Andrew Gabriel wrote:
Probably want to exhaust the air on the upstairs side facing
the sun, and the coolest air to draw in is likely to be on
a downstairs side away from the sun or north facing.

That was what I was thinking of.

In the summer, I replace my loft hatch with one which has a
10" vent-axia extractor fan, which serves both to extract
the hot air from upstairs, and to help cool the extremely
hot air in the attic.

Hmm. There's an idea. My cellar is always noticable cool,
even in the heights of summer. I could do something to
draw that cold air into the rest of the house - passive
air conditioning

--
JGH