I know we gripe about the weather, but we actually have a very mild climate here. It never gets very cold and we get plenty of rain. I know we don't get a huge amount of sunshine, but that doesn't mean we can't grow grapes and make wine.
I have heard of vineyards in Munster (as well as in the UK where the climate is similar) and while shelter, like walls or fencing helps, I don't think they actually need to be in a greenhouse.