Edwin Pawlowski wrote:

Ceiling fans just circulate the hot air already in the room...
You have to blow hot air out and draw cooler air in.

And make sure the cool air scrubs the heat out of the room surfaces, vs
just passing through rooms with still air near the surfaces (including
people surfaces, which feel cooler in moving air.) Ceiling fans can help
whole house fans. Picture surface thermal mass in series with an airfilm
conductance Ga that increases with air velocity (Ga = 2+V/2 Btu/h-F-ft^2,
with V in mph, approximately) in series with a conductance to outdoor air
(cfm Btu/h-F, approximately), like this, viewed in a fixed font:

1/cfm 1/(AGa)
Tout ---www------www----------- Tsurf
|
|
--- Csurf = 0.5A Btu/F/ft^2
---
| for A ft^2 of 1/2" drywall.
|
-

A 10'x20' room with 880 ft^2 of drywall might have Csurf = 440 Btu/F.
With a 1000 cfm window fan and a ceiling fan that raises the airspeed
near the surface to V = 2 mph, it might have a natural time constant
RC = Csurf(1/cfm+1/(A(2+V/2)) = 440(1/1000+1/(880(2+2/2)) = 0.6 hours.

In 2 hours with Tout = 70 F, a Tsurf = 80 F room would would cool to
70+(80-70)e^-(2/0.6) = 70.4 F. With a 500 cfm window fan and no ceiling
fan, RC = 1.1 hours, so it might only cool to 70+(80-70)e^-(2/1.1)
= 71.7, or more, if the bulk of the air near the surface stays warm,
hardly moving at all.

With R20 walls, after 8 hours with Tout = 90 F with the window fan off
and no internal heat gains and RC = 10 hours, the 70.4 F drywall temp
would climb to 90+(70.4-90)e^-(8/10) = 81.2, or less, with 2 layers of
drywall with RC = 20 hours and 90+(70.4-90)e^-(8/20) = 76.9. We might
have a lot more mass and a lower temp if we cooled a basement at night
and circulated house air through the basement during the day.

Nick