Thermal comfort of buildings in Reunion:

Let's favour natural ventilation over air conditioning

In order to meet our thermal comfort requirements, the use of air conditioning is constantly increasing in Reunion Island. However, in order to meet the challenges of the energy and ecological transition, it is necessary to considerably reduce our energy consumption and our greenhouse gas emissions.

Figure 1 - Dominant winds in Reunion Island (Source : PREBAT-Reunion Natural Ventilation)

The ecological issue of air conditioning

Air conditioning aims to introduce refreshed and dehumidified air into a room using an active system such as a heat pump. To give some figures, it is estimated for example that, for a tertiary building in Reunion Island, air conditioning represents between 40 and 60% of its electrical consumption. In addition to the impact of consumption linked to this use, air conditioning equipment uses refrigerants. These systems are not perfectly hermetic and leak up to 10% per year depending on the installation. These fluids are powerful greenhouse gases (between 600 and 3,260 times higher than CO2).

It is therefore imperative to adapt one's behavior, habits and building to passive solutions, in order to guarantee thermal comfort with less use of air conditioning.

Natural ventilation, an alternative to air conditioning

An interesting lever to improve the thermal comfort of the occupants without having to resort to air conditioning is to rely on natural ventilation. This tool is particularly adapted to the humid tropical climate of Reunion Island. Indeed, external temperatures in the wet season rarely exceed 32°C (except in the western zone where 35°C can be reached), and sustained and well-defined winds exist such as trade winds and thermal breezes.

The interest of natural ventilation in terms of comfort is twofold:

  • Evacuate heat that accumulates inside the building;
  • Create interior air currents to reduce the temperature felt. An air speed of 1 m/s, i.e. 3,6km/h, allows to lower the temperature felt by 3 to 4°C.

Natural ventilation is fully integrated into bioclimatic design, which consists of designing a building logically based on the assets of its environment. This solution is also economical, as it relies on a free natural resource (the wind) rather than implementing energy-consuming methods such as air conditioning. Thus, it is natural to favor this type of solution when possible.

The installation of natural ventilation should preferably be taken into consideration from the design of the building and is imperatively associated with a good thermal design of the envelope (solar protection, insulation, inertia, etc.). The interior organization of the building must be considered. The objective is to define the internal air circuits of the buildings which will be appropriate to the uses.

Figure 2 - Illustration of the interest of generating an indoor airflow for the comfort of the occupants (Source: PREBAT-Reunion Natural Ventilation)

Air conditioning or ventilation, hybrid solutions

Air conditioning and natural ventilation are not incompatible. In particular, it is possible to design buildings with mixed operation in order to limit the use of air conditioning to the strict minimum, for example, during the four hottest months of the year. The rest of the time, the building is cooled by natural ventilation.

If the wind potential is not sufficient, air movers, which consume much less energy than a conventional air conditioning system, can reduce the use of air conditioning and complement natural ventilation by creating air movement.

Whether the building uses air conditioning or natural ventilation, the involvement of the users is essential to guarantee a control of its consumption and a good thermal comfort. Some eco-actions are to be known: limit the solar contributions by closing the solar protections, ensure a through ventilation by opening the windows, use the air fans, adapt the temperature of setting...

A demonstration project of bioclimatic design, the Moufia amphitheater

Large-scale projects have been carried out on the principle of natural ventilation in La Réunion. For example, the Moufia amphitheater was designed to function without the use of air conditioning. Feedback from users has been very positive and post studies have confirmed good thermal comfort. Finally, the budget initially planned to install an air conditioning system was reinvested in the installation of solar panels, further reducing the environmental impact of the Moufia amphitheater.

Figure 3 - Aeraulic functioning of the Moufia amphitheater - University of La Réunion

Natural ventilation: obvious for INTEGRALE

Since 2004, INTEGRALE Ingénierie and the engineers of the QEB (Environmental Quality of the Building) division have been assisting building owners in the Indian Ocean with the bioclimatic design of their buildings.
Natural ventilation is a priority at INTEGRALE and the subject is integrated in all our projects.

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