A Zero-Energy Building (ZEB), also called a Net Zero-Energy (NZE) building, is a building that uses as much energy as it produces in a year. This energy is created on the building’s site or from other places using renewable sources, such as solar panels, heat pumps, energy-efficient windows, and good insulation.

The goal of these buildings is to release fewer greenhouse gases into the atmosphere compared to similar buildings that are not NZE. Sometimes, these buildings use non-renewable energy and produce greenhouse gases, but at other times, they save energy and reduce emissions in other areas by the same amount. People build these structures to help protect the environment. Tax breaks and lower energy bills also make these buildings financially practical.

Different places use different terms to describe these buildings. For example, the International Energy Agency (IEA) and European Union (EU) often use "Net Zero Energy," while the term "zero net" is more common in the United States. A similar idea, called Nearly Zero Energy Building (nZEB), was approved by the EU and other countries. The goal was for all new buildings in the region to meet nZEB standards by 2020. However, D'Agostino and Mazzarella (2019) explain that the meaning of nZEB varies by country. This is because each country has different weather, rules, and ways to calculate energy use, making it difficult to compare buildings or create a single standard for all areas.

Overview

Buildings that follow energy rules use about 40% of the fossil fuel energy in the US and European Union. They are major sources of greenhouse gases. To reduce energy use, many buildings are now aiming for carbon neutrality, which means reducing carbon emissions and relying less on fossil fuels. Although zero-energy buildings are still rare, even in developed countries, they are becoming more common.

Zero-energy buildings often use the electrical grid to store energy, but some are not connected to the grid and have energy storage on-site. These buildings are sometimes called "energy-plus buildings" or "low-energy homes." They produce energy on-site using renewable sources like solar and wind power. They also use highly efficient lighting and heating, ventilation, and air conditioning (HVAC) systems to use less energy overall. As renewable energy costs drop and fossil fuel costs rise, achieving zero-energy goals is becoming more realistic.

An example is the Zero Building in Spain, which shows how an office building can reach net-zero energy use or even produce more energy than it uses through good design, passive strategies, and renewable systems.

Modern zero-energy buildings are possible because of new technologies and construction methods. These include highly insulating spray-foam insulation, high-efficiency solar panels, heat pumps, and windows with special coatings that reduce heat loss. Academic research helps improve these technologies by collecting energy data from buildings and using computer models to test designs. A study compared how countries like Italy, Germany, and Denmark approach nearly zero-energy buildings. It found that while the technical solutions are similar, the goals and methods vary (D'Agostino & Mazzarella, 2019).

Zero-energy buildings can connect to a smart grid. Some benefits include:
– Using renewable energy sources
– Supporting electric vehicles that can send energy back to the grid (vehicle-to-grid)
– Applying zero-energy design principles

Energy is usually the first resource targeted for reduction because:
– Energy, especially electricity and heating fuel like natural gas, is expensive. Saving energy can lower costs for building owners. Water and waste are cheaper to manage.
– Energy use has a large carbon footprint. Reducing it helps lower a building's overall emissions.
– There are proven ways to cut energy use, such as adding insulation, using heat pumps, installing efficient windows, and adding solar panels.
– Some governments offer financial support for energy-efficient upgrades like insulation, solar panels, and heat pumps.

Zero-energy buildings make buildings more efficient and reduce emissions during their operation. However, buildings still create pollution from "embodied carbon," which is the carbon released during the production and transport of building materials and construction. Embodied carbon accounts for 11% of global greenhouse gas emissions and 28% of emissions from the building sector. In newer, efficient buildings, embodied carbon can make up 47% of a building's lifetime emissions. Focusing on reducing embodied carbon is important for achieving true zero carbon emissions, as it requires different strategies than just improving energy efficiency.

A 2019 study found that between 2020 and 2030, reducing upfront carbon emissions and switching to clean energy is more important than improving building efficiency. This is because using carbon-heavy materials in energy-efficient buildings can create more emissions than basic buildings. The study also said that "net-zero energy codes" alone may not reduce emissions quickly enough, so policies should aim for "true net-zero carbon buildings" instead of just "net-zero energy buildings."

One way to reduce embodied carbon is by using low-carbon materials like straw, wood, linoleum, or cedar. For materials like concrete and steel, methods to cut emissions exist, but they are not widely available yet. In conclusion, the best design for reducing greenhouse gases appears to be four-story multifamily buildings made from low-carbon materials, which could serve as a model for future low-emission structures.

