Towards Sustainable Cities: A Review of Zero Energy Buildings Techniques and Global Activities in Residential Buildings

: Under rapid urbanization-induced global warming and resource depletion, growing interest in zero-energy building (ZEB) and zero-emission building (ZEB) technologies have emerged globally to improve energy performance in homes and shape sustainable cities. Although several countries have released ZEB-enhanced strategies and set national standards and policies to promote ZEBs, construction projects are still limited to demonstration projects. This paper reviews global ZEB activities and state-of-the-art technologies for energy-efﬁcient residential building technologies [based on an evaluation of 40 residential buildings]. Over 40 residential buildings on different continents were reviewed, and their technical details and performance were evaluated. Our results show that 62.5% of the buildings achieved the +ZEB standard, 25% of the buildings were net-zero energy buildings, and only 12.5% of the buildings were near-zero energy buildings. Solar PV is the most widely used renewable energy source in the studied cases, while in warmer climates, advanced cooling technologies and heat pumps are the preferred technologies. A building envelope and thermal ventilation with heat recovery are essential in cold climates. Our systematic analysis reveals that the thermal performance of the building envelope and solar energy are the most effective mechanisms for achieving energy efﬁciency and shaping sustainable cities.


Introduction
Climate-change-induced high temperatures and CO 2 emissions have sparked widespread concern globally in increasingly risk-exposed cities [1,2].Climate change is one of society's most significant and pressing challenges today and harms human life, communities, nature, and the environment [3].Greenhouse gas emissions (GHG) from fuel consumption to cool buildings have significantly accelerated global warming [4,5].When the temperature rises to abnormal levels, this is usually accompanied by an increase in energy consumption for cooling, affecting the high energy expenditure share.As a result, designing zero-energy sustainable buildings as a significant part of the city becomes a requirement rather than a risk-mitigation option [6,7].The transition to renewable energy and meeting the climate goals of the Paris Agreement depend significantly on cities. Buildings are essential to sustainable development because they consume approximately 40% of the primary energy worldwide and contribute about 24% of greenhouse gas emissions [8].In the Middle East, buildings consume 45% of the primary energy; during the summer, 70% of this is expended on air conditioning [9].The ambient temperature can exceed 40 • C for more than 300 h in summer, and this value is expected to double by 2025.Since 2006, many slogans have been used, such as "net-zero-energy buildings", "zero-energy-cost buildings", "nearly-zero-energy buildings", "zero-emission buildings", and "net-zero-energy buildings" [10].All refer to a ZEB with high energy performance, which means that the Energies 2023, 16, 3775 2 of 26 total amount of energy used by the building comes from renewable energy sources using technology such as heat pumps, high-efficiency windows and insulation, and solar panels.These techniques release less greenhouse gas into the atmosphere during their operation [11].
Energy consumption and resource depletion will continue until residential buildings are designed to satisfy people's living demands using technology that utilizes sustainable sources on-site or nearby to meet the growing energy demand [12].Many countries have proposed initiatives to promote zero-energy buildings, such as the 2020 Energy Strategy and the United States program for sustainable cities [10].These aim to develop building codes, construct ZEBs that are commercially sustainable, and achieve "marketing ZEBs and zero-energy commercial buildings by 2025" [13].Other countries, such as China, Japan, Korea, and the GCC countries, have followed suit to chart their policies toward ZEBs by 2025 [14].In a global effort, 50 demonstration solar heating and cooling projects of the International Energy Agency (IEA) have been built according to the passive house standard [15].Twenty low-energy houses have been constructed in Sweden to help people worldwide agree on defining passive homes and low-energy dwellings [16].
One of the most effective zero-energy techniques is passive solar design, which involves orienting a building to take advantage of the sun's natural heating and cooling effects [17].This can be achieved through large windows and skylights, shading devices, and thermal mass materials [18,19].Another technique involves using energy-efficient materials and technologies, such as insulation, high-efficiency HVAC systems, and LED lighting [20].These can help reduce the energy needed to heat, cool, and power a building, thus reducing its environmental impact [21].This research reviewed the global progress of ZEBs and effective technologies adopted in practice by 40 selected zero-energy houses from different climates around the world in detail.The chosen cases cover all ZEBs and are thoroughly discussed for theoretical comparisons with general practices worldwide.This study aims to help architects design energy-neutral houses with existing materials and non-complex technologies.

Literature Review 2.1. Zero-Energy Buildings
Zero-energy buildings (ZEBs) are structures designed to consume only as much energy as they can produce through renewable energy sources over the course of a year.ZEBs are also referred to as net-zero-energy buildings (NZEBs) [22].The goal of ZEBs is to minimize energy consumption by using energy-efficient technologies and renewable energy sources, such as solar panels, wind turbines, and geothermal systems.This can include features such as high levels of insulation, energy-efficient lighting and appliances, and passive solar design [23].ZEBs are becoming increasingly popular to reduce greenhouse gas emissions and combat climate change.In addition to being environmentally friendly, ZEBs can also offer cost savings over time, as owners and occupants can save money on energy bills [24].ZEBs can be designed for a variety of uses, including residential, commercial, and industrial buildings [10].However, designing and constructing a ZEB can be more complex and expensive than designing and constructing a traditional building and requires a multidisciplinary approach involving architects, engineers, builders, and energy experts.Despite the challenges, ZEBs are seen as an important part of the transition to a more sustainable and low-carbon future and have the potential to greatly reduce energy consumption and greenhouse gas emissions in the built environment [25].
Various advancements in energy efficiency and numerous initiatives to reduce the environmental impact of building emissions, which rose by around 2% for the second year between 2017 and 2018, have been released [26].These gains were mostly caused by expanding the world's population and a steadily expanding building floor area.In 2018, the building and construction sector was responsible for 36% of final energy use and 39% of carbon dioxide (CO 2 ) emissions from energy processes [27].Buildings play a crucial role in the transition to clean energy [28,29].In response to the Paris Agreement in 2015, Energies 2023, 16, 3775 3 of 26 the European Union (EU) set the lofty target of reducing greenhouse gas (GHG) emissions by at least 40% below 1990 levels by 2030 [30].The EU has embraced a variety of steps to become the first climate-neutral continent by 2050, including moving to a clean, circular, and sustainable economy [31].With the Renovation Wave (European Commission, 2020b), a component of the Green Deal, the European Union aims to double the yearly energy renovation rate of residential and non-residential buildings and repair 35 million building units by 2030 [3,6].In 2018, an updated Renewable Energy Directive was implemented to promote using renewable energy sources, especially within the built environment [32].The Energy Performance of Buildings of 2010 and its recast in 2018 will significantly contribute to making Europe's buildings highly energy efficient and decarbonized by 2050 [12].Additionally, it facilitates the cost-effective transformation of existing buildings into nearly zero-energy buildings.
Furthermore, all new buildings have had to use negligible amounts of energy since 2020 [9].Following Horizon 2020, a EUR 80 billion EU research and innovation program that funded many research projects on these topics from 2014 to 2020, Horizon Europe (European Commission, 2019a) will invest EUR 100 billion to pursue its targets between 2021 and 2028 [8].Two factors are crucial in environmentally friendly urban planning; by 2030, Europe will be climate-proof and equitable.Europe will be prepared to recover quickly from natural disasters and adapt to the changing climate, and 100 climate-neutral cities will be run by and for their residents by 2030 [33,34].These missions highlight the EU's aspirations to combat the environmental impact of the building sector.Additionally, positive energy communities, districts, and blocks can efficiently use their capacity to generate and store renewable energy [11,19].With roughly 67% of the global population and accounting for approximately 70% of global energy consumption and CO 2 emissions, urban areas are undeniably crucial to the ongoing transition to renewable energies and low-emission technologies [3,9].
For this reason, in 2018, the European Union launched the "Positive Energy Districts and Neighborhoods for Sustainable Urban Development" program as part of the Strategic Energy Technology (SET) Plan "Smart Cities and Communities [35]."By 2025, this program will have helped to plan, deploy, and replicate 100 Positive Energy Districts (PED) to make buildings and cities more sustainable [21].Regarding the above, many studies have investigated the impact of the windcatcher, which is an environmentally friendly technique and a viable and attractive strategy for sustainable building concepts to provide thermal comfort, indoor air quality, and low energy consumption [36].

