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Building energy policies play a key role in reducing energy consumption in the EU building sector towards climate neutrality goals. This study conducts a comparative analysis of building regulations across EU Member States, with a focus on the building envelope efficiency. It examines thermal transmittance limits for windows, walls, floor, and roof to highlight regulatory differences and propose ways to improve harmonization. Challenges arise from the lack of a centralised data source, needing reliance on national regulations and similar studies to fill gaps and increase compliance with the Energy Performance of Buildings Directive (EPBD). Integrating data from various sources, including national reports and scientific literature, the study clarifies the current regulatory landscape for new and existing buildings, stressing the importance of improving the efficiency of the building envelope to minimise energy losses, and includes national climate zones for comprehensive coverage of regional climates. Variability in regulations underlines the need for a higher uniformity. Suggested steps include the development of a unified climate zone system, the establishment of guidelines for each zone, and the definition of harmonized thermal transmittance limits to facilitate a consistent regulatory framework. While this study focuses primarily on thermal transmittance, it provides a basis for future research efforts to address differences in European building codes and progress towards climate neutrality. Future developments could include the analysis of additional parameters to provide a holistic view of building energy performance and regulations supporting sustainability goals in the EU. [Display omitted] • Envelope requirements are determinant to achieve climate neutrality in Europe. • High variability characterizes building energy requirements across Member States. • Climate-consistent thermal transmittance limits can increase energy savings in buildings. • Targeted guidance is required for establishing interventions on the envelope. • Harmonization of envelope requirements aid compliance with European regulations. [ABSTRACT FROM AUTHOR]

• Worldwide mapping of the thermal behaviour of solar greenhouses by varying glasses. • Operative temperature in the free-floating regime to control the indoor microclimate. • In tropical/megathermal climates, high temperatures are reached also with the optimal glass. • In dry and temperate/mesothermal climates, the best solutions work better in winter than in summer. • In continental/microthermal and polar climates, the best solutions strongly reduce the external cold. Solar greenhouses are currently the most energy-intensive agricultural sector. In literature, there is no worldwide mapping of solar greenhouse performance under different climate scenarios. This study analyzes the performance of a Venlo solar greenhouse for 48 localities around the world. Solar greenhouses are mainly made of a transparent envelope and the effect of the direct and diffuse component of solar radiation impacts the internal plant well-being. This study aims to identify the best solution of a transparent envelope on locations with different latitudes and evenly distributed around the globe. The simulations are carried out using TRNsys, considering different thermal phenomena three-dimensional shortwave and longwave radiative exchange, airflow exchanges, presence of lamps with their exact 3D position, ground, plant evapotranspiration, and convective heat transfer coefficients. A total of 336 simulations are performed in the free-floating regime. A new index for the identification of the best glass solutions based on annual average deviation is defined. For all climates, the best glass solutions work better in winter than in summer. The optimal choice of the glass must be combined with effective scheduling of openings for natural ventilation to avoid internal overheating phenomena. [ABSTRACT FROM AUTHOR]

This study demonstrates how it is possible to increase the performances of an air-cooled heat pump by the use of Horizontal Air-Ground Heat Exchanger (HAGHE): the analysis has been earned out varying the air flow rate and heat conductivity of the ground. For a warm climate, the air treatment using HAGHE involves an improvement of the Energy Efficiency Ratio (EER) of the heat pump for the entire summertime. About the wintertime, the coefficient of performance (COP) results improved from November to February, but it is possible to install a by-pass to permit to the heat pump to work at the best conditions. [ABSTRACT FROM AUTHOR]

As a result of recent geopolitical events, zero-energy buildings must include a climate change prevention strategy. Policies are moving in the direction of an energy transition. Italian regulations, complying with European directives, are driving toward increasingly thermally insulated buildings. An important objective of this study is to determine whether updates to building energy efficiency regulations from 2005, particularly for the envelope, will result in increased envelope resilience to climate change. The building was analyzed without air conditioning, simulating an extreme case of a long period without gas supply. It has been located in all Italian climate zones and adapted to respect the local requirements imposed by national regulations for each climate zone. The legal requirements investigated are Italian Legislative Decree 192/2005, Italian Ministerial Decree 26/6/2015, and Italian Ministerial Decree 6/8/2020. The forecasting analyses were carried out considering the years 2030, 2050, and 2070 and three Representative Concentration Pathway scenarios (RCP 2.6, 4.5, and 8.5). The analysis of the results focused on trends of heating, cooling and total thermal performance index from the years 2030–2070. For all RCP scenarios, the 2015 and 2020 requirements optimize total envelope performance in terms of total thermal performance index and perform particularly well with the 2020 limits. It is clean that lowering the transmittance of the envelope components leads to an improvement in the total thermal performance index which, however, by maintaining the same trend over the years with the different scenarios, suggests that the resilience of the envelope to climate change is actually little affected by the transmittance value of the component structures. • Thermal transmittance of envelope components has little effect on climate resilience. • Heat demand will rise in summer and decrease in winter as the external temperatures rise. • Total thermal performance index decreases with transmittance, maintaining its trend over time. • Super-insulation is not the most effective energy-saving solution in the summer regime. • The optimal thickness of thermal insulation depends on the building's seasonal use. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated rehabilitation project of an abandoned farmhouse in a rural area in Southern Italy. The building underwent a functional recovery to become a tourist accommodation. The use of natural materials can reduce energy consumption and carbon footprints considering environmental sustainability aspects. A proper selection of interventions targeted for the specific warm climate has led to benefits for heating, cooling and lighting in the interior spaces. The project also includes the integration of hydraulic facilities and landscaping, such as planting hedges, green barriers and native trees. [ABSTRACT FROM AUTHOR]

