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International audience; Electricity plays a significant role in daily life and is the main component of countless applications. Thus, ongoing research is necessary to improve the existing approaches, or find new approaches, to enhancing power generation. The thermoelectric generator (TEG) is among the notable and widespread technologies used to produce electricity, and converts waste energy into electrical energy using the Seebeck effect. Due to the Seebeck effect, temperature change can be turned into electrical energy; hence, a TEG can be applied whenever there is a temperature difference. The present paper presents the theoretical background of the TEG, in addition to a comprehensive review of the TEG and its implementation in various fields. This paper also sheds light on the new technologies of the TEG and their related challenges. Notably, it was found that the TEG is efficient in hybrid heat recovery systems, such as the phase change material (PCM), heat pipe (HP), and proton exchange membrane (PEM), and the efficiency of the TEG has increased due to a set of improvements in the TEG’s materials. Moreover, results show that the TEG technology has been frequently applied in recent years, and all of the investigated papers agree that the TEG is a promising technology in power generation and heat recovery systems.

International audience; Energy has become the backbone of humanities daily activities. Heating, ventilating, and air conditioning systems (HVAC), which consume around 39% of energy in the residential sector, have turned into an essential constituent for providing fresh air, especially after COVD-19, not only in hospitals but also in any simple construction. Thus, decreasing this percentage or recovering part of the energy lost is an essential issue in today’s energy management scenarios. In this context, the present manuscript suggests a comprehensive review, classifications, critical analysis, and potential recommendations for energy recovery in air conditioning systems. It classifies energy recovery into two main categories: using lost energy for external uses, such as heating domestic water, or with other devices; and using lost energy for internal uses, such as the hot airflow which can be reused again for increasing efficiency of HVAC. In addition, this paper presents a summary of previous research and undertakes a review of the devices used for recovering energy. Furthermore, this review identifies superior devices in terms of climate and weather conditions. These objectives are accomplished by investigating around 190 published papers to conclude that energy recovery devices show a considerable effect on energy consumption in HVAC, mainly the heat pipe, fixed plate, and rotary wheel devices.

The use of phase change materials in buildings as a thermal energy storage system gained the attention of researchers all over the world. In the current study, coconut oil bio-based PCM is macro-encapsulated with enhanced thermal conductivity containers and coupled with hydronic radiant floor heating system. The study follows experimental aspect utilizing two identical small scale modular test prototypes. Investigations are directed toward studying the effect of the active CO-PCM system under different weather conditions, effect of combining active and passive systems, effect of PCM choice/type and effect of PCM location within the active floor, on the thermal and energy storage performances. Results revealed that coupling CO-PCM to active floor, passive wall and passive roof is capable of achieving load shifting and energy savings; and is affected by the control method, weather conditions, electricity tariff policy and PCM position and type. Further discussions, conclusions and perspective recommendations are summarized within the article.

The key-element in any heat recovery application is the heat exchanger. Many heat exchangers have been suggested for heat recovery applications among them Multi-Tube Tank (MTT). MTT is a heat excha...

In this paper, a new design to enhance the thermal performance of residential water heaters is suggested and investigated. The new design consists of using a mixer inside the water tank driven by electrical power. To proceed, experimental measurements are made by using thermocouples implemented in a water heater to study the thermal behavior. It is proved that the mixer could reduce the heating time about 20 min to heat water from 25 °C to 70 °C. In addition, the temperature homogeneity is also studied and it was shown that the temperature without the mixer could not be homogeneous within the water volume.

The present work proposes the engagement of relatively cold air exhausted from Heating, Ventilating and Air Conditioning (HVAC) systems, that exist in structures such as residential commercial and industrial, to reduce the PV modules’ operational temperature. To proceed, a thermal resistance model in steady state is developed along with its corresponding iterative procedure and calculations which are carried out for different configurations and scenarios. The thermal modeling was validated by comparing it to experimental measurement found in the literature. It was revealed that the PV modules’ temperature can be reduced with increasing the mass flow rate of the exhaust air. However, the air mass flow rate depends on the cooling load need; which increases with increasing the cooling load. The efficiency of the PV has shown an increase from 11 to 18% when the cooling load increases from 0 to 160 kW for a solar radiation of 500 W/m2. Moreover, there is an optimum height for the exhaust air duct for each cooling load that must be determined.

