Just spotted this in the grauniad

cheers

Jacob

Scientists' survival tip: go with the flow

Tim Radford, science editor
Thursday August 7, 2003
The Guardian

British scientists have just issued a hot tip for survival when the
fan has broken down and the thermometer is up. It saves energy and
exploits everyday household technology.

Just open a window, says Gary Hunt, who leads research at Imperial
College London into the fluid mechanics of natural ventilation. It
helps to have a sash window in the right place and at the right
height.

"Many of us have forgotten how to correctly use the sash windows so
carefully installed by the Edwardians and Victorians to maximise
airflow," he said. "If used correctly it is possible to significantly
improve comfort in the office or at home without using air
conditioning units that place high demands on energy and increase
carbon dioxide emissions."

He used a small laboratory model to simulate the average home as a
hothouse and keep track of cool airflow through rooms and buildings.
It is best to have your sash window open equally top and bottom. That
way cooler air flows into the room through the lower opening and
flushes the warm air out through the top.

If the windows are too small, or badly placed, however, hot air is
trapped at ceiling level and extends down to make the inhabitants
unpleasantly hot and muggy.

"Our research shows a good strategy is to leave sash windows in the
mid-position overnight - providing it is safe to do so," he says.

"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."