This work presents the performances of an Air-Cooled Heat Pump combined with Horizontal Air Ground Heat Exchanger. The Horizontal Air Ground Heat Exchanger has been used not for the direct ventilation of the room, but for the treatment of the outside air flux of an Air-Cooled Heat Pump; consequently, the heat pump works with colder and warmer air than outside one in summer and winter, respectively. The results are exposed in terms of the Coefficient of Performance and Energy Efficiency Ratio of the Air-Cooled Heat Pump. [ABSTRACT FROM AUTHOR]

The European Energy Performance of Buildings Directive (EPBD) recast proposes, a comparative methodology to calculate cost-optimal levels of minimum energy performance requirements for buildings. This paper presents a method able to select the best retrofit action for lighting system, selectively analysing the daylight conditions and applying the cost-optimal methodology for different scenarios proposed for two existing educational buildings located in Italy. With the aim to improve both energy efficient and visual comfort conditions, the retrofit scenarios include lighting solutions with different combinations. They consider the replacement of lamps with more efficient lighting sources and the application of lighting control. [ABSTRACT FROM AUTHOR]

Daylight access and indoor thermal comfort are key issues for high design level of sustainable buildings. In fact, daylight provides energy savings and visual comfort condition that can foster higher productivity and performance. This paper proposes a case study of sizing of daylight devices for zenith light. It enables the decision-making process of the designer to reach high levels of daylight factor. The proposed method is shown with an example of application. For the case study, a room in south of Italy, 24 different solar tunnels configurations and 12 cases with different number of skylights have been evaluated. [ABSTRACT FROM AUTHOR]

The reliability of hygrothermal simulations of building components is key for designing energy efficiency measures, assessing living comfort, and preventing building damage. The model accuracy is related to the reliability of the selection of input parameters. Due to the high uncertainty, the selection of the input values is challenging. This work aims to calibrate a hygrothermal simulation model exploiting monitored values recorded in a case study located in Settequerce (Italy), to understand how close to reality a numerical model can be. Moreover, a sensitivity analysis, based on the Morris method together with a Latin Hypercube sampling, is applied to identify the input parameters that affect most significantly the simulation. The results of the calibration indicated that is possible to obtain reliable outputs by appropriately selecting materials within the database. The sensitivity analysis showed that the relative humidity under the insulation is largely influenced by the water vapor diffusion resistance factor of the plaster, applied during the renovation phase both on the internal and external side. Among the coefficients describing the coupling with the boundary conditions, only the external convective heat coefficient and the coefficient of short-wave solar radiation influence slightly the objective function. • Assessing the reliability of hygrothermal simulations. • Description of monitoring conducted in a historic building. • Calibration of the model compared to monitoring data. • Validation of the numerical model. • Sensitivity analysis of materials parameters and boundary condition coefficients. [ABSTRACT FROM AUTHOR]

