Unheated - What Do I use It For?

"would just a couple of french bean plants be the same"

I have had Dwarf French beans that have sat there and done nothing (probably through lack of watering outside though) but when they have grown they crop surprisingly heavily for such a small guy!

Half a dozen plants crops like a medium length row of climbers (generalising a bit ...)

You could also try growing climbing French beans in the greenhouse if you are tight for space? I grew some for an early crop this year, but all I got was leaf - I reckon there was too much manure in my greenhouse border ... so this Autumn I'm trying both Dwarf and Climbing French. I reckon the dwarf can't keep on growing if there is excess Nitrogen, so they will have to fruit!! I'll keep you posted ...

(French beans, unlike Runners, don't need pollination to set pods, so are better suited to greenhouse)