The central air conditioner in the home we purchased a couple years ago is fairly old and is in need of replacement. I do not wish to install a new system, however, since my future remodeling/redesigning of the house needs to come first, and I hope to do a geo-thermal system anyway on the basis of the those changes.
So what to do in the meantime when the upstairs temperatures hit 90 degrees?
My first option was to pull out the window AC unit I bought two years ago from Lowes. It is okay, but inefficient for our needs, as it will only cool the kitchen and part of the living room--leaving the rest of the house pretty hot. Moreover, in order to maintain even these temperatures it has to be running constantly at full blast, which when you see your electric bill becomes something of a shock. In other words, costs clearly exceed the returns.
Yesterday I began experimenting with a variation of an age-old remedy that people used long ago; namely natural convection and air displacement. Our partially finished basement maintains a consistent temperature of 65 degrees F. Upstairs it was 90 degrees F. The question was how to get cold air (which does not rise) to take the place of warm air. Here was (and is) the approach I have taken:
First, we have a whole house fan mounted in our ceiling and centrally located in the house. It essentially draws air from the house and exhausts it into the attic where it exits through the vents in the ends of the house (gables). In cool evenings, the process is simple: open windows around the house, turn the whole-house fan on and the cooler outside air rushes in and displaces the hot air that is being drawn up and out of the attic. No problem.
But what about when the outside air is just as hot or hotter than the air inside the house? You can turn the whole house fan on, but if you open the windows, it becomes even hotter in the house. If you open no windows at all, you are effectively accomplishing nothing except wasting electricity while the whole house fan just churns air with no real movement or displacement.
This is precisely the point at which I desire to get that 65 degree air from the basement to move upstairs where we need it. Since cold air does not rise, the challenge is to guide it efficiently upstairs. Here is what I have done so far to accomplish this:
1. First, turn on the whole house fan. This is the main engine for the process.
2. Close all house windows and lower any drapes to keep sunlight out (eliminate greenhouse effect).
3. I then place a large fan at the bottom of the basement steps at an angle pointing up the steps. In and of itself, this will do very little, as the warm air upstairs is a very effective barrier to any of the cold air coming up and at it. It simple will not penetrate that barrier--unless, I suppose you used a fan with hurricane force winds--sort of a brute-force and inefficient approach (though welding shops and barns often used these industrial sized fans in precisely this fashion).
4. Here is the key: I slightly open the door leading from the basement to the garage. The air in the garage is not as cool as the air in the basement, but it is in fact cooler than what is outside. It is sort of a "staging area" for starting the cooling process. I don't open the door much--only enough to allow what the whole-house fan is displacing upstairs to be drawn in from the garage to the basement. That air in turn begins a stream or current of air, which includes the cool 65 degree air. The stream goes through the basement, up the stairs (with a little assistance from the fan), and into the upstairs living space. The warm air, which ordinarily would block it, is exiting out the ceiling into the attic. Think of the upstairs of our house as a pond, the cool downstairs air as the inlet of cool spring water, and the whole house fan blowing into the attic as the water overflow or outlet.
The results are immediately evident. You have created a vacuum pathway for the cool 65 degree air to flow naturally and displace the hot air upstairs. The vacuum is so strong that my children have a hard time closing doors that they open. There is no wind outside, but if you go outside my garage (I keep all those doors shut so as not to get too much hot air in all at once), it sounds like the wail of a miniature hurricane!
You can then selectively partially open a window (not too many or you lose the power of your vacuum stream). For example, my wife was reading yesterday in our bedroom, so I cracked open the window next to her. Even though there was no wind blowing outside, a rush of air came flowing in and over her. Since moving air cools us (i.e., wind chill factor), it was the equivalent of a nice strong breeze blowing on her, even though it was blazing hot outside. But don't do too much of this around the house, as the real key is to keep a "stream" of air flowing from the basement to the upstairs. It seems to be working fairly well so far.
One more thing: It is good to start this process early in the morning before temperatures rise upstairs. Otherwise you really are only going to be able to keep it from getting as hot as it possible could get upstairs (you will simply maintain a hot temperature).
I hope some of you find this money-saving project helpful. :-)