MODELLING GHG REDUCTION THROUGH EMISSION REDUCTION AT LOG WOOD STOVES
The following model calculation of GHG emissions as CO2 equivalents for estimating the potential of emission reduction measures at log wood stoves was based on the assumption of qualified estimated values and many years of experience for flue gas emissions from manually fed domestic single-room furnaces such as wood-burning stoves. For the real observation and data collection at a concrete individual unit, direct emission measurements at this unit are required.
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For an average wood stove currently available on the market, total particulate matter values of 100 mg/m³ (i.N.) at 13 vol.-% O2, OGC emissions of 200 mg/m³ (i.N.) at 13 vol.-% O2, and CO emissions of 2000 mg/m³ (i.N.) at 13 vol.-% O2 were assumed under practical conditions (hereinafter referred to as raw real emissions). These raw real emissions (C_RRE) are emitted as an average when untrained users operate a stove without emission control technology. Emissions can be reduced considerably by training the users, which has been demonstrated by measurements carried out by DBI Freiberg as part of the "Stove operator's license" project (UBA project). In order to enable a qualified realistic estimation, the following user reduction rates (X_Min) were used for so-called clean emission values with emission abatement. The total dust reduction is at least 0.5, the OGC reduction is at least 0.5, and the CO reduction is at least 0.6. From these reduction ratios, the clean values by emission reduction (C_REN) can be calculated. The GHG CO2 equivalents for C_RRE and C_REN calculated from the emission values are related to the greenhouse effects of the exhaust gas constituents black carbon (BC, GWP100 = 460), methane (CH4, GWP = 28), and carbon monoxide (CO, GWP = 2.1). The mean BC concentration in the exhaust gas was calculated from the total dust value and an assumed 50% share of total dust. The mean CH4 concentration in the exhaust gas was calculated from the OGC value and an assumed share of 50% OGC. For further consideration (see FNR: Mediathek - CO2-Emissionsfaktoren der Wärmebereitstellung 2020, https://mediathek.fnr.de/grafiken/daten-und-fakten/bioenergie/fest-biobrennstoffe/co2-emissionsfaktoren-der-warmebereitstellung.html, accessed 12.05.2023) it was assumed that in the case of sustainable wood use ("significantly less wood is used than grows" and "100% fossil energy sources are substituted by wood combustion") only the CO2 emissions from the prechain of a wood stove (EFCO2 Vorkette Holzofen) are to be set at 23.7 g/kWh. If, on the other hand, no fossil energy source is substituted and the use of wood is not sustainable, the CO2 emissions from wood combustion (EFCO2 Holzfeuer*) must be included at least proportionally (e.g. with a factor of 0.5) with 380 g/kWh. For comparison purposes, the CO2 emission factors for an air source heat pump using the current electricity mix (EFCO2LuftWP) were used at 154.9 g/kWh and for a natural gas boiler at 241.1 g/kWh.