Exergo-environmental cost optimization of a combined cooling, heating and power system using the emergy concept and equivalent emissions as ecological boundary.

District energy systems, in particular combined cooling, heating and power (CCHP) systems, can provide cost-effective energy products, reduce fossil fuel consumption and emissions. A gas-fired CCHP system is considered here employing an internal combustion engine, whose exhaust gas is split between an organic Rankine cycle unit and absorption heat pump. A simulation model of the system is constructed and validated. An emergy based exergo-environmental cost method is proposed here to optimize the exhaust gas allocation ratio based on specific working conditions considering the equivalent emissions of the whole life-cycle chain from an ecological view. The emergy consumption in each process stage is evaluated accompanied with a sensitivity analysis. The results show that the minimize specific system cost is 310050 seJ/J when 63% of the exhaust gas flows to the ORC-unit. The ICE and AHP are responsible for >98% of the emergy consumption, dominated by the operation of the system. The sensitivity analysis shows that heating is the most sensitive of all products against key parameter variations, while electricity is the least. Increasing the service period and the operating hours, the economic performance could be improved, while the transformity of emission enlarges the cost. • A novel natural gas-fired CCHP system allocating exhaust gas to drive ORC and AHP units. • Emergy based exergo-environmental optimization with ecological boundary. • Equivalent CO 2 and SO x emissions in life-cycle chain. • Sensitivity analysis against crucial parameters. [ABSTRACT FROM AUTHOR]