Some units have some form of air-conditioning, many don't. When it's hot out, they're hot. And it's usually recirculated air laced with concrete dust and other particles. The exercise yard is not really a yard. It is a concrete box covered by wire so thick rain barely seeps through, even during a downpour.
Prisoners never see a tree or a blade of grass.
This is the only place where they are exposed to a little sunlight.