The Sun-path

Dowell ThermaLine^TM

The simplest way to assess the passage of sun across a site is by observation. A site visit can also help identify site-specific conditions, how obstructions such as adjacent buildings, trees and landforms will impact on the site and the potential design, how the site’s shape, slope and orientation affect solar access.

By analysing the impact of the sun on a site, the designer can take full advantage of passive solar design features and increase the energy efficiency and comfort of the building.

Sun-path diagrams provide a broader overview of the sun on a site, as they map the path of the sun across the sky at different times during the day throughout the year. They can help establish the position of the sun relative to a site and can be used to determine the effect of shadows cast by buildings, trees and landforms on and around the site.

In the sun-path diagrams, the centre is the point of observation and the arcs represent the sun’s altitude angle at different times of the day throughout the year, using a 24 hour clock (12 hours ahead of GMT), rather than solar time. They are accurate to approximately 1 degree north or south of the allotted latitudes, however it is important to have accurate contour lines when using them.

Altitude and azimuth

The position of the sun with respect to an observer is commonly represented by two angles – altitude and azimuth. Altitude is the angle of the sun’s rays compared with the horizon. At sunrise and sunset, the altitude is zero, and in the southern hemisphere, the maximum altitude of the sun at any specific location occurs at solar noon on 21/22 December (longest days of the year).

Azimuth (sometimes known as bearing) is the direction of the sun as shown on a compass. Solar or ultraviolet (UV) radiation is the energy from the sun. The amount of solar radiation available on a site depends on the latitude and the sunlight hours received.

Shade is often required in summer, but in most parts of the country, winter sun is desirable. Obstructions on a site may block sunlight access at times when it is required.

When considering sunlight and building design, assess the impact of obstructions in the future as well as the present. For example, a small tree on an adjacent site may grow into a large one that blocks sun, a building may be erected on a currently vacant site or an existing building may be demolished and replaced by a larger one. Alternatively, existing trees may be retained for summer shade.

Calculating the sun-path

Using web based tools to calculate the sun path can easily determine which window configuration would be most suitable on a particular side of the building. Resulting in a clever design combination of Dowell Thermaline™ and Dowell standard double glazed or single glazed windows to achieve maximum cost-energy efficiency building solution.

Reference source: Level, SunCalc and Sunearthtools.com; [online], Available: www.level.org.nz/site-analysis; www.suncalc.net; www.sunearthtools.com (13 November 2014).