The problem of designing a crude distillation unit (CDU) is not only a distillation design. It has the added complexity that the properties of crudes are different around the world, sometimes from heavy to light. In this work, we focused our attention on designing a predistillation scheme suitable for heavy crude oils by thermodynamic analysis. The exergy efficiencies and losses were analyzed to evaluate available schemes indicating that the two-preflash-drums case, with the highest exergy efficiencies, lowest exergy losses, and lowest furnace duty, is the best choice for heavy crude oils. In addition, the method of selecting the optimum process for energy saving may benefit the process optimization of other distillation units.