Comfortable & Energy Efficient Buildings in Mauritius
Buildings in Mauritius were traditionally built with due consideration of shading of interior spaces from solar radiation. However, over time, with the advent of mechanical ventilation and active cooling systems as well as artificial lighting, less attention has been paid to passive design principles with greater emphasis to cyclone resistance. Rightly so, but how can we bring back the sustainability-based passive design paradigm in our concrete built environment. The current design methodology has led to a built environment with a direct correlation between energy consumption, floor area and prevailing climatic conditions, with an increased use of active energy systems, which is in itself unsustainable due to the vicious cycle it locks us in with increased greenhouse gas emissions and associated warmer summer temperatures. The recent surge in electrical consumption during peak summer period is a clear sign of the large share air conditioning energy represents in our energy mix, and the unsustainable coupling between prevailing climatic conditions and the indoor environment.
It is of prime importance to revisit the passive design principles, including the particular solar path Mauritius experiences over a year and how this affects thermal and visual comfort of interior spaces. This has a direct bearing on the layout of spaces, and can also provide essential knowledge for the design of simple passive shading devices. Combined intelligently, these two passive design approaches can go a long way to avoiding undesirable heat gains to the interior. Furthermore, given the high thermal mass of our concrete fabric for buildings, surface temperatures of both walls and roofs reach high levels in evenings, which leads to undesirable radiative heat exposure for the occupants in residential buildings. This is particularly experienced in interior spaces located in west and south-west orientations which become exposed to the settling sun.
The high thermal mass of our walls is beneficial for office spaces which are occupied mostly during sunshine hours, so means to flush the heat accumulated during the day needs to be considered, especially those using the lower ambient air temperature prevailing at night. Given that our roofs are predominantly flat represents a major shortcoming in keeping heat gains out, given that the high elevation angle (almost 90 degrees) sun during peak summer times impact the roof perpendicularly and leads to significant heating and heat gains to the interior. One of the most effective method to reduce thermal discomfiture and lessen, if not eliminate, the need for air-conditioning is to shield the roof from this intense solar radiation. Several approaches can be considered, ranging from simple shading using canvas or metal sheets to green roofs, including the use of reflective roof finishes, known as cool roof.