Buildings consume almost half of the energy provided in the United States and are responsible for nearly half of the carbon emissions. Sustainable building trends have progressed rapidly since the adoption of LEED in 1993, which set the bar for high-performance buildings. During the last 25 years, more stringent criteria have been adopted with increasing environmental concerns in order to drive the industry. Net-zero buildings are part of the latest movement of building with the future in mind.
The term “net zero” can be used to describe a variety of elements in a building. One of the most common definitions, adopted recently by the U.S. Department of Energy, describes buildings designed to be energy-efficient and produce as much energy as is delivered to the project. Other interpretations make distinctions between site and source energy. Site energy refers to energy used in the building whereas source adds in the cost to deliver energy to the building. Additional standards have also been proposed that would require buildings to be net neutral to the environment as a whole. These often include carbon production and offsets, as well as ensuring water and waste are self-sufficient systems.
To ensure a building achieves net-zero energy status, a holistic design process must be employed. Early in the design phase, a commitment must be made to optimize energy performance. However, this should not focus entirely on the energy-generation part of the equation.
The purpose is to balance production with efficiencies. While there are buildings claiming to be net zero by supplying enough onsite renewable energy to offset their typical loads, a true net-zero building focuses first on tightening the envelope and maximizing efficiency. In fact, several certification bodies require a minimum Energy Use Intensity (EUI) measured by kbtu/square foot/year for the building to be considered for net-zero status.
Over and above the certification aspect of net zero, there are real economic incentives in achieving this goal. Assuming your local electricity grid allows the facility to sell energy back to the grid, the cost of the project can often be offset through energy sales over time. In the long-term, the building can actually generate income for the owner or tenants on the energy side.
Several tools exist to determine the target EUI of the building. One of the most simplistic is the Energy Star Target Finder, a free online tool from the EPA that allows designers to enter basic assumptions about the building and location before a project begins. Target Finder also allows users to set a goal for reduction in energy compared to the median building or a specific Energy Star score.
More sophisticated modeling techniques can be used throughout the design process to ensure the building maintains the targeted EUI while exploring different measures as the project moves through critical design stages. Energy modeling software can be used to provide an estimate of real world conditions of the building once fully operational. This number will also help to inform the size of the renewable energy system for the project, whether it be photovoltaics, wind turbines, biomass, geothermal, or hydroelectric.
Once a building is constructed, a simplified measurement and verification process can be employed to determine whether net zero has been achieved. At least 12 months of utility bills through the performance period should be collected to review actual energy use compared to the total renewable generation, on an annual basis. In some cases, a third-party auditor is required to certify performance.
Two key organizations in the net-zero movement — the International Living Future Institute (ILFI) and the New Buildings Institute (NBI) — recently joined forces to concentrate their efforts. ILFI, a non-profit organization focused on creating healthy and sustainable