Can I use in a room without a window?

Evaporative cooling works by drawing in hot, dry air, and fanning out cooler, somewhat moister air. After a while, though, your room will need ventilation or a cross-breeze to circulate the more humid air out the room and restart the process with dry air. It doesn’t necessarily need air from outdoors, but it does need some type of airflow to keep the cooling action moving. Check out this blog post for more on this.