Definitions

The term "zero net energy" can have different meanings depending on where it is used, especially between North America and Europe.

Off-the-grid buildings are independent structures that do not connect to external energy sources. These buildings rely on local renewable energy, such as solar or wind power, and use energy storage systems to provide power when the sun is not shining or the wind is not blowing. An energy self-sufficient house is a building that balances its energy use and production on an hourly basis or even more frequently. These houses can operate without being connected to the main energy grid.

When balancing energy use, several factors must be considered:

• Building System Boundaries: This includes deciding which renewable energy sources are counted (such as those within the building’s area, on-site, or from other locations) and how many buildings are included in the balance (a single building or a group of buildings). It also involves determining which energy uses are included, such as heating, cooling, lighting, and electricity for appliances or vehicles. Renewable energy sources may be prioritized based on factors like how easily they can be transported, how long they are available, or how well they can be used in the future.

• Weighting System: This method converts different types of energy into a single, comparable measure (such as energy cost, carbon emissions, or energy credits). This allows energy from different sources to be compared and balanced (for example, electricity from solar panels can offset energy from biomass). However, political decisions or time-related factors can influence how energy types are valued.

• Balancing Period: The most common time frame for balancing energy use is one year. Shorter periods, like a month or season, or the entire life cycle of a building (including energy used during construction) can also be used.

• Energy Balance Types: There are two main ways to balance energy:
• Import/Export Balance: This tracks how much energy is used or produced over time, including energy generated on-site.
• Demand/Generation Balance: This compares how much energy is needed (based on typical use patterns) with how much energy is produced. A monthly balance could also be used, where leftover energy each month is added to create an annual total. This can be seen as either a load/generation balance or a special type of import/export balance.

• Additional Characteristics: Zero net energy buildings can be evaluated based on how well they match energy production with energy use (load matching) or how they support the local energy grid (grid interaction). These features can be measured using specific tools for assessment.

Design and construction

The most effective way to reduce a building's energy use is during the design phase. To use energy efficiently, zero energy buildings use methods very different from traditional construction. Good zero energy building designs often use proven passive solar techniques or artificial heating and cooling systems that work with the building's natural features. Sunlight, solar heat, natural wind, and the cool ground beneath a building can provide light and stable indoor temperatures with little need for mechanical systems. Zero energy buildings are usually designed to use passive solar heat in winter, shading to block summer heat, and materials that store heat to keep temperatures steady throughout the day. These buildings are also highly insulated in most climates. All the tools and materials needed to build zero energy buildings are available today.

Special computer tools can show how a building will use energy based on different design choices, such as the building's direction (related to the sun's position), window and door types, insulation materials, air tightness, and the efficiency of heating, cooling, lighting, and other systems. These tools help designers predict a building's performance before construction and analyze how costs and benefits change over time.

Zero energy buildings include many energy-saving features. Heating and cooling needs are reduced by using efficient equipment, such as heat pumps (which are about four times more efficient than furnaces), extra insulation (especially in attics and basements), high-efficiency windows, draft-proofing, efficient appliances, and LED lighting. These buildings also use passive solar heating in winter, shading in summer, and natural ventilation. Features vary based on the climate. Water heating needs are reduced by using water-saving fixtures, heat recovery systems, and solar water heaters. Daylight from skylights or solar tubes can provide all the light needed during the day. Night lighting uses fluorescent or LED lights, which use much less energy than traditional lights and do not create extra heat. Energy use from other devices is reduced by using efficient appliances and reducing standby power. Other methods, depending on the climate, include building underground, using straw-bale insulation, prefabricated panels, and landscaping for shade.

After reducing energy use, buildings can generate all needed energy on-site using solar panels on the roof.

Zero energy buildings often use energy from everyday appliances in two ways. For example, heat from refrigerators can warm water, ventilation air, or showers. Heat from computers, office machines, and body heat can also be used to warm the building. These buildings capture heat that traditional buildings might waste. They may use systems like heat recovery ventilation, hot water recycling, combined heat and power, and absorption chillers.

Energy harvest

Zero Energy Buildings (ZEBs) collect energy from the sun and other sources to provide electricity and heating or cooling. The most common way to collect energy is by using solar panels on rooftops to turn sunlight into electricity. Energy can also be collected using solar thermal collectors, which use the sun's heat to warm water for buildings. Heat pumps can collect heat from the air near a building or from the ground (called geothermal). Although heat pumps move heat instead of collecting it, they help reduce energy use and carbon emissions. For individual homes, small energy systems like solar panels, wind turbines, or biofuels can provide electricity and heat. Some systems use solar thermal collectors with seasonal thermal energy storage (STES) to store heat for winter or cold for summer. To manage energy needs, ZEBs often connect to the electricity grid, sending extra power to the grid when they produce more than they need and drawing power when they need more. Some buildings may operate completely without outside energy.