Zero-Energy Building Strategies
Net-zero buildings are designed to use as little energy as possible by using passive building design [7,11,21].Passive building design is a strategy that makes the most of natural sources of light, heat, and ventilation.For example, the Sustainable Energy Fund Office Building in Pennsylvania, as mentioned in gbdmagazine.com, is the first energypositive building in the Lehigh Valley [12].This building uses a combination of geothermal heating, triple-glazed curtain walls, and energy-efficient lighting to achieve net-zero energy consumption [22].Similarly, the Joyce Centre for Partnership & Innovation in Canada, as mentioned in gbdmagazine.com,uses geothermal heating and cooling, radiant heating and cooling, and a building envelope that maximizes natural light to achieve net-zero energy consumption [37].Another example of zero-energy buildings describes nearly zero-energy mixed-use buildings in China.These buildings are powered by rooftop photovoltaic panels and house 3000 students, faculty, and staff [12].
The development also encourages low-carbon transportation.These case studies demonstrate how materials that increase the energy efficiency of building projects, such as ROCKWOOL insulation, can be used to reduce the environmental footprint of buildings [38].For example, the nearly zero-energy family house built in Glostrup, Denmark, uses a combination of insulation, heat recovery, and solar panels to achieve net-zero energy consumption [19].energy than the building needs, ZEBs and Net ZEBs producing as much energy as needed, and buildings near ZEBs having less energy than their needs [11].In this paper, ZEB refers to a building that is connected to one or more utility grids, such as heating and cooling systems, gas pipe networks, biomass networks, or an electricity grid, so that the building can export and import energy from the grids to avoid energy storage on the site [18].Over the past 2 decades, at least 300 projects have been completed with a zero-energy balance worldwide.

Case Study Definition
Energy Plus Building (+ZEB) Sunlight House-Austria [39] -Buildings that generate their energy from renewable and sustainable sources -They produce more energy than their consumption and deliver more energy to the supply systems over more than a year The development also encourages low-carbon transportation.These case studies demonstrate how materials that increase the energy efficiency of building projects, such as ROCKWOOL insulation, can be used to reduce the environmental footprint of buildings [38].For example, the nearly zero-energy family house built in Glostrup, Denmark, uses a combination of insulation, heat recovery, and solar panels to achieve net-zero energy consumption [19].Table 1 lists the most used ZEB terms, such as ZEBs producing more energy than the building needs, ZEBs and Net ZEBs producing as much energy as needed, and buildings near ZEBs having less energy than their needs [11].In this paper, ZEB refers to a building that is connected to one or more utility grids, such as heating and cooling systems, gas pipe networks, biomass networks, or an electricity grid, so that the building can export and import energy from the grids to avoid energy storage on the site [18].Over the past 2 decades, at least 300 projects have been completed with a zero-energy balance worldwide.

Category Case Study Definition
Energy Plus Building (+ZEB) Sunlight House-Austria [39] -Buildings that generate their energy from renewable and sustainable sources -They produce more energy than their consumption and deliver more energy to the supply systems over more than a year Zero Energy Building (ZEB) Efficiency House Plus-Germany [39] -Independent buildings that do not require connection to the grid even as a backup -They produce as much energy as they need and can store excess energy for use at nighttime Net-Zero Energy Building (Net ZEB) Energy Flex House-Denmark [7] -Buildings that rely on neutral energy for over a year and do not need any fossil fuels -They produce as much energy as they need and take a lot of energy from the grid and deliver it to the supply grid.
Near Zero Energy Building (Near ZEB) Carbon Light Home-UK [40] -Buildings that have high-energy performance -They deliver more energy to the supply -They produce less energy than they need -The amount of energy required is covered to an extent by energy from other sources

Methodological Framework
The effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings can be evaluated in several ways.One approach is to measure the energy performance of the building over time and compare it to industry standards or benchmarks.This can help identify areas where improvements can be made and demonstrate the techniques' effectiveness.Another approach is to assess the building's overall environmental impact, considering factors such as carbon emissions, water consumption, and waste generation.This can provide a more comprehensive picture of the building's sustainability and help identify areas for further improvements.
This research aims to look at high-efficiency, zero-energy homes to improve thermal performance and lower the energy needed to cool homes.Thus, looking into the expected benefits, energy savings from renewable and sustainable sources, and thermal comfort of the people living in the house is important.Our results should encourage ZEB techniques Zero Energy Building (ZEB) Efficiency House Plus-Germany [39] -Independent buildings that do not require connection to the grid even as a backup -They produce as much energy as they need and can store excess energy for use at nighttime The development also encourages low-carbon transportation.These case studies demonstrate how materials that increase the energy efficiency of building projects, such as ROCKWOOL insulation, can be used to reduce the environmental footprint of buildings [38].For example, the nearly zero-energy family house built in Glostrup, Denmark, uses a combination of insulation, heat recovery, and solar panels to achieve net-zero energy consumption [19].Table 1 lists the most used ZEB terms, such as ZEBs producing more energy than the building needs, ZEBs and Net ZEBs producing as much energy as needed, and buildings near ZEBs having less energy than their needs [11].In this paper, ZEB refers to a building that is connected to one or more utility grids, such as heating and cooling systems, gas pipe networks, biomass networks, or an electricity grid, so that the building can export and import energy from the grids to avoid energy storage on the site [18].Over the past 2 decades, at least 300 projects have been completed with a zero-energy balance worldwide.

