Projection of the Solar Path. Position of the Sun: Shadows, Methods Employed
Projection of the Solar Path. By using a stereographic projection – (9), the path of the sun can be determined for each degree of latitude (for the 21st day of each month) as a function of time of year and time of day.
Solar position, clock time and determination of time. The position of the sun determines the daylight conditions according to the time of day and time of year. The true local time (TLT) is the usual reference for time of day (e.g. in the solar position charts) in determining daylight. Each location is allocated to a time zone, within which the same time (zone time) applies. If the time zone input is of interest, then the TLT must be converted to the appropriate time zone.
Position of the Sun: Shadows, Methods Employed. The following methods are employed to determine and verify the actual solar radiation and shadow, both inside and outside buildings, as a function of geographical location, time of year and time of day, structural features and surrounding conditions.
Graphical construction of shadows. Determination of the shadows cast by a building can be accomplished using the projected (apparent) course of the sun, represented in - (9) (see previous page), by means of a plan and an elevation. As an example, the shadows in a courtyard in Brighton, latitude 51°N, will be constructed for 21 March, at 16.00. The sun appears at this time at an azimuth angle (as1) of 245° and an elevation (ys1) of 20° - (9) + (10).
The positional plan is orientated with the north. The directions of the shadows are determined by the horizontal edges of the building, that is, a parallel shift of the direction of the sunshine (as1 = 245°) due to the corners of the building. The length of the shadow is determined by the vertical edges of the building, that is, a rotation of the true height of the building (h) and application of the elevation angle of 20°. The point of intersection with the direction of the shadow gives the length of the shadow.
Panorama mask. In many countries, a representation of the path of the sun is available for various geographical areas. These representations are printed on clear film, and include data on azimuth and elevation angles, as well as time of year and time of day. In use, a copy of the relevant sheet is bent in a curve and positioned in the direction of the sun – (11). By looking through the panorama mask, any encroachment of shadows from the surroundings and from overhead shadows is transferred to the printed path of the sun, on a scale of 1:1 – (12). The film can then be used to analyse the occurrence of shadows and sunshine on fagades and on sections of buildings to the correct scale.
Horizontoscope. The horizontoscope is an aid to determining the true conditions of sunshine and shadow on building sites and on and in buildings. The horizontoscope consists of a transparent dome, a compass, the base and exchangeable curved sheets which are placed on the base, according to the task in hand, to investigate light, radiation or heat, etc.
The purpose of the horizontoscope is to construct the light and shade conditions which exist in a room, e.g. – (13). At a particular point in the room, the opening for incident light can be assessed by means of a window cut-out projected on the dome and at the same time on the curved sheet underneath. It is therefore possible to determine both the radiation conditions and light effects in the room for each point in the room, and for any time of day and time of year, depending on the alignment of the building (13).
Model simulation. In order to simulate and establish accurate annual shadow and solar radiation effects in and on a building, it is possible to construct a true-to-scale model and to test it under an artificial sun (parallel light) – (14).
Date added: 2023-01-01; views: 270;