• Forecast analysis of the behavior of air source heat pumps for the next 50 years for all climate zones. • The winter heating season is expected to shorten and the summer season to lengthen. • Winter operating hours will increase in very cold climates and decrease in temperate climates. • Rising temperatures will force air source heat pumps to work in extreme conditions for longer periods in hot climates. • Under extreme winter conditions, exceeding the TOL (operating limit temperature) occurs for an increasing number of hours. Climate change will impact the building sector, but the related consequences are not fully known, especially at energy system level. This paper investigates the effect of a changing climate on heat pumps, worldwide recognized as one of the most promising technology to decarbonize the building sector. Being highly dependent on outdoor temperature, the research aims to understand how air-source heat pumps (ASHPs) will perform within climate change depending on locations and scenarios. ASHPs are considered in several locations around the world selected to cover the climate variability of the Köppen-Geiger climate classification. Future projected climate scenarios to the years 2030, 2050, and 2070 are studied under three Representative Concentration Pathways (RCPs: 2.6, 4.5, 8.5) that reflect an increasing climate change severity. The forecast analysis is conducted in terms of ASHPs seasonal coefficients of performance, working hours, seasonal and annual energy consumption. Results show how a rising average temperature facilitates, in winter, the energy transition to the use of electric heat pumps to replace fossil fuels. However, differences are found among locations, scenarios, and RCPs. The research illustrates how the two effects of heating decrease and cooling increase offset or whether one seasonal consumption prevails and where this occurs. The general trend foresees a noteworthy reduction of winter energy consumption in all climate zones. Higher decreases are found for RCP 8.5 compared to RCP 2.6 and RCP 4.5 scenarios, for both radiant floor panels and fan coils, with most variations in Hanoi (-48,24 % in 2070) and Cairo (-39,59 % in 2070). Concurrently, a major rise is estimated in cooling consumption in almost each climate zone, with wider differences within RCP 8.5. In this scenario, the increase in summer energy consumption is more extreme, ranging from a minimum in Singapore (+4.20 %) and Mombasa (+4.66 %), to a maximum in Anchorage (+87.31 %), Reykjavik (+49.89 %) and Lethbridge (+56.53 %). This increase is only partly offset by the reduction in winter energy consumption, with an overall net increment in the forecasted building's energy consumption. [ABSTRACT FROM AUTHOR]

Nowadays, the design of Zero Energy Buildings requires a technology of light multi-layered walls and the envelope represents a key element to reach high level of thermal behaviour and indoor comfort. This paper illustrates a method based on a multi-criteria analysis for the design of energy-efficient precast walls in the cold climate. It encourages the use of eco-friendly building materials and local materials, in accordance with the directions of the Building Sustainable Protocols, like LEED and Itaca. The designed methodology involves the use of MatLab rel.7.0 for the computational procedure and the modeFRONTIER rel.4.3 optimization tool to evaluate the dynamic behaviour of the building components and to obtain a multitude of high efficiency configurations. The optimization has been performed in terms of steady thermal transmittance, periodic thermal transmittance, decrement factor, time shift, areal heat capacity, thermal admittance, surface mass, thickness, supply and installation costs and eco-friendly score. Furthermore, hygro-thermal and acoustic check have been evaluated for three walls, selected between the most efficient. The walls present no interstitial condensation. The results highlights that it is possible to rich high efficiency precast walls also by thin and ultra-thin thicknesses. [ABSTRACT FROM AUTHOR]

The main goal of the EPBD (Energy Performance Buildings Directive) is the improvement of the energy performance of the European buildings. The internal comfort is critically dependent on the envelope that plays a key role in the thermal balance of the entire building. In particular, the windows are one of the most critical elements in terms of solar gains, heat losses and thermal bridges; therefore, the design of high efficiency frames is requested, both in cold and warm climate, but with different peculiarity. The UNI EN ISO 10077-2 provides a methodology to evaluate the frame thermal behaviour and it proposes the criteria to validate the numerical model. This paper presents a two-dimensional numerical method for the thermal behaviour evaluation of the frame sections using GAMBIT 2.2 and ANSYS FLUENT 14.5 CFD code. The results have been validated in accordance with the UNI EN ISO 10077-2. The standard ISO replaces the air gas with a fictitious material “air solid” into the cavities. Besides the simulation carried out with ideal gas entails higher internal surface temperature than the air solid case. Therefore, the standard ISO imposes preventive computational conditions. The proposed numerical method can be implemented for several frame profiles with different features in terms of geometry and materials, representing a valid support in the design of new high thermal performance frames. [ABSTRACT FROM AUTHOR]

The improvement of energy efficiency and the integration of renewable energy in buildings are key elements of current European policies. According to the recast of the Directive EPBD (Energy Performance of Buildings), Member States have to target nZEBs (nearly zero energy buildings) and minimum energy performance requirements within a cost-optimal framework by 2020. This study reports the comparative methodology reported in the EPBD, aimed at the establishment of cost-optimality in office buildings located in a warm climate. A number of energy efficiency measures have been selected and applied to the envelope and the systems of a virtual reference office building. Technical features and energy performance calculations have been assessed for the obtained configurations. Primary energy consumption and global costs have been derived to identify the cost-optimal configuration from a financial and macroeconomic analysis. The paper shows the suitability of the methodology to support the design of cost-effective energy efficient solutions in new office buildings. Results show technical variants selection able to a decrease primary energy consumption by 39% and CO 2 emissions by 41% at the lowest cost. They also illustrate how to design cost-optimal nZEBs for a warm climate in compliance with EU (European Union) policies. [ABSTRACT FROM AUTHOR]

