Fuel-Conversion Efficiency This is the percentage of the fuel that is converted to heat in the flame. If the burner is set for zero smoke, then all the fuel has been burned and the fuel-conversion efficiency is almost 100%. There are no unburned hydrocarbons left in the combustion gases. Combustion Efficiency or Steady State Efficiency Combustion efficiency includes fuel conversion efficiency, the amount of excess air used and the efficiency of the heat exchanger. It is the test technicians perform in the field, when the burner is firing at steady state. After testing the burner, a smoke test is performed. At that point, the amount of excess air is determined by testing for carbon dioxide or oxygen and the net stack temperature (gross National Oilheat Research Alliance 15 the draft regulator and installation factors including the location of the heating unit within the building. Air infiltration loss is greatest for heating appliances that operate with large quantities of excess combustion air, or units that have large off-cycle airflows. Efficient boiler-burner or furnace-burner combinations will operate with low air infiltration losses. The best solution for air infiltration loss is isolated combustion, whereby outdoor air is piped directly to the burner air intake. Figure 6. Infiltration losses from new units with isolated combustion air that require no draft regulator can be almost zero. Types of Efficiency There are many types of heating systems and many different definitions for efficiency. The most commonly used efficiencies we deal with in heating are as follows. Figure 6 Infiltration Loss Heated Air and Exhaust Gases Chimney Outdoor Air 0 - 60°F Cold Outdoor Air Enters House to Replace Exhausted Air Indoor Air 70°F House Exhausted Air by Heating Unit and Chimney Draft Regulator To Draft Damper To Burner Boiler
NORA Advanced Efficiency
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