Category Case Study Definition
Energy Plus Building (+ZEB) Sunlight House-Austria [39] -Buildings that generate their energy from renewable and sustainable sources -They produce more energy than their consumption and deliver more energy to the supply systems over more than a year Zero Energy Building (ZEB) Efficiency House Plus-Germany [39] -Independent buildings that do not require connection to the grid even as a backup -They produce as much energy as they need and can store excess energy for use at nighttime Net-Zero Energy Building (Net ZEB) Energy Flex House-Denmark [7] -Buildings that rely on neutral energy for over a year and do not need any fossil fuels -They produce as much energy as they need and take a lot of energy from the grid and deliver it to the supply grid.
Near Zero Energy Building (Near ZEB) Carbon Light Home-UK [40] -Buildings that have high-energy performance -They deliver more energy to the supply -They produce less energy than they need -The amount of energy required is covered to an extent by energy from other sources

Methodological Framework
The effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings can be evaluated in several ways.One approach is to measure the energy performance of the building over time and compare it to industry standards or benchmarks.This can help identify areas where improvements can be made and demonstrate the techniques' effectiveness.Another approach is to assess the building's overall environmental impact, considering factors such as carbon emissions, water consumption, and waste generation.This can provide a more comprehensive picture of the building's sustainability and help identify areas for further improvements.
This research aims to look at high-efficiency, zero-energy homes to improve thermal performance and lower the energy needed to cool homes.Thus, looking into the expected benefits, energy savings from renewable and sustainable sources, and thermal comfort of the people living in the house is important.Our results should encourage ZEB techniques Net-Zero Energy Building (Net ZEB) Energy Flex House-Denmark [7] -Buildings that rely on neutral energy for over a year and do not need any fossil fuels -They produce as much energy as they need and take a lot of energy from the grid and deliver it to the supply grid.
The development also encourages low-carbon transportation.These case studies demonstrate how materials that increase the energy efficiency of building projects, such as ROCKWOOL insulation, can be used to reduce the environmental footprint of buildings [38].For example, the nearly zero-energy family house built in Glostrup, Denmark, uses a combination of insulation, heat recovery, and solar panels to achieve net-zero energy consumption [19].Table 1 lists the most used ZEB terms, such as ZEBs producing more energy than the building needs, ZEBs and Net ZEBs producing as much energy as needed, and buildings near ZEBs having less energy than their needs [11].In this paper, ZEB refers to a building that is connected to one or more utility grids, such as heating and cooling systems, gas pipe networks, biomass networks, or an electricity grid, so that the building can export and import energy from the grids to avoid energy storage on the site [18].Over the past 2 decades, at least 300 projects have been completed with a zero-energy balance worldwide.

Category Case Study Definition
Energy Plus Building (+ZEB) Sunlight House-Austria [39] -Buildings that generate their energy from renewable and sustainable sources -They produce more energy than their consumption and deliver more energy to the supply systems over more than a year Zero Energy Building (ZEB) Efficiency House Plus-Germany [39] -Independent buildings that do not require connection to the grid even as a backup -They produce as much energy as they need and can store excess energy for use at nighttime Net-Zero Energy Building (Net ZEB) Energy Flex House-Denmark [7] -Buildings that rely on neutral energy for over a year and do not need any fossil fuels -They produce as much energy as they need and take a lot of energy from the grid and deliver it to the supply grid.
Near Zero Energy Building (Near ZEB) Carbon Light Home-UK [40] -Buildings that have high-energy performance -They deliver more energy to the supply -They produce less energy than they need -The amount of energy required is covered to an extent by energy from other sources

Methodological Framework
The effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings can be evaluated in several ways.One approach is to measure the energy performance of the building over time and compare it to industry standards or benchmarks.This can help identify areas where improvements can be made and demonstrate the techniques' effectiveness.Another approach is to assess the building's overall environmental impact, considering factors such as carbon emissions, water consumption, and waste generation.This can provide a more comprehensive picture of the building's sustainability and help identify areas for further improvements.
This research aims to look at high-efficiency, zero-energy homes to improve thermal performance and lower the energy needed to cool homes.Thus, looking into the expected benefits, energy savings from renewable and sustainable sources, and thermal comfort of the people living in the house is important.Our results should encourage ZEB techniques The development also encourages low-carbon transportation.These case studies demonstrate how materials that increase the energy efficiency of building projects, such as ROCKWOOL insulation, can be used to reduce the environmental footprint of buildings [38].For example, the nearly zero-energy family house built in Glostrup, Denmark, uses a combination of insulation, heat recovery, and solar panels to achieve net-zero energy consumption [19].Table 1 lists the most used ZEB terms, such as ZEBs producing more energy than the building needs, ZEBs and Net ZEBs producing as much energy as needed, and buildings near ZEBs having less energy than their needs [11].In this paper, ZEB refers to a building that is connected to one or more utility grids, such as heating and cooling systems, gas pipe networks, biomass networks, or an electricity grid, so that the building can export and import energy from the grids to avoid energy storage on the site [18].Over the past 2 decades, at least 300 projects have been completed with a zero-energy balance worldwide.

Category Case Study Definition
Energy Plus Building (+ZEB) Sunlight House-Austria [39] -Buildings that generate their energy from renewable and sustainable sources -They produce more energy than their consumption and deliver more energy to the supply systems over more than a year Zero Energy Building (ZEB) Efficiency House Plus-Germany [39] -Independent buildings that do not require connection to the grid even as a backup -They produce as much energy as they need and can store excess energy for use at nighttime Net-Zero Energy Building (Net ZEB) Energy Flex House-Denmark [7] -Buildings that rely on neutral energy for over a year and do not need any fossil fuels -They produce as much energy as they need and take a lot of energy from the grid and deliver it to the supply grid.
Near Zero Energy Building (Near ZEB) Carbon Light Home-UK [40] -Buildings that have high-energy performance -They deliver more energy to the supply -They produce less energy than they need -The amount of energy required is covered to an extent by energy from other sources

Methodological Framework
The effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings can be evaluated in several ways.One approach is to measure the energy performance of the building over time and compare it to industry standards or benchmarks.This can help identify areas where improvements can be made and demonstrate the techniques' effectiveness.Another approach is to assess the building's overall environmental impact, considering factors such as carbon emissions, water consumption, and waste generation.This can provide a more comprehensive picture of the building's sustainability and help identify areas for further improvements.
This research aims to look at high-efficiency, zero-energy homes to improve thermal performance and lower the energy needed to cool homes.Thus, looking into the expected benefits, energy savings from renewable and sustainable sources, and thermal comfort of the people living in the house is important.Our results should encourage ZEB techniques

Methodological Framework
The effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings can be evaluated in several ways.One approach is to measure the energy performance of the building over time and compare it to industry standards or benchmarks.This can help identify areas where improvements can be made and demonstrate the techniques' effectiveness.Another approach is to assess the building's overall environmental impact, considering factors such as carbon emissions, water consumption, and waste generation.This can provide a more comprehensive picture of the building's sustainability and help identify areas for further improvements.
This research aims to look at high-efficiency, zero-energy homes to improve thermal performance and lower the energy needed to cool homes.Thus, looking into the expected benefits, energy savings from renewable and sustainable sources, and thermal comfort of the people living in the house is important.Our results should encourage ZEB techniques to be used in the building process of a zero-energy-efficient model in the residential sector of a hot and humid climate.This study used a descriptive-analytical method and conducted a mix of statistical, quantitative, and qualitative data analyses regarding energy performance.We analyzed the related performance indicators and extrapolated the various techniques and climate data.Literature reviews and online searches were used to collect data on global ZEB activities and cutting-edge technologies.A total of 40 zero-energy houses constructed in several countries worldwide were selected to examine zero-energy technologies and to identify their similarities, differences, and local adaptations.The criteria for choosing Energies 2023, 16, 3775 5 of 26 cases were as follows: (1) buildings are detached or semi-detached single-family houses; (2) the buildings cover different climates and various challenges.The results are presented in Section 3: passive energy techniques in buildings, service systems techniques (annual energy supply and annual energy consumption), and renewable energy generation.

