Performance assessment of cogeneration plants

In this paper, performance assessment of various building cogeneration systems is conducted through energy and exergy efficiencies. The cogeneration plants considered include steam-turbine system, gas-turbine system, diesel-engine system, and geothermal system. Here, the cogeneration operation refers to the simultaneous generation of electrical power and heating for buildings (especially for space heating and hot water). Selected actual operating data are employed for analysis and performance assessment. The same amount of electrical and thermal product outputs is considered for all systems, except the diesel, to facilitate comparisons. Also, the effects of certain operating parameters (e.g., steam pressure, water temperature) on the energy and exergy efficiencies are investigated. The diesel-engine and geothermal systems appear to be thermodynamically more attractive, in that they have higher exergy efficiencies, than steam-turbine and gas-turbine systems. The results demonstrate that exergy analysis is a useful tool in performance assessments of cogeneration systems and permits meaningful comparisons of different cogeneration systems based on their merits. Such results can allow the efficiency of cogeneration systems to be increased, and the applications of cogeneration in larger energy systems to be configured more beneficially, leading to reductions in fuel use and environmental emissions.