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Net-zero energy buildings (NZEBs) have been considered as an efficient solution to limit the growing energy consumption and pollution emissions from buildings. The configurations and the capacities of the implemented renewable energy systems in NZEBs should be wisely selected to ensure the intended performance objective. This study aims to optimize, investigate and compare six renewable energy solution sets for designing NZEBs in three different climates: Indore (cooling dominant), Tromso (heating dominant), and Beijing (mixed climate). The optimization is carried out using a multi-criteria decision-making methodology. The implemented methodology is composed of two phases. In the first phase, the optimal sizes of solution sets in each climate are derived and analyzed. The effectiveness of optimal solution sets is evaluated with respect to economy, environment, energy and grid stress. In the second phase, recommendations for each region are offered according to the overall performance evaluation results. The evaluation criteria include life cycle cost, payback period, levelized cost of energy, CO 2 eq emissions, grid interaction index, load matching index, and total energy consumption. The analyses show that, in Indore (hot climate), it is recommended to utilize the solution set composed of air source heat pump for cooling and flat plate solar collectors for domestic hot water (DHW) production. In Tromso (cold climate), the use of a biodiesel generator is promising to produce both electricity and hot steam for heating as well as DHW use. In Beijing (mixed climate), it is recommended to utilize electric chillers for cooling and natural gas condensing boiler for heating and DHW usage. • Renewable energy solution sets for net zero energy building are optimized. • Hot, cold and mixed climates are investigated. • Building performance is analyzed in terms of energy, cost, and CO 2eq emissions. • Load matching and grid stress analysis is conducted. • Suitable design options for each climate are offered. [ABSTRACT FROM AUTHOR]

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. Highlights • Residential building's passive design parameters are optimized. • Effect of different climates of Köppen Geiger classification is studied. • Thermal comfort and energy performance of the case-studies are significantly enhanced. • Passive cooling strategies lead to adequate thermal comfort and fewer cooling systems. [ABSTRACT FROM AUTHOR]

Enhancing efficiency, meeting environmental standards, and preserving fuel resources are highly important objectives in power generation systems, at a time where world is endangered by several energetic, environmental, and health crises. Thus, better designs are constantly sought to increase the performance of such systems. In this study, an environment friendly trigeneration system based on solid oxide fuel cell (SOFC) is selected and designed for domestic applications. Negligible emissions are thus recorded as the SOFC is fueled solely by hydrogen. The system is modeled following three steps: the energy simulation of residential building to determine its demands, the system’s prime mover–SOFC, and the trigeneration recovery system ensuring the maximum coverage of heating, cooling, and domestic hot water loads respectively. The system is then evaluated under the 4-E assessment criteria: energy, exergy, economy, and environment. Depending on these criteria, the system is multi-objectively optimized. Two operation strategies are adopted: off-grid following electrical load and on-grid base load operations. Optimization results show that the trigeneration system is energetically and economically superior and performs well under both strategies. The maximum energy and exergy efficiencies (65.2% and 45.77%) and minimum system cost rate (22.2 cents/kWh) are obtained under on-grid base load operation. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a dynamic simulation model to predict the performance of an ASHPWH (air source heat pump water heater). The developed model is used to assess its performance in the Lebanese context. It is shown that for the four Lebanese climatic zones, the expected monthly values of the average COP (coefficient of performance) varies from 2.9 to 5, leading to high efficiencies compared with conventional electric water heaters. The energy savings and GHG (greenhouse gas) emissions reduction are investigated for each zone. Furthermore, it is recommended to use the ASHPWH during the period of highest daily ambient temperatures (noon or afternoon), assuming that the electricity tariff and hot water loads are constant. In addition, an optimal management model for the ASHPWH is developed and applied for a typical winter day of Beirut. Moreover, the developed dynamic model of ASHPWH is used to compare the performance of three similar systems that differ only with the condenser geometry, where results show that using mini-condenser geometries increase the COP (coefficient of performance) and consequently, more energy is saved as well as more GHG emissions are reduced. In addition, the condenser “surface compactness” is increased giving rise to an efficient compact heat exchanger. [Copyright &y& Elsevier]

Abstract: This paper presents a review of the energy status, conventional and renewable, in Lebanon and illustrates their problems with the suggested recommendations. In addition, a detailed review of the principal directorates of the electricity of Lebanon Company (EDL) is also presented all along with the existing problems and recommended solutions. An economic, environmental optimization of different power sources is studied, where three scenarios are introduced based on the fuel source of different CCGT power plants. The results emphasized on the maximum possible use of wind energy and natural gas in electricity generation. Based on the optimization study, a five-year master plan for electricity generation is modeled. The suggested plan has an investment capital cost of 5553 M$ with the savings and additional incomes being 5900 M$ compared to EDL financial status in the adopted base year, 2009. In addition, this plan exceeds the trend to introduce a 12% share of renewable energy in the power sector by 2020, where the share is supposed to be about 15% out of the total installed capacity before this date. The concluding remarks highlight the role of politics in the development of the energy sector. [Copyright &y& Elsevier]

Integrating heat exchanger pipes with structural foundations in one system has created a new renewable solution for buildings' thermal loads. However, the interaction between thermal and geotechnical loads makes their design more complex and challenging. This review-study represents the current state of knowledge about the thermal and thermo-mechanical behaviors of energy piles. It also investigates the key parameters that affect their design concerning the piles' dimensions, the arrangement of pipes, concrete admixture, and fluid characteristics. It is found that the thermal efficiency improves significantly by increasing the number of pipes inside the piles and by adding thermally conductive materials to the concrete within acceptable limits. Besides, this paper reviews most of the studies conducted on optimizing vertical ground heat exchangers coupled with heat pumps. Objective functions, decision variables, design constraints, and optimization methods are specified and listed. It is concluded that a multi-objective optimization is highly recommended to enhance the dual performance of an energy pile system coupled with a heat pump using the 4E evaluation criteria (energy, exergy, economy, and environment) while ensuring the safety of the foundation under thermal cyclic loads. [ABSTRACT FROM AUTHOR]

• A comprehensive review on building retrofit measures towards net-zero energy buildings is conducted. • Climate and occupant activities of fifty case studies are surveyed. • Passive, active, and renewable building energy retrofit measures are discussed. • The assessment methodology of retrofit measure selection is detailed. • Future studies are proposed to fully explore the potential of net zero energy buildings as sustainable structures. High energy consumption is a critical problem that governments are trying to overcome. The concept of Net Zero Energy Building (NZEB) has recently emerged as one of the solutions that can help address this problem, reduce pollution impacts, and mitigate the effects of global warming. The present paper discusses the current research on building energy retrofitting through a comprehensive review of more than fifty case studies, highlighting the ones that aimed to reach a NZEB. The passive, active, and renewable retrofit measures used are discussed. The assessment methodology for choosing the retrofit measures are classified into multi-criteria and optimization approaches and the available simulation tools and algorithms are detailed. The review also indicates that photovoltaic panels are used in retrofitting in all case studies to achieve NZEB, with the tilt angles of photovoltaic panels and solar collectors steeper in colder climates. It is noted that retrofitted residential NZEB buildings exhibit the lowest total energy consumption across all climate types when compared to other NZEB types, such as educational, business, and institutional buildings. Needed research directions include taking into account climate change in the modeling, and the use of bio-based materials to further reduce the building carbon footprint. [ABSTRACT FROM AUTHOR]