Energy, economic, and environmental analysis of combined heating and power-organic Rankine cycle and combined cooling, heating, and power-organic Rankine cycle systems

Abstract

Combined heating and power (CHP) and combined cooling, heating, and power (CCHP) systems generate electricity and usable heat on-site from one fuel source while organic Rankine cycles (ORC) generate power from low-temperature heat sources. During the operation of CHP and CCHP systems, there are many instances when the recovered exhaust heat is greater than the required thermal load of the building. In these situations, an ORC can be used to capture the excess heat in order to produce additional electricity. Therefore, combining an ORC system with a CHP system (CHP-ORC) or a CCHP system (CCHP-ORC) can further increase the fuel utilization of the system, thereby reducing the operational costs, primary energy consumption (PEC), and carbon dioxide emissions (CDE). This article examines the economic, energetic, and environmental performance of CHP-ORC and CCHP-ORC systems under the operational strategies of follow the electric load (FEL) and follow the electric load with the option of turning off (FEL/OFF) for the city of Boulder, Colorado. Their performance is compared to a stand-alone CHP and CCHP system, respectively, between systems, and to a reference building. Results show that under the FEL operation, the addition of an ORC to either the CHP or CCHP system lowered the operational costs, PEC, and CDE by about 12 per cent, 13 per cent, and 17 per cent, respectively, from the standalone system. In addition, only when the systems operate FEL/OFF strategy minimizing cost or PEC, the cost and PEC could be reduced below the levels of the reference building.