It's not unusual for the first bean flowers not to set - it's almost as if the bees take a while to learn how to enter them, and thereby 'trip' and pollinate them (there are in fact some species whose tongues are too short to reach the nectar, so they chew through the back of the flower instead, which doesn't therefore get pollinated.)
Some say that misting with water helps flower set, but I've also heard that doing that actually deters bees, which still need to visit the flowers to set them.
It's probably more important to keep the plants themselves well watered.
Not much help to you this year, but there are some varieties whose flowers set without the help of insects - 'Firestorm' is an example.
Hope your luck improves soon.