I know that you indicated post and timber, but I would recommend looking very carefully at the envelope and shell options. Regardless of your heating system, 30 percent of the heat is lost to ?infiltration,? or cracks in the envelope, so you would be best served by building the most efficient shell possible. I would guide you toward Insulating Concrete Forms (ICFs) or Structural Insulated Panels (SIPs). Once the shell is as efficient as you can make it, you can finish the interior walls and space with post and beam or timber framing to give it the architectural feel you are seeking.
When designing your new home for maximum energy efficiency, pay attention to the following elements, in this order: the primary envelope (walls and roof); the windows; the floor; and the heating, cooling and electrical systems.
Here is a list of great resources for learning about passive solar design and energy efficiency.
For more information:
"Passive Solar Design for the Home," a guide from the Energy Efficiency and Renewable Energy Clearinghouse
The Department of Energy?s Building Toolbox (information on site planning, passive solar design, building envelope design, and more)
Whole Building Design Guide (This site is a little more commercial, but includes lots of useful information. Get started by searching for ?daylighting,? ?passive solar? and ?windows and glazing.?)
The government-sponsored Energy Star program (information on energy-efficient appliances, air sealing and insulation)
Build Central?s Green Building Talk forums (topics include ICFs and SIPs, as well as a general green building forum)