Case Studies
Table 2 lists the location, climates, building area, techniques, legislative context, climate challenges, and energy performance of 40 ZEB projects around the world .Data were available in terms of technical documentation, physical characteristics, size, and type of dwelling, as well as the energy needs of each building.Figure 1 gives an overview and global indication of the activities of the ZEBs (For more details, see Appendix A, Tables A1-A5).The architectural features of the 40 pilot energy-efficient building projects selected from the Annex 52/(IEA) Task 40 project database were used for analysis [21].We consider the indicators of the ZEBs' activities based on Thomsen and Wittchen's approach.to be used in the building process of a zero-energy-efficient model in the residential sector of a hot and humid climate.This study used a descriptive-analytical method and conducted a mix of statistical, quantitative, and qualitative data analyses regarding energy performance.We analyzed the related performance indicators and extrapolated the various techniques and climate data.Literature reviews and online searches were used to collect data on global ZEB activities and cutting-edge technologies.A total of 40 zero-energy houses constructed in several countries worldwide were selected to examine zero-energy technologies and to identify their similarities, differences, and local adaptations.The criteria for choosing cases were as follows: (1) buildings are detached or semi-detached single-family houses; (2) the buildings cover different climates and various challenges.The results are presented in Section 3: passive energy techniques in buildings, service systems techniques (annual energy supply and annual energy consumption), and renewable energy generation.

Case Studies
Table 2 lists the location, climates, building area, techniques, legislative context, climate challenges, and energy performance of 40 ZEB projects around the world .Data were available in terms of technical documentation, physical characteristics, size, and type of dwelling, as well as the energy needs of each building.Figure 1 gives an overview and global indication of the activities of the ZEBs (For more details, see Appendix A, Tables A1-A5).The architectural features of the 40 pilot energy-efficient building projects selected from the Annex 52/(IEA) Task 40 project database were used for analysis [21].We consider the indicators of the ZEBs' activities based on Thomsen and Wittchen's approach.

Residential Building Type and Scale
The chosen ZEBs varied in size and had building floor areas ranging from 55.8 to 550 m 2 .In comparison, the average floor area of a global dwelling is 85 m 2 .The Para Eco House, despite being the smallest in size, is an integrated house, and the technologies used in the building could easily be scaled up to create single-story buildings that are designed to be very efficient to minimize energy consumption and reduce the passive impact on the environment.Solar and wind power technologies in these buildings require a large installation area either within the site footprint or somewhere near the building.For small residential buildings with limited roof areas, it can be technically difficult to achieve the goal of a zero-energy building.

Climatic Zones
To classify the collected ZEBs by climatic zone, a common methodology was developed.Within each region, homogeneous or different climatic zones were considered to understand the difference in building energy use and renewable energy generation caused by climate variations (see Figure 2).The climatic zones were divided into five regions, and a roadmap was developed, warm temperate (19), polar (4), arid (4), Mediterranean (5), and snow (8).Since energy demand in regions of moderate to high temperature and humidity increases drastically, an emphasis is placed on moisture control.by climate variations (see Figure 2).The climatic zones were divided into five regions, and a roadmap was developed, warm temperate (19), polar (4), arid (4), Mediterranean (5), and snow (8).Since energy demand in regions of moderate to high temperature and humidity increases drastically, an emphasis is placed on moisture control.

The State-of-the-Art Technologies
General strategies of ZEBs include (1) reducing the need for energy through energyefficient technologies and (2) adopting renewable energy [22].Not all technologies are suitable for each building, and some technologies' implementation can be limited by a small building area.This study groups all technologies into four categories: passive technologies, active technologies, energy management, and renewable energy.

Passive Energy Technologies
Passive technologies are energy-saving techniques that consume no or negligible energy during operation.They have a long history in residential buildings compared with active strategies.Passive technology can be grouped in general into four categories: energy efficiency, building envelope (thermal insulation), passive cooling or heating, and thermal energy storage.

Buildings Envelope
An efficient building envelope can effectively reduce heat loss or gain through heat transfer.In hot climates, building envelopes are designed to reduce the penetration of solar radiation.The technical indicators are U-values and solar heat gain coefficients.Other than their unusually high levels of floor insulation, most ZEBs use relatively traditional foundations.Internal insulation systems are common; however, external insulation is often added to control thermal heat from the soil.As for the U-values of floors, the maximum value range is between 0.07 W/m 2 •K and 0.90 W/m 2 •K.In cold weather zones, a strict minimum standard (UF < 0.07 W/m 2 •K to a maximum value of 0.15 W/m 2 •K) is set for efficient insulation.Figure 3 summarizes the mean U-values of the ZEBs' envelopes.
Regarding exterior wall systems in all the buildings, various types of wall systems ranging from relatively standard frame constructions with an insulated exterior shell to the SIPS system were used to double up the walls.Insulation levels usually range from about 20 cm to 30 cm.U-values vary between 0.08 W/m 2 •K as a minimum value and 0.90 W/m 2 •K as a maximum value.Perhaps the biggest problem with wall systems is the cost.There are many ways to reduce airflow through walls, and the cost is more than double

The State-of-the-Art Technologies
General strategies of ZEBs include (1) reducing the need for energy through energyefficient technologies and (2) adopting renewable energy [22].Not all technologies are suitable for each building, and some technologies' implementation can be limited by a small building area.This study groups all technologies into four categories: passive technologies, active technologies, energy management, and renewable energy.

Passive Energy Technologies
Passive technologies are energy-saving techniques that consume no or negligible energy during operation.They have a long history in residential buildings compared with active strategies.Passive technology can be grouped in general into four categories: energy efficiency, building envelope (thermal insulation), passive cooling or heating, and thermal energy storage.

