Variable speed control of the boiler fan

Having variable speed control for boiler fans allows you to:

• make electrical energy savings across the firing range and improve efficiency at low fire by facilitating greater control of the air supply to the burner
• significantly reduce boiler house noise; typically by around 50% at low fire
• prolong the life of fan motors by reducing the number of revolutions needed to do the job

With both mechanical cam and basic electronic fuel:air ratio control, combustion efficiency at low fire is sacrificed to achieve improvements in burner turn-down.

Some air dampers leak and even when fully closed the air flow can be significant. In effect, fuel:air ratio controls can reduce the fuel valve setting but cannot reduce the air supply to match. Combustion efficiency can be improved at low fire if the fan speed is reduced.

Fan speed control is an easy-to-add option to ETC's electronic controls. By adding fan speed control, burner turn-down can be increased without compromising efficiency, and additional fuel savings can be achieved.

The benefits of variable speed control do not end here. When an inverter is used to slow the speed of an A/C electric motor, electrical energy savings result. For example, when a fan motor is slowed to 25Hz (half speed), an 80% electrical energy saving is achieved.

As a further illustration of the savings that can be made, when ETC customer Warwick International installed ETC variable speed control on their boiler fans, they achieved electrical savings of 114,000kWh p.a. per boiler. The resultant reduction in CO2 emissions at the electricity generating station was 59,148 tonnes p.a.

Warwick International also chose ETC oxygen trim systems and have reduced their fuel bill by 3.5% p.a.

74% noise reduction and £15,000 energy saving in the Mead Speciality boilerhouse

ETC variable speed oxygen trim was fitted to Hamworthy WD17 burners on a 38,000lb/hour twin fired Babcock Steamblock boiler. The ETC system automatically and continuously maintains the correct fuel:air ratio.

Boiler efficiency has been improved by 5%, fuel and electrical savings amount to £15,000 p.a., emissions are under control, and noise in the boilerhouse has been reduced so much that the burners were thought to be off!