Emission measurement data of a wood log stove in natural draft operation compared to constant draft
Description
In the public debate about air pollutants, log fired appliances and especially wood-burning stoves are increasingly being criticized. The assertion that the furnaces only comply with the required emission limit values as part of the approval test is being asserted more and more. Furthermore, the emissions would only be achieved by creating "optimal conditions". This generally describes the test according to the standard with a constant draft in the measuring section. The assertion is usually supported by measurements based on the approval test procedure with different parameters. The manufacturer's specification "minimum flue draft" refers to the pressure that the flue gas system should at least reach during operation at nominal heat output in the worst case; with deviating outputs, depending on the insulation standard and the mass of the chimney in real operation, there will be a correspondingly deviating pressure. Basically, the question should be investigated whether and under which boundary conditions a performance-independent constant draft can actually be regarded as the optimal test condition. In addition, the emissions, which are determined with natural draft, are to be set in relation to the emission factors with which modern log wood furnaces also burden the emission inventory.
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Steps to reproduce
For the measurement in natural draft mode, the "LEDA Corna" stove was used, which was additionally equipped with a catalyst. This device was chosen because several measurements had already been carried out with the "Corna" with a catalyst as part of the BImSchV revision. The stove has a central air slide, which regulates the primary and secondary air equally and is also equipped with a pre-heating function, which has an enlarged air cross-section adapted to the static pressure of the chimney. As part of the approval, the device was tested with three outputs (3 kW with catalytic converter or 4 / 6 kW without catalytic converter) and is also equipped with a heating aid. This monitors the heating behavior and is also intended to ensure the correct function of the catalytic converter. In another series of tests, the standard air valve is replaced by a valve with tension adjustment, which was presented for the first time in 2019 as a "volume flow controller". The volume flow controller can be used to adjust to the draft conditions to be expected in connection with the chimney system used. 1.3 kg of wood is specified as the optimum feed mass for achieving the nominal heat output; with partial load, the fuel mass is reduced to 1.0 kg. The test chimney in the technical center of the DBFZ enables the effective heights of 4m and 6m. The top of the chimney ends in a suction bell in the interior, which induces a negative pressure by means of a blower, which is to be expected as idle pressure in accordance with the active height in real operation. The test thus largely corresponds to real natural draft operation, but the influence of wind and possibly changing outside temperatures have no influence on the measurement. The test sequence thus corresponds to the sequence according to "BeReal", the draft (12 Pa constant, 12/8 Pa constant, natural draft), the refill criterion (25% of the CO2 peak, "flame out"), the type of evaluation (BeReal, 16510) and the type of air valve (standard air valve “SLV”, new air valve “NLV”) are varied. Tests under standard test conditions according to EN 16510 serve as a reference. Contrary to the applicable test standard, the only criterion "flame off" visible to the end customer was selected as the refilling criterion in natural draft operation, since the refilling criterion used today in the standard (4 +/- 0.5% CO2) can also only be used at constant pressure and can only be determined with the appropriate measuring device.