The building sector emits such huge amounts of greenhouse gases that urgent action is necessary to avert climate disaster. Net zero energy buildings will play a big role in curbing global warming in the decades to come.
Most people probably think of fossil fuels in transportation when they think of global warming and greenhouse gas emissions. So it’s surprising — and important — to note that the building sector produces nearly 40% of the world’s emissions.
To meet the goals of the Paris Agreement, the building sector must attain net zero carbon by 2050. That means billions of buildings worldwide will need to comply to keep global warming below 2 degrees Celsius. The Biden administration also set a goal of net zero carbon emissions by 2050.
What Is a Net Zero Energy Building?
Net zero energy buildings are buildings that make, or supply, their energy through renewable resources, which results in zero carbon emissions. Put simply, a net zero energy building is one that produces as much energy as it consumes on an annual basis.
These types of buildings can take energy from electrical grids, and send unused energy back to offset their energy consumption.
Don’t be confused by conflicting terms. NZEB stands for “net zero energy building.” ZNE is short for “zero net energy building.”
They all mean the same thing. They also might be referred to as “green buildings.”
There is a difference between “net zero” and “zero.” For example, New York state law says 85% of reductions must come from the state’s own industrial and energy emissions. The remaining 15% may come from carbon offsets, including in forestry and agriculture.
Carbon offsets work whether an organization stops its own emissions or offsets its emission reductions elsewhere. The climate effects are the same.
During the 1970s, solar panels on the roofs of homes began harnessing the sun’s power. This reduced energy costs and helped the environment at the same time. California and other states created programs to encourage their use, but they haven’t gotten us where we need to be. And while solar panels are important, they can’t do the job alone.
This is because net zero energy building has to be far more holistic in its approach. It needs to include a number of factors that promote energy conservation. It also should go well beyond single-family renewable energy homes and residential buildings. It must include other building types, including commercial buildings.
Some of the ways to achieve net zero energy will be covered in the sections that follow.
How Does a Building Achieve Net Zero Energy?
Several factors go into designing an energy-efficient building that achieves net zero energy goals.
To construct a net zero energy building, you must take several conditions into consideration. The building site, where you are building, the climate and the building’s exposure all have an effect.
Among other things, take into account:
- Wind patterns
- Rain patterns
The orientation of the building depends on the success of achieving net zero energy. Certain renewable energy generation mechanisms, like solar panels, work best when the building is facing south.
But factors that conserve energy are also important. Besides harnessing the sun’s energy, you can conserve by orienting your building to take maximum advantage of the shade. In warm climates, this means you’ll need to use the air conditioning less to keep your building cool.
Lighting is another important factor. Lighting systems can account for almost 25% of a building’s total energy consumption. Orienting your building to take advantage of natural lighting can reduce that load. Window arrangement and the use of skylights are strategies that can be considered when deciding on a building’s orientation.
You can also situate your building to take advantage of natural breezes. Using natural resources to power your building’s energy systems and reduce energy requirements, will conserve resources at the same time.
Building design is next. Make sure to select the best-insulating materials possible so the building conserves as much energy as possible. Windows (dual- or, better, triple-pane and effectively sealed) can pose a major factor in conserving energy.
Passive strategies aren’t about energy production. They’re about minimizing energy usage — and maximizing energy performance. In fact, they operate without energy use, which is why they help buildings achieve net zero energy use:
- High-efficiency appliances require less energy and lighten the overall energy load.
- Low-energy HVAC systems do the same.
- Air sealing prevents cooled or heated air from escaping through cracks, often around openings such as windows and doors. This results in less need for air conditioning or heating to maintain climate control.
- Insulation performs the same function by providing an extra barrier between the interior and exterior of a building. This layer traps heat (in winter) and cool air-conditioned air (in summer) that otherwise might escape through walls, ceilings, etc.
The effectiveness of insulation is rated in R-values. These vary based on the thickness, density, and type of insulation: the higher the R-value, the better. Types of insulation include:
- Foam boards or blocks
- Ventilation is particularly important in tropical climates. It’s necessary to replace stale air with fresh air. This can help to moderate internal temperature while reducing the build-up of moisture that can cause mold and bad odors. The energy used to maintain proper ventilation, by using electrical fans, for example, can be reduced significantly by employing natural strategies.
