Methods for converting heat into mechanical energy and/or useful heat

A method of utilizing the heat content of a heated carrier agent in response to variations in predetermined atmospheric temperatures comprising indirectly contacting said heated carrier agent with a working fluid having a boiling point lower than that of water, said working fluid being maintained at a predetermined elevated working fluid pressure, thereby vaporizing said working fluid, producing mechanical energy by expanding said working fluid to first and second reduced pressures, said first reduced pressure comprising the condensation pressure of said working fluid corresponding to said predetermined atmospheric temperature, and said second reduced pressure comprising an intermediate pressure between said predetermined elevated working fluid pressure and said condensation pressure, separating said working fluids into first and second working fluid streams comprising said working fluids expanded to said first and second reduced pressures, respectively, condensing said first working fluid stream by indirect contact with the atmosphere at said predetermined atmospheric temperature, condensing said second working fluid stream by indirect contact with a liquid heat carrier so as to produce useful heat therefrom, and pressurizing said first and second working fluid streams to said predetermined elevated working fluid pressure.