In some areas, they do open up community service buildings for the homeless in times of severe cold and heat. However, I have never seen a jail or prison do it.

I couldn’t imagine it would be worth the security risk since we’re talking a building that’s supposed to be pretty secure, and you can’t just have people entering and leaving it willy-nilly. That requires upkeep costs and staffing to be able to control and that doesn’t come free.

I guess they could convert visitation areas if it has it, but that’s going to restrict actual prison operation. But it’s not like they can just have them go in the empty cells because those cell blocks are still going to be inhabited by other prisoners. And they can’t just have civilians wandering a secure facility like that.