- Architectural design in new buildings maximizes efficiency and promotes sustainability.
ASHRAE, or the American Society of Heating, Refrigeration, and Air Conditioning Engineers, has created standards that apply to building design. The group, founded in 1894, has 87 active standards and guideline project committees that address some of the following topics:
- Thermal comfort
- Energy conservation in buildings
- Reduction of refrigerant emissions
- Indoor air quality
The final step in designing high-performance buildings is determining the most relevant renewable energy sources based on the building. If the building is industrial scale, wind generators might be used on-site rather than off-site. Solar panels might be the way to go for new homes or even ones that can be converted.
Active strategies reduce energy consumption during the building process through the use of renewable energy strategies, such as:
- Photovoltaics — Photovoltaics is the direct conversion of light into electric power using semiconducting materials such as silicon. Each solar panel contains numerous photovoltaic cells, which work together to produce electricity.
- Wind power — Wind is a kind of solar energy produced by three factors. It’s affected by the sun unevenly heating the atmosphere, irregularities in the Earth’s surface, and the planet’s rotation. The resulting wind turns propeller blades around a rotor, which spins a generator, creating electricity. Wind farms in mountain passes near San Bernardino (San Gorgonio Pass) and Northern California (Altamont Pass) contain hundreds of huge propellers.
- Hydroelectric power — Hydroelectric plants capture the energy of falling water and convert it into electricity. Water flows downhill and is captured by a reservoir behind a dam. This reservoir acts like a battery, releasing water during periods of peak demand to produce power.
- Biomass — Biomass stores chemical energy from the sun, produced by plants through photosynthesis. It can be burned directly to produce heat or can be converted into renewable liquid and gas fuels. Biomass can be as simple as a log on a fire. It’s like a solar battery, which releases bioenergy.
- Geothermal power — Geothermal power involves water pressure in the form of steam. Geothermal wells drilled a mile or two underground pump hot water to the surface. There, the pressure drops and the water turns into steam. The steam spins a turbine connected to a generator, producing electricity.
- Solar power — Sunlight shining on a panel is absorbed by photovoltaic cells in the panel. This creates an electrical charge in response to an electrical field in the cell, producing electricity.
- Solar thermal — Solar thermal power systems use mirrors to collect sunlight and concentrate it. This raises the temperature until it is high enough to produce electricity. Examples include curved parabolic troughs, such as those used in the Mojave Desert.
Net zero energy buildings react in various ways to their local electricity grid. Whether the grid is integrated or conventional affects the way it interacts with buildings and strategies (such as renewable energy sources).
- Energy moves between the grid and conventional energy buildings in a single direction. It flows from the grid to the building, utilizing conventional metering.
- Moderately responsive buildings have interactive demand response.
- Buildings that are fully integrated with the grid include passive efficiency features as well as renewable energy production onsite.
Put another way, the two types of ZNE building typologies must work together to optimize grid performance:
- Renewable-oriented (active strategies)
- Efficiency-oriented (passive strategies)
Utilizing both passive and active strategies will prove most beneficial to the relationship between the utility grid and ZNE buildings.
Net Zero Retrofits for Existing Buildings
Energy retrofit can be defined as adding new technologies to existing buildings to reduce energy consumption. The process of retrofitting a building takes time, planning, plus substantial materials, construction equipment, and labor.
Retrofitting existing buildings usually is more environmentally friendly and less expensive than new construction. This is true when the building location, current design, and building stability are considered.
Here’s what we do know, based on studies, about the success rates of retrofitting as well as associated costs:
- The more compact a building is, the more energy-efficient it will be if it undergoes energy retrofit.
- Buildings in areas with mild and harsh climates were the closest to attaining net zero energy savings.
- The less expensive a retrofit construction project is, the more likely the building will save on net zero energy. Between $200 per square foot and $450 per square foot is ideal.
- The elements that contribute the most to the net zero efficiency are solar panels and window replacements.
- New building construction accounts for an overwhelming amount of negative environmental impacts. New construction for an energy-efficient building will negatively impact the environment 10 to 80 years after completion.
- When compared to retrofitting buildings, new construction is best for increasing energy performance and savings and maintenance costs.
