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

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 southern 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 IV 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

Impact of passive cooling techniques on the thermal behavior of residential buildings in hot and arid regions -An experimental study-

The thermal performance of the roof is one of the most important factors for a comfortable environment. As 50% of the thermal loads received by a building come from the roof, this research seeks to find the roofing system that opposes the transmission of heat during the hottest days and promotes indoor thermal comfort. In this regard, this paper presents an experimental study carried out on four (04) testing cells constructed on a reduced scale and submitted to climatic external conditions. Three (03) cells were used to test passive cooling strategies through the roof, namely: the cool roof, ventilated roof and a roof with inverted earth pots. The fourth cell that served as cell-reference, for its part, a conventional roof. The experimentation concerned the types of roofs most used in residential buildings in Biskra, Algeria. The measurements process was effectuated in an exposed field during the month of July, prevailing the metrological data of the hot and arid climate. The obtained results show that the use of the cool-roof technique makes it possible to record the lowest internal temperatures in comparison with the other systems. Thus, the reflective coating technique is capable of reducing the internal temperature from 3.33 °C to 4.80 °C, also the internal and external surface temperature of the roofs from 5.31 °C to 10.18 °C, respectively. These experimental results confirm the effectiveness of the "cool roof" technique as an innovative and efficient solution that contributes to the achievement of the comfort conditions in a hot and arid climate by eliminating heat gains through the roof

Suppression of crown and root rot of wheat by the rhizobacterium Paenibacillus polymyxa

A seedling bioassay was developed for screening a wheat root-associated rhizobacterial strain of Paenibacillus polymyxa for ability to suppress crown and root rot pathogens of wheat. The primary aim was to evaluate the ability of P. polymyxa to suppress Fusarium graminearum, F. culmorum, F. verticillioides and Microdochium nivale, the fungal pathogens responsible for Fusarium crown and root rot and head blight of wheat in Algeria. Bioassays conducted under controlled conditions indicated that seed treatments with P. polymyxa strain SGK2 significantly reduced disease symptoms caused by all four fungal pathogens. Plant growth promotion (increased shoot and root dry weights), however, depended on the pathogen tested. Our results indicate that seed treatments with a biocontrol agent could be an additional strategy for management of wheat crown and root rot pathogens

The Potential of Using Passive Cooling Roof Techniques to Improve Thermal Performance and Energy Efficiency of Residential Buildings in Hot Arid Regions

In hot dry regions, the building envelope receives abundant solar radiation, which contributes to heat stress and indoor thermal discomfort. To mitigate overheating inside spaces, cooling is the main basic requirement during most of the year. However, due to the harsh climatic conditions, buildings fail to provide passively the required comfort conditions. Consequently, they are fully dependent on-air conditioning systems, which are huge energy consumers. As roofs are exposed to the sun throughout the daytime, they are estimated to be the main source of heat stress. In return, they can contribute significantly to achieve optimum comfort and energy savings when efficient design strategies are used in an early design stage. To examine the potential for cooling load reduction and thermal comfort enhancement by using cooling roof techniques in residential buildings, a study was performed in the city of Biskra (southern Algeria). Accordingly, an in-field measurement campaign was carried out on test-cells during five days in summer. Three different cooling roof techniques were addressed: (a) cool reflective white paint (CR), (b) white ceramic tiles (CT) and (c) a cool-ventilated roof (C-VR). These roofing alternatives were investigated by monitoring both roof surface temperatures and indoor temperatures. Comparative analysis showed that a cool-ventilated roof is the most efficient solution, reducing the average indoor temperature by 4.95 °C. A dynamic simulation study was also performed based on TRNSYS software to determine the best roofing system alternatives in terms of thermal comfort and energy consumption, considering the hottest month of the year. Simulation tests were run on a base-case model representing the common individual residential buildings in Biskra. Results showed that a double-skin roof combined with cool-reflective paint is the most efficient roofing solution. By comparison to a conventional flat roof, meaningful improvements have been achieved, including reducing thermal discomfort hours by 45.29% and lowering cooling loads from 1121.91 kWh to 741.09 kWh

An Investigation on Using Passive Cooling Roofs Techniques for Improving Climatic Performance of Residential Buildings in Hot Arid Regions based on Post-Occupancy Evaluation of Inhabitants’ Thermal Comfort Appreciations

 In hot dry climates, employing passive cooling roofs systems can providecooling needs with less amount of electrical energy. Furthermore, when focusing onliving spaces in terms of indoor thermal comfort and energy performance issues,occupant’s interaction with the building should not be underestimated. Recent studieswith occupant-based focus have shown that human behaviour significantly impactsenergy consumption, even more than building design. Likewise, understandingoccupant’s interactions within buildings plays a key role in enhancing the indoorenvironment performance. To examine the potential for cooling load reduction andthermal comfort enhancement by using cool roofs in residential buildings, a study wasperformed. Considering a sample of twelve multi-story houses located in the city ofBiskra (southern Algeria), thermal comfort conditions were analysed on the basis of apost-occupancy evaluation (POE) survey and in situ recorded measurementscampaign. The POE household survey indicated that out of 43 respondents, 54%perceive indoor thermal conditions as “hot” during summer period, while 79.33% ofthem operate HVAC device day and night. Using interviews, the study also exploressocial acceptability toward implementing passive roofing techniques. Results showedthat cool roof and cool tiles were the best accepted systems with 100% and 90% votedstrongly agree. Furthermore, the potential of thermal comfort and energy-efficiencyimprovements due to cool roofs was investigated through a dynamic simulation usingTRNSYS software. Results indicated that air temperature was reduced by an averageof 4.11°C to 3.28°C, and cooling loads have decreased to 508.60kWh/m² and384.54kWh/m² respectively during the hottest period of summer. Therefore, user-centric satisfaction as a research method would enhance future buildings design