Taking into account the global environmental problems, there is the urgent need to reduce energy consumption and the greenhouse gas emissions in the construction sector. Environmental awareness can be achieved through the extensive application of precast systems in buildings construction. A multi-criteria analysis has been used to obtain energy-efficient precast walls for Zero Energy Building in warm climate focusing on eco-friendly building materials. The modeFRONTIER optimization tool, with the use of computational procedures developed in Matlab, has been used to assess the thermal dynamics of building components. The optimization has been carried out in terms of steady thermal transmittance, periodic thermal transmittance, decrement factor, time shift, areal heat capacity, thermal admittance, surface mass, small thickness, eco sustainability score, light-weight and costs. The best sequences of layers show repetitive features: high surface mass for the first layer (internal side), followed by eco-friendly insulating materials for the middle layer and common insulating materials for the outer layer. The results illustrate that it is possible to obtain high performance precast multi-layered walls also with light and thin solutions; in particular, the superficial mass and the internal areal heat capacity have an important role to obtain the best performance in the warm climate. [ABSTRACT FROM AUTHOR]

The recast of EU (European Union) Directive on EPBD (Energy Performance of Buildings) requires nZEBs (nearly zero energy buildings) as the building target from 2018 onwards and the establishment of cost-optimal levels of minimum energy performance requirements in buildings. This paper presents the results of the application of a methodology to identify cost-optimal levels in new residential buildings located in a warm climate. Mono-residential buildings have been considered as virtual reference buildings in this study. Different energy efficiency measures have been selected for the envelope and the systems. A combination of technical variants has been then applied to the reference case in order to obtain several configurations to be compared in terms of primary energy consumption and global costs. The cost-optimal solution is identified assessing technical features and energy performance. Standard and high efficiency buildings are analysed to show how the selected configuration allows a decrease of primary energy consumption and CO 2 emissions at the lowest cost. Results are useful for comparison with other climates and building types. They also show the feasibility of the methodology to comply with EU requirements and to support the choice of economically efficient nZEBs solutions at the design stage. [ABSTRACT FROM AUTHOR]

Zero Energy Buildings (ZEBs) are expected to play a significant role in reducing energy consumption and combating climate change. Despite this awareness, there is a lack of approaches and indicators at the regulatory level to quantify the long-term potential of strategies applied to buildings today. This study concerns the dynamic thermal modeling over the years, until 2080, of a multi-residential building located in Lecce, a city in southeastern Italy, characterized by a Mediterranean hot summer climate. Over time, Italian legislation has brought increasingly stringent limits on the design of the building envelope. Although with different regulatory limits, in the different climates across Italy, a growing trend towards a more insulated envelope, characterized by very low transmittances, has been observed over the years. This study shows how, in hot climates, buildings constructed within the legal limits will suffer from overheating over the years, necessarily leading to a disproportionate, and more extensive, use of cooling systems throughout the year. This study proposes a critical analysis of the long-term effectiveness of national strategies applied to the building envelope to date to achieve the ZEB goal, emphasizing that long-term predictive analyses become relevant in current building design and should be considered in regulations. • Building behaviour under climatic changes. • Prediction of milder winters and warmer summers. • Need to adapt energy regulations to expected climate change. • Summer air conditioning will predominate in terms of energy consumption. [ABSTRACT FROM AUTHOR]

• Micro-climate and materials characteristics strongly influence rising damp. • The evaporation rate depends on indoor temperature and relative humidity. • Lecce Stone and Carparo, typical Southern Italy materials, were investigated. • The rising damp height decreases with the increase of the evaporation rate. • The stationary state was reached one month after starting the test. Rising damp is considered one of the most widespread and damaging deterioration processes in buildings, architectural and cultural heritage. A widespread lack of knowledge of this phenomenon has often led to inadequate corrective measures with the consequent accelerated masonry deterioration. This work focuses on the dynamic evaluation of rising damp in two typical and widely used building stones in Southern Italy (Salento peninsula): Lecce Stone and Carparo. Under controlled and monitored microclimatic conditions, an experimental campaign has been carried out in laboratory, starting from two dry monolithic blocks. The blocks were periodically wetted, weighed and the height of rising damp measured in the tested materials. At the end of the campaign, the rising damp behaviour has been derived using the well-known mathematical model of Christopher Hall and William D. Hoff. Finally, the theoretical model was adapted to the case study, modifying the model constants based on the collected experimental data. The results were analysed, and the study showed a good agreement between the numerical and experimental data in both tested materials. [ABSTRACT FROM AUTHOR]

