If you've traveled out of country, you've definitely seen those funky air conditioners/heaters mounted on the walls of apartments in, say, France, or somewhere in Asia. Those with a curious mind may also wonder how they work. I know I did when I first encountered one in a vacation rental in Provence. It wasn't a window unit, so there was seemingly nowhere for any air to draw from.
But HVAC systems not exactly being my primary concern while eating my way across France, I didn't give it much thought.