Lindsey Schiller wrote:Jim -- and Peter --
I've worked with a lot of greenhouses professionally and seen first hand how difficult it can be to control their climates. Most glazing materials (glass or plastic) are so hugely incredibly inefficient compared to a wall, building an attached greenhouses with no separator is a lot like asking for a climate burden on the home (particularly in Arizona. I think there are more justifications for Michigan). So I would always recommend a separator like sliding glass doors and leave them open when it's nice out. BUT if you realllly want the open floor plan concept, there's a few things you can do:
1. add a ton of thermal mass in the greenhouse. You want something extra to absorb the excess heat, other than the air of your home. A partial trombe wall between the spaces would be interesting here. I don't have any examples, but have always thought it would be a great idea.
2. Upgrade to really good glazing materials... worth the investment for your future heating cooling bills. Amory Lovins greenhouse / home uses an R-14 windows! Maybe you don't need to go that far, but choose a glazing that is as efficient as possible.
3. As Kit already said Jim should be using an insulated roof, or heavy shading cloth to control heat gain. Basically, alter the structure to reduce direct light into the home. Be sure to make a sketch of the greenhouse with solar angles for different times of the year to ensure you are not getting a ton of direct heat gain into the home in the summer.
The one successful example of an integrated floor plan / greenhouse I have seen is Amory Lovins home from the Rocky Mountain Insitute. I write about it as a case study in my recent book
The Year Round Solar Greenhouse
I'd also recommend the book for other tips... I have a chapter on attached greenhouses and how to build them successfully.