• A new protocol for the evaluation of the energy-environmental sustainability of the urban districts. • The new district protocol is a direct extension of the Apulia ITACA – Building Protocol. • Suitable for residential and non-residential buildings, current state, new construction or renovation. • The proposed district protocol can be strategically applied in the Mediterranean region. • The district protocol can be an excellent tool for territorial planning. The analysis of urban districts involves many critical issues and different design constraints related to the urban context. The characteristics of district area are based on climatic properties, geometrical design, type and number of buildings, places of construction, distances, shading patterns. This work proposes a tool able to integrate heterogeneous data coming from different users on different spatial and territorial scales, to implement efficient management of energy flows in the district. The proposed protocol is an extension of the Apulia ITACA – Building Protocol to the assessment of urban areas. It permits to evaluate any type of district, without limitation of extension and with any number of buildings. The objectivity of the evaluation using indicators applied to various thematic areas including site quality, resource consumption, environmental loads, indoor environmental quality, and quality of services is granted. It is based on a global scoring system, using the weighting on the usable surface of the buildings present in the selected urban area. The protocol permits to display the interactions between each variable within the district, evaluating the benefits in terms of costs of the targeted interventions. This work is split into two parts: Part I: the model and Part II: the case study. [ABSTRACT FROM AUTHOR]

• A new protocol for the evaluation of the energy-environmental sustainability of the urban districts. • The new district protocol is a direct extension of the ITACA Apulia protocol for buildings. • Suitable for residential and non-residential buildings, current state, new construction, or renovation. • The proposed district protocol can be strategically applied in the Mediterranean region. • The district protocol can be an excellent tool for territorial planning. Nowadays, the goal of national and international policies is to define strategies to achieve Zero Energy Districts (ZEDs). The transition from ZEBs to ZEDs entails an increase in complexity and one of the main challenges is the definition of criteria for assessing the district sustainability performances. Part I of this paper presents a new methodology for assessing all aspects related to the sustainability of a district. The new Apulia ITACA - District Protocol is the extension to the district level of the existing and widely used Italian Apulia ITACA –Building Protocol. The proposed Protocol permits the assessment of any type of district, with no extension limitations. Part II shows an application of the Protocol for the evaluation of the current state of a small district of Lecce, a city in the south-east of Italy with a Mediterranean climate. The district falls in a peripheral social housing area and is composed of two residential buildings and a school. Several strategies have been proposed to improve the overall score of the district, showing both an ideal and realistic renovation. The high flexibility of the protocol in the direct identification of the weaknesses and strengths of the district was demonstrated. [ABSTRACT FROM AUTHOR]

• Innovative micro CAES – TES trigeneration system powered by the extra-production of green energy. • Compressed air energy storage instead of electrochemical batteries for small and residential use. • No typical electrochemical battery recovery and disposal problems. • Energy storage with extremely long lifetime, absence of hysteresis cycles. • Micro CAES – TES trigeneration system coupled with HVAC system. This paper proposes the application on microscale of an innovative trigeneration system with micro CAES (Compressed Air Energy Storage) – TES (Thermal Energy Storage) and the integration of renewable energy production, focusing on the potential use for air conditioning and domestic hot water systems. The system allows storing mechanical energy in the form of elastic and thermal potential of compressed air through two thermal storage units, HTTES (High Temperature Thermal Energy Storage) and LTTES (Low Temperature Thermal Energy Storage). The proposed system is tested on a single-family building in a warm climate. The analysis is carried out for integrated and independent operating modes. In integrated mode, the LTTES refrigerant charge and the vapor compression chiller operate simultaneously to cover the building's thermal load. In this case the energy expenditure is only related to the power supply of the chiller. In independent mode, the cold storage and the chiller work alternately during evening operation to limit the absorption of energy from the distribution network. The results show that, in integrated operating mode with partial recirculation and internal temperature conditions of 26 °C and 50% of relative humidity, the system reaches, in relation to the peak thermal load, a maximum operating time of 236 min. The minimum operating time of 26 min is reached using the full external air operating mode with an internal temperature of 26 °C and relative humidity of 40%. In independent operation mode, it is possible to sustain the evening thermal load for up to a maximum of 5 h without electricity absorption from the distribution network. [ABSTRACT FROM AUTHOR]

• An ASHP coupled with an EAHX system is proposed and modelled. • The ASHP- EAHX behaviour is tested in four locations with different climates. • The model has been validated with a real case. • The ASHP- EAHX allows to use ASHP also with lower external temperatures. • For cold extremely climate, the reduction of the shutdown periods of ASHP. Geothermal energy has a huge potential in building applications. This paper proposes the use of an Air-Source Heat Pump (ASHP) system coupled with a Horizontal Earth-To-Air Heat Exchanger (EAHX) to reduce energy consumption in buildings. The novelty is to geothermally pre-heat or pre-cool the air source of the ASHP through the EAHX, reducing the electric power needed, keeping constant heating/cooling capacity. The behaviour of ASHP-EAHX system has been investigated by a numerical model implemented in TRNSYS. A total of 54 combinations have been obtained and tested varying ground thermal properties, burial depth, air flow rate and pipe length. The model has been validated with a real case showing a good agreement between simulated and monitored data. The study is focused on the city of Turin (North of Italy), compared with Brindisi (South of Italy), and extremely cold and hot climates like Tromsø (Norway) and Béchar (Algeria), respectively. The ASHP-EAXH performance has been investigated, by the comparison with the traditional ASHP, using different coefficients, such as the Coefficient of Performance (COP), the Energy Efficiency Ratio (EER), the Seasonal Coefficient of Performance (SCOP), and the Seasonal Energy Efficiency Ratio (SEER). The paper reveals how the ASHP-EAHX system show higher performance compared to the traditional ASHP, in all seasons. The overall merit is, for cold extremely climate, the reduction of the shutdown periods, when the outside temperature is below the limit operating temperature, and to allow the extension of the use of the heat pump to locations, where it is currently not convenient for the average outside temperature lower than the limit operating temperature of the heat pump. [ABSTRACT FROM AUTHOR]

