There are several alternatives to conventional compression refrigerant-based air conditioning which consume less electricity/energy per unit of cooling power produced.
Evaporative coolers consist of a fan and some water-soaked material. Air blown by the fan passes through the water-soaked material and is cooled by the water before being blown into the room or building. Evaporative coolers work best in hot dry climates (where air humidity is low). Both centralised systems and units for individual rooms are available.
How an evaporative cooler works.
The strength of the cooling effect provided by evaporative coolers depends on temperature and relative humidity. For example:
Outdoor air temperature 32 °C + 15% relative humidity → indoor air temperature about 16 °C
Outdoor air temperature 32 °C and 50% relative humidity → indoor air temperature about 24 °C
Outdoor air temperature 40 °C and 15% relative humidity → indoor air temperature about 21 °C
Diagram of an ancient Persian wind tower and qanat, used for evaporative cooling of buildings. Air is drawn into the tunnel at some distance away and is cooled both by contact with the cool tunnel walls/water.
Geothermal cooling (geothermal heat pumps) systems transfer heat to the earth or a body of water, either directly or via a heat exchanger, drawing it from a building by circulating air or via a network of pipes embedded in floors, walls or ceilings (radiant cooling).
Example of a geothermal heat pump cooling a building.
Sorption chillers, both ABsorption and ADsorption, which use a thermal compressor instead of a mechanical compressor, can offer an efficient solution if a source of waste heat available. These can also be powered by a solar thermal system using evacuated tube solar collectors, and can supply a building with cool air and cold water, and cold for refrigeration. Systems are large, ranging from 10kW to 5MW power output. Several cooling technologies are used: absorption, adsorption, and solid and liquid desiccant cooling.