• Energy Research

Le défi dans la conception de bâtiments à énergie zéro (ZEB) est de trouver la meilleure combinaison de stratégies de conception qui seraient confrontées aux problèmes de performance énergétique d'un bâtiment particulier. Cet article décrit la méthodologie et le potentiel de rentabilité pour optimiser la conception d'un bâtiment à énergie nette nulle (NZEB) dans une région à climat froid au Liban ; Cèdres. Plus précisément, l'algorithme génétique de non tri (NSGA-II) est choisi afin de minimiser les demandes thermiques, électriques et le coût du cycle de vie (LCC) tout en atteignant le bilan énergétique net nul ; et ainsi obtenir le front de Pareto. Une technique de prise de décision de classement (ELECTRE III) est appliquée au front de Pareto afin d'obtenir une solution optimale. Un large éventail de mesures d'efficacité énergétique sont étudiées, en plus des systèmes d'énergie solaire utilisés pour produire l'électricité et l'eau chaude nécessaires à des fins domestiques. Les résultats indiquent clairement que, pour la conception d'un NZEB résidentiel en climat froid, il est essentiel de minimiser la charge thermique de l'espace à travers une enveloppe de bâtiment à haute performance thermique. Envelopper un niveau élevé d'isolation est une étape essentielle pour réduire la forte demande de chauffage. Les charges thermiques des bâtiments sont réduites de 33,19 %. De plus, le LCC est diminué de 31,09%. El desafío en el diseño de edificios de energía cero (ZEB) es encontrar la mejor combinación de estrategias de diseño que enfrenten los problemas de rendimiento energético de un edificio en particular. Este documento describe la metodología y el potencial de rentabilidad para optimizar el diseño de edificios de energía neta cero (NZEB) en una región de clima frío en el Líbano; Cedars. Específicamente, se elige el algoritmo genético no clasificador (NSGA-II) para minimizar las demandas térmicas, eléctricas y el coste del ciclo de vida (LCC) mientras se alcanza el balance energético neto cero; y así obtener el frente de Pareto. Se aplica una técnica de toma de decisiones de clasificación (ELECTRE III) al frente de Pareto para obtener una solución óptima. Se investiga una amplia gama de medidas de eficiencia energética, además de que se emplean sistemas de energía solar para producir la electricidad y el agua caliente necesarios para fines domésticos. Los resultados indican claramente que, para diseñar un NZEB residencial en clima frío, es esencial minimizar la carga térmica del espacio a través de una envolvente de edificio con alto rendimiento térmico. Envolver un alto nivel de aislamiento es un paso esencial para disminuir la alta demanda de calefacción. Las cargas térmicas de los edificios disminuyen un 33,19%. Además, el LCC se reduce en un 31,09%. The challenge in Zero energy building (ZEB) design is to find the best combination of design strategies that would face the energy performance problems of a particular building. This paper outlines the methodology and the cost-effectiveness potential for optimizing the design of net-zero energy building (NZEB) in a cold climate region in Lebanon; Cedars. Specifically, the non-sorting genetic algorithm (NSGA-II) is chosen in order to minimize thermal, electrical demands and life cycle cost (LCC) while reaching the net zero energy balance; and thus getting the Pareto-front. A ranking decision making technique (ELECTRE III) is applied to the Pareto-front so as to obtain one optimal solution. A wide range of energy efficiency measures are investigated, besides solar energy systems are employed to produce required electricity and hot water for domestic purposes. The results clearly indicate that, for designing a residential NZEB in cold climate, it is essential to minimize the space thermal load through a building envelope with high thermal performance. Envelop high level of insulation is an essential step to decrease the high heating demand. Building thermal loads are decreased by 33.19%. Moreover the LCC is decreased by 31.09%. يتمثل التحدي في تصميم مبنى الطاقة الصفرية (ZEB) في العثور على أفضل مزيج من استراتيجيات التصميم التي ستواجه مشاكل أداء الطاقة لمبنى معين. تحدد هذه الورقة المنهجية وإمكانية الفعالية من حيث التكلفة لتحسين تصميم بناء الطاقة الصافية الصفرية (NZEB) في منطقة مناخية باردة في لبنان ؛ الأرز. على وجه التحديد، يتم اختيار الخوارزمية الجينية غير الفرز (NSGA - II) من أجل تقليل المتطلبات الحرارية والكهربائية وتكلفة دورة الحياة (LCC) مع الوصول إلى صافي توازن الطاقة الصفري ؛ وبالتالي الحصول على واجهة باريتو. يتم تطبيق تقنية اتخاذ القرار التصنيفي (ELECTRE III) على واجهة باريتو للحصول على حل مثالي واحد. يتم التحقيق في مجموعة واسعة من تدابير كفاءة الطاقة، إلى جانب استخدام أنظمة الطاقة الشمسية لإنتاج الكهرباء والماء الساخن المطلوبين للأغراض المنزلية. تشير النتائج بوضوح إلى أنه لتصميم NZEB سكني في المناخ البارد، من الضروري تقليل الحمل الحراري الفضائي من خلال غلاف مبنى ذو أداء حراري عالٍ. يعد غلاف مستوى عالٍ من العزل خطوة أساسية لتقليل الطلب المرتفع على التدفئة. انخفضت الأحمال الحرارية للمبنى بنسبة 33.19 ٪. علاوة على ذلك، انخفض LCC بنسبة 31.09 ٪.

