They are also ideal for humid climates. As the outside air passes through a fine mist of water, it gives up much of its heat through evaporation. In direct evaporative systems, the evaporation process humidifies the air. In indirect evaporative systems, the evaporation process is isolated from the air stream, and uses a heat exchanger to cool the air. The Rankine-cycle cooling process uses a vapor compression cycle similar to that of a conventional air conditioner.
Solar collectors heat the working fluid, which has a very low vaporization point.
The working fluid then drives a Rankine-cycle heat engine. This technology, however, is mainly experimental, and is not used often because it needs a large system size to do any meaningful amount of cooling. It is possible to design a PV array to provide some or all of the electricity to operate these types of systems. Systems used for vaccine refrigeration are becoming widely used in remote areas of developing countries. 10-12, December 2000.