Lately I've been asking myself the same sorts of questions,
as I've tried to keep my house comfortable without air
conditioning. Fortunately, here in Utah the nighttime
temperatures almost always drop below 70 F, even when
the afternoon highs are over 100. If I open and close
windows at the optimal times, and use window shades
to block any direct sunlight from coming in, but don't
use any fans, the indoor temperature range is about
10 F less than outdoors on both the high and low
ends (so it's perhaps 80 - 90 on a day when outdoors
the range is 70 to 100). My puny 12-inch fan doesn't
help much, probably because the thermal mass of the
house itself is so much more than that of the air
inside. But it occurs to me that thermal mass could
be the key to greater comfort. Has anyone ever designed
a system to pump water in and out of the house, to
exchange heat rapidly at night and then slow the
warm-up during the day?