The thermal conductivity of commonly used phase change materials (PCM) for thermal energy storage (TES), such as, fatty acids, paraffin etc., is relatively poor, which is one of the main drawbacks for limiting their utility. In the recent past, few attempts have been made to enhance the thermal conductivity of PCM by mixing different additives in the appropriate amount. Graphene nanoparticles, having higher thermal conductivity may be a potential candidate for the same, when mixed appropriately with different PCM. In present study authors have carried out the numerical investigation for the melting of graphene nano-particles dispersed PCM filled in an aluminum square cavity heated from one side. In this work, the graphene nanoparticles are mixed in three different volumetric ratios (1%, 3%, and 5%), with three different commonly used categories of organic, inorganic and paraffin PCM (namely, Capric Acid, CaCl2·6H2O, and n-octadecane) to see the effect on melting of composite PCM developed. The resulting transient isotherms, velocity fields, and melting front and melt fractions thus have been deliberated in detail. These results clearly indicate that the addition of graphene nanoparticles increases melting rate but can also hamper the convection heat transfer within large cavities. The study also shows that such enhanced PCM can be effectively used for different TES applications in different fields. The prediction of temperature variation and rate of melting or solidification may be found useful especially for designing such TES devices.

Abstract Worldwide, the residential buildings are consuming a considerable amount of energy. The high potential of buildings towards energy efficiency has drawn special attention to the passive design parameters. A comprehensive study on optimal passive design for residential buildings is presented in this paper. Twenty-five different climates are simulated with the aim to produce best practices to reduce building energy demands (for cooling and heating) in addition to the life-cycle cost (LCC). The occupants' adaptive thermal comfort is also improved by implementing the appropriate passive cooling strategies such as blinds and natural ventilation. In this respect, the implemented methodology is composed of four phases: building energy simulation, optimization, Multi-criteria Decision Making (MCDM), sensitivity study, and finally an adaptive comfort analysis. An optimal passive solution of the studied building indicates the potential to save up to 54%, 87% and 52% of the cooling demands (Qcool), heating demands (Qheat) and LCC respectively with respect to the initial configuration. The obtained optimal passive parameters are validated with the National Renewable Energy Laboratory NREL benchmark for low energy building's envelope. Additionally, the integrated passive cooling strategies have demonstrated its competency since it leads to a significant overheating decrease.

