the Efficiency of Combustion Efficient combustion being based upon a clean flame and certainproportions of oil and air employed, it is possible to determine the results) by analyzing the gases formed by the combustion process. An Orsat 216 CHAPTER 11. AUTOMATIC FUEL BURNING EQUIPMENT apparatus is a device which measures the volume of carbon dioxide (COj), oxygen (Os)'and carbon monoxide (CO) in. the flue gases. Except in the case of a non-luminous flame it is usually sufficient to analyze only for carbon dioxide (OOj). A showing of 10 to 12 per cent indicates the best adjustment if the flame is clean. Most of the good.installations at the present time show from 8 to 10 per cent COt. Taking into account the potential hazard of oil or- air fluctuations with low excess air. (high COi) a setting to give 10 per cent COt constitutes a reasonable standard for most oil burners. This is particularly true of non-luminous flame burners which will not function properly with less than 10 per cent CO%. Controls Oil burner controls may be divided into two parts: (a) devices to regulate burner operation so the desired house heating result may be obtained, and (V) devices for the safety and protection of the boiler and burner. For control devices generally consult Chapter 38. The room thermostat has recently been improved to provide more frequent burner operation and greater uniformity of room temperature. Class (b) controls comprise a device to shut off the burner if the oil fails to ignite or if the flame should cease due to lack of oil ; a device actuated by steam boiler pressure to shut off the burner when the pressure reaches some pre determined value; a device on the boiler to shut off the burner if the water level acts too low for safety or one which automatically feeds additional water to the boiler; a device on warm air furnaces to shut off the burner if the air temperature gets too high; a valve in the oil supply line which automatically closes in the event of fire in or near the cellar; and a device to keep the temperature of the boiler water within certain limits when it is being used to heat domestic hot water. GAS-FIRED APPLIANCES The increased use of gas for house heating purposes has resulted in the production of such a large number of different types of gas heating systems and appliances that today there is probably a greater variety of them than there is for any other kind of fuel. Gas-fired heating systems may be classified as follows: I. Gas-Designed Heating Systems. A. Central Heating Plants. 1. Steam, hot water, and vapor boilers. 2. Warm air furnaces. B. Unit Heating Systems. 1. Warm air floor furnaces. 2. Industrial unit heaters. 3. Space heaters. 4. Garage heaters. II. Conversion Heating Systems. A. Central Heating Plants. 1. Steam, hot water and vapor boilers. 2. Warm air basement furnaces. 217