Collecting energy is often more efficient and less costly when done together in groups, such as neighborhoods or villages, rather than in single homes. This approach reduces energy loss during transmission. Using solar panels on rooftops eliminates these losses entirely. In commercial and industrial buildings, energy collection should consider the land's features. Locations without shade can generate large amounts of solar electricity, and most places can use geothermal or air-source heat pumps. Producing goods with zero fossil fuel use requires areas with geothermal, solar, wind, or water resources.

Zero-energy neighborhoods, like the BedZED project in the UK and growing developments in California and China, use shared energy systems. These may include shared wind turbines or district heating. Plans are underway to build entire cities that use ZEB technologies and require no outside energy.

A major debate in ZEB design focuses on balancing energy conservation (like using less energy through better insulation) with collecting renewable energy (like solar or wind). Most ZEBs use both methods together.

Because of government support for solar panels and wind turbines, some people think a ZEB is just a regular home with renewable energy systems. However, many homes labeled "Zero Energy" still have utility bills. Collecting energy without conserving energy may not be cost-effective, depending on local electricity prices. Studies compare the savings from energy conservation (like adding insulation) to the savings from collecting energy (like solar panels).

Since the 1980s, passive solar design and passive houses have reduced heating energy use by 70% to 90% in many areas without active energy systems. For new buildings, these methods can be added with little extra cost. Few experts know how to fully use passive design, which is more cost-effective than adding solar panels to inefficient buildings. Small solar panels may only reduce outside energy needs by 15% to 30%. A high-efficiency air conditioner may need more than 7 kilowatts of solar power to operate, which is not enough for nighttime use without backup. Passive cooling and better engineering can reduce air conditioning needs by 70% to 90%. Solar energy becomes more cost-effective when overall energy use is lower.

Companies in Germany and the Netherlands offer quick upgrades for older buildings, adding insulation and improving energy systems like heat pumps. Similar projects are being tested in the US.

Energy use in buildings depends on how occupants use the space. Comfort preferences vary widely. Studies show that identical homes in the same area can use up to 20 times more energy for heating. Differences in thermostat settings, lighting, hot water use, window operation, and use of electronic devices affect energy use.

Utility concerns

Utility companies are usually required by law to keep the electrical systems that deliver power to cities, neighborhoods, and homes. These companies typically own the electrical equipment up to the edge of a property, and sometimes own it on private land as well.

In the United States, utility companies have raised concerns that using Net Metering for zero-net-energy homes might reduce their income. This could make it harder for them to maintain the parts of the electrical grid they are responsible for. Some states with Net Metering rules might cause non-zero-net-energy homes to pay more for electricity, as those homes would cover the cost of grid maintenance while zero-net-energy homes might not pay anything if they achieve their energy goals. This could create fairness issues, as lower-income households might end up paying more. One possible solution is to require all homes connected to the grid to pay a basic fee, so zero-net-energy homeowners would still pay for grid services regardless of their electricity use.

Another concern is that local and large electrical grids were not built to send electricity in both directions, which might be needed as more homes generate their own electricity. Fixing this problem could require major upgrades to the grid, but as of 2010, this was not considered a big issue unless renewable energy use became much higher.

Development efforts

Many people may need more help from the government to use zero-energy building technology. This could include financial support, rules for building standards, or higher costs for traditional energy sources. For example, Google and Microsoft used government financial help and subsidies, especially in California, to build large solar power projects. California now gives $3.2 billion in subsidies for nearly zero-energy homes and businesses. Other states in the U.S. also offer financial support for renewable energy, up to $5 per watt. Information about these programs can be found in the Database of State Incentives for Renewables and Efficiency. The Florida Solar Energy Center also has slides showing recent progress in this area.

The World Business Council for Sustainable Development started a major project to help develop zero-energy buildings. Led by leaders from United Technologies and Lafarge, the group includes support from large companies and experts who can help governments and businesses work together. Their first report found that people overestimate the cost of building green by 300%. The report also showed that buildings are responsible for about 40% of global greenhouse gas emissions, not 19% as some people think.

