The Solar Transformity of Power and Heat in Combined Heat and Power Production

Power and heat are the primary energies for the industry and communities. Combined heat and power (CHP) is a process of heat and power cogeneration, which is designed to meet the needs of both users. In previous studies of emergy analysis on CHP, the transformity was simply calculated by dividing the total emergy input by the amount of production. The result always showed that transformity of electricity is lower than the transformity of steam, which is not logical since electricity is thermodynamically higher value energy than heat. Neither can it illustrate that the co-production process is more efficient than an independent one because The efficiency of co-production is calculated by considering the available energy of the two products together and comparing it with the available energy of the electricity only in another plant. According to emergy analysis rules, the emergy is thought to be the energy history that cannot be separated for inseparable co-production. However, if the product can be produced separately in the system, the emergy could be split. In principle power and heat can be produced independently in CHP plants. We could argue that CHP can be considered as a separated production. The possibilities in splitting the emergy by different alternatives are discussed. A biomass-based CHP plant is analyzed as a case study for emergy division by exergy and maximum production. The results provided reasonable transformities of electricity and heat in CHP plant.