On Sat, 15 Jul 2017 14:44:03 GMT, FanOfWholeHouseFans
m wrote:

replying to JimT, FanOfWholeHouseFans wrote:
I beg to differ with "better than nothing." . Living in a dry climate where
the nights cool down very nicely, a whole house fan is the way to go for
cooling cheaply and sustainably in an overtaxed climate, and it works well.
Shut curtains and Windows all day to keep cool air in and hot air out. Then,
once the evening outside temp drops near or below the inside temp, we open
every window and switch on the whole house fan, which cools down the house
lickety split with fresh air. BUT, these things are loud and we could not
sleep with it on or watch tv or talK on the phone. So I too keep looking for a
variable speed fan that we can run quietly on low all night and when we need
to hear. Would someone please manufacture these. There are lots of us out here
who hate AC and want to do things more sustainably and who prefer exchanging
stale house sir with fresh air, and who live in places where cool night air in
summer is the best way of truly conditioning the ai!

We are in SW Florida and still benefit from whole house fans for about
half the year. I agree with Trader, even with two 22" fans running on
high, I never get the 1600 sq/ft attic below that mythical "5 degrees
above ambient" if the sun is shining.
As for variable speed, the best way is with multi speed motors.
You size the blade to the motor running on high and it will work OK at
the lower speeds. If the blade is not properly sized, you will burn up
the motor (too much pitch) or simply waste energy with it not moving
enough air (too little pitch).
The Grainger catalog has charts that will help you with this
selection.
One of my fans is 2 speed, one is 4 speed. (probably overkill since we
still only use two).