Burner Controls - Burner above 1200kW

Gas fired burners with a thermal output above 1,200kW, must have microprocessor-based controls that continuously modulate burner output in response to measured boiler temperature or pressure values, over a turndown ratio of at least four to one. The microprocessor must use PID control, or more advanced equivalents to control fuel and air flows. It must also control the air/fuel ratio, so oxygen levels in the exhaust gases can be set at a maximum of 3% at 100% rating, 4% at 50% rating and 5.5% at 25% rating. Carbon monoxide (CO) levels in the exhaust gases must not exceed 50 ppm throughout the range. These combustion tests must be done in accordance with the procedures laid down in EN676.

All gas burner control elements including combustion air dampers and fuel valves must be fitted with a precision servomotor, which must be separately controlled and include positional or flow based feedback control. All burners must be fitted with air dampers that fully close on burner shutdown.

Oil fired burners with a thermal output above 1,200kW must have microprocessor-based controls that modulate burner output in response to measured boiler temperature or pressure values, either continuously over a turndown ratio of at least 2.5 to one, or step wise across at least three stages of output. The microprocessor must use PID control, or more advanced equivalents to control fuel and air flows. It must also control the air/fuel ratio, so oxygen levels in the exhaust can be set at a maximum of 3% at 100% rating, 4% at 50% rating and 4.5% at 40% rating. Carbon monoxide (CO) levels in the exhaust gases must not exceed 100 ppm throughout the range. These combustion tests must be done in accordance with the procedures laid down in EN267.

For oil burners, combustion air dampers and continuously modulating fuel values (where used) must be fitted with a precision servomotor, which must be separately controlled and include positional or flow based feedback control. All burners must be fitted with air dampers that fully close on burner shutdown.

In addition, all gas fired and dual fired burners rated above 1,200kW must have a variable speed drive fitted to the forced draught fan.

Important Note: Burners with high turn down ratios should be only fitted to boilers that are capable of working with equivalent turn down ratios.