建築に関わる木質バイオマス循環のエントロピー評価の試み

<p> This paper describes the trial and its results of entropy analysis on wood biomass circulation relating building. The reason for conducting an entropy evaluation is that the circulation of working matter and entropy disposal obtained from that are the indispensable requirements against the sustainability of all the working systems. The purpose of this paper is to show the methodology of entropy analysis on wood biomass circulation relating building and characteristics and requirements on biomass circulation based upon entropy.</p><p> The wood biomass circulation system was assumed to be composed of five subsystems: forest subsystem, logging subsystem, timber production subsystem, biomass-fuel production subsystem and biomass-fuel combustion subsystem. The amount of carbon dioxide and water vapor emission from the biomass-fuel combustion subsystem was assumed to be the same amount of those to be used for photosynthesis in the forest subsystem. This assumption enables us to articulate matter balance from wood biomass to carbon dioxide and water vapor and their vice versa as the working matter in wood biomass circulation like water circulation in closed loop. The authors calculated matter balance, energy balance and entropy balance in all the subsystems. We also developed an approximate formula for calculating absolute entropy of wood biomass which has no chemical formula.</p><p> The results obtained from this study are following.</p><p> 1) The developed approximate formula for calculating absolute entropy of wood biomass enables us to estimate absolute entropy of high molecule-organic compounds like wood biomass with high approximation accuracy.</p><p> 2) Modelling biomass circulation with the same output of carbon dioxide and water vapor in biomass combustion subsystem as input of those in forest subsystem, it was found that entropy of biomass is much smaller than other materials in working matter of the wood biomass circulation in spite of used material and utilizing wood biomass as low-entropy fuel can make biomass circulation complete as one closed loop.</p><p> 3) If both material and thermal use of wood biomass are not realized, total entropy disposal becomes much smaller than that in case with material and thermal use of wood biomass, even though the amount of entropy contained by combustion gas of wood biomass are compensated with wood biomass circulation.</p><p> 4) If the care condition of forest becomes bad, the absolute entropy storage gets beyond 0.222 GJ/K in the forest subsystem.</p><p> 5) On one hand, the share of thermal flux entropy in total entropy input is 9.9 % in forest subsystem. On the other hand, that in output is 60.1 %. The share of thermal flux entropy in total entropy output becomes larger than that in total entropy input in forest subsystem.</p>