Due to global warming and environmental issues in recent times, the world's concern is oriented nowadays toward discovering new renewable energy sources and energy management methods. Particularly, researchers are emphasizing on heat recovery technologies and applications in both residential and industrial sectors. While there are plenty of review papers in the literature on the subject matter, there is always a necessity to update the literature with the new advancements in the field. In this context, the purpose of this paper is to present a recent and complete systematic comprehensive review along with critical analysis and potential recommendations related to waste heat recovery (WHR) methodologies and applications. In methodologies, heat exchangers, Rankine cycle and thermoelectric generators are studied. Moreover, applications of WHR are discussed in automotive, and in both residential and industrial zones. Studies show that the optimization of heat recovery systems lead to significant magnitudes of energy savings. On the other hand, hybrid heat recovery systems prove to be the most trending research subject nowadays. For future work, the negative effect of backpressure should be taken into consideration when recovering energy from exhaust gases of engines and power generators, and more importance should be given to hybrid systems.

International audience; Sharing of renewable energy and reduction of conventional energy consumption as an attempt to ameliorate environmental issues such as global warming has become the main concern for current developing scientific engineering research. Moreover, with the drastic increase in cooling and heating requirements in the building sector worldwide, the need for suitable technology that enables improvement in thermal performance of buildings is addressed. Utilizing phase change materials (PCMs) for thermal energy storage strategies in buildings can meet the potential thermal comfort requirements when selected properly. The current research article presents an overview of different PCM cooling applications in buildings. The reviewed applications are classified into active and passive systems. A summary of the used PCMs and their respective properties are presented as well. Primary results of the studied systems are demonstrated to be efficient in reducing indoor temperature fluctuations and energy demand during cold seasons along with the capability of triggering load reduction or shifting. Highlights  A state-of-the-art review on cooling applications of PCM in buildings  Cooling PCM applications are classified as active and passive systems  PCM serves as a promising technology for energy-efficient buildings  Combining active and passive systems can be a potential step toward NZEB

International audience; In the present study, coconut oil was used as a new bio-based phase change material (PCM) to be integrated with a quarter-scale insulated prototype of an underfloor heating system and its performance was investigated. Two different cases were studied. In the first case, the PCM was placed in an aluminum container that was positioned above an electrical heater, and the adaptation of the PCM to the floor was investigated. The second case was a control test in the absence of PCM plates. To simulate real severe winter conditions, the prototype was tested in an agricultural refrigerator to ensure constant low ambient temperature. The versatility of the underfloor system with PCM facilitates a reduction in heating load during winter while maintaining residential thermal comfort. An economic study was then conducted based on contemporary electricity shifts to inspect the system's ability in peak load shifting. The results show that the PCM achieved an increase of 53.7 % in the duration of energy transfer across charging and discharging. Furthermore, the use of the bio-PCM facilitated a shift in electricity consumption from peak time to off-peak time, yielding an annual cost reduction of 58.9% when compared with that achieved in the control test.

International audience; The present manuscript deals with experimental investigations on thermal effects of air leakage zones at the boundaries of the vehicle hood. Measurements are carried out on a Peugeot 207 (Front Wheel Drive) in wind tunnel. The front wheels are activated by the car's engine and rolling on controlling rollers built in the wind tunnel. In parallel, the wind velocity is well controlled in order to simulate real conditions of driving. The underhood compartment is equipped with 80 thermocouples distributed on different components. Three operating conditions are studied according to the engine's rpm, to the wind and wheels velocities. The leakage zones are purposely clogged with five different configurations. The effect of the leakage zones has shown significant impact on the temperature field and has been physically analyzed.

In this work, numerical results focused on the enhancement of water-air heat exchanger thermal performance are presented. New designs consisting of using diffusers between the front end openings of the vehicle and the first exchanger facing the airflow are suggested. The diffuser will reduce the velocity magnitude but over a larger area through the exchanger. This will reduce the air velocity non-uniformity upstream the exchanger and then increase its thermal performance. An in-house code is established to evaluate the thermal performance of the exchanger based on known parameters; namely, the ratio of the area of the air inlet opening to the area of the exchanger, the distance between the air inlet opening and the first exchanger at its downstream, the angle of the diffuser, and the water and air mass flow rates. It was shown that the thermal performance of the exchanger can be enhanced by up to 67% when the diffuser is present depending on the configuration.