Modeling and unit-cost optimization of a water-heated humidification-dehumidification (HDH) desalination system were presented in previous work of the authors. The system controlled the saline water flow rate to prevent salts from precipitating at higher water temperatures. It was then realized that this scheme had a negative impact on condensation performance when the controlled flow rate was not sufficiently high. This work builds on the previous system by disconnecting the condenser from the saline water cycle and by introducing a solar air heater to further augment the humidification performance. In addition, improved models for the condenser and the humidifier were used to obtain more accurate productivity estimations. The Heuristic Gradient Projection (HGP) optimization procedure was also refactored to result in reduced number of function evaluations to reach the global optimum compared to Genetic Algorithms (GA’s). A case study which assumes a desalination plant on the Red Sea near the city of Hurghada is presented. The unit-cost of produced fresh water for the new optimum system is $0.5/m3 compared to $5.9/m3 for the HDH system from previous work and less than the reported minimum cost of reverse osmoses systems.Copyright © 2014 by ASME