Determination of the Sunshine on Structures

Application. The path of sunshine on a planned structure can be obtained directly from the following procedure if a plan of the structure, drawn on transparent paper, is laid in its correct celestial orientation over the appropriate solar path diagram. The following solar path data relate to the latitude region 51.5°N (London, Cardiff).

For more northern areas, e.g. at 55°N (Newcastle), 3.5° should be subtracted. The values in degrees given inside the outer ring relate to the 'azimuth', i.e. the angle by which the apparent east-west movement of the sun is measured in its projection on the horizontal plane. The local times given in the outer ring correspond to the standard time for longitude 0° (Greenwich, i.e. the meridian of Greenwich Mean Time).

At locations on degrees of longitude east of this, the local time is 4 min earlier, per degree of longitude, than the standard time. For every degree of longitude to the west of 0°, the local time is 4 min later than the standard time.

Duration of sunshine.The potential duration of sunshine per day is almost the same from 21 May to 21 July, i.e. 16-16³/4h, and from 21 November to 21 January, i.e. 8V4-7¹/2h. In the months outside these dates, the duration of sunshine varies monthly by almost 2h. The effective duration of sunshine is barely 40% of the figures given above, owing to mist and cloud formation. This degree of efficacy varies considerably depending on the location. Exact information is available from the regional observation centres of the areas in question.

Sun and heat. The natural heat in the open air depends on the position of the sun and the ability of the surface of the Earth to give out heat. For this reason, the heat curve lags approximately 1 month behind the curve of solar altitude, i.e. the warmest day is not 21 June, but in the last days of July, and the coldest day is not 21 December, but in the last days of January. Again, this phenomenon is such that local conditions are extraordinarily varied.

To establish the duration of sunshine or shadow on a building at a particular time of year and time of day (e g. 11.00 on the equinox), the azimuth in the plan view is constructed on the corner of the building in question. This determines the boundary of the shadow in the plan view upon which the solar altitude (effective light beam) is constructed by rotation about the azimuth line. The intersection x at right angles to the plan view shadow, translated to the elevation, provides the boundary of the shadow on the front of the building as a distance below the upper edge of the building.

Shortly after 11.00 shadow begins to form on the north-east side; shortly after 13.00 the south-east side is also in shadow, whilst the other sides are in sunlight at the corresponding times.