Optimal temperature differences in the evaporator and condenser of a refrigeration or Organic Rankine Cycle system based on exergoeconomic analysis.

An increase in the temperature difference in the evaporator and/or condenser of a refrigeration system or Organic Rankine Cycle (ORC), leads in the first case to the increase in the compressor mechanical work consumption and for the ORC, to a decrease in the mechanical work production, accompanied in both cases by the decrease in the heat transfer surfaces. Larger temperature differences in the evaporator or/and condenser lead to an increase in the operating cost of the system but in the same time by reducing the size of the heat transfer surfaces the investment cost decreases. The challenge between the operating cost and the investment one gives the objective function for optimization. For the refrigeration system the objective function to minimize is the total yearly cost of the plant and for the ORC the objective function to minimize will be the unitary cost of the mechanical work produced.