In some areas, small programs that give advice and help with building designs have made it easier to use zero-energy building ideas. These programs teach homeowners and builders about keeping buildings airtight, modeling energy use, and following local efficiency rules. For example, Canada and the Pacific Northwest have community energy advisors who test and evaluate homes to help turn zero-energy policies into practical building projects. Groups like Green Canada Energy Advisors and Blue Vision Design Inc. provide services such as energy evaluations and building energy modeling to support zero-energy building projects.

People who built passive houses and zero-energy homes over the last 30 years helped improve new technologies step by step. The zero-energy building idea has grown from earlier low-energy building designs, such as Canada’s R-2000 and Germany’s passive house standards. Government projects, like the superinsulated Saskatchewan House and the International Energy Agency’s Task 13, also helped advance these ideas.

The U.S. National Renewable Energy Laboratory (NREL) created a report called Net-Zero Energy Buildings: A Classification System Based on Renewable Energy Supply Options. This is the first report to explain a full classification system for net-zero energy buildings. It includes four main categories:

• NZEB:A – A building that uses renewable energy on its own footprint
• NZEB:B – A building that uses renewable energy on its own site
• NZEB:C – A building that uses renewable energy brought in from other places
• NZEB:D – A building that uses renewable energy purchased from off-site sources

Using this system means any building can become net zero with the right mix of technologies, such as solar panels, geothermal heating and cooling, energy efficiency, wind power, and electric batteries. A graphic from the Net Zero Foundation shows how following these guidelines could reduce U.S. fossil fuel use by 39% if all homes and businesses became net zero. If natural gas is still used for cooking, the savings could be 37%.

Many universities have said they want to stop using fossil fuels completely. With new advances in solar, geothermal, and battery technologies, this is becoming easier. Large hydroelectric projects, like those built before 1900, are already in use. An example is the Net Zero Foundation’s plan to make MIT’s campus completely free of fossil fuels. This plan shows how zero-energy building technologies can be used at a larger scale, like in entire districts.

Advantages and disadvantages

Zero energy buildings (ZEBs) offer several benefits. They protect building owners from future increases in energy prices. They also create more comfortable indoor spaces with even temperatures, which can be shown using temperature maps. These buildings cost less over time because they use energy more efficiently. Monthly living costs are also lower. They reduce the chance of losing power during grid outages. ZEBs help avoid future energy price rises and reduce the need for energy restrictions or carbon taxes. They are more reliable because solar panels often last 25 years and work well during bad weather. For example, solar panels at Walt Disney World’s EPCOT Energy Pavilion were still working in 2018, even after three hurricanes, though they were removed for a new ride. ZEBs may sell for more because people want them more than they are available. Their value increases as energy costs rise. They help society by providing clean energy to the grid and reducing the need to expand power systems. Improving models of building energy use can help predict how buildings use energy more accurately.

However, ZEBs also have challenges. Initial costs can be higher, and it may take effort to qualify for subsidies. Few builders have the skills to create ZEBs. If future renewable energy prices drop, the value of energy efficiency investments might decrease. Solar technology costs are falling, which could reduce the value of solar systems. Selling a ZEB might be harder if buyers cannot recover initial costs, though new energy rating systems are being developed. ZEBs may not always reduce blackout risks because they might need grid power during peak times. Without proper insulation, energy use can be higher than needed. Solar panels only work well in sunny areas, not in shaded or wooded locations. ZEBs are not completely free of carbon emissions, as materials like glass require energy to make. Building rules, such as height limits or fire codes, might limit the use of solar or wind power.

Green buildings and ZEBs share goals but focus on different areas. Green buildings aim to use resources efficiently and reduce environmental harm. ZEBs specifically produce as much renewable energy as they use in a year, lowering greenhouse gas emissions. To be a ZEB, clear goals must be set during the design process. While ZEBs may not always be "green" in all aspects, like reducing waste or using recycled materials, they generally have a smaller environmental impact than other green buildings that rely on imported energy or fossil fuels.

Green buildings and ZEBs have similarities and differences. Green buildings often focus on energy used during operation but may not consider carbon emissions from construction materials. By 2050, carbon emissions from building materials could make up half of total emissions. ZEBs are designed to meet their own energy needs with renewable sources, while green buildings are defined as structures that reduce negative environmental impacts. Green buildings must use energy and water efficiently, use recycled materials, ensure good indoor air quality, and use ethical, non-toxic materials. They must also adapt to climate changes and consider the environment and quality of life for occupants. Green building practices include using resources efficiently from design to deconstruction. Unlike ZEBs, green buildings consider all environmental effects, such as water pollution, while ZEBs focus only on energy use.

