I have a garage-workshop, that I have (years ago) insulated and put in a window-type air conditioner. It's quite air tight and well insulated. I live in Los Angeles, so it gets hot during the day and frequently quite cool at night. It bugs me that my AC runs all day and into the evening after it's siginificantly cooler outside than in. I want to keep the place "sealed", as I also need to keep the room dehumidified for my machine-shop type tools so they won't rust, and so during the day I'm not letting in lots of hot air.

My thought is to test the temperature and humidity outside and inside and when it's not too humid, and the temperature differential is right, open a vent high in the wall at the peak under the roof, and another lower and either let convection do it's thing, or have a fan help it along. The electronics are not a problem, I can handle that part, and it will be fun.

My issue is that I wand a smallish (no bugger that say 18" square, preferably more like 12" square) electrically operated vent that seals pretty well when it's closed, for both the in vent and the out vent. I've looked on Amazon, and not really found what I want, and can't seem to find anything. Some attic fans (Gable fans I think they are called) sort of blow open the louvers, but they are generally pretty big, and they don't have to seal so well, it's just an attic. As far as I can tell, bathroom vents just stay open to the outside, and that doesn't solve my incoming air issue either.

Any ideas or sources would be appreciated.