Buildings Envelope
An efficient building envelope can effectively reduce heat loss or gain through heat transfer.In hot climates, building envelopes are designed to reduce the penetration of solar radiation.The technical indicators are U-values and solar heat gain coefficients.Other than their unusually high levels of floor insulation, most ZEBs use relatively traditional foundations.Internal insulation systems are common; however, external insulation is often added to control thermal heat from the soil.As for the U-values of floors, the maximum value range is between 0.07 W/m 2 •K and 0.90 W/m 2 •K.In cold weather zones, a strict minimum standard (UF < 0.07 W/m 2 •K to a maximum value of 0.15 W/m 2 •K) is set for efficient insulation.Figure 3 summarizes the mean U-values of the ZEBs' envelopes.
Regarding exterior wall systems in all the buildings, various types of wall systems ranging from relatively standard frame constructions with an insulated exterior shell to the SIPS system were used to double up the walls.Insulation levels usually range from about 20 cm to 30 cm.U-values vary between 0.08 W/m 2 •K as a minimum value and 0.90 W/m 2 •K as a maximum value.Perhaps the biggest problem with wall systems is the cost.There are many ways to reduce airflow through walls, and the cost is more than double the cost of a conventional building wall, which costs anywhere from USD 20 to USD 70 per m 2 .
In all buildings (except buildings with flat surfaces), the sharp angles restrict the installation of insulating materials in the sloping ceilings at the ends of the truss.These angles are not well suited to glass fiber insulation due to the interstitial condensation in the fiberglass layer.This reduces the total sufficient RSI value of the roof, and the problem is worse for low-sloping roofs.The Sabic and J&P house [31] and The Para Eco House [30] (arid climate) are characterized by a flat roof of reinforced concrete developed with a combination of thermal insulation and radiation reflectors that demonstrated a significant reduction in the heat passing through the concrete roof.According to Figure 3, all buildings' U-values are between 0.07 W/m 2 •K and 1.46 W/m 2 •K.Heat gain/loss through roof systems in case study buildings is more critical in low-rise buildings.Energy-efficient roof technologies include insulated and reflective roofs that reflect solar radiation, which are efficient in cooling-dominant climates.As for windows, U-values vary between 0.50 W/m 2 •K and 1.65 W/m 2 •K, which suggests low values that are very close to the Passive House standard.A clear and interesting feature regarding windows' U-values is that the buildings with the best net-zero-energy performance (The NZERTF [29], Home for Life [23], Solar House [25], Lighthouse [26], and Para Eco House [30]) undergo heating and cooling challenges that are characterized by the U-values being greater than the values indicated in the windows for other buildings with cooling challenges (the Baytna villa [49] and Eco House [39]).This is a clear and interesting feature.However, insulation may not be very effective in cooling-dominant buildings with large internal heat loads in warm climates.Thus, the selection of the window may be more important for ZEB case studies than previously thought.The aim of most of the ZEB buildings' designs (all case studies) is to use the most technologically advanced window (the most energy efficient).The best reflective glass is selected to reduce solar heat and gain more energy efficiently.However, smaller or better-insulated window systems (arid climate) also reduce light absorption.

Passive Heating
Passive heating technologies are strategies for using natural energy sources, such as solar energy or the ambient environment, to harvest energy with no or limited energy costs.Common techniques include the Trombe wall, ventilated double-skin façades, and solar houses.One of the most effective zero-energy techniques is passive solar design, which involves orienting a building to take advantage of the sun's natural heating and cooling effects.This can be achieved through large windows and skylights, shading In all buildings (except buildings with flat surfaces), the sharp angles restrict the installation of insulating materials in the sloping ceilings at the ends of the truss.These angles are not well suited to glass fiber insulation due to the interstitial condensation in the fiberglass layer.This reduces the total sufficient RSI value of the roof, and the problem is worse for low-sloping roofs.The Sabic and J&P house [31] and The Para Eco House [30] (arid climate) are characterized by a flat roof of reinforced concrete developed with a combination of thermal insulation and radiation reflectors that demonstrated a significant reduction in the heat passing through the concrete roof.According to Figure 3, all buildings' U-values are between 0.07 W/m 2 •K and 1.46 W/m 2 •K.Heat gain/loss through roof systems in case study buildings is more critical in low-rise buildings.Energy-efficient roof technologies include insulated and reflective roofs that reflect solar radiation, which are efficient in cooling-dominant climates.
As for windows, U-values vary between 0.50 W/m 2 •K and 1.65 W/m 2 •K, which sug- gests low values that are very close to the Passive House standard.A clear and interesting feature regarding windows' U-values is that the buildings with the best net-zero-energy performance (The NZERTF [29], Home for Life [23], Solar House [25], Lighthouse [26], and Para Eco House [30]) undergo heating and cooling challenges that are characterized by the U-values being greater than the values indicated in the windows for other buildings with cooling challenges (the Baytna villa [49] and Eco House [39]).This is a clear and interesting feature.However, insulation may not be very effective in cooling-dominant buildings with large internal heat loads in warm climates.Thus, the selection of the window may be more important for ZEB case studies than previously thought.The aim of most of the ZEB buildings' designs (all case studies) is to use the most technologically advanced window (the most energy efficient).The best reflective glass is selected to reduce solar heat and gain more energy efficiently.However, smaller or better-insulated window systems (arid climate) also reduce light absorption.

Passive Heating
Passive heating technologies are strategies for using natural energy sources, such as solar energy or the ambient environment, to harvest energy with no or limited energy costs.Common techniques include the Trombe wall, ventilated double-skin façades, and solar houses.One of the most effective zero-energy techniques is passive solar design, which involves orienting a building to take advantage of the sun's natural heating and cooling effects.This can be achieved through large windows and skylights, shading devices, and thermal mass materials.Other techniques use energy-efficient materials and technologies, such as insulation, high-efficiency HVAC systems, and LED lighting.These can help reduce the energy needed to heat, cool, and power a building, thus reducing its environmental impact.A "solar house" [25] is another example of a passive strategy that uses direct solar irradiation for space heating.

Passive Cooling
Thermal mass is the most commonly used passive cooling technique to reduce daytime peak load and internal daytime temperatures.In the case study buildings, thermal mass benefits are systematically assessed using a sensitivity analysis.It is generally believed that thermal mass should be combined with night ventilation (natural/mechanical) to take full advantage of its energy-saving potential.This design strategy in buildings in dry and Mediterranean climates has proven effective at avoiding the summer heat and reducing cooling requirements.A ventilation system is used in all ZEB case studies.Outdoor air is supplied via heat recovery ventilators (HRV), and this unit brings outdoor air into the house and continuously exhausts indoor air.This design strategy has proven effective at avoiding the summer heat and reducing cooling requirements in the "Sabic & J&P House" [31], "Eco House" [39], "solar village" [40], and "baytna villa" [49].Passive cooling technology's contribution to reducing total energy consumption is 486 KWh/m 2 /year, which is 17% of the total annual energy consumption in the 40 ZEB case studies, as shown in Tables A4 and A5 and Figure 4.
Energies 2023, 16, x FOR PEER REVIEW 9 of 25 devices, and thermal mass materials.Other techniques use energy-efficient materials and technologies, such as insulation, high-efficiency HVAC systems, and LED lighting.These can help reduce the energy needed to heat, cool, and power a building, thus reducing its environmental impact.A "solar house" [25] is another example of a passive strategy that uses direct solar irradiation for space heating.

