Brahim BENHAMOU
Professor & project – University Cadi Ayad of Marrakesh
The building sector is one of the most dynamic areas in economically emerging countries, due to high growth rates in population and urbanization. In the Southern and Eastern Mediterranean (SEMED) countries, it is estimated that in 2025, urban population will increase by about 100 millions additional inhabitants relatively to 2000 [1]. Hence, the housing demand increases drastically making the construction sector one of the main drivers of the global economic growth in these countries. In the SEMED region, buildings energy consumption represents more than 30% of the consumed energy. Besides, traditional buildings, which are integrated in their climate environment and thus energy efficient, are substituted by “modern” buildings with poor energy performance. Specifically, in the Moroccan traditional way of life, people developed empirical solutions (architectural, but also behavioral) to reach a minimal level of thermal comfort. However the rapid growth of income induces higher comfort requirements, which are mostly achieved through the use of electric air-conditioning equipment. This leads to a significant increase in energy consumption and in greenhouse gas emissions. Furthermore, the impact of air conditioners usage on electricity demand is a serious issue as the peak electricity load increases continuously, forcing the National Electricity Authority (ONEE) to build additional plants. Morocco, which is highly dependent on energy imports, has in the past decade taken determined steps to tap into its significant renewable energy resources. In 2009, the Moroccan public authorities launched a national energy strategy, setting clear targets for wind, solar and hydropower. It was one of the first countries in the MENA region to scrap most fossil energy subsidies while at the same time adopting energy efficiency measures to reduce energy consumption with a target of 12% by 2020 and 15% by 2030. Thus, a wider deployment of energy efficiency technologies across all sectors of the economy is needed. The construction sector, which accounts for more than 25% of the final energy consumption in Morocco [3], is one of the key sectors for achieving the energy efficiency target. To achieve the goal of the best environmentally friendly thermal comfort within a building having lowered conventional energy consumption, it is advisable to make use of passive or low-energy cooling strategies, including the reduction of the cooling and heating loads of the building. Moreover, it is often possible to fulfill thermal comfort requirements at low energy cost, taking advantage of the particular climate features by an appropriate design of the building [2]. A specific research was conducted at Cadi Ayyad University of Marrakech on the impact of passive systems for air refreshment on energy saving, in terms of cooling and heating, in buildings in Marrakech region. Many passive systems are studied including (but not limited to): thermal inertia, the earth-to-air heat exchanger, the ventilated double hollow core slab, solar chimney, thermal insulation, composite eco-friendly construction materials. This study showed that these systems has significant impact on energy saving in buildings. In this way, it was stated that thermal insulation of the roof is the most significant parameter that reduce the energy demand of a house in Marrakech region. However, the walls thermal insulation using conventional insulation materials (polystyrene, glass wool and so on…) is not mandatory. The usual way for construction of external walls in Marrakech consisting in double walls with an air gap of around 5cm (the so-called “cavity wall” technique) is largely sufficient. Indeed, our research showed that, the combination of the “cavity wall” technique and thermal insulation of the roof contributes to an energy saving of up to 40%. Further thermal insulation, especially for the slab-on-grade floors (house’s floor in contact with soil), is not recommended as it increases significantly the cooling demand. On the other hand, thermal inertia plays major role in the reduction of the ambient air amplitude which are large in Marrakech climate. On top of the recommended thermal insulation and relatively high thermal inertia, large double glazing areas oriented South, will led to the erasure of the heating demand of the building. Of course, these glazing areas should be equipped with overhangs to ovoid summer overheating. In addition solar protections of West facing façades are mandatory. The glazing areas oriented West or East, if any, should be minimized. Regarding the residual cooling load of the building, it may be met by means of semi-passive systems, such as the Earth-to-Air Heat Exchanger (the so-called “Canadian Well”). This system consists of a fan that pushes ambient hot air into a pipe buried under the ground at around 3m. The hot air is then cooled to almost 20°C, thanks to the soil inertia. This system may therefore supply the required cool air to the building.
Brahim BENHAMOU, Professor & project – University Cadi Ayad of Marrakesh
