SUMMARYHeating and cooling energy requirements for buildings are usually supplied by separated systems such as furnaces or boilers for heating, and vapor compression systems for cooling. For these types of buildings, the use of combined cooling, heating, and power (CCHP) systems or combined heating and power (CHP) systems are an alternative for energy savings. Different researchers have claimed that the use of CCHP and CHP systems reduces the energy consumption related to transmission and distribution of energy. However, most of these analyses are based on reduction of operating cost without measuring the actual energy use and emissions reduction. The objective of this study is to analyze the performance of CCHP and CHP systems operating following the electric load (FEL) and operating following the thermal load (FTL), based on primary energy consumption (PEC), operation cost, and carbon dioxide emissions (CDE) for different climate conditions. Results show that CCHP and CHP systems operated FTL reduce the PEC for all the evaluated cities. On the other hand, CHP systems operated FEL always increases the PEC. The only operation mode that reduces PEC and CDE while reducing the cost is CHP-FTL.
This article presents a second-law analysis for the use of organic Rankine cycle (ORC) to convert waste energy to power from low-grade heat sources. The organic working fluids were selected to investigate the effect of the fluid boiling point temperature on the performance of ORCs. The working fluids under investigation are R134a, R113, R245ca, R245fa, R123, isobutane, and propane, with boiling points between 243 and 48 °C. The results are compared with those of water under similar conditions. A combined first- and second-law analysis is performed by varying some system operating parameters at various reference temperatures. Some of the results demonstrate that ORC using R113 shows the maximum efficiency among the evaluated organic fluids for temperatures >430 K; R123, R245ca, and R245fa show the best efficiencies for temperatures between 380 and 430 K; and for temperatures <380 K, isobutane shows the best efficiency. Also, it is shown that the organic-fluid boiling point has a strong influence on the system thermal efficiency.
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