Carbon footprint and emergy combination for eco-environmental assessment of cleaner heat production

The aim of this paper is to study via environmental indicators to which extent, replacing fossil fuel with biomass for heating is an environmentally friendly solution. The environmental impact of using biomass depends mostly on the transportation process. Authors define the notion of maximum supply distance, beyond which biomass transportation becomes too environmentally intensive compared to a fossil fuel fired heating system. In this work a carbon footprint analysis and an emergy evaluation, has been chosen to study the substitution of wood for natural gas. The comparative study seeks to examine, via the two approaches, two heating systems: one is fired with wood, transported by trucks and the other one is fired with natural gas transported by pipelines. The results are expressed in terms of maximum supply distance of wood. In the emergy evaluation it represents the maximum supply distance permitting wood to be more emergy saving than natural gas. In the carbon footprint analysis, it represents the maximum supply distance permitting wood to be a carbon saving alternative to natural gas. Furthermore, the unification of carbon footprint and emergy evaluation permits to define, for both approaches, the minimum theoretical wood burner first law efficiency that allows, CO2 or emergy to be saved, when there is no wood transport. In order to identify the impacts of the main parameters of the study a sensitivity analysis has been carried out. The case study investigated in this paper shows that there is a large gap between the results. The maximum supply distances calculated via carbon footprint and emergy evaluation are about 5000 km and 1000 km, respectively, anthe minimum theoretical wood burner efficiencies are about 5% and 54%, respectively. (C) 2012 Elsevier Ltd. All rights reserved.