Etude de l’impact des procédés de rafraîchissement passif de type « Cool Roof » sur la performance énergétique des bâtiments dans les régions chaudes et arides

Abstract

Algeria, like many emerging countries, improving energy performance, while ensuring the thermal and environmental quality of buildings has become an essential theme in the current situation of sustainable development. Currently, the high rate of growth of urban areas and the unsuitability of construction techniques result in a building stock that is perfectly indifferent to its context, uncomfortable and energy-consuming, which continues to grow unceasingly. As such, the residential building sector is particularly is not only a substantial energy consumer but also a contributor to greenhouse gas emissions, particularly in the in outhern regions of Algeria where desert conditions prevail. Moreover, in a hot and dry climate, the continuous exposure of the roof to intense solar radiation mainly contributes to significant internal overheating and extreme thermal discomfort; making space cooling a basic requirement of occupants for most of the year. This total dependence on air conditioning systems leads to considerable energy consumption. However, the roofs of buildings offer significant opportunities to anticipate climate change and meet contemporary energy challenges. This requires improving the thermal behaviour of roofs by incorporating passive cooling processes. In this regard, the objective of this study is to assess the ability of "Cool Roof" to achieve energy savings and to ensure an acceptable level of thermal comfort in contemporary homes in Biskra. As part of our contribution to this problem, a rigorous methodology based on three complementary approaches has been adopted. As a start, an empirical study was carried out on a sample of 12 houses representing the most commonly used roofing types in the city of Biskra. Subsequently, through in-situ measurements and a questionnaire survey, the real impact of flat, reinforced concrete roofs on the conditions of indoor thermal comfort was assessed. Additionally, an experimental study was carried out by constructing four small-scale models, where six passive cooling techniques were evaluated over two consecutive periods, under real summer conditions. This experiment aimed to compare the thermal feasibility, economic accessibility and social acceptance of the different solutions, thereby identifying the most suitable options for the local context. Finally, a numerical simulation using the “TRNSYS” software was carried out to study the influence of the most promising passive alternatives identified in the experimental study on the energy, thermal, and environmental efficiency of buildings. The overarching goal was to offer a roof adapted to the local context, simple, cost-effective and easy to implement on existing surfaces or under construction, while meeting modern lifestyle requirements. The study's findings clearly demonstrated that by ensuring adequate protection of roofs, particularly by optimizing its thermal properties and selecting appropriate roofing materials, it is possible to improve significantly energy performance of buildings while ensuring a favourable level of thermal comfort at the same time, reducing carbon footprint.