The challenge in Net Zero Energy Building (NZEB) design is to find the best combination of design strategies that will face the energy performance problems of a particular building. This paper presents a methodology for the simulation-based multi-criteria optimization of NZEBs. Its main features include four steps: building simulation, optimization process, multi-criteria decision making (MCDM) and testing solution's robustness. The methodology is applied to investigate the cost-effectiveness potential for optimizing the design of NZEBs in different case studies taken as diverse climatic zones in Lebanon and France. The investigated design parameters include: external walls and roof insulation thickness, windows glazing type, cooling and heating set points, and window to wall ratio. Furthermore, the inspected RE systems include: solar domestic hot water (SDHW) and photovoltaic (PV) array. The proposed methodology is a useful tool to enhance NZEBs design and to facilitate decision making in early phases of building design. Specifically, the non-dominated sorting genetic algorithm (NSGA-II) is chosen in order to minimize thermal, electrical demands and life cycle cost (LCC) while reaching the net zero energy balance; thus getting the Pareto-front. A ranking decision making technique Elimination and Choice Expressing the Reality (ELECTRE III) is applied to the Pareto-front so as to obtain one optimal solution.

The double-skin roofs investigated in this paper are formed by adding a metallic screen on an existing sheet metal roof. The system enhances passive cooling of dwellings and can help diminishing power costs for air conditioning in summer or in tropical and arid countries. In this work, radiation, convection and conduction heat transfers are investigated. Depending on its surface properties, the screen reflects a large amount of oncoming solar radiation. Natural convection in the channel underneath drives off the residual heat. The bi-dimensional numerical simulation of the heat transfers through the double skin reveals the most important parameters for the system's efficiency. They are, by order of importance, the sheet metal surface emissivity, the screen internal and external surface emissivity, the insulation thickness and the inclination angle for a channel width over 6 cm. The influence of those parameters on Rayleigh and Nusselt numbers is also investigated. Temperature and air velocity profiles on several channel cross-sections are plotted and discussed.

Thermal bridges are weak areas of the building envelope in which they can significantly increase the energy load of houses. In this study, we tackle the thermal bridges resulting from windows offset from exterior walls. First, we present an innovative insulating coating which can be used to limit thermal bridge effects. Second, we compute the cooling/heating load coming from the windows offset thermal bridges of a typical French house before and after adding the insulating coating. Third, we compare the time lag and decrement factor when the 2D heat transfer effects of the thermal bridge are taken into consideration. The methodology is to incorporate 2D heat transfer into a whole building energy simulation program. This is done through co-simulation between a 2D heat transfer model developed in MATLAB and the building energy simulation software EnergyPlus using the software BCVTB. This latter enables us to link the two programs and allow them to exchange data at each simulation time step. Results showed that the windows offset thermal bridges energy load percentage of the total house load constitutes around 2-8% depending whether exterior walls have interior insulation or not. Applying 1 cm and 2 cm of the coating on these thermal bridges reduces the windows offset energy load by about 24-50%. Concerning time lag and decrement factor, we obtain high values for decrement factor and low values for the time lag for wall positions near the thermal bridge. Applying the coating decreases, significantly, the decrement factor and increases the time lag.

Solar Photovoltaic (PV) cells can absorb up to 80% of the incident solar radiation obtained from the solar band, however, only a small amount of this absorbed incident energy is transformed into electricity depending on the conversion efficiency of the PV cells and part of remainder energy increases the temperature of PV cell. High solar radiation and ambient temperature lead to an elevated photovoltaic cell operating temperature, which affects its lifespan and power output adversely. Number of techniques have been attempted to maintain the temperature of photovoltaic cells close to their nominal operating value. In the present review various cooling techniques such as natural and forced air cooling, hydraulic cooling, heat pipe cooling, cooling with phase change materials and thermoelectric cooling of PV panels are discussed at length. It is important to note that, though cooling techniques are highly needed to regulate the PV module temperature, especially for mega installations, these should be economically viable too.