The fan in the window: an inny or an outy?
On a hot summer should the fan in the window be setup to blow cold air
into the dwelling or should it the reverse? For the purposes of this
discussion assume an expanding universe.

From a practical standpoint, the expansion of the universe is
immaterial.  If the fan blows outward, the air is sucked up more or
less evenly from the whole hemisphere around the back of the fan, and
air leaks in to replace it around doors and windows throughout the
house.  If the fan blows inward, it creates a concentrated jet inside
the house, promoting circulation and mixing.  This "wind" enhances
evaporation of sweat from skin.  So I'd point the fan inward.

Two arguments which might be made for the opposite case both seem
silly:

1) Pressure in the house is greater when the fan blows inward, so
sweat does not evaporate as quickly.  Also, when the fan is turned on,
the slight increase in pressure causes an adiabatic increase in
temperature.

2) The fan motor generates heat, and increases the temperature of the
air around it.  If the fan blows inward, this warmer air is advected
in to the house, whereas if the fan blows outward, it is carried
outside.

Greetings Grthumongous:

I vote for inward, too, *and* it's even better when you can have a fan
on the opposite side of the house pulling air.  Say one fan is in the
bedroom and the other in the living room - when sleeping, have the
bedroom fan blowing and the living room fan pulling.  Then reverse
when you're spending time in the living room.  Better circulation.

Best regards,
juornalist-ga