• A novel compressed air energy storage for small and residential use. • Trigeneration powered by the extra-production of green energy and thermal and mechanical storage. • Potential direct use of compressed air for residential applications, e.g. air conditioning, tooling. • Energy storage with extremely long lifetime, absence of hysteresis cycles. • An energy storage system with very low environmental impact. There is not a real "storage market" and the range of technical solutions for electrical storage appears to be underdeveloped. The use of electrochemical batteries seems to be the easiest and cheapest way, but some problems related to disposal, average life span and storage capacity, still put a brake on their diffusion. The micro CAES-TES (Compressed Air Energy Storage – Thermal Energy Storage) systems with small renewable energy plants for cogeneration and trigeneration represent an important development perspective thank to the reuse of the heat generated at the stage of air compression (for heating) and air expansion (for cooling). This improves the complexity of the entire system because of the heat exchange and thermal storage units must match the capacities and performances of the air compression/expansion units. The paper presents a new mathematical model for micro CAES-TES systems, implemented in Matlab software environment. The novelty is the use of air compressed energy storage in small and residential applications, a trigeneration due to reuse of heat from air compression and expansion stage, only renewable energy used. By keeping the initial investment low, the analysis is extended to the optimal system configuration and identifies key parameters that have a dominant influence on improving system efficiency and provides useful guidance for CAES-TES system design. The results show that, for an air storage volume of 4 m3, the optimal configuration is with a compression ratio of 15 splitted in two stages, charging time 5 h, mechanical storage efficiency 48%, compression air flow rate 3.73 kg/hour. The proposed system has a possible future development overall if combined with new possible scenarios of direct use of compressed air in the residential sector. [ABSTRACT FROM AUTHOR]

• A novel decision-making procedure for the hybrid system analysis is proposed. • A new set of dimensionless energy, economic and environmental indicators are defined. • A width parametric analysis for different system configurations and loads is made. • Multi-objective optimization with the selection of the best system configurations. • Impact of battery lifespan increase and incentives is evaluated. The development of hybrid renewable systems is an economically competitive solution to reach energy decarbonization and reduction of greenhouse gasses. Based on the literature, energy, economic and environmental indicators were rarely simultaneously employed in the optimization of a hybrid renewable system. In addition, there is no procedures or a set of indicators to be applied uniformly in all applications for the shared analysis. The paper presents a novel energy-economic-environmental multi-criteria decision-making in the optimization of a hybrid renewable system, based on a new set of dimensionless indicators, proposed as a standard for future applications. The procedure compares the entire PV-wind-battery system configuration with the PV-wind, PV-battery and wind-battery system sub-configurations. A width parametric and multi-optimization analysis permit the identification of the most proper nominal powers of each system component. The procedure proposed was applied in a Mediterranean residential building, demonstrating that some system configurations allow complying simultaneously with at least two of the three energy objectives proposed, the cost-optimal level and the maximum reduction of emissions, for specific values of the load. The solar source was the most suitable both from energy, environmental and economic point of view, while the use of the wind source leads to a greater system operating time in the nominal power conditions. The study pointed out and quantified that, for specific loads, PV, wind and battery powers, the development of specific incentives for wind systems and of battery systems with a higher lifespan can help to make the hybrid systems more economically competitive. [ABSTRACT FROM AUTHOR]

Coupling water electrolyzers with solar and wind sources may be a promising solution in the near future for utilizing excess renewable energy. Indeed, many researchers have investigated various green hydrogen production systems, but a systematic approach should be developed to compare them. In addition, it is crucial to understand which solar and wind-based green hydrogen production systems have been studied and the literature gap on this topic. This review presents the latest research on green hydrogen production systems integrated with solar and wind technologies. One of the most significant novelties of this paper is to suggest a preliminary pathway and standardization strategy for the comparison of different green hydrogen production systems based on solar and wind sources. Various data and information are extracted from the most relevant papers in this field, such as renewable systems investigated, the location of the studied system, connection with the electrical grid, research type developed, final utilization of hydrogen considered, and performance indicators employed. This work will be an introductory guide for the community interested in green hydrogen production systems. • Comparison of solar and wind-based hydrogen production systems. • The combination of a water electrolyzer with solar and wind energy may be a promising solution. • More attention is needed on transient electrolyzer behaviour, battery degradation, and grid stability. [ABSTRACT FROM AUTHOR]

