Net-zero energy buildings, also known as net-zero carbon buildings or NZEBs, are buildings that don’t have any carbon emissions during their operations. They achieve this via architectural elements that provide high levels of both energy efficiency and generation, and are the result of years of efforts to try a solution to climate change and energy consumption.
As a 2016 article for the Whole Building Design Guide says, while the “zero energy” and “net zero energy” concepts are relatively new, there are not yet definitive, widely accepted zero-energy metrics. The Department of Energy (DOE) and the National Renewable Energy Laboratory (NREL) have spearheaded much of the work on net zero energy buildings to date. NREL presents several definitions for “net zero energy”, and they encourage building designers, owners, and operators to select the metric that best fits their project. The NREL publication Zero Energy Buildings: A Critical Look at the Definition explores definitions in detail, and it suggests four ways in which net zero energy may be defined:
- Net Zero Site Energy
- Net Zero Source Energy
- Net Zero Energy Costs
- Net Zero Energy Emissions
Site Energy refers to the energy consumed and generated at a site (e.g. a building), regardless of where or how that energy originated. In a net zero site energy building, for every unit of energy the building consumes over a year, it must generate a unit of energy.
Source Energy refers to primary energy needed to extract and deliver energy to a site, including the energy that may be lost or wasted in the process of generation, transmission and distribution. For example, a coal-burning power plant may generate 1 Joule of electricity for every 3 Joules of energy in the coal consumed. If natural gas is used at a site, for every 20 Joules consumed, 1 Joule may be needed to extract and distribute the gas to the site. Metrics for net zero source energy buildings account for these factors, though exact metrics can vary depending on site and utility factors.
Net Zero Energy Cost is perhaps the simplest metric to use: it means that the building has an energy utility bill of $0 over the course of a year. In some cases, building owners or operators may take advantage of selling Renewable Energy Credits (RECs) from on-site renewable generation.
Many conventional energy sources result in emissions of carbon dioxide, nitrogen oxides, sulfur dioxide, etc. A Net Zero Energy Emissions building either uses no energy which results in emissions or offsets the emissions by exporting emissions-free energy (typically from on-site renewable energy systems).
Other interesting insights into net-zero energy buildings can be found in a study by Maher Shehadi, whose purpose is to discuss benefits and design guidelines for this kind of building. NZEBs have tremendous potential to transform the way buildings use energy. In response to regulatory mandates, federal government agencies in the US and many other states and local governments across the world are beginning to move toward targets for NZEBs.
The urge for a change
Global warming and climate change are rising issues during the last couple of decades. Buildings including commercial and residential ones are major contributors to energy consumption. Energy consumption in buildings significantly increases on a yearly basis due to the increased human comfort needs and services. Multiple factors affect the energy consumption used for cooling buildings such as wall structure, window to wall ratio, and building orientation in addition to weather conditions. Energy consumed by buildings was reported to compose a relatively large proportion of the global energy consumption. The building construction and the way it is operated and maintained have a significant impact on the total energy and water usage of the world resources.
Buildings are the primary energy consumers contributing to more than 40% of the US energy usage. According to the US Department of Energy (DoE), the heating, ventilation, and air-conditioning (HVAC) systems consume approximately 17–20% of the total energy bill of any facility or building. The world equipment demand for HVAC systems has increased worldwide from approximately 50 billion US dollars in 2004 to more than 90 billion US dollars in 2014 and for the United States from almost 11 billion to 19 billion US dollars over the same period.
Thermal characteristics of building envelopes have become of rising significance for designers and owners due to its relation to energy consumption reduction. Improper thermal insulations in buildings can lead to higher chances of surface condensation when air has relative humidity higher than 80% and when the convective and radiative heat transfer coefficients of the exterior walls are small.
Worrying over the next future
Stephanie Ossenbach too reports how buildings and construction are responsible for 39% of the carbon emissions in the world. Operational emissions, meaning the energy required to heat, cool, or light a building, account for 28% of overall emissions. As the construction sector is a significant driver of climate change, there’s substantial potential for improvement and environmental action. The World Green Building Council believes that the building and construction sector can eliminate carbon emission by 2050, through the global spread of net-zero energy buildings.
Even so, Envirotec Magazine reports the words of William Gillett, Energy Programme Director of the European Academies’ Science Advisory Council (EASAC): “We cannot rely on linear developments and a steady energy transition over the next 30 years to 2050”. The group believes the European Commission’s public consultation on the revision of the renewable energy directive provides an opportunity to remind the EU to step up its game. “Scientific evidence shows we have less than 15 years left to avoid a grim future”, he said.
