I sometimes have to use my AC even in winter! My apartment building has reinforced concrete floors with in-floor radiant heating. My upstairs neighbour used to keep his apartment toasty-warm (~25C), and since that is the ceiling of my bedroom, I would use the AC to cool the room to about 22C. It's too noisey in my neighboorhood to sleep with the windows open. Of course I never have to pay to heat my apartment in winter either!

John