Optimum burner temper­a­ture

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.

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.