The biggest source of GHG emissions in the EU is the use of fossil fuels in industry, buildings and transport. The overriding principle for a revision to the renewable energy directive must therefore be to strengthen requirements that will maximise reductions in GHG emissions before 2030 by increasing the use of truly no-carbon renewables together with the best energy efficiency measures in these sectors.
For net-zero energy buildings, this means that they’ll have to be a must in our future. To promote NZEB for the “renovation wave” would then become consistent with promoting deep renovations together with the use of renewable energy, cogeneration and waste heat from external sources and self-consumption.
Stephanie Ossenbach also provides examples of net-zero energy buildings: from a modest holiday villa to a large office, these net-zero energy buildings of various sizes are bellwethers to a shifting mindset in architecture.
A Net-Zero Energy Headquarters in Maryland (US)
Most urban offices are cramped for space — nevermind the ability to generate energy through on-site solar panels or wind turbines. But the biotechnology company United Therapeutics took on the arduous challenge of building a net-zero building in the middle of a bustling city — and succeeded in it.
The Maryland-based headquarters of the company, known as Unisphere, is currently the largest commercial net-zero building globally. It uses a mix of advanced technologies such as geo-exchange wells drilled into the ground and 3,000 solar panels to generate more energy than it needs.
United Therapeutics claimed that the cost of this campus wasn’t much more than some of the company’s earlier ones, although there’s no doubt the net-zero energy building will also save them large amounts in the long run.
A Net-Zero Energy Design School in Singapore
The National University of Singapore (NUS) makes sure to multiply the zero-energy buildings by raising architects and designers in them.
Launched in 2019, the SDE4 building of NUS School of Design and Environment generates its energy by some 1,200 photo-voltaic solar panels, saving up to USD 180,000 a year.
SDE4 also boasts a hybrid cooling and ventilation systems and architectural structures that provide much-needed shade in the tropical climate of the island-nation.
Nirmal Kishnani, then Vice Dean at NUS SDE says: “Sustainability has become an important part of what we teach. The architecture of the school needed to match the pedagogy of the school. If this is done right it would not only add credibility to what we teach but it would allow the use of the building as a teaching aid and research scaffold.”
A Holiday Home in Rural Spain
A holiday home in Natural Park of Valles Pasiegos in Northern Spain named Villa Slow proves that zero-energy buildings can be accessible to the masses.
Architect Laura Alvarez, who grew up in the region, designed the net-zero energy building as she longed for “a place where you can be warm when it is cold outside and be fully connected to the outside when the sun shines”.
“The heat pump is connected to the network and produces five kilowatts of energy for each kilowatt that it takes from the network. So, it produces more energy than it consumes,” said Alvarez. She modeled the design over a traditional “cabaña pasiega” (peasant cabin) and used ancient stone walls to maximize insulation.
As the number of net-zero energy buildings continues to soar, the unassuming house proves that they don’t always have to be large-scale commercial or public projects to make a difference.
The net-zero energy holiday home “Villa Slow” in Northern Spain, designed by architect Laura Alvarez.
Another example of excellence are the vertical forests from Italian architect Stefano Boeri, and other useful examples of NZEBs can be found in a report from late 2014, sign that science and architecture have taken this road a long time ago.
If you want to know more about a green technology that can help you start lowering the energy consumption in your house, look at this innovative depurative paint: we talked about it here.
Read the full articles and more here:
- Steven Winter Associates, Inc., February 2016, Net Zero Energy Buildings (https://www.wbdg.org/resources/net-zero-energy-buildings)
- World Green Building Council, March 2021 (date of visit), Green & Healthy Work Spaces
- Hans Erhorn, Heike Erhorn-Kluttig, 2014, Selected examples of Nearly ZeroEnergy Buildings – Detailed Report
- Envirotec, 26 February, 2021, “Global warming won’t wait until 2050,” says European science advisory group
- Stephanie Ossenbach, November 2020, Big, Medium, Small: 3 Net-Zero Energy Buildings
- Maher Shehadi, April 2020, Net-Zero Energy Buildings: Principles and Applications (https://www.intechopen.com/books/zero-energy-buildings-new-approaches-and-technologies/net-zero-energy-buildings-principles-and-applications)