"The cool external air flushes the warm air of of the room and also
cools the walls, floor and ceiling. The cool walls absorb the heat the
following day and prevent the internal from temperatures rising as
high."

This is completely pointless, however, when the external air is not cool -
as it wasn't last August, or the August before that or the August before
that.

Another afterthought - if Simon doesn't think opening windows has any
benefit in hot weather does this mean that he has spent the last 3
very hot Augusts with windows closed?
If so he would have been extremely uncomfortable. This could account
for his enthusiasm for air conditioning, which most of us can do
without, having discovered the benefits of opening windows in hot
weather.
Conversely I wonder if he opens all his windows in winter and turns up
the central heating?

cheers

Jacob