The technology has advanced since then, now white paints with high emissivity in the infrared window are being researched. So if you cover the entire building with that you would get some free, always-on cooling that way.
- the humidity has to be comfortably low
- the outside temperature has to be low enough
Historically, this is usually the case.
In the last few weeks, I've had one or both of those fail to apply on the majority of nights. Dropping to 65F doesn't help when the outside air is also at 99% humidity. If the overnight low is 75F, we're not getting much cooling out of it.
I dream of getting a geothermal heat pump for my 1850s farm house which is normally heated with two wood stoves but has a propane backup. (e.g. the kind of compact heater that you see all the time in people's apartments in anime)
At points south the capacity of that kind of system is set by cooling demand but where I live it is set by heating demand. The woodstove could pick up the slack on the coldest days, but that defeats the main selling point of the heat pump which is extreme comfort (e.g. it switches seamlessly from heating to cooling)
Between pollen count and pollution this is not always the case, and keeping the windows closed and running both the AC and an air filter unfortunately has health benefits for some individuals.
Given that I only have one portable fan, what is the best setup at night if it is colder outside than inside:
1. Open the windows and put fan so that it blows air out of one window
2. Open the windows and have fan mix the air inside the room
3. Open the windows and put fan on balcony to blow air from outside in.
I would suspect you will also see different results depending if you have multiple windows or just 1. For example, if you have more than 1 window and can seal the opening except the fan, then the fan will move x amount of air in or out and will have similar results.
Simply mixing the air inside the room seems like it's probably the least effective because it will result in very little heat exchange at the windows themselves. However, making the temperature within your house more even may make it more comfortable on the average inside your house.
Seriously though, it depends. If you have no other way to intake or exhaust air, probably 3, since fans are more effective at blowing than sucking. (IE: 1. would spend some of its power recirculating inside and outside air rather than just pulling inside air out.)
Most likely your bathroom and hopefully stove have exhaust fans, so even better would be to turn one or both of those on, and have the fan blow in a window on the opposite side of the house. It may not even be ideal to open all the windows. You want cool air flowing through the whole house. In an extreme example, if you have the fan blowing in the balcony and an open window right beside the balcony, it could just circulate air there, rather than reaching the rest. Likewise with exhaust, if you have a fan in the bathroom and the bathroom window open. So you'd need to experiment a bit to see what flows air best through the house.
Things also change if you have a central blower.
> Experiments and anemometer measurements to figure out where to best place a fan to optimally air out the house to cool it down at night.
- Blowing out is better than blowing in.
- Fan should be some distance to window otherwise it is ineffective.
The premise is...cooler air falls, warmer air rises. You want to blow in the low(cool) elevation air, and exhaust the high(warm) air.
I got decent cooling results with two separate window fans, opposite sides of house, one blowing in one blowing out. Of course, all other windows are closed.
Depending on your window frame style, these types of dual fans fit inside a window frame and don't leak air. They can be set to: both in, 1 in 1 out, both out. So quite flexible. https://www.amazon.com/Bionaire-BW2300-N-Reversible-Airflow-...
A single window fan of the above style can cool a single room quite well, blowing cool air in and blowing hot air out.
As others have mentioned, depending on breeze and temperature, opening all the windows can sometimes work better than multiple fans.
Fans are just no substitute for a real AC unit, which can lower indoor air temp to below outside air temp and can also extract moisture from the inside air.