Air acts as insulator

Press, 22 June 1989, Page 31

Air acts as insulator

The theory behind double glazing is really very simple. Air, provided it is still, is an excellent insulator. A warm blanket traps small pockets of air in its fibres, as do fibreglass batts.

A down quilt, though very bulky, weighs very little as it is mostly air trapped by the feathers within. The sealed window unit is separated by a narrow aluminium spacer of limited width to avoid a large volume of air being

present. This presents thermal currents from occurring between the inner and outer pane. This, in effect, is like placing an invisible blanket over the window. The climate of a room will undergo a dramatic change once sealed insulating units have been fitted.

Depending on what direction the window faces, this type of insulation can prevent as much as 60 per cent of heat loss. This means that not only will a room heat up

more quickly, but it will require much less energy to retain that heat. In areas facing the sun, passive solar heating becomes far more efficient, because although the sun’s rays suffer minor reflections, a far greater proportion of the sun’s warmth is retained. So even without the use of drapes, the sun’s warmth can be felt long after nightfall. There is another climatic change, possibly more. dramatic, which cannot be substituted by

turning up the heater. As room temperatures rise, so does the warm air. It will accumulate near the ceiling right across the room where it will come into contact with the cold surface of the window, which will cool down z any air coming in contact with it. As the air cools it continues to drop, displacing the warm air and forcing it across the floor in a current. The air warms up as it crosses the room and

rises, therefore the whole cycle begins again. These convection currents are the cause of cold feet in a warm room. People will go to great lengths trying to seal draughts around the window, when in most cases the main cause of the draught is the convection current described. By fitting sealed insulating glass, the cooling effect at the window is significantly reduced, therefore arresting the air flow.