Fuel burn rate, emissions and gas temperature from a domestic two-stage wood-fired hydronic heater

An experimental study is conducted of a two-stage wood-fired hydronic heater (WFHH). The WFHH contains two combustion chambers. The first is associated primarily with wood pyrolysis while the second, located down-stream, is designed for secondary burning of undesirable emissions while generating more heat. A piezo-electric based load cell apparatus is developed to obtain direct measurements of fuel burn rate (FBR) - avoiding possible inaccuracies of standardized (full appliance weighing) approaches used for certification. In order to check the internal consistency of the experimental measurement, a theoretical mass loss relation is developed and used for reducing data and to explain the physical mechanism responsible for the existence of the experimentally observed global maximum burn rate. A system level numerical model is also developed based on a combination of well-stirred reactor theory to provide estimates of emissions products and gas temperature. Overall agreement between experiments and model predictions are reasonable for temperature and major combustion species. As the first known reported measurements of a domestic WFHH, the experimental measurements are found to be internally self-consistent and provide guidance for more complete theoretical studies.