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NORA Oilheat Technicians Manual

Excess air reduces efficiency and flame retention burners operate with less excess air than older burner designs. Flame retention burners require 20 to 30% excess air while older burners need 50 to 100% more to achieve low smoke numbers. The difference in the flue heat loss for these burners is often about 10%. The second advantage of flame retention burners is reduced off-cycle heat loss. The flow of off-cycle air through the heating unit is reduced by the narrow openings of the air band and the flame retention head. Therefore, off-cycle heat loss is less. This improves the heating system efficiency. See Figure 16-9. Installation requirements Be sure to check the condition of the combustion chamber before installing a new burner. Many older chambers are not suitable for the flame produced by a flame retention burner. Modification of the combustion chamber may be required. See Chapter 5 for more details about chamber upgrades. Be extra careful when installing new burners into dry-base boilers and older furnaces because it may be possible to burn through the base. Important considerations in an installation procedure include: • Select the most efficient fuel nozzle size for the job. Many boilers and furnaces are overfired and operate at lowered efficiency. Remember that flame retention burners operate with higher efficiency and a smaller nozzle is usually advisable. • Inspect the combustion chamber and repair or replace it. Add a high temperature Lower On-Cycle Loss Less Excess Combustion Air ceramic liner insert if needed. Less Excess Off-Cycle Air Flow Air • Install the new burner. Carefully follow the recommendations of the burner manufacturers. • Seal all air leaks around the heat exchanger, and the burner air tube. Air leaks can increase both on-cycle and off-cycle heat loss. • Adjust the burner using combustion test equipment to an efficiency of 80% or higher. Some burners have adjustable head positions. Use the setting recommended by the manufacturer for the installed fuel nozzle size. If a fixed retention head is used, be sure that the head is the correct size. Use the head size that matches the fuel nozzle rating. • Test all safety controls for proper operation. • Perform final checks of burner operation. Installation of flame retention head burners as replacements for older units can be an effective and economic means for Chapter 16 Energy Conservation Lower Off-Cycle Loss Figure 16-9: Flame retention burners operate with less heat loss. Chapter 16—Energy Conservation 16-13


NORA Oilheat Technicians Manual
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