Retrofit energy projects are often used to improve efficiency. There’s a pressing need for them because the average age of the U.S. home is nearly 40 years. But it isn’t just important for buildings that went up in the early or mid-20th century. Buildings constructed to meet energy codes in place as recently as 1999 use 67% more energy than those built today.
Retrofits not only work as efficiency measures; they’re also cost-effective because they can reduce operational costs. Two strategies are particularly useful:
- Building reskinning — In simple terms, this process means the exteriors of existing buildings are retrofitted with more insulation. A three-dimensional scan is made of a building’s exterior. Then the scan is used to create insulating panels that can be fitted over the building and installed quickly onsite.
- Packaged mechanicals — This process simplifies the components of mechanicals into a single unit for easier installation, connection, and control. It decreases the amount of work needed onsite. A package can include a heat pump, solar hot water pumps, and energy monitoring within one integrated control module.
Before undertaking an energy retrofit, it’s helpful to create an action plan that includes the following steps.
- Determine which systems to replace for the highest efficiency. Some systems may be operating at peak levels already and won’t need to be replaced.
- Review utility bills from the past few years. This can tell whether energy consumption has risen.
- Perform energy audits to make adjustments accordingly. An energy audit can reveal which systems need to be upgraded. It identifies things like clogged filters, leaks, disabled sensors, and bad wiring.
- Examine the building envelope for proper ventilation and insulation. Check for gaps around vents and pipes, poorly sealed windows, and areas where moisture is coming in.
5 Ways to Retrofit a Building for Net Zero Energy Savings
Simply retrofitting your building won’t automatically create net zero energy savings. Slight changes might not be enough.
Furthermore, every case is different, so there’s no one-size-fits-all approach to retrofitting. The amount of work depends on how extensive the modifications need to be. That, and several other factors: the climate, the building’s original design, its structural stability, and materials you use. These also affect the cost of a project.
Although retrofitting is almost always less expensive than starting from scratch, older buildings that need extensive work can require significant investments in terms of materials, equipment, demolition disposal, and labor.
Tax incentives and other stimulus can offset some of the long-term costs, along with future energy savings.
Here are five ways to retrofit your building to make progress toward a net zero goal:
1. Replace outdated mechanical systems.
- Trade out the furnace/boiler/window air conditioner for central systems and/or solar water heating.
2. Insulate leaks.
- Insulate basements to reduce mold.
- Insulate roofs and foundations with spray foam to keep building interiors cool in the summer and warm in the winter.
- Insulate empty walls to effectively warm an older house.
3. Replace old windows.
Windows are similar to insulation. They prevent climate-controlled air from escaping while keeping air and water from getting into the house. Energy Star provides a list of efficient windows.
- Triple-pane glass windows are the best option for maximum energy efficiency. While a dual-pane design can almost double the level of window insulation, a triple-pane window is even more efficient.
- Windows should be installed properly to prevent water damage or air infiltration for optimal energy efficiency.
- Window placement can increase your energy efficiency. For example, windows placed on east or west walls can waste twice as much energy as those facing north or south. This is because they face direct sunlight in the mornings and afternoons, respectively.
- Low-emissivity glass coatings reduce the amount of infrared and ultraviolet light that passes through the glass. However, these low-e coatings do not affect the amount of visible light that comes through. This allows you to:
- Keep your interior cool by reflecting heat in the summer.
- Retain warmth by reflecting cold air during the winter
- Prevent fade damage by blocking UV rays.
4. Purchase Energy Star products.
- These types of products are the best for saving energy and reducing electricity bills. Energy Star offers an online portfolio manager to benchmark the energy use of any building. It measures it against similar buildings in terms of consumption and performance level.
- Since 1992, Energy Star and its partners have helped businesses and families save $450 billion in energy costs. They’ve also achieved 4 billion metric tons in greenhouse gas reduction and saved 5 trillion kilowatt hours of electricity.
- Energy Star is perhaps best known to consumers for certifying an array of appliances and electronics, including:
- Refrigerators and freezers
- Washers and dryers
- Air purifiers and dehumidifiers
- Digital media players
- However, it also certifies building products, including:
- Roofing products
- Sealing and insulation
- Storm windows
- Residential windows, doors, and skylights
- In addition, it certifies heating and cooling products, which play a role in a building’s energy efficiency, including:
- Central and room air conditioners
- Geothermal and air-source heat pumps
- Ductless heating and cooling
- Smart thermostats
- Ventilation fans
5. Switch to renewable energy.
- Produce your own energy using various types of renewable energy sources to help conserve energy and reduce costs. These can be solar, wind power, hydroelectric, and photovoltaic.