• A comparison between the experimental and numerical results has been done. • CFD analysis of a Horizontal air-ground heat exchangers (HAGHE). • Experimental data of a real HAGHE application. • HAGHE behaviour shows a low dependence from the ground thermal conductivity. • Burial depth influences the HAGHE behaviour in the first ground layers. A large part of primary energy is used for heating and cooling the buildings. The exploitation of renewable resources in the building sector is still critical to ensure a high level of energy and environmental sustainability. Nowadays, a great attention is focused on geothermal energy, which reduces heating and cooling in buildings, allowing natural pre-heating and pre-cooling of the inlet air. The effect of different burial depth and thermal conductivity of ground on thermal performance of HAGHE under transient conditions has been analyzed. The results show that the transient thermal performance of HAGHE is independent from the thermal conductivity of the ground but is dependent on burial depth. In this work, it is presented the experimental validation of a mathematical model implemented by the CFD Fluent for the simulation of heat exchange that takes place within a HAGHE for geothermal heat pumps. The validation of the model is based on a comparison between the experimental data, obtained from the software, and real data, for a HAGHE located in the town of Rubiana (Turin-Italy). [ABSTRACT FROM AUTHOR]

A multi-objective optimization method for the dimensioning of hybrid photovoltaic-wind-battery systems HPWBS characterized by high-energy reliability is proposed. The energy reliability-constrained (ERC) method permits choosing the most proper indicators combination to be constrained or optimized as a function of the specific application. The ERC method is applicable to grid-connected and stand-alone hybrid systems with and without storage battery, for residential as well as for other uses. The reliability indicators defined are: the photovoltaic-wind fraction, energy fraction required by the load satisfied by the HPWBS; the utilization factor, energy fraction produced sent to the load; the manufacturability that characterizes the energy produced sent to the load in relation to the nominal power of the system. The ERC method was employed for the multi-objective optimization of a grid-connected hybrid system with and without storage battery for the electric energy supply to an urban residential building in a Mediterranean climate. A parametric analysis, for different loads, by varying the photovoltaic and wind power and the battery storage capacity, was developed to evaluate the annual energy reliability in a dimensionless form of 450 system configurations. The results allowed obtaining empiric correlations to be used in the system design. Finally, the ERC method application allowed achieving optimal system configurations with greater reliability compared with those provided by the Pareto-front method. [ABSTRACT FROM AUTHOR]

This paper delves into the potential impact of a changing climate on the energy performance of European buildings. Research aims to provide a comprehensive evaluation of current energy requirements focusing on the envelope, considering existing regulations in national policies. Energy simulations are conducted at 94 locations across the European Union to cover the climatic variability and Koppen climate classification. The research analyzes future climate scenarios for the years 2030, 2050, and 2070, using three different Representative Concentration Pathways (RCP 2.6, 4.5, 8.5). According to a comprehensive analysis of heating, cooling, and overall energy performance, climate plays a significant role in buildings' energy balance. In moderately cool climate countries, the demand for air conditioning is projected to decrease in the years ahead. Conversely, in countries with a warm climate, there is a projected increase in the overall energy demand. Consequently, a revision of current energy regulations should be a priority. Providing insights into the relation between building design, energy efficiency, and climate change, the research identifies policy adjustments to ensure buildings can effectively respond to changing climatic conditions. A holistic and dynamic approach can support building design accounting for long-term impacts of climate change to create resilient and energy-efficient structures. • National building energy regulations of European Member States do not tackle climate change. • Over next decades, a decrease in heating demand is forecasted across all climate zones. • There is potential for a future considerable increase of cooling demand in Europe. • A reduction in total building energy demand in colder climates and an increase in warmer climates can be expected. • Revise national energy regulations, especially in warmer zones, to curb the expected rise in Europe's total energy demand. [ABSTRACT FROM AUTHOR]

