There are too many variables to consider in order to give you direction, however, I suggest you consider reviewing your heating and AC system as well as your building construction and insulation first...size of equipment, amount of outlets, location of outlets, possibility of separate zone for the room, etc. etc. Call in a couple of professional HVAC contractors for advice.

If you have caulked your doors you may be realizing a "draft feeling" due to conduction of cold/heat through the glass and if your door frames are metal, the conduction is increased. A knee wall will not do anything for this condition.

As you can see, your solutions will most likely be a combination of several approaches to best handle the circumstances.

Your dining room is quite inviting!

I'll take a new photo-the window coverings have all been removed and changed to filmy organza panels and we lost our insulation in the process. The cabinets to the right are going to be relocated exposing more glass, too. Great for light, lowsy for temp control. I want to frost part of the window using a relief method to put our logo and restaurant name on the glass-I think that will provide some shade. We lined the walkway with patio umbrellas on the afternoon sun side too.

This is the configuration we are leaning toward today.