Passive houses are homes that are warm enough in winter (even in snowy climates such as Germany) and cool enough in summer but require little or no energy for heating and cooling.  The key is in the design – air flows are carefully managed and insulation is extra-good. Think about it this way — we want fresh air to come into our houses so they don’t get stuffy, but as we exchange our stale air for new air in the winter time, we don’t want to also lose heat. Passive houses use a heat exchange wheel so that outgoing air transfers its heat to the incoming air. Check out the details in this great diagram. http://www.nytimes.com/interactive/2009/04/30/business/energy-environment/20090430_businessofgreen_house.html?ref=businessspecial2

From Treehugger, you can also get a clarification on the official designation awarded by the PassivHaus Institute, which sets standards for homes to meet, in the same vein as LEED. http://www.treehugger.com/files/2009/05/passive-design-not-passive-house.php As the bar graph about half-way down illustrates, meeting this standard represents a tremendous energy savings over a normal house. To see the savings of good insulation visually, check out this thermal photo comparing a passive house to a normal house in the background. http://greenlineblog.com/passive-house-passiv-haus-building-standard/ (Again, you need to scroll about half-way down.)

There has been a lot of discussion on renewable energy lately and about whether renewable can provide enough energy to meet our demand. I think passive houses illustrate just how flexible and elastic that demand could be.