Heat Gain and Heat Loss
In a properly constructed and insulated home the greatest opportunity for heat gain and heat loss will be through the windows and skylights via radiation, conduction and convection.
Inside the home we are able to minimise heat loss by the use of heavy drapes fitted to create a still air space against the glass. The aim is to reduce convective currents on the face of the glass to minimise heat transfer to the cooler outside.
Outside, the most effective way of stopping heat radiating into a room is to place a solid screen across the window. Obviously this is not always a practical solution.
Due to the different paths of the sun between summer and winter, north facing glass areas are readily controllable to minimise heat gains in summer and still allow ample penetrationof light into rooms. Full screening of east and west windows in summer is desirable.
This simplified diagram shows the basic principal of one form of configuring summer shading. In reality the situation is complicated by low morning and afternoon hot sun penetrating under the shading. Deciduous vines are an alternative to removable items such as slats or shade cloth, but they do tend to provide unwanted screening in autumn and spring. On the other hand, even with the best of intentions, the installation and removal of fixtures twice a year can go by the wayside.
This diagram shows sun angles at 10am on 22nd of each month in Tamworth N.S.W. for a wall facing true north.
The screening shown is 1800mm wide.
January angle 59.21 degrees
February 53.80 March 47.35
April 38.91 May 31.87
June 28.25 July 30.82
August 38.78 September 50.05
October 59.99 November 64.80
December 63.47
The basic principals are straight forward but the execution at the design stage does require careful consideration.