Abstract
A comprehensive thermodynamic study is conducted of a diesel based Combined Heat and Power (CHP) system, based on a diesel engine and an Organic Rankine Cycle (ORC). Present research covers both energy and exergy analyses along with a multi-objective optimization. In order to determine the irreversibilities in each component of the CHP system and assess the system performance, a complete parametric study is performed to investigate the effects of major design parameters and operating conditions on the system’s performance. The main contribution of the current research study is to conduct both exergy and multi-objective optimization of a system using different working fluid for low-grade heat recovery. In order to conduct the evolutionary based optimization, two objective functions are considered in the optimization; namely the system exergy efficiency, and the total cost rate of the system, which is a combination of the cost associated with environmental impact and the purchase cost of each component. Therefore, in the optimization approach, the overall cycle exergy efficiency is maximized satisfying several constraints while the total cost rate of the system is minimized. To provide a better understanding of the system under study, the Pareto frontier is shown for multi-objective optimization and also an equation is derived to fit the optimized point. In addition, a closed form relationship between exergy efficiency and total cost rate is derived.
Highlights
Efficiency improvement of energy systems has been a focus among researchers and designers during the last few decades
Performance assessments of different working fluids are conducted to see the effect of the different fluids on exergy efficiency of the diesel engine Combined Heat and Power (CHP)
In this study the exergy efficiency, total exergy destruction and total cost rate of the CHP system are calculated for different working fluids
Summary
Efficiency improvement of energy systems has been a focus among researchers and designers during the last few decades. Alanne et al [18] conducted a study to determine optimal strategies for the integration of a sterling engine based micro cogeneration system in residential buildings by comparing the performance of various system configurations and operational strategies with that of a reference system, i.e. hydraulic heating and a low temperature gas boiler in standard and passive house constructions located in different climates. They suggested that an optimally operated micro-cogeneration system encompassing heat recovery and appropriate thermal storage would result in 3–5% decrease in primary energy consumption and CO2 emissions when compared with a conventional hydraulic heating system.
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