Building energy efficiency and thermal comfort in tropical climates Presentation of a numerical approach for predicting the percentage of well-ventilated living spaces in buildings using natural ventilation Alain Bastide * , Philippe Lauret, Franc¸ois Garde, Harry Boyer Laboratoire de Physique du Baˆtiment et des Syste`mes, Universite´ de La Re´union 40, Av de Soweto, 97410 Saint-Pierre, Ile de La Re´union, France Received 30 September 2005; received in revised form 24 November 2005; accepted 5 December 2005 Abstract The paper deals with the optimization of building energy efficiency in tropical climates by reducing the period of air-conditioning thanks to natural ventilation and a better bioclimatic design. A bioclimatic approach to designing comfortable buildings in hot and humid tropical regions requires, firstly, some preliminary, important work on the building envelope to limit the energy contributions, and secondly, an airflow optimization based on the analysis of natural ventilation airflow networks. For the first step, tools such as nodal or zonal models have been largely implemented in building energy codes to evaluate energy transport between indoor and outdoor. For the second step, the assessment of air velocities, in three dimensions and in a large space, can only be performed through the use of detailed models such as with CFD. A new modelling approach based on the derivation of a new quantity—i.e. the well-ventilated percentage of a living space is proposed. The well-ventilated percentage of a space allows a time analysis of the air motion behaviour of the building in its environment. These percentages can be over a period such as 1 day, a season or a year. Twelve living spaces with different configuration of openings have been studied to compare the performance of ventilation function of the opening distribution. Results and discussion are presented in the paper. This method is helpful for an architect to design the rooms according to their use, and their environment. Finally, the developed models can be used in building projects to estimate the period of the natural ventilation and to reduce the energy consumption due to air-conditioning. # 2006 Elsevier B.V. All rights reserved. Keywords: Natural ventilation; CFD; Large openings; Tropical climates; Bioclimatic design 1. Introduction 1.1. Demand side management in insular countries The energy situation in emerging and insular countries is becoming alarming. The demand for electric power continues to grow whereas the means of production remain limited. A great number of these countries are in the inter-tropical zone and are thus subjected to high temperatures and humidity all year round. These climates and the increase in the purchasing power of the populations lead to greater use of air-conditioners. Air-conditioning is often seen as the only mean to reach thermal comfort during the hot season and unfortunately is very energy consumer. The electric power produced from fossil energies such as coal, oil, or gas, or from uranium, will disappear in the coming decades. Before the disappearance of these resources, galloping inflation, due mainly to the scarcity of these fuels, will make their purchase at reasonable prices impossible. It will then become too expensive to operate these air conditioning systems. The French government [1] and the European Union [2] plan to reduce four-fold their CO 2 emissions over the next few decades, and the building sector is one of the principal energy consumers. For this reason, a particular effort is being made so that the buildings in Northern Europe consume low electric power during the cold season. In the tropical ultra-peripheral regions (UPR), this objective of cost reduction is adapted to the local climatic constraints. The reduction of the energy costs www.elsevier.com/locate/enbuild Energy and Buildings 38 (2006) 1093–1103 * Corresponding author. Tel.: +33 2 62 96 28 90; fax: +33 2 62 96 28 99. E-mail address: alain.bastide@univ-reunion.fr (A. Bastide). 0378-7788/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.enbuild.2005.12.005