Net Zero Energy Buildings and the Grid
Despite the increased production of renewable energy, we don’t have the technology to store the energy on a large scale. Hydroelectric dams alone aren’t nearly enough.
As discussed earlier, a grid connection is needed to help buildings achieve net zero energy. It sends any excess energy buildings produce back to the utility grid.
This involves a concept called load flexibility, under which demand can be shifted to accommodate fluctuations in wind and solar supply. There will be times of peak demand. But there will also be times when surplus power is generated using active renewable energy strategies.
Load flexibility involves full connectedness to the grid, which works like this:
- Integrating a building with the grid to produce your own energy lets you rely on that energy when climate conditions allow. In other words, you produce energy when the sun is shining, water is running, or the wind is blowing.
- Any excess electricity you produce during these periods is fed back into the grid. Most states and utilities employ net metering, which “turns back” your electricity meter as you send power to the grid. Utility grids need to be responsive and interactive. They need to work with all types of renewable energy sources to attain net zero energy.
- When conditions don’t allow you to create your own energy, you can access energy supplied by the grid. This means when the sun isn’t shining, water isn’t running, and the wind isn’t blowing.
- To pursue this option, you’ll need to know:
- What equipment you need to connect to the grid, including meters, power conditioning equipment, and safety equipment.
- What requirements your power provider has set.
- What state and community codes and requirements you’ll have to meet.
There are two different net zero building typologies: renewable-oriented and efficiency-oriented.
- Renewable-oriented buildings:
- Use more energy but also generate more energy.
- Rely on active strategies such as mechanical HVAC systems, thermal storage, demand response, and night ventilation.
- Efficiency-oriented buildings:
- Use and generate less energy.
- Rely on passive strategies like effective insulation, built-in shading, daylighting, and building orientation.
The Future of Net Zero Energy Buildings
Billions of buildings need to be renovated or built at net zero to reduce global warming and meet the Paris Agreement.
Sharing these goals, the National Renewable Energy Laboratory works on the research and development of renewable energy and energy-efficient technologies.
The current U.S. presidential administration’s American Jobs Plan seeks to invest $2 trillion in jobs, renewable energy, and renewed infrastructure.
This investment will impact the climate crisis by:
- Providing infrastructure to reduce impacts on the environment and communities.
- Supporting clean energy technologies to lessen the impact of greenhouse gases.
- Removing current environmentally damaging energy sources.
The Department of Energy has set goals or metrics to focus on energy efficiency and renewable energy. Among them:
- Deploy 30 gigawatts of offshore wind within the decade. This will help:
- Create jobs for Americans.
- Reduce carbon dioxide emissions.
- Generate clean energy to power millions of homes.
- Cut the current cost of solar energy by 60% by 2030 by improving solar technology and supporting new jobs. This will help put the U.S. on a path to achieving 100% clean electricity by 2035.
States’ initiatives for net zero energy buildings
States are getting into the act, too. New York’s 2019 legislation created goals of 100% carbon-free electricity by 2040 and net zero emissions by 2050. Hawaii adopted a 100% target in 2015. And California, Colorado, Maine, New Jersey, New Mexico, Oregon, and Washington have passed major climate change legislation.
Among other things, California’s plan calls for all new commercial construction to be zero net energy. It also requires half of existing commercial buildings to be retrofitted to zero net energy use by 2030.
Net zero energy buildings in the private sector
In the private sector, continued expansion in the retrofit market combines with new construction for net zero energy buildings.
Still, to make a significant difference in global warming, energy efficiency investments and grid interactivity must increase dramatically. This means increasing building retrofit rates from about 1% a year to more than 5% a year.
Active and passive strategies must be employed in concert. But builders can’t stop at energy efficiency. Buildings must be fully interactive with the grid and able to take advantage of flexible load management.
The challenges are significant, but the methods of meeting and overcoming them are known. We just need to accelerate the methods and make them work together to maximize energy efficiency. If we do this for new and existing buildings, we can meet the goals we’ve set for 2030 and 2040. We can even meet those for 2050, as we work to identify new, longer-term goals.