Orientation & Zoning

Positioning buildings to reduce solar gain can improve energy efficiency

Building orientation has a major effect on solar gain. Proper orientation can significantly reduce the cooling load and improve energy efficiency. Photo by seier +seier licensed under creative commons.

This section is intended to be an introduction to orientation and zoning, with the purpose of demonstrating how passive cooling opportunities can be maximised.

It should be noted that site-specific considerations need to be taken into account when deciding on building orientation. In some cases, shade from existing buildings, landscape and geographic features can contribute to passive design measures.

Reducing Solar Gain

Reducing solar gain on buildings in Rio de Janeiro should be a major design objective – serving to lighten the cooling load and improve energy efficiency.

In terms of building orientation, preventing solar gain is probably more important than the facilitation of natural ventilation and buildings should be designed with this in mind [1].

Vertical Surfaces & Solar Gain

The horizontal surfaces of buildings receive the most intense solar radiation due to the high sun angle in Rio de Janeiro. Solar heat gain on these surfaces can be reduced by the use of light coloured paints and green roofs. Roof ponds and other evaporative cooling measures may also help reduce solar gain on horizontal surfaces.

During winter, the next highest intensity is received by north facing walls. In summer, when cooling loads are most significant, east and west façades receive the most solar radiation and are hence most likely to contribute to solar gain.

The following table shows incident solar radiation on vertical surfaces in Rio de Janeiro:

Season Winter kWh/m2 Summer kWh/m2
North 340 180
East/West 220 305
South 95 220

Data relate to kWh per square metre measured over the three months of summer and winter periods of the year [2].

West facing surfaces pose a particular problem in Rio de Janeiro, since the maximum intensity of solar radiation received by west walls coincides with the hottest part of the day [1].

Where possible, buildings in Rio de Janeiro should be oriented so that east and west exposure to the sun is minimized. Only minor openings of unimportant rooms should be sited on the east and west sides of buildings, and windows on these façades should be limited. Vertical service cores should be sited on east and west sides to provide buffer zones to insulate internal spaces and shading to occupied areas [3].

Transitional zones should be sited on the north side of buildings. This zone receives less solar radiation during the summer months. Total climatic control in these spaces can likely be avoided, once natural ventilation has been maximised [4].

Natural Ventilation

In terms of building orientation, natural ventilation can be maximised by exposing windows and openings to prevailing breezes. Prevailing winds in Rio tend to be southerly, with occasional northerly winds. Buildings oriented on an east-west long axis could be expected to have the lowest possible solar gain whilst providing good opportunities for cross-ventilation. See the natural ventilation section of this toolkit for more information.wind frequency map Rio de Janeiro

Cross-Sectional Shape: High Rise Buildings

For high rise buildings, 87% of total annual solar insolation is incident on vertical surfaces. This means that manipulating the cross-sectional shape of a building can strongly influence solar gain.

Research suggests that a circular shape with a width to length ratio of 1:1 is optimal for minimising total solar insolation in high-rise buildings. For square shaped buildings, a width to length ratio 1:1 in a north-south orientation receives the lowest annual total solar insolation. Square shaped high rise buildings can receive as much as 33% more solar radiation compared with buildings having a circular cross section [5]. Building shape should be carefully considered when planning for high-rise developments in Rio de Janeiro.

References

  1. “Building Orientation: Tropics & Equator,” Low Energy Architecture Research Unit (LEARN) of London Metropolian University. [Online]. Available: http://www.new-learn.info/packages/clear/thermal/buildings/configuration/building_orientation.html  [Accessed: 22-Oct-2012].
  2. O. D. Corbella, “Learning from Built Examples in Rio de Janeiro: 18th Int. Conference on Passive & Low Energy Architecture,” 2001. [Online]. Available: http://www.usp.br/fau/cursos/graduacao/arq_urbanismo/disciplinas/aut0264/Material_de_Apoio/Corbella_Yannas_2001_Rio.pdf
  3. M. H. Ahmad, D. R. Ossen, and C. S. Ling, “Impact Of Solar Radiation On High-Rise Built Form In Tropical Climate.” [Online]. Available: http://eprints.utm.my/881/1/Chia_Sok_Ling_(Malaysia).pdf
  4. “CAFA notes: Tropical Design Module 4: Passive Cooling.” [Online]. Available: http://pupclass.blogspot.ie/2008/05/tropical-design-module-4-passive.html  [Accessed: 19-Oct-2012].
  5. C. S. Ling, M. H. Ahmad, and D. R. Ossen, “The Effect of Geometric Shape and Building Orientation on Minimising Solar Insolation on High-Rise Buildings in Hot Humid Climate,” 2007. [Online]. Available: http://myais.fsktm.um.edu.my/6750/1/2__Chia_Sook_Ling_.pdf