Designing ZEBs can be difficult because the technology is new. Designers must use natural resources like sunlight, ventilation, and thermal mass. They must also test new materials and technologies to make them more affordable. A challenge is the lack of clear standards to measure nearly zero energy performance.

Advances in window technology may lead to "zero heating buildings" in the EU, which use less energy for heating and allow more flexible designs. These buildings need less winter power and have lower heating demands. They are easier to design and operate, such as not needing adjustable shading.

Common green building certifications include Passive House and LEED. Passive House focuses on extreme energy efficiency, reducing heating and cooling use. LEED evaluates buildings across many categories for sustainability. Another certification, Net Zero Energy Building (NZEB), is part of the Living Building Challenge. This certification was simplified to "Zero Energy Building Certification" in 2017. The BCA Green Mark system also evaluates building performance and environmental impact.

Worldwide

To address global warming and rising greenhouse gas emissions, countries worldwide have been developing policies to promote Zero Energy Buildings (ZEBs). From 2008 to 2013, researchers in Australia, Austria, Belgium, Canada, Denmark, Finland, France, Germany, Italy, South Korea, New Zealand, Norway, Portugal, Singapore, Spain, Sweden, Switzerland, the United Kingdom, and the United States collaborated on a program called "Towards Net Zero Energy Solar Buildings." This program was part of the International Energy Agency (IEA) Solar Heating and Cooling Program (SHC) Task 40 and Energy in Buildings and Communities (EBC) Annex 52. Its goal was to create shared definitions for net-zero and very low energy buildings by dividing the work into smaller tasks.

The European Union required all new buildings to be nearly zero-energy by 2020 (and public buildings by 2018). However, D'Agostino and Mazzarella (2019) noted that this rule was applied differently in various countries. Some focused on primary energy use, while others prioritized reducing carbon dioxide emissions or increasing renewable energy.

In 2015, the Paris Agreement was created under the United Nations Framework Convention on Climate Change (UNFCCC). Its aim was to limit global temperature increases to below 2 degrees Celsius this century and to 1.5 degrees Celsius by reducing greenhouse gas emissions. While not legally binding for all countries, 197 nations signed the agreement. Developed countries had legal obligations to update their climate goals every five years and report progress annually.

ZEBs are widely used globally because they improve energy efficiency and reduce carbon emissions, helping solve energy and environmental challenges in construction.

In Australia, the "Trajectory for Low Energy Buildings and its Addendum" was agreed upon by all energy ministers in 2019. This plan aims to create zero-energy and carbon-ready buildings by 2030, supporting Australia’s goal to improve energy productivity by 40% by that year. In 2023, the Energy and Climate Change Ministerial Council agreed to update the Trajectory by 2024. The updates will help achieve net-zero emissions in buildings by 2050, build on past successes, and guide future policies.

Council House 2 (CH2), located in Melbourne, Australia, is an office building that achieved the highest Green Star rating in 2005.

In Belgium, the city of Leuven aims to become climate-neutral by 2030.

In Brazil, Ordinance No. 42 (2021) established rules for classifying the energy efficiency of commercial, service, and public buildings. It includes guidelines for renewable energy use and standards for Near Zero Energy Buildings (NZEBs) and Positive Energy Buildings (PEBs).

In Canada, the Net Zero Homes certification label is managed by the Canadian Home Builders Association. British Columbia’s BC Energy Step Code, introduced in 2017, sets higher energy efficiency standards for new buildings, aiming for net-zero performance by 2032. Canada’s "Build Smart" strategy, launched in 2017, seeks to improve building energy efficiency nationwide. The Net-Zero Energy Home Coalition promotes ZEB construction. The Canada Mortgage and Housing Corporation supports the EQuilibrium Sustainable Housing Competition, which includes zero-energy demonstration projects. The EcoTerra House in Quebec and the Varennes Public Library in Quebec are examples of ZEBs in Canada. Mohawk College plans to build Hamilton’s first net-zero building.

China, with a population of over 1.4 billion, is a major contributor to greenhouse gas emissions due to rapid urbanization. Despite this, China’s energy use has grown more slowly than its economic growth since the 1970s. China has launched policies to improve ZEB standards and incentives for ZEB projects. In 2015, the Ministry of Housing and Urban-Rural Development released a guide for passive and low-energy green residential buildings. China aims to peak carbon emissions by 2030 and achieve carbon neutrality by 2060, as declared by President Xi Jinping in 2020.