<http://schema.org/about>
"One of the most important components of a tightly sealed house or a super-sealed Passive House is a fresh air system. Often they are heat recovery ventilators, and others have used earth tubes running under the home or in the garden. Japan's Geo Power"^^<http://www.w3.org/2001/XMLSchema#string>
<http://www.treehugger.com/sustainable-product-design/geo-power-system-preheats-and-precools-the-air-with-a-vertical-earth-tube.html>