Earth Tubes: Low Tech, Low Energy
Brian Jonas at Greenline, the great sustainability blog from Ziger/Snead Architects, shows a great picture of an earth tube being installed at the Aldo Leopold Legacy Center. Earth tubes are the dead-simple way of bringing fresh air into a building at a reasonable temperature- just run the air through pipes buried in the earth, cool in summer and warm in winter. Result: it comes out at a nice, comfortable temperature. Unfortunately it is a nice temperature for mildew and bacteria, not to mention a great place for animals to nest; Brian notes that "Ductwork or pipes rated for underground use are employed, the ducts must slope to drain to avoid water and mildew build-up and additional filtration is sometimes required to eliminate mold and bacteria." Radon buildup can also be a problem, so they need to be tightly sealed. ::Greenline
, good Wikipedia coverage too.