Numerical modelling of air-supply and chimney of B 11 type gas appliances DR. LAJOS BARNA DR. LÁSZLÓ GARBAI RÓBERT GODA Department of Building Service Engineering Budapest University of Technology and Economics 1111 Budapest, Műegyetem rkp. 9. HUNGARY tanszek@epgep.bme.hu http://www.host.epgep.bme.hu Abstract: In Hungary, most operating gas appliances are B 11 type devices. In the case of these appliances, the coordinated operation of the gas appliance and the chimney, as well as the supply of combustion air raise important questions. Chimneys with natural draught are very sensitive to the changes in the amount of combustion air which may be caused by inside or outside ambient phenomena or by forced effects. The presented model seeks to examine the section between the air inlet of the room and the outlet of the chimney (air inlet – room – gas appliance – chimney). For the purposes of modelling, a numerical simulation (CFD method) can be used. The aim of numeric modelling is to investigate velocity and temperature conditions around the flue gas outlet and in the room and, subsequently, to define design approaches and the requirements for different conditions. Key words: air supply, chimney, gas appliances, CFD method, numerical modelling 1 Introduction “B” type gas appliances have an open combustion chamber; combustion air comes from the room in which the equipment operates, while flue gases leave through a chimney. The two primary groups of “B” type gas appliances according to the European grouping are as follows [8]: – Appliances with atmospheric burner and draught hood, connected to a chimney with natural draught (e.g. B 11 , B 41 ), – Appliances, which have burners installed with ventilators, connected directly to the chimney, without draught hood (e.g. B 23 , B 33 , B 53 ). In Hungary, the use of gas is of a significant proportion as compared to other energy sources. Small consumers – with a gas meter no greater than 20 m 3 /h nominal volume flow, including domestic consumers – make up almost 50% of the market. 9-10 million gas appliances are estimated to operate in Hungary, most of which are connected to a chimney and have open combustion chamber (B 11 type, Fig.1). In the case of these appliances, flue gas has immediate contact with the air of the room in which the machine is installed. Thus, if the air-flow conditions are unfavourable, the flue gas may re- enter the space. In recent years, this phenomenon has caused several accidents in Hungary, some of which turned out to be fatal. Regulations have not been updated to follow the innovations of gas appliance designs and they do not include the drastic decrease of air-change rates due to air-tight windows and doors. This is why special attention is paid to the modelling of B 11 type gas appliances. With a theoretically established background, the placement, design and operation of the appliance becomes easier. The mathematical modelling and its’ results for the B 11 type gas appliances are included in last year’s WSEAS Conference Proceedings ([4], [5]); in this paper, the theoretical basis of numerical modelling is summarized. Fig.1 B 11 type gas appliance according to [8] Proceedings of the 4th WSEAS Int. Conf. on HEAT TRANSFER, THERMAL ENGINEERING and ENVIRONMENT, Elounda, Greece, August 21-23, 2006 (pp16-21)