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NORA Oilheat Technicians Manual

Flow rate Atomizing nozzles are Whenever it is possible, determine the available in a wide range of flow rates. Generally, with hydronic and warm air heating systems, the smallest firing rate that will adequately heat the building on the coldest day of the year is the proper size to use. Another guideline is to select a flow rate that provides a reasonable net stack temperature regardless of the connected load. This avoids acid condensing in the stack, which occurs at about 150 to 200°F. If the appliance is undersized for the load (highly unlikely), it may be necessary to fire to the load and ignore the efficiency. A nozzle that is too small will not produce adequate heat and hot water. A nozzle that is too large will cause the unit to short cycle, reducing efficiency and wasting fuel. Whenever it is possible, determine the manufacturer’s recommendations on nozzle selection and never overfire the rating of a heating appliance. Dual filtration manufacturer’s recommendations Double filtration nozzles are available for mobile home installations and other units with very low firing rates. In addition to the standard nozzle filter, these nozzles have a secondary internal filter located immediately before the metering slots. This extra filter gives the nozzle 35% more nozzle filtration. The internal filter does not change the nozzle’s performance; it just increases its longevity. There is also a nozzle available from Delavan Spray Technologies for low firing rates that uses two swirl chambers and short metering slots, keeping the oil contaminants in suspension and flushing them from the orifice. Particles are not allowed to collect or stick together, limiting buildup and plugging. Burner air patterns Burner air patterns are much like nozzle spray patterns in that they fall into solid and hollow classifications. Burners with solid air patterns are often referred to as open-end burners. There is no restrictive air cone in the end of the air tube to direct the air effectively in any desired pattern. This produces high velocity air down the middle of the air pattern and works best with a solid nozzle and narrow spray angles. This situation does not apply to flame retention burners. Flame retention burners are equipped with air handling devices in the air tube that afford better mixing of air and oil vapor in the combustion area. Many flame retention burners can fire both solid and hollow nozzles with good results because of the strong recirculation air pattern they produce. This recirculation of air and oil in the chamber also affects the fire box pressure. In the flame retention burner, the flame front is held very near the burner head. It creates a flame that is less likely to pulsate or produce soot. Nozzle selection for these burners should follow manufacturer’s recommendations and the following general guidelines: • Burners with flow rates up to 2 GPH: Hollow nozzles can be used successfully for most applications, even on burners with most of the air down the middle. Hollow nozzles in lower firing rates produce the quietest operation. It is often better, especially in furnaces, to sacrifice 1 or 2 points in efficiency for quiet operation. • Burners with flow rates between 2 and 3 GPH: You may use hollow or solid nozzles depending upon the burner air 5-8 Nozzles and Combustion Chambers on nozzle selection and never overfire the rating of a heating appliance. Chapter 5 Nozzles and Chambers


NORA Oilheat Technicians Manual
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