It has been very hot in San Jose the last few days. One solution is air conditioning, which we have and sometimes use. The other is to open the windows in the evening, when it cools off, close them in the morning. Sometimes–last night, for instance–that cools the house faster than air conditioning. And it doesn't show up on our electric bill.
I have long wondered why there isn't an automated version available, or if there is and I haven't come across it. It would be easy enough to have an insert for a window that was controlled by a simple thermostat. If the inside temperature is both above your optimal and higher than the outside temperature, open to let air in, if not close. A few such inserts should do, automatically and more reliably, what we do by hand. For an improved version, provide the insert with a fan--that uses some power, but much less than an air conditioner.
Does anyone know of a commercially available version of such a system for home use? Alternatively, am I missing some reason why it isn't as good an idea as I think?