In recent years, research has shown a growing interest in the use of hybrid wind photovoltaic (PV) systems that provide better performance compared to the use of a single component due to complementarity in meeting electricity demand. Over the past twenty-five years, hundreds of articles have addressed the topic of hybrid systems considering different configurations and final uses and, over the past decades, many reviews have made a comprehensive summary of various results obtained. However, some reviews deal with the research in a too general and qualitative way, without providing quantitative data, and other reviews are too focused on a specific topic aspect. To provide a qualitative-quantitative prospect of the research trend in the last twenty-five years, the present work is aimed at carrying out a literature review and statistical analysis starting from data extracted from the 550 most relevant and recent articles concerning hybrid systems, published between 1995 and 2020. The review aim was to produce an upgradable matrix literature database that schematizes the content of all articles in terms of different categories, such as the geographical distribution, their component configurations, operating mode and the auxiliary components used to support it, their intended uses and study methodologies (simulation, experimental, economic, energy, environmental and social analysis etc.) and software used. In addition, all the optimization algorithm, energy, economic, environmental and social indicators available in the literature were extracted and elaborated to identify the most used. The 550 articles were analysed, compared, and classified into several categories to provide an overall framework of the state of the art. The objective is to clearly and appropriately show important trends and findings in the development of hybrid wind and solar PV experimental, simulation and optimization projects. Data are elaborated to obtain a statistical analysis for each category or a combination of categories. In particular, the analysis highlighted that research is more focused on testing systems in warm or temperate localities, with the Köppen climate groups B and C prevalent over the others. From the geographical point of view, Asia is the continent most involved in world research (with China, India and Iran the first three countries for total publications produced). However, also in other parts of the world, a growing interest was noticed in this technology. The prevalent tested system configuration mode is the stand-alone hybrid systems, in a wide variety of climates and especially for residential uses. Simulations are mostly implemented in the analysed publications, mainly through HOMER and MATLAB software. Parametric analysis is widely used for optimal system design with a large variety of techniques. In particular, the system performance is examined mostly from an energy point of view. Economic analysis is also very common, alone or in combination with energy analysis. The most frequently used optimization algorithms are the particle swarm optimization (PSO) and genetic algorithm (GA), while the loss of power supply probability (LPSP) and renewable fraction (RE) for the energy analysis, the net present cost (NPC) and cost of energy (COE) for the economic analysis and the emissions (E) of CO 2 for the environmental analysis are most widespread indicators. Finally, an analysis on the size of the system components is performed to study which renewable source is more preferred at low and high installed power, for stand-alone, grid-connected systems and overall, considering different intended uses. The analysis highlights that PV systems are preferred at low installed powers, especially for residential use and stand-alone mode, while wind systems, in addition to being extensively used for low installed powers, demonstrates higher employment compared to PV systems as the power increases. The paper findings and upgradable matrix literature database are proposed as a valuable tool for engineers, experts and national and international policymakers. • 550 relevant papers were reviewed and used to create an upgradable matrix literature database. • Asia is the continent most involved in world research with Iran, India, and China. • The dry and temperate climate zones of Köppen climate group BWh are the most investigated. • Stand-alone hybrid systems and residential use are the most explored applications. • The use of photovoltaic system is preferred for low installed powers, while wind systems also for high installed powers. [ABSTRACT FROM AUTHOR]

• Worldwide techno-economic optimization of PV-wind hybrid renewable energy system (HRES). • Optimal stand-alone (SA) and grid-connected (GD) HRES in 48 localities were mapped. • Yearly average solar and wind source around 300–400 W/m2 and 1.5–2.5 m/s make HRES reliable. • SA HRES are mainly based on the PV-battery system and are more reliable and cheaper. • GC HRES are mainly based on the wind system and are very profitable with the feed-in-tariff. In the last years, a significant interest in research in stand-alone (SA) and grid-connected (GC) photovoltaic (PV)-wind hybrid renewable energy systems (HRES) is observed for their complementary in the satisfaction of the electrical energy demand in many sectors. However, direct comparisons between the techno-economic performance of two system modes under the same operating conditions are rarely carried out. Additionally, most of the researches are limited to specific weather conditions. This work aims to bridge the lack of this type of investigations providing a worldwide techno-economic mapping and optimization of SA and GC PV-wind HRES to supply the electrical demand of an office building district. For this purpose, energy and economic optimization problems were formulated to find the optimal SA and GC systems worldwide among 343 HRES system power configurations located in 48 different localities, uniformly divided in the sub-group of the Koppen classification. The energy reliability and economic profitability of optimal systems were geographically mapped worldwide. In general, the energy or economic optimizations of SA HRES do not lead to highly profitable systems; instead, feed-in-tariff to sell the energy in excess assures viable GC HRES in many localities. However, economically optimal SA and GC HRES, respectively, do not everywhere comply with the threshold value of 70% of the satisfied energy required by the load and are characterized by a high level of energy exchanged with the grid. The study highlighted that the most suitable climate conditions to install a SA HRES are: (i) Toamasina (Madagascar) from an energy point of view, with 76% of load satisfied and 76% of the energy generated utilized to supply the load; (ii) Cambridge Bay (Canada) from an economic point of view, with 11.1% of the capital cost recovered each year; instead, the most suitable climate conditions to install a GC HRES are: (iii) New Delhi (India) from an energy point of view, with 48% of energy exchanged with the grid per each kWh required by the load; (iv) Lihue (Hawaii, United States) from an economic point of view, with 24.3% of the capital cost recovered each year. [ABSTRACT FROM AUTHOR]