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Optimum burner temperature

LambdaConstant: the future of gas condensing boiler controls


LambdaConstant is a newly designed control system for combustion in gas condensing boilers in which the combustion temperature is measured directly at the gas burner. The measurement uses thermocouples on the surface of the burner. Taking measurements in the oxidising flame, with highly stressed electrodes that require very accurate positioning, is now unnecessary. The programmed LambdaConstant curve allows the optimum burner temperature to be set accurately, without the usual safety margins for limiting gases. The operative ranges for commercially available gas burners can be extended significantly to a high modulation range of 1: 10. This high modulation range cannot be attained currently with conventional gas condensing boilers.

The already high efficiency of gas condensing boilers can be increased even more in the partial load range, as energy losses in cyclic operation are minimised by pre- and post-flushing phases. This is referred to specifically by the draft of the European EuP environmental design directive. The great advantage of the LambdaConstant system is that the mass flow of the supply of combustion air is measured directly at the gas blower using a digital mass flow sensor. The specially developed laminar flow element with extremely low pressure drop ensures a stable sensor signal over the entire modulation range from 1:10, even with small mass flows and in dirty ambient conditions. The mass flow signal is transmitted via an intrinsically safe digital bus system from the blower directly to the burner controller, where it is processed. The blower also has a highly accurate built-in gas control valve that allows even small changes in the air-fuel ratio to be adjusted for quickly.

lambdaconstant Das Massenstromsignal wird über ein digitales, eigensicheres Bussystem vom Gebläse direkt an den Feuerungsautomaten weitergeleitet und dort verarbeitet. Am Gebläse ist außerdem ein sehr genaues und auf den Verbrennungsprozess abgestimmtes Gasregelventil integriert, mit dem sich auch kleine Änderungen in der Luftzahl sehr schnell ausregeln lassen.

The air mass flow and burner temperature are evaluated in the LambdaConstant burner controller by a dynamic target value regulation with adapted time constants and the gas control valve is adjusted according to the target values, even if the air mass flow changes quickly. The low pressure drop in the laminar flow element allows the same gas blowers to be used with higher air supply and exhaust pipe lengths; with the same pipe lengths, the gas blower power consumption is lower. The effects of different exhaust pipe lengths or wind for different pressure zones of a house are compensated for by the continuous measurement of the mass flow. The ignition mass flow for optimal ignition is adjusted automatically. Even at great installation heights, the unit output is kept consistent due to the mass flow measurement. The adaptation of minimum or maximum heat output commonly required in the Alpine regions or certain regions of the USA is not necessary.

A significant advantage of the Lambda-Constant system is the independence of the gas type and gas family. Pure methane from Russia, North Sea gas with nitrogen or hydrogen admixtures and biogas with CO2 content have virtually no effect on the burner curve. Even when switching to propane and butane mixtures, the system adapts exceptionally well. This allows the number of heating unit variants to be reduced significantly for manufacturers, wholesalers and heating contractors. In sum, the LambdaConstant combustion control system is another great improvement in today’s generation of gas condensing boilers in terms of efficiency, deployment, robustness, and number of variants.

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