Organic Rankine cycles are innovative power cycles which allow good performances for low enthalpy thermal sources and ensure condensation above the atmospheric pressure, thus avoiding deaerators and large cross sectional area in the heat rejection units. Moreover, with respect to steam Rankine cycles, ORC have a higher flexibility in handling low power sizes, allowing significant compactness. Typical applications of ORC cover: waste heat recovery plants, geothermal plants, biomass plants and waste to energy power plants.