A method and system using at least two different working fluids to be supplied to an expander to cause it to do mechanical work. The expander is started by providing a compressed gaseous working fluid at a sufficient pressure to the expander. At the same time the compressed gaseous working fluid is provided to the expander, a second working fluid that is liquid at ambient temperatures is provided to a heater to be heated. The second working fluid is heated to its boiling point and converted to pressurized gas Once the pressure is increased to a sufficient level, the second working fluid is injected into the expander to generate power, and the supply of the first working fluid may be stopped. After expansion in the expander, the working fluids are is exhausted from the expander, and the second working fluid may be condensed for separation from the first working fluid. Control circuitry controls the admission of the first and second working fluids responsive to monitoring the load on the expander.Waste heat in the exhaust from the expander can be used to heat or alternatively to dry an element in a device that can be operated as a desiccator to dry air when operated in a summer mode, or to heat air when operated in a winter mode. The air having been dried or alternatively heated is then ducted to an evaporative cooler which cools the dried air in summer mode and humidifies the heated air in winter mode.