This is a fairly basic idea -- if the temperature in your house (or room, in the case of a window unit) is hotter than the temperature outside, then the cheapest way to cool your house/room off is with a ventilation system -- a whole house exhaust fan, or a window fan.
If the temperature in your house or room is higher than the temperature outside, then the unwanted heat must be forced outside by means of an air conditioner.
I would like a device with a thermometer inside and a thermometer outside, which can compare the two temperatures and cool the room in whichever way is more appropriate.
Since I live in a rented room, I'd prefer that such a device exist in window-mountable form, similar to a window fan or window AC.-- goldbb, May 27 2010 This is [widely-known-to-exist], [goldbb].
"Smart" Heat/Cool/Suck/Blow A/C units have been around since the 1970's.
We suggest you delete this, lest it become a repository for fishbones and MFD's.-- 8th of 7, May 27 2010 random, halfbakery