Passive solar design Planning and site considerations

Whether it is important to encourage or exclude solar radiation, it is necessary to appreciate the degree to which solar access is available, so that the likelihood of solar heat gain can be determined. At the earliest stage of design one must consider the following parameters in relation to the site:

• the sun's position relative to the principal facades of the building (solar altitude and azimuth);

• site orientation and slope;

• existing obstructions on the site;

• potential for overshadowing from obstructions outside the site boundary.

For the development itself, the following factors need consideration:

• grouping and orientation of buildings;

• road layout and services distribution;

• proposed glazing types and areas, and facade design;

• nature of internal spaces into which solar radiation penetrates.

Chapter 5 referred to the stereographic sun chart and computer programs as a means of assessing the level of insolation enjoyed by a building. Physical models can also be tested by means of the heliodon.

The thermal efficiency of a building can also be affected by its plan form and orientation in respect of the prevailing wind direction. There are a number of guidelines:

• The larger building elevation should not face into the predominating wind direction, i.e. the long axis should be parallel to the wind flow.

• Tall buildings should, where possible, have a facade which is staggered and stepped back away from the wind; protection for pedestrians can be provided by use of canopies and podiums which reduce downdraught at ground level; curved facades moderate the impact of wind, for example the Swiss Re Offices, London, pp. 157-58.

• Sheer vertical faces to tall buildings can generate substantial down-draughts, which can obstruct pedestrian access, and even be dangerous. An example is the 19 storey Arts Tower in the University of Sheffield where the downdraught has knocked people over close to the entrance.

• Buildings can be grouped in irregular arrays, but within each group the heights should be similar and spacing between them kept to a minimum (no more than about a ratio of 2:1 in building heights).

• Building layout should avoid creating a tunnelling effect between two adjacent buildings.

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