Human Comfort in the Tropics

The vastness of Western Australia and the variances in its climatic conditions calls for a variety of responses to its developing built environment. What is considered a suitable and sustainable architectural design in Perth will undoubtedly be less effective in Broome or Port Hedland.

Western Australia displays a large diversity of climate zones, ranging from the temperate south to desert and tropical conditions in the north. CODA’s involvement in remote projects within Western Australia has resulted in a substantial body of research and knowledge as to the climatic conditions within these regions. The resultant research forms design guidelines that outline how best to approach new built works. Amongst social and cultural benefits these guidelines essentially promote sustainability through climate-responsive design. Design guidelines for projects in the Kimberly and Pilbara clearly articulate the most effective way to build for comfort, without necessarily having to rely on artificial cooling.

Human comfort is a specific thermal level that is considered universally comfortable. External temperature, air movement and the ability for the body to warm or cool itself to maintain a required 36.9oC work together to influence our perception of comfort[1]. Within tropical climates, such as Broome, an ever-present humidity has to be taken into account. High levels of humidity generally lead to a feeling of discomfort as the increased levels of moisture in the air impede the body’s ability to perspire and cool itself through evaporation. Unlike sunlight and temperature humidity is a factor that is much harder to design for in the built environment, it cannot be controlled through shade as we do the sun, or insulated against as we do for the heat and cold. Instead, ventilation becomes the essential design consideration in controlling the effects of humidity.

The tropical climate of the Kimberly region is characterised by a distinct wet and dry season and warm, humid conditions throughout most of the year. There is also a notably low diurnal range meaning that there is very little variation in temperature from day to night. The Design Guidelines put forward for Broome establish the most suitable built form for comfortable living in the Kimberley. Low mass construction, light coloured external skins to decrease the absorption of heat, reflective insulation and careful positioning of openings to maximise the effect of ventilation [2] are all important in this climate.

In comparison, in climates where there is a broad diurnal range (where temperatures significantly drop at night) thermal mass works effectively in re-radiating the absorbed heat throughout the night. Places with low diurnal ranges, such as Broome, rely heavily on evening breezes to ventilate and so we must design to allow this to happen efficiently. In essence lightweight construction works most effectively, it does not store heat throughout the day, thus eliminating the consequent ‘heat blanket’ as the heat is re-radiated. This ‘blanket’ of warm air around and within the building would impede the cooling effect of any breezes throughout the night. Lightweight construction in combination with the careful positioning of openings to allow for cross ventilation is the most efficient means to providing comfort within a humid climate.

With this in mind the physical orientation of the home is crucial in maximising the effect of breezes. As a guide it is considered that within Broome, for example, the most beneficial breezes are westerly followed by those from the north-west and south-west.  Primary openings should be positioned to capture these and allow them to move through the home with as little obstruction as possible in order to flush warm air from the interior spaces. Focusing the principal living areas with respect to the prevailing breezes will essentially help in reducing the need for air-conditioning within the home.

The tropics are a unique climate because of the humidity factor but, despite this, it should not automatically be presumed that air-conditioning be the only solution for internal cooling. It is most certainly a climate that requires comprehensive consideration and planning, particularly in relation to the materials chosen and their thermal performance. Essentially the key to passive urban design within a tropical environment is to minimise exposure to direct sunlight, and to design openings that ensure sufficient airflow can pass through the whole building.

[1] Queensland University of Technology 2009

[2] Broome North Design Guidelines, CODA/Landcorp