Long before there were air conditioners, ancient builders tinted or painted roofs and walls light colors to reflect the sun’s warming rays back into space. These old homes also had thick, dense walls. The walls would absorb indoor heat by day and release it to the outdoors, slowly, at night. That slow release kept indoor air from getting too cold.

Clever roofing, walls and vents cool by moving heat and air — without electricity.

Before air conditioners existed, architects used passive cooling for homes in hot and dry regions. Even large structures stayed cool, like this Taos Pueblo built by Native American architects in the 14th century. New studies have updated this technology for cooling in hot and dry climates today.

Utah’s Zion Canyon Visitor Center (left) has natural venting and almost-passive cooling. Hot air enters the top of two cooling towers. Water pumped through pads inside the tower cools the air. Cooled air sinks to the lobby, keeping visitors comfortable. The idea borrows from Iranian windcatchers (right).