they are insect polllinated, usually by bees ... how many bumbley-bees have you seen in your greenhouse?!
that & the heat & dryness will account for the lack of beans.
live & learn as they say (or pollinate with a paintbrush!) 
 You can set runner beans with a very fine rose  spray on a hose pipe I'vre done it many times when the late bean flowers really took off and the temps dropped to 50 oF.( bees stop flying in any numbers ) . 
Old Mr Digwell  gave me that one years ago ,  so it's back to growing in the green house unless you have trashed them .  If you have auto roof vents like I have insects geting in are no problem but for a precaution I have a rabbits tail on a bit of cane to pollinate  the tomatoes , capsicums, strawberries and aubergines etc. just incase there are a few  areas missed .
 I charged it with pollen from two big bunches of supermarket flowers I purchased for my lass and also gave every weed flower  in the front garden a wee wipe with it before I zapped them with a hefty dose of round up.