Try posting your question to the Green Building Advisor Q&A section. (http://www.greenbuildingadvisor.com) . You'll get feedback from some really knowledgeable energy efficient building folks.

Hi Margaret, sounds like a fun project. Creative design and aesthetics aside, I think you are right to be concerned about the description of your passive solar design. To me, it sounds like an outdated form of passive solar and is similar to many of the Earthship designs. I agree that the double wall or sunspace, blocks your connection to the outdoors, needlessly complicates the architecture and usually leads to more problems than it solves. A detached or partially attached greenhouse would be a better fit for such a space IMO.

There are some climates and times of year that the solar chimney concept can work great but I think humidity is the bigger concern and would rather close the house up tight, air-condition and utilize an HRV/ERV for outdoor air ventilation most of the year. Even with the solar chimney concept, properly placed operable windows are almost as effective at much reduced cost. You could probably put the extra expenses of your sunspace into a PV system that would offset your AC, perhaps even getting you close to net-zero.

Good passive solar design is not much different than conventional designs and should most importantly rely on proven airtightness (with a blower door test) and international code or better insulation. They use high SHGC glass at 5-12% south window to floor area and use simple overhangs for summer shading. Minimal windows on east and especially west with a reflective roof finish are often as important as the free winter heat gained by the south facing windows.