How does external shading impact highly glazed office buildings in terms of heat gains and daylighting?   

Mairéad Whelan

Test Methods
Case Study
Physical Prototype (solar test cell)

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David Knight
Darren Bergin

Although external shading devices are commonly used as a method of optimising daylighting and solar heat gains, they are often overspecifed by designers to serve a more aesthetic purpose.

In Europe, the building industry has the highest rate of energy consumption over any other sector, accounting for 39% of all global energy consumption. This is higher than both the transportation and industrial sectors. In order to achieve a reduction in energy consumption, solar heat gains and daylighting need to be optimised1. This can be achieved by controlling the amount of sunlight that enters a building. With this in mind, this study examines how the energy performance of glazed office buildings in Ireland can be improved in instances where fixed external shading is utilised, specifically focusing on vertical, horizontal and eggcrate shading devices.

The research involved the analysis of a case study building using the FenestraPro design software. The building in question was highly glazed, using solar control glass and also consisted of three types of external shading systems. A daylighting percentage was generated for the whole building while the solar loads were calculated using the fifth floor as a baseline for results. Physical testing was also carried out on a small scale using a solar test cell building to evaluate the impact of horizontal shading devices on the room within. The room was set up with a lux meter and temperature sensor in the centre of the room, to measure the daylighting and temperature difference within the room. The room was tested on separate four days, with the horizontal canopy adjusted on each day as required. The results from these tests were then validated through the use of manual calulations.

The results obtained reveal that when no shading was applied to the case study building, only the west facade exceeded the daylighting recommendations. Also, the use of the solar control glass would have been sufficient to maintain solar heat gains. This suggests that excessive external shading is not necessary from a performance point of view and instead serves a more aesthetic purpose. As for the physical tests, the horizontal shading was effective in optimising the daylight factor percentage, but was unsuccessful in maintaining optimum solar heat gains. This shows that solar control glass would still be a requirement, even when external shading is utilised.