In order to meet the environmental regulation due to global warming issues, the new energy resource such as ocean temperature between surface and deep see level or wasted heat resources from power plant have received much attentions as a renewable energy, which is not used in conventional power cycle using a water-steam phase change. Instead, organic Rankine cycle (ORC) based on a properly selected refrigerant can be used for power generation by utilizing the relatively hot source from cooling water from conventional power plants, internal combustion engines and industrial processes. To operate ORC cycle in low temperature difference, a proper selection of working fluid is very essential to design the ORC system for industrial application. However, the selection of working fluid is currently very limited due to ozone depletion by CFC as well as global warming issues by CO2 emission. Under new regulations, we should design and select appropriate refrigerants which can meet the environmental regulation for lower global warming potential (GWP) and lower ozone depletion potential (ODP). In this study, the convective heat transfer coefficients of single, binary or ternary refrigerants were studied through a pool boiling test. Also, the selected refrigerants were tested by lab scaled ORC system.