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A primary driving force of today's urban environment is the development or enhancement of building stock with a focus on minimizing its environmental footprint, eliminating its dependence on fossil fuels, enforcing its energy efficiency and self-sufficiency, and helping alleviate climate change. Therefore, in the present study, an up-to-date review regarding the passive building retrofitting techniques for sustainable and energy efficiency design is conducted. Numerous passive building solutions and design concepts are thoroughly examined in terms of innovation and energy-saving potential. The examined techniques include novel thermal insulation materials, innovative windows systems, high thermal mass technologies, optically advanced coatings appropriate for cooling abatement, and various energy-efficient bioclimatic designs, for instance, shading techniques, mechanical ventilation in combination with heat recovery, and green roofs and façades. The scope of the present review is to thoroughly and comparatively investigate passive building energy retrofit solutions as presented in the recent scientific literature mainly within the last five or up to ten years. The passive, energy-mitigating solutions are examined in terms of energy savings primarily in residential buildings, but also in tertiary buildings, as well as of specific investment costs. Lastly, an extensive discussion evaluating the comparative advantages and disadvantages of the examined passive envelope technologies is conducted, allowing a comprehensive and multilevel comparison. [ABSTRACT FROM AUTHOR]

The present study investigates the incorporation of renewable rooftop photovoltaic systems in fully electrified residential buildings and estimates the zero-energy demand building potential in relation to the climatic data of Greece. Specifically, the aim of the analysis is to calculate the maximum possible number of stories and therefore the total building height for a complete transformation to zero-net-energy building. The energy analysis, which is conducted using the DesignBuilder software, focuses on single-floor up to seven-story buildings. The importance of the present work lies in the acknowledgment of the diversity of the Greek residential sector, the adherence to national energy policies, and the European goal of fully electrified buildings. The examined case studies are equipped with electrically driven air-to-air heat pumps serving the space heating and cooling demands and with an air-to-water heat pump covering the domestic hot water requirements. The investigated locations are the four main cities of Greece, Athens, Thessaloniki, Chania, and Kastoria, which represent the country's four climatic categories. The conducted analysis allows for the mapping of the zero-energy building potential for the climatic data of Greece, demonstrating the possibility of striking a positive building energy balance through the integration of on-site renewable energy sources and the production of necessary electrical energy. The novelty of the present work lies in the identification of a key factor, namely, the building height, which determines the feasibility of transforming multifamily buildings into zero-energy buildings. According to the analysis results, the critical number of stories is calculated at six for Chania, five for Athens, four for Thessaloniki, and two for Kastoria. Regarding a three-story residential building, the incorporation of a renewable photovoltaic system can result in an annual surplus electricity production of 13,741 kWh (Chania), 10,424 kWh (Athens), and 6931 kWh (Thessaloniki), and a corresponding coverage of 100% (Chania), 69.0% (Athens), 38.9% (Thessaloniki) and 0% (Kastoria). [ABSTRACT FROM AUTHOR]

Renewable energy source-fed heat pumps (HPs) may perform up to very high-efficiency standards, offering a promising tool in the wider residential heat decarbonization effort. In this context, this paper investigates different heating configurations utilizing various renewable thermal sources in conjunction with an HP-based system in order to determine the optimal configuration in terms of efficiency, using an existing, fully functioning residential building in Zaragoza, Spain, as our case study, comprising 40 dwellings. Four different HP configurations are investigated:, (i) an air-source system, (ii) a ground-source system, (iii) a dual-source system with solar thermal collectors, and (iv) a triple-source system based on solar, geothermal, and ambient sources. For the purpose of such investigation, detailed dynamic energy simulations are conducted through the use of the INTEMA.building tool (developed in Modelica), applying a multi-objective optimization process that aims at minimizing both the annual electricity consumption and the net present cost. It is demonstrated that the renewable thermally driven HPs are more efficient than the conventional, air-source ones, with the seasonal coefficient of performance increasing by 9.98% (ground source), 4.57% (dual source), and 17.40% (triple source), compared to the air-source heat pump system. Finally, it is revealed (via integrated techno-economic analyses) that the most effective and economical design is the dual source system, while the most expensive is the ground-source configuration. These findings can guide the ongoing design efforts on green residential heat solutions at both research and commercial implementation level. [ABSTRACT FROM AUTHOR]

The primary scope of the present work is the comprehensive investigation of a novel multigeneration system that exploits renewable energy sources, i.e. solar energy, geothermal energy, and biomass, and produces four useful outputs, i.e. electricity, heating, cooling, and green hydrogen. Solar irradiation is the primary energy source, which is exploited by parabolic trough collectors and powers a supercritical CO 2 regenerative Brayton cycle, while a biomass boiler serves as an auxiliary energy input. In addition, the whole installation includes a proton exchange membrane water electrolyzer, a water heater, as well as an absorption chiller, where a geothermal well is used for heat rejection. Apart from the thermal energy storage tank, which is coupled with the collectors, hydrogen production is used as a secondary energy storage method, as the excess produced renewable electricity feeds the electrolyzer. Consequently, the installation is examined parametrically, and optimized on steady-state conditions. Then, a dynamic simulation study is conducted for the climate data of Athens, Greece. According to the results, at the optimum operation point on steady-state conditions, the energy efficiency is determined at 37.89%, and the exergy efficiency at 20.86%. Moreover, the annual energy and exergy efficiencies are defined at 32.52%, and 18.51%, respectively. The economic evaluation analysis indicates that the payback period is about 11 years, while the internal rate of return, and the net present value are determined at 10.62% and 7,753,905 €, respectively. In addition, the system is estimated to save 3072.6 tons of CO 2 equivalent per annum. In conclusion, the proposed multigeneration system can address the various energy needs and recent environmental challenges, as a totally renewable, economically feasible, and environmentally friendly solution. • A multigeneration system that produces four useful outputs is examined. • The unit exploits three renewable sources, solar, biomass, and geothermal. • Both steady-state and dynamic analyses are carried out. • The annual energy and exergy efficiencies are defined at 32.52% and 18.51%. • The system payback period is found at 11 years, while it saves 3072.6 tn CO2-eq. [ABSTRACT FROM AUTHOR]

The focus of the current study is on a cogeneration unit designed to produce both electricity and hydrogen, which is made up of a parabolic trough collectors' field associated with a storage tank, a recuperative organic Rankine cycle module, and a proton exchange membrane water electrolyzer. The latter system operates using electricity generated by the organic Rankine cycle to produce hydrogen, which can subsequently be used as either a fuel or a storage medium for seasonal storage. The study begins with a thermodynamic investigation under both steady-state and dynamic conditions. The solar field is simulated using the Engineering Equation Solver, while the organic Rankine cycle and the electrolyzer are modeled in Aspen Plus. The analysis extends to economic and environmental evaluations, along with an optimization procedure based on techno-economic criteria. Regarding the optimum design case, the annual net electricity yield is determined at 333.8 MWh, the yearly hydrogen production amount is equal to 6236.6 kg, while the yearly energy efficiency is calculated at 14.9% and the yearly exergy efficiency at 15.9%. Finally, the economic investigation indicates the net present value is about 645,555 €, while the system contributes to saving 198.1 tn CO2-eq during the yearly operation. [Display omitted] • A solar-driven electricity and hydrogen cogeneration unit is investigated. • Thermodynamic, economic, and environmental aspects are examined. • The net electricity production is found at 333.8 MWh per year. • The hydrogen production amount is determined at 6236.6 kg per year. • The investment NPV is 645,555 €, while it saves 198.1 tn CO2-eq per year. [ABSTRACT FROM AUTHOR]