Solar Shading for Buildings in Rio de Janeiro
Minimising solar heat gain can improve thermal comfort for building occupants. This helps reduce the demand for air conditioning, thereby improving energy efficiency.
Solar heat gain can be reduced by sensible building orientation, proper window design and by providing adequate shading solutions. Well designed shading solutions and fenestration can reduce the energy required for cooling by up to 15 % .
Shading is most effective when placed externally, as it prevents solar heat from entering the building. External shading can consist of vegetation (trees), hard landscaping elements or building-installed external shades like brise soleil and cladding.
Effective shading depends on the orientation of the building façade. In Rio de Janeiro, fixed horizontal shades or roof overhangs will reduce solar gain effectively on north-facing windows when sun angles are high.
However, the same device will not be effective on west-facing windows – in this case, solar gain occurs at a lower sun angle and will not be blocked by horizontal shading. Solar gains to east and west windows usually require adjustable shading devices or high performance glass.
External shading is a highly effective way of reducing solar heat gain
Where possible, windows should be minimised on east and west façades, as these are harder to shade. The glass used on buildings in Rio de Janeiro should allow a high degree of light transmittance but should minimise solar heat gain when the sun angle is low. This is particularly important on east and west façades, where low shading coefficient glass should be specified .
In the case of north facing windows protected from direct solar radiation by overhangs, low-e glazing should be considered to prevent heat gain from indirect radiation .
Planting tall trees to the east and west sides of buildings will help to reduce solar gain from low morning and afternoon sun. If possible, tall trees should be used to shade or partly shade the roof. This strategy will obviously need to be integrated with plans for roof-mounted solar panels. Another way of using vegetation to reduce solar gain is to incorporate green roofs and walls.
Low growing vegetation should be selected for breeze filtering rather than blocking since trees and shrubs help to cool air passing into buildings .
Brise soleil are exterior shading devices that help to reduce solar gain. They range from adapted concrete walls to elaborate wing-like mechanisms that shade large areas. The Gustavo Capanema Palace building in Rio de Janeiro has adjustable louvre type brise soleil covering the North-East façade, allowing the building to operate without air-conditioning . The building is a historical example of the effective use of brise soleil, with manually adjusted louvres.
In today’s context, these systems are likely to be far more effective. Modern technology allows brise soleil to be designed with control mechanisms that track the path of the sun and optimise the setting of the louvres. In Rio de Janeiro, brise soleil are likely to be most useful on east and west façades.
- D. Prowler and N. I. of B. Sciences, “Sun Control and Shading Devices | Whole Building Design Guide,” Whole Building Design Guide, National Institute of Building Sciences, 2008. [Online]. Available: http://www.wbdg.org/resources/suncontrol.php?r=env_hvac_integration [Accessed: 18-Oct-2012].
- Cairns Regional Council, “Sustainable Tropical Building Design: Guidelines for Commercial Buildings,” 2011. [Online]. Available: http://www.cairns.qld.gov.au/__data/assets/pdf_file/0003/45642/BuildingDesign.pdf [Accessed: 18-Oct-2012].
- S. G. Tavares and C. Silva, “BRAZILIAN SOLAR ARCHITECTURE – AN ANALYSIS OF MESP DAYLIGHTING,” in ISES – Solar World Congress, 2007, no. 1941, pp. 1–4.
- “Building Envelope Design Guide – Atria Systems | Whole Building Design Guide.” [Online]. Available: http://www.wbdg.org/design/env_atria.php. [Accessed: 23-Oct-2012].