There are various factors that can affect draf. Measuring draft is important because draft measurement shows how rapidly the gases pass through the furnace or boiler. Draft measurements ensure that there is continuous negative pressure (systems without forced ventilation) in the combustion system. Excessive draft increases stack temperature and therefore decreases combustion efficiency.

Changes in draft, could indicate possible problems with the chimney or the air supply.

Basically, atmospheric burners produce draught due to the pressure difference caused by the height of the stack. In operation, this is increased by temperature effects from the combustion process, however, there must be a certain amount of draught present from the start. Too little draught will cause flue gases to exit into the boiler room, producing a risk of asphyxiation and reducing the efficiency of the burner. Too much draft will cause the heat to exit the chimney or stack without contributing any useful work.

Tall chimneys and chimneys with a large internal flue area will require more heat to avoid condensation forming inside the chimney. This can be considered very broadly: Stack gas is anything that comes out of a burner chimney or stack in gaseous form. This is, however, not so simple as it sounds! Stack gas will contain water in vapour form when it is hot. (recommended pellets for use with the eurofire have 8-10% moisture content) This water will liquefy when the stack gas cools down, reducing the volume and producing condensate. As a guideline the flue-gas temperature should be at least 80°C from a point one metre down from the top and inside the chimney.

Flue Draft Stabiliser
Chimney draft is influenced by how tall a chimney is built. The taller the chimney, the more draft created. Tall chimneys and chimneys in areas of strong wind produce increased “chimney affect”. This in turn affects the efficiency of the eurofire burner which requires the correct settings to suit the prevailing circumstances for efficient pellets firing. A flue draft stabiliser can be fitted, it is a metal spring door mounted behind the boiler at the base of the chimney. The flue draft stabiliser helps level any variations in draft and ensures correct ventilation of the chimney.

A chimney can be made of bricks, a steel tube lining or an approved prefabricated steel tube chimney. A chimney draft of 10- 20 Pa is sufficient to run a eurofire burner at optimum. If the internal area of the chimney is too large to allow 10-20 pa, a metal tube can be installed to decrease the flue area.

Excess Air
Lambda

Lambda is related closely to excess air. Lambda is the amount of air in the combustion process related to the amount needed. A Lambda value of 1.0 would mean that exactly the theoretical quantity of air needed for complete combustion is present. Lambda is generally expressed as a number not a percentage and includes the air necessary for complete combustion. In other words, Lambda will always be in excess of unity. Lambda must be carefully balanced to avoid excessive losses due to unnecessary air being heated and simply vented to the atmosphere. There is always a balancing act between Lambda and carbon monoxide content. Too much air will lead to losses and too little will lead to carbon monoxide production and incomplete combustion. Lambda is one of the major factors in adjustment of a burner system for correct combustion.

The quality of the eurofire burner system is determined by a maximum percentage of complete combustion with a minimum of excess air. It is important to ensure the air-intake volume to the boiler room is equal to the chimney draft volume to the out-side air and air-inlets are open. Pellet-heating when in operation requires more air supply than oil-heating operation. Chimney fans for use with atmospheric burners are available on the market. When the boiler thermostat calls for heat, the chimney fan will start-up. When the fail-safe supervision confirms sufficient chimney draft the boiler burner will be released and the fan speed adjusts to the commissioning value. When the burner stops the fan stops too.

Environmentally friendly combustion and burner adjustment

Due to the use of many types of combustion processes, the environment is required to deal with an ever larger concentration of pollutants. Acid rain, smog formation and a constantly increasing number of allergies are a direct result of this development.

The path to environmentally friendly energy production must lead to a reduction in green-house gas emissions and of pollutants, this is only possible when the existing equipment is working correctly and defective equipment is taken off line. Flue gas analysis enable the measurement of the concentrations of pollutants present and subsequent adjustment of burners for optimal combustion.

What is Pellet Fuel?

Pellet fuel is a renewable, clean-burning and cost stable heating alternative used throughout Europe and North America. It is a biomass product made of renewable substances – generally recycled wood waste. There are no additives. Pellets are packed with energy. In Europe there are over 2 million homes and other large-scale environments such as schools, prisons and even whole villages, using wood pellets for energy production. Pellets are produced in manufacturing facilities mainly in Northern Europe and are available for purchase and delivery now throughout the UK. The pellet fuel combustion process holds emissions far below non-renewable fossil fuels. Pellets are renewable and CO 2 neutral.