Passive Cooling
Thermal mass is the most commonly used passive cooling technique to reduce daytime peak load and internal daytime temperatures.In the case study buildings, thermal mass benefits are systematically assessed using a sensitivity analysis.It is generally believed that thermal mass should be combined with night ventilation (natural/mechanical) to take full advantage of its energy-saving potential.This design strategy in buildings in dry and Mediterranean climates has proven effective at avoiding the summer heat and reducing cooling requirements.A ventilation system is used in all ZEB case studies.Outdoor air is supplied via heat recovery ventilators (HRV), and this unit brings outdoor air into the house and continuously exhausts indoor air.This design strategy has proven effective at avoiding the summer heat and reducing cooling requirements in the "Sabic & J&P House" [31], "Eco House" [39], "solar village" [40], and "baytna villa" [49].Passive cooling technology's contribution to reducing total energy consumption is 486 KWh/m²/year, which is 17% of the total annual energy consumption in the 40 ZEB case studies, as shown in Tables A4 and A5 and Figure 4.

Thermal Energy Storage
Passive thermal storage energy is another practical approach to building thermal control that relies primarily on the storage of latent heat that is released through the thermal mass in the building or LED lighting, which has attracted increasing interest in research for decades.Although 17 ZEB case studies (43% of the 40 ZEBs) use LED lighting in practice, it is suggested that the combination of LED and night ventilation can achieve greater energy efficiency (see Figure 4).Thus, the LED would be effective in all 40 ZEB cases.The "Lighthouse" [26], Riverdale House [34], Green Lighthouse, Sun Lighthouse [37], Bed

Thermal Energy Storage
Passive thermal storage energy is another practical approach to building thermal control that relies primarily on the storage of latent heat that is released through the thermal mass in the building or LED lighting, which has attracted increasing interest in research for decades.Although 17 ZEB case studies (43% of the 40 ZEBs) use LED lighting in practice, it is suggested that the combination of LED and night ventilation can achieve greater energy efficiency (see Figure 4).Thus, the LED would be effective in all 40 ZEB cases.The "Lighthouse" [26], Riverdale House [34], Green Lighthouse, Sun Lighthouse [37], Bed ZED House, Solar Settlement [38], Habitat Home [41], Jiao Tong House [44], Maison DOISY, urban semi-house [45], zero-energy home [47], and single-family house [46] are examples where thermal energy storage is used for space heating and cooling.

Operational Energy Demand
The annual energy demand of the chosen ZEBs varies between 17.1 KWh/m 2 /year for the Solar House [25] and 120 KWh/m 2 /year for the Solar Decathlon [43].However, these are not comparable in terms of magnitude because they are not located at similar latitudes.The energy demand includes heating, cooling, DHW, ventilation, lighting, and appliances.In terms of energy-efficiency systems for heating and cooling, most of the projects use low-exergy systems in the form of radiant heating (in North America and Europe), cooling (hot humid climate zones), and mechanical ventilation by air heat recovery (all 40 ZEB cases).On the other hand, the use of low-energy lighting and energy-efficient electrical equipment, such as washing machines with hot water, is a strategy to meet the balance of energy consumption.However, the data on the use of operational energy added to the total primary energy are not clear.Despite this, all 40  ZED House, Solar Settlement [38], Habitat Home [41], Jiao Tong House [44], Maison DOISY, urban semi-house [45], zero-energy home [47], and single-family house [46] are examples where thermal energy storage is used for space heating and cooling.

Operational Energy Demand
The annual energy demand of the chosen ZEBs varies between 17.1 KWh/m 2 /year for the Solar House [25] and 120 KWh/m 2 /year for the Solar Decathlon [43].However, these are not comparable in terms of magnitude because they are not located at similar latitudes.The energy demand includes heating, cooling, DHW, ventilation, lighting, and appliances.In terms of energy-efficiency systems for heating and cooling, most of the projects use low-exergy systems in the form of radiant heating (in North America and Europe), cooling (hot humid climate zones), and mechanical ventilation by air heat recovery (all 40 ZEB cases).On the other hand, the use of low-energy lighting and energy-efficient electrical equipment, such as washing machines with hot water, is a strategy to meet the balance of energy consumption.However, the data on the use of operational energy added to the total primary energy are not clear.Despite this, all 40 projects have achieved low levels of energy demand.Used in a total of 38 out of the 40 study cases, energy demand for heating accounts for about 27.2% of the final annual energy consumption.Domestic hot water (DHW) is used in 40 cases and accounts for about 19.4% of the final annual energy consumption.Energy demand for cooling is present in 17 cases (42.5% of cases), representing about 11.6% of the final annual energy consumption.Ventilation is present in 40 cases, representing about 4.4% of the final annual energy consumption.Energy demand for lighting is present in 40 cases, accounting for about 8.4% of the final annual energy consumption, and appliances are present in 40 cases, representing about 29.1% of the final annual energy consumption.These data are shown in Figure 5.The average heating consumption of newly constructed residential buildings is 21kWh/m 2 /year, while renovated houses achieve a similar level of 25kWh/m 2 /year, slightly lower due to restrictions involving thermal bridges, lack of good insulation in the slab, etc.The lowest overall consumption of energy is 25 kWh/ m 2 /year, and the lowest domestic cooling hot water consumption is 12 kWh/ m 2 /year.
Regarding HVAC systems, all the case houses use a solar thermal system for DHW preheating coupled with an electric, instantaneous standby heater.Some projects used preheated water from the solar energy system.Heat recovery systems are also common in these case studies.In the case of the DHW system, heat recovery can reduce the DHW load by about 17% to 26%.It has proven to be an effective and reliable technology.The The average heating consumption of newly constructed residential buildings is 21 kWh/m 2 /year, while renovated houses achieve a similar level of 25 kWh/m 2 /year, slightly lower due to restrictions involving thermal bridges, lack of good insulation in the slab, etc.The lowest overall consumption of energy is 25 kWh/ m 2 /year, and the lowest domestic cooling hot water consumption is 12 kWh/ m 2 /year.
Regarding HVAC systems, all the case houses use a solar thermal system for DHW preheating coupled with an electric, instantaneous standby heater.Some projects used preheated water from the solar energy system.Heat recovery systems are also common in these case studies.In the case of the DHW system, heat recovery can reduce the DHW load by about 17% to 26%.It has proven to be an effective and reliable technology.The ZEBs are usually quite airtight, and most ventilation air required is delivered by the mechanical system.Almost all buildings used heat recovery ventilators (HRV) for fresh air.They use a motion detection sensor that shuts down the HRV when the house is unoccupied.

On-Site Renewable Energy Systems
Thirty-eight of the case studies use various renewable energy supply options, ideally involving the application of low-energy technologies, which use sources that are available on-site from initial sources.Solar heat collectors, photovoltaic systems, biomass systems, and geothermal heat pumps are renewable energy technologies that are used as energy demand reduction technology.Figure 6a ZEBs are usually quite airtight, and most ventilation air required is delivered by the mechanical system.Almost all buildings used heat recovery ventilators (HRV) for fresh air.They use a motion detection sensor that shuts down the HRV when the house is unoccupied.

