Method for operating a premix gas burner, a premix gas burner and a boiler

A premix gas burner comprising:

• a burner housing with a burner deck;
• a supply channel configured to supply a combustible mixture to the premix gas burner;
• a fan configured to supply air or the combustible mixture to the supply channel;
• a fuel gas supply including a fuel gas control valve configured to supply a fuel gas to the supply channel;
• a mixing area configured to mix the air and the fuel gas so as to form the combustible mixture;
• and
• an electronic controller configured to control the rotational speed of the fan and the fuel gas control valve;
• wherein the electronic controller comprises a memory in which a desired air excess factor relation (λd(I)) of the mixture is stored which defines the relation between a desired air excess factor and a chosen input variable (I), wherein the input variable (I) is one of the following parameters:
• a heat demand related value (Q);
• an air flow rate related value (F) indicative of a flow rate of the flow of air;
• or
• a fuel gas flow rate related value (FG) indicative of an actual fuel gas flow rate,
• wherein the desired air excess factor (λd(I)) is not a constant factor but varies for different values of the input variable (I),
• wherein the desired air excess factor (λd(I)) is defined as a ratio of the desired air to fuel gas ratio of a mixture relative to a stoichiometric air to fuel gas ratio;
• wherein the electronic controller is configured to:
• determine an actual value (Ia) of the input variable (I);
• determine an actual air excess factor (λa), wherein the actual air excess factor (λa) is defined as the ratio of the actual air to fuel gas ratio of the mixture relative to the stoichiometric air to fuel gas ratio;
• control the fuel gas flow rate (FG) and/or the air flow rate (F) such that:
• the actual air excess factor (λa) converges towards the desired air excess factor (λd(I)) belonging to the actual value (Ia) of the input variable (I);
• and that
• the heat generated with the premix burner remains in accordance with an acquired heat demand related value (Q).