Previous modeling work on a novel heat-driven refrigerator has generated overall COP numbers in the range of 0.45 using pure helium gas. The modeled conditions are for commercial or air-conditioning cooling temperatures, with a hot drive temperature of 400 °C. The method used for these results involved the manual optimization of a modest number of engine parameters. New modeling work utilizes optimization algorithms in conjunction with a larger parameter set. A more aggressive choice of operating conditions including binary gas mixtures and higher drive temperatures are also explored, resulting in much higher overall COP values. [Work supported by the Office of Naval Research.]