Experimental study of a pellet stove

The present work is a preliminary report of an experimental investigation of a commercial pellet stove aimed to fully understand which parameters influence its total efficiency. The long tem goal of this activity is to identify criteria for performance improvements of the stove. In the first part of the paper we present an analytic model of the thermal behaviour of the stove that accounts for the heat exchange between the flue gases, including flame, and the stove and between the stove and surrounding environment. Results of experimental tests are presented and discussed, comparing results with those predicted by the model. In the second part of the paper we present an experimental study of the influence on the combustion efficiency of the excess of air and of its distribution along the height of the furnace. Experimental tests show that the production of CO was very affected by both factors. The best results are obtained when the total amount of air supplied is about twice the stoichiometric quantity, for any geometry of combustion grid. In the last part of the paper we address the different behaviour of a pellet stove in real operating conditions compared with operating condition during a certification test according the standard UNI EN 14785, in which measurements of efficiency and emissions are performed when the thermal transient is certainly concluded. Instead, in real case, the stove works mainly in transient conditions and this affects both the global efficiency and the CO emissions.