As heavily populated countries like China, India, and Brazil become more affluent, the demand for air conditioners is rising with the oceans, and creating the energy to run those chill machines for many millions of homes will be difficult and climatically expensive.

Sustainability researcher Michael Sivak on NPR’s Science Friday estimates that the potential demand for energy to cool Mumbai, India, based on the city's large population and high temperatures, would equal a quarter of the energy used to cool the entire United States. He suggests that AC units could be designed with much more efficiency, and that other countries please not adopt the uniquely American need for extra chilly homes and offices, where many workers bring jackets in July to keep their teeth from chattering.

Also on the show was Kiel Moe, a professor of architecture and energy at Harvard, who discussed new – and very old – ways to more sustainably keep our cool. Many hundreds of years before modern air conditioning was invented by Willis Carrier in 1902, man has been using building and design techniques to control heat. Professor Moe suggests we revisit these strategies, augmented with current technologies, and then get them into our housing design pipeline - both here and abroad - ASAP.

These technologies include:

Thermal mass - the ability of a material to absorb and store heat energy. A lot of heat energy is required to change the temperature of high-density materials like bricks, tiles, and concrete. They are therefore said to have a high thermal mass - the thick walls that kept castles, caves, and adobe houses cool.

Thermally active buildings – this means using the consistently cool temperatures underground for cooling water or air, and also the cycle of dumping heated air out through vents and the pulling in of cooler air. In addition, making use of available breezes and directing them is also an essential part of the thermal activity in a non air-conditioned house.

Thermal flushing – at night when the outdoor temperature and humidity are low enough, homeowners should be able to ventilate the house using cooling chimneys and whole house fans to exchange warmer indoor air with cooler outdoor air. Then, in the morning, close up the house, trapping the cool air inside for the day. For this to be effective, enough operable and properly positioned windows and vents must be provided in the design.

Orientation - if you are building a new house, orienting the building so that more of the windows face south rather than either east or west will control heat. During the summer months far more sunlight enters a house through east or west-facing windows than through south or north-facing windows.

Deep overhangs, eves, and cantilevered designs - south and western exposures benefit from these design elements as the summer sun is much higher in the sky than in the winter — when that sunlight is beneficial for heating. On east and west windows fixed overhangs do not work well for shading, because the sun’s path through the sky is fairly low as it rises and falls during the day. For these orientations vertical louvers, exterior shades and screens, operable awnings, and deciduous plantings can provide effective shading.

Read more about the passively cooled buildings at left via Houzz and Gizmag. Photos courtesy of Houzz and Gizmag.