What is a zero-energy building?
A zero-energy building (ZEB) has such high energy efficiency that it consumes no net energy from the energy grid. Such buildings should generate enough energy from their own renewable sources – such as solar panels – to cover their annual energy requirements. A nearly zero-energy building (NZEB) has achieved almost the same levels, requiring minimal energy from external sources.
A related term is zero-emission building, a highly efficient building that uses only energy from non-emitting, renewable sources. Several bodies have developed their own zero-emission certification programs. At Skanska, we are part of an expert advisory group, working to set science-based targets for this area.
Efficiency versus generation
Achieving zero emissions involves two key areas: energy efficiency and emission-free energy. This article focuses mostly on energy efficiency.
Building envelope insulation
Many solutions are applicable in most markets. One key aspect is optimizing the building envelope insulation, which allows a building to withstand both heat and cold better.
Leading insulation manufacturer Rockwool writes that optimization of building energy efficiency typically considers elements such as lighting, walls and roof, glazing, heating, ventilation and air conditioning, as well as renewable energy sources and building usage: “Each of the above variables works together to ultimately reach the goal of net zero energy. However, an air-tight, highly insulated building envelope is an integral part of the NZEB strategy.”
Even here though, balance is important. At a certain point, the carbon cost of adding ever more insulation, heavier glazing and a thicker envelope exceeds the winnings in energy savings.
Design is vital
Windows and glass surfaces are an important component here, in several ways. Double and triple glazing, and the material choice for windows, stop them from leaking heat. Such window solutions are often standard in colder climates such as the Nordic region. Yet better insulated windows, when closed, also provide protection from excess heat in warmer regions.
And the overall design should ensure that windows are shaded from the sun during hot days but can let in light during winter.
In warmer climates, designing for passive crossflow ventilation can help with cooling without having to rely on air-conditioning.
Additional systems, such as mechanical ventilation, lighting, heating and cooling need to be optimized both for energy efficiency and for the purpose of the building. An office will have different needs than a residential kitchen, and the design must be fit for purpose.
International initiatives
International, national, state and city authorities, as well as building, development and sustainability organizations, are working to increase the number of zero-energy buildings and energy efficiency in the built environment. Some use regulations, while others prefer subsidies and incentives.
As Rockwool writes, California set aside USD 3.2 billion in subsidies and incentives to promote net-zero construction, while New York has legislated stricter energy requirements for new buildings and retrofit construction (see more below).
The European Commission has developed regulatory frameworks to help increase the number of zero-emission buildings.
- The proposed Zero Energy Building (ZEB) requirement should apply as of January 1, 2030, to all new buildings, and as of January 1, 2027, to all new buildings occupied or owned by public authorities.
- The previous Energy Performance of Buildings Directive required that EU countries had to ensure that all new buildings were nearly zero-energy by the end of 2020 while all new public buildings had to be nearly zero-energy after the end of 2018.
As with all European legislation and regulation, it is up to each member country to implement this regulation and achieve the targets in their own markets.
What appears to be a simple EU concept is however complicated to implement at country level. Some national standards are comparatively low, meaning inefficient buildings can still be approved, while others are much higher.
Shifting to efficient heating and cooling
In Central and Eastern Europe, where coal and natural gas have been predominant energy sources for heating, we have been pioneers in improving energy efficiency. Measures have included introducing the use of more efficient heat pumps – which can both warm and cool a building – even before the energy crisis provoked by Russia’s invasion of Ukraine. This strategic shift began in our residential operations and later expanded into commercial properties.
All our residential buildings in the region are connected to district heating, but many of these systems are still coal powered, so we are working to broaden the use of heat pumps. Hot water is the biggest component of the primary energy demand (PED), so we can reduce the PED by heating water more efficiently. At a pilot project with 155 apartments in Krakow, Poland – our first project there using heat pumps – we aim for a 25 percent reduction in PED compared with the 2020 average which is the benchmark.
Solar panels
Solen, a project being built in Warsaw, is using photovoltaic (solar) panels to provide 20 percent of energy demands, powering lighting in common spaces and support systems. Residents will also have access to a smart home-management system providing real-time data on heat and electricity use, as well as carbon footprint. Residents will also be able to adjust the temperature using the related app.
In the Czech Republic, heat recovery from ventilation systems is standard in all residential projects, and is also being implemented across Poland.
These and other initiatives are examples of a systematic approach we are taking in Central and Eastern Europe to reduce energy consumption and improve energy efficiency, and where we are also collecting data to ensure we reduce the non-renewable PED in line with Skanska Group targets.
States and cities leading the way
Even though the EU directive is one of the most progressive in the world, the United States continues to introduce cutting-edge solutions in energy efficiency and renewable energy. Although there is no national building or energy code, many states have adopted aggressive energy efficiency and renewable energy requirements, and California, Oregon, New York and Washington have committed to leading the way to net-zero buildings.
California, for example, is one of the leading jurisdictions worldwide in addressing climate change. Along with its cap-and-trade regulation, renewable portfolio standard for electricity generation and zero emission vehicle regulation, increasing efficiency in buildings is a key state policy toward decreasing greenhouse gas emissions by 80 percent below 1990 levels by 2050.
Under its own building energy code, it aims to make new residential and commercial buildings zero-net energy (ZNE) by 2020 and 2030 respectively. In addition, half of the existing commercial building stock must be renovated to ZNE performance levels by 2030 and half of the new major renovations of state buildings will be ZNE by 2025.
Higher energy savings
In addition to state-wide base energy efficiency codes, many cities implement their own stretch codes, local frameworks that are even more aggressive, resulting in buildings that achieve higher energy savings. Some cities also adopt local stand-alone energy-efficiency and renewable energy requirements.
- In New York City, for example, commitments to reduce emissions from the building sector include
- 100 percent net-zero new buildings by 2030
- No fossil fuel hook-ups in new constructions and major renovations by 2030
- 20 percent reduction in energy consumption for City buildings by 2025.
Across the USA, 82 cities and counties have adopted policies that require or encourage the move away from fossil fuels to all-electric homes and buildings. As of September 2022, nearly 31 million people across 12 states and Washington DC live in jurisdictions where local policies favor fossil fuel-free buildings.
Cordilleras Mental Health Center Replacement project – California: Incorporating renewable power, this project will be the first net-zero energy mental health campus in California. There will be solar panels on every roof, including on the shade structures over the parking areas. The facility will have natural ventilation in shared areas and an air-to-water heat recovery system to allow for pre-heating of the domestic hot water system. The project is targeting LEED® Silver certification.
Even in markets where requirements are not legislated, commercial imperatives are driving companies and public authorities to pursue energy efficiency in new buildings and projects. Reducing energy costs means lower costs, no matter the motivation.
Conclusion
Regulatory regimes are one force driving progress towards zero-energy buildings. The economic argument of lower energy costs is another, and is particularly relevant in today’s environment. Subsidies and incentives also play a role.
Much can be done to improve the energy efficiency of buildings with solutions already available today. From the design phase, through selection of materials and construction, and even once in use, decisions to reduce energy consumption and use only renewable energy have a huge impact on the road to zero-energy and zero-emission buildings.