On-Site Renewable Energy Systems
Thirty-eight of the case studies use various renewable energy supply options, ideally involving the application of low-energy technologies, which use sources that are available on-site from initial sources.Solar heat collectors, photovoltaic systems, biomass systems, and geothermal heat pumps are renewable energy technologies that are used as energy demand reduction technology.Figure 6a

PV (Photovoltaic)
Photovoltaic energy is one of the most sustainable renewable energy technologies.In our ZEB case studies, photovoltaic (PV) systems including solar panels installed on the build-ings' roofs and facades accounted for 35 cases, representing 87.5% of our ZEB cases.The estimated total annual photovoltaic with solar collector production is 1550 KWh/m 2 /year.The electricity generation from PV systems on average covered 51.5% of the final annual energy supply in these buildings.The Solar Decathlon has the highest photovoltaic energy production with 137.5 kWh/m 2 /year, [43], while the EcoTerra house has the lowest electricity production with 11.1 kWh/m 2 /year [28].

Solar Water Heaters
In residential buildings, energy use for domestic hot water represents a large proportion of the overall household energy consumption.ZEBs utilize solutions and innovative developments to improve energy efficiency.For example, a low-profile complex hot water storage system has been developed to address the issue of architectural aesthetics.Solar thermal collectors for DHW and heating are present in 33 cases, representing 82.5% of the total, and they provide 13.8% of the final annual energy supply.

Heat Pumps
Heat pumps for selected ZEBs provide viable alternatives by restoring heat from different energy sources for use in different building applications.Recent advances in heat pump technologies focus on advanced cycle designs for heat and work systems, improved cycles, and wider use of applications.Geothermal heat pump systems are used in 22 cases, representing 55% of the total, and they provide 16.3% of the final annual energy supply.

Bioenergy
Bioenergy is a major source of high-demand performance for multiple uses in the building sector and is derived from forestry and agricultural waste.Biomass boilers in selected ZEBs applied a large number of residual resources to electricity production, DHW, and cooking.Fuel and biomass systems are present in 16 cases, representing about 40% of the total, and they provide 15.6% of the final annual energy supply.

Wind Turbines
Wind power generation differs from traditional thermal generation due to the irregular nature of the wind.The Lighthouse [26] and the Wind House [42] include wind power generation to deal with supply demand compatibility challenges in the electrical system.Wind power is used in 2 cases, representing 5% of the total, and it provides 2.8% of the final annual energy supply.Renewable energy systems should either generate energy for heating and cooling or provide the fuel necessary to run heating and cooling systems.With this in mind, most strategies make use of solar thermal collectors for the production of DHW and heating (the EcoTerra house [28] is not equipped with solar thermal collectors) and photovoltaic systems for electricity generation (the Lighthouse [26] does not have an on-site electricity generation system).For space heating and cooling using solar thermal heating (radiant heating) and on-site geothermal heat pump sources (heating/cooling), the use of biomass for heating purposes depends on the cost (Lighthouse) [26]; however, the availability of biomass from renewable sources is limited.Air source heat pumps are used to transfer heat (in the Home for Life [23], Maison Air et Lumière [24], Lighthouse [26], NZERTF [29], and Hybrid Z [32] ZEBs).Some buildings use a hydrogen fuel station (Solar House [25]), an auxiliary boiler and power plant fired by wood chips and natural gas (Leaf House [27]), and wind (the Wind House [42]) to generate energy.There is an opportunity to export excess electricity (Hybrid Z [32] and Solar House [25]), as is shown in Figure 6.For some years, solar thermal systems have increasingly been used due to their increased efficiency and small size.Solar energy is the most popular form of renewable energy used in buildings.Over the past decade, the number of zero-energy buildings that use geothermal heat pumps has increased due to improved heat pump technology, decreased investment costs, and the fact that there is no need to build chimneys or store fuel in buildings.

Energy Efficiency in ZEB Case Studies
There were five types of load distribution according to the climate characteristics as follows: (1) the cooling load is dominant in tropical regions; (2) space heating is dominant in North America and Europe; (3) both heating and cooling are important in the southern European region as it has a moderate climate; (4) South and East Asia feature a hot, humid climate where dehumidification is an important factor; and (5) cooling is dominant in West Asia (Qatar-Saudi-Oman) as it features a hot, arid climate.It can be seen from Figure 7 that not all chosen cases are strictly ZEBs.Some exhibit high primary energy consumption and high energy production; some have low energy consumption and low energy production.The Solar Decathlon [43] has the highest annual consumption of primary energy (120 KWh/m 2 /year), with a value close to that of a typical high-performance building.The Solar House [25], on the other hand, has the lowest annual consumption of primary energy (17.1 KWh/m 2 /year).For buildings with high energy consumption, there is a greater need for renewable and sustainable energy sources to compensate for the high demand for energy.In this study, 25 cases, representing 62.5% of the total, are categorized as plus-energy buildings; 8 cases, representing 20% of the total, are categorized as net-zero-energy buildings; and 7 cases, representing 17.5% of the total, are categorized as near zero-energy buildings.

Zero-Energy Buildings' Role in Shaping Sustainable Cities
Zero-energy buildings (ZEBs) can play a significant role in shaping sustainable cit by reducing greenhouse gas emissions and improving the overall energy efficiency buildings [58,59].ZEBs can contribute to sustainable cities in various ways.(1) Reduc Energy Consumption: ZEBs consume less energy than conventional buildings, which duces the demand for fossil fuels and the associated greenhouse gas emissions.This c help mitigate climate change and improve the air quality of urban areas.(2) Improved A Quality: ZEBs typically use renewable energy sources, which do not produce harm emissions.This can improve air quality and reduce the health risks associated with pollution [4].By improving the energy required to power buildings, enhancing resilien and using renewable energy sources, ZEBs can help urban areas achieve their carbon n trality aims and create healthier, more equitable spaces.(3) Economic Benefits: ZEBs c There must be a focus on buildings that are directly linked to energy infrastructure and not on independent buildings.In northern regions (North America and Europe), improving district heating energy efficiency is a priority; however, advanced cooling technologies are a priority in Asia.In moderate climatic regions, bi-modal heat pumps are a priority.
There are differences in the annual energy consumption of case study buildings in America, the EU, and Asia.In the US and Canada (5 cases), 25% of building energy consumption is accounted for by space heating, more than 19% is accounted for by water heating, 20% is accounted for by space cooling and ventilation, and 27% is accounted for by appliances and service equipment.In the EU (26 cases), 28% of energy consumption is accounted for by space heating, more than 25% is accounted for by water heating, and 43% is accounted for by appliances and service equipment.In Asia (9 cases), space heating and water heating account for 10% and 21% of total final energy demand, respectively; cooling accounts for 28% of energy consumption, which is much higher than in the US; and appliances and equipment account for 35% of energy use.The difference in the ZEB penetration in each country is due to many factors analyzed under the zero-energy building projects of 2020.One critical reason is the lack of a scientific methodology regarding how to define a zero-energy building, which leads to a wide range of limits for primary energy in different countries.

