This paper covers the thermodynamic and techno-economic optimization of ORCs for low-to-medium temperature heat source applications, when ammonia, propylene, R152a and R32 are used as cycle working fluids. Results were obtained for a varying hot source inlet temperature, from 120°C to 250°C, and different capacity power plants, showing that the most efficient ORC power plants always had a higher Specific Investment Costs (SIC) for the studied cases. Large capacity power plant (power output between 1 and 2.5 MW) are more expensive than the small-capacity ones (power output below 1 MW) but the SIC of large capacity systems can be half of that of small-capacity systems. Minimizing the SIC of ORCs tends to higher evaporating and condensing temperatures than the ones that result from the thermodynamic optimization.
Keywords Organic Rankine Cycle, heat exchanger, shell and tube, plates, second law, exergy, efficiency