He also hasn't said much about energy consumption. He's said a great deal about how well his supposedly undersized system keeps his house comfortable.
We tend to get overly hung up on energy costs, IMO. Comfort drives energy costs. If people aren't comfortable, they'll run their HVAC into the ground to get comfortable, and faint when the high bills come since they can never meet their goal.
Paul has an advantage over many of us. Should the electrical grid drop power to his house in the dead of winter or on a 110 degree day like we had yesterday, he's not immediately in a world of hurt. Unless he has a backup generator, he could probably coast through the cold or heat until power can be restored without a great deal of discomfort.
What Paul has, over and above low energy cost, is a house that is truly a shelter in more ways than one. Not only will it keep him dry, it keeps him warm and cool easily. I also suspect he does not live in a cave. When you begin to understand what makes buildings that are difficult and costly to heat and cool be that way, you begin to realize it's not always what folks want to blame for being the culprit. And sometimes it's a combination of the obvious and less obvious. That is why energy audits can have value, but if I had my way they'd be called "comfort audits", because low bills are just one source of comfort. Peace of mind that your house won't freeze you to death or kill you via heat stroke is another form of comfort.
As one who participated in earth-sheltered housing concepts in my younger days, there are good and bad examples of this concept, as is true with anything. If you want an example of an early prototype berm home that was light and airy, check this one out:There's no free lunch. You cna live in a berm home and have very low bills and low constructon costs, but then you have to live in a berm home... a cave.
This house was designed by Frank Lloyd Wright and built in the 1940's. Some would say it's a bit heavy on glass, and on cloudy winter days that might be an issue, but think about when this house was made, and what could be done with current technology.