Zero-Energy Buildings' Role in Shaping Sustainable Cities
Zero-energy buildings (ZEBs) can play a significant role in shaping sustainable cities by reducing greenhouse gas emissions and improving the overall energy efficiency of buildings [58,59].ZEBs can contribute to sustainable cities in various ways.(1) Reduced Energy Consumption: ZEBs consume less energy than conventional buildings, which reduces the demand for fossil fuels and the associated greenhouse gas emissions.This can help mitigate climate change and improve the air quality of urban areas.(2) Improved Air Quality: ZEBs typically use renewable energy sources, which do not produce harmful emissions.This can improve air quality and reduce the health risks associated with air pollution [4].By improving the energy required to power buildings, enhancing resilience, and using renewable energy sources, ZEBs can help urban areas achieve their carbon neutrality aims and create healthier, more equitable spaces.(3) Economic Benefits: ZEBs can provide economic benefits to building owners and tenants by reducing energy costs and improving the value of the property.In addition, the development and maintenance of ZEBs help create jobs in the renewable energy sector.(4) Community Engagement: ZEBs can serve as a focal point for community engagement and education on sustainable building practices.They can also demonstrate the feasibility and benefits of sustainable buildings to the wider community [60].(5) Urban Resilience: ZEBs can improve urban resilience by reducing the reliance on centralized energy systems and increasing energy independence.In case of a power outage or natural disaster, ZEBs can continue to operate using onsite renewable energy sources.In conclusion, zero-energy buildings are an innovative solution to reducing energy consumption, minimizing the carbon footprint of buildings, and promoting sustainability.Passive building design, renewable energy sources, and energy-efficient materials are some of the key features of zero-energy buildings.Multiple examples of zero-energy buildings from around the world demonstrate the feasibility and effectiveness of this approach.

Conclusions
Considering the variety of techniques and combinations of passive measures used to achieve the performance objectives of zero-energy buildings, ZEBs have the potential to reduce energy use, address increasing building energy demands, and generate energy from sustainable, renewable sources.Although several countries have released enhanced ZEB strategies, the implemented projects are still limited and face many challenges.This paper reviews two aspects of ZEBs: a strategic approach to ZEBs (or global ZEB activities) and state-of-the-art, energy-efficient building technologies, focusing on residential buildings.Over 40 residential buildings on different continents were reviewed, and their technical details and performance were evaluated.A total of 62.5% of the buildings included in this study achieved the +ZEB standard; 25% were net-zero-energy buildings; and only 12.5% were near-zero-energy buildings.Solar PV is the most widely used renewable energy source in the studied cases, but in warmer climates, advanced cooling technologies and heat pumps are preferred.Building envelopes and thermal ventilation with heat recovery is essential in cold climates.
We suggest that buildings be more environmentally friendly by connecting to a municipal and regional energy network that uses energy from renewable sources to make the supply side as reliable and flexible as possible.Using energy-saving solid measures to ensure that annual local energy consumption stays below the amount of renewable energy generated locally allows for more renewable energy to be used in existing regional power grids, making them more flexible, allowing consumers to change their use based on demand, and allowing for the better management of energy storage.Sustainable energy sources must be combined with the built environment to create value and social incentives.This includes renewable energy sources, recycled materials, and more (i.e., local storage, smart energy grids, demand-response, cutting-edge energy management systems, user interaction, and ICT).Finally, low-cost housing that enhances indoor energy quality should be provided to boost residents' health and happiness.Some improvements to building envelope technologies are cost-effective, but others are still in the research and development stage.These challenges are particularly significant if a project aims to be a zero-energy building.Achieving a zero-energy building goal for small residential buildings with limited roof areas and constructing a passive house combined with photovoltaic and solar thermal collectors can be technically challenging.Exploring different topics and points of view shows how many additional problems cities could face.As a result, thorough plans for low-carbon resilience need to consider many different factors.More in-depth and ongoing research on low-carbon resilience is essential if these problems are to be solved, and effective and efficient urban governance is necessary to help reach Sustainable Development Goals.In summary, zero-energy techniques can be highly effective in shaping climate-resilient sustainable buildings, and their effectiveness can be evaluated via a range of methods, including energy performance monitoring, environmental impact assessments, and resilience testing.These techniques are critical for promoting sustainability and resilience in the built environment and for reducing the environmental impact of buildings.
Despite research discussions on the effectiveness of zero-energy techniques in shaping climate-resilient sustainable buildings, there are also several potential gaps in this research topic that need to be addressed.(1) Lack of long-term data: Many studies on the effectiveness of zero-energy techniques focus on short-term performance data, often only for a few years after a building is constructed.However, it is important to evaluate the long-term performance of these techniques over the lifetime of the building.Long-term data can help identify any issues or weaknesses in the design or implementation of zero-energy techniques and provide insights for future improvements.(2) While zero-energy techniques can significantly reduce energy consumption in buildings, occupants' behavior can also significantly impact energy use.A lot of research is needed to examine the role of occupant behavior in shaping the effectiveness of zero-energy techniques and that identifies strategies for promoting sustainable behaviors.(3) Lack of standardization: There is currently a lack of standardization in the evaluation and certification of zero-energy buildings, making it difficult to compare and evaluate the effectiveness of different techniques.A more standardized approach to evaluating zero-energy buildings could help identify best practices and promote the more widespread adoption of these techniques.
energy to the supply -They produce less energy than they need -The amount of energy required is covered to an extent by energy from other sources

Figure 1 .
Figure 1.Number of ZEBs in different countries.

Figure 1 .
Figure 1.Number of ZEBs in different countries.

Figure 2 .
Figure 2. Number of ZEBs in different climate types.

Figure 2 .
Figure 2. Number of ZEBs in different climate types.
projects have achieved low levels of energy demand.Used in a total of 38 out of the 40 study cases, energy demand for heating accounts for about 27.2% of the final annual energy consumption.Domestic hot water (DHW) is used in 40 cases and accounts for about 19.4% of the final annual energy consumption.Energy demand for cooling is present in 17 cases (42.5% of cases), representing about 11.6% of the final annual energy consumption.Ventilation is present in 40 cases, representing about 4.4% of the final annual energy consumption.Energy demand for lighting is present in 40 cases, accounting for about 8.4% of the final annual energy consumption, and appliances are present in 40 cases, representing about 29.1% of the final annual energy consumption.These data are shown in Figure 5. Energies 2023, 16, x FOR PEER REVIEW 10 of 25

Figure 5 .
Figure 5.The total energy demand for the ZEB case

Figure 5 .
Figure 5.The total energy demand for the ZEB case.
,b illustrates the mean technologies applied in different ZEB typologies.Energies 2023, 16, x FOR PEER REVIEW 11 of 25

Figure 6 .
Figure 6.The total renewable energy supply.(a) Mean of the total energy demand for the ZEB cases.(b) The technologies applied in different ZEB typologies.

Figure 7 .
Figure 7.The energy efficiency of the ZEB cases according to the buildings' use and climate.

Figure 7 .
Figure 7.The energy efficiency of the ZEB cases according to the buildings' use and climate.
Table 1 lists the most used ZEB terms, such as ZEBs producing more

Table 1 .
Summary of zero-energy building categories.

Table 1 .
Summary of zero-energy building categories.

Table 1 .
Summary of zero-energy building categories.

Table 1 .
Summary of zero-energy building categories.

Table 1 .
Summary of zero-energy building categories.

Table A3 .
Mean U-values of the climates and different buildings envelope.

Table A5 .
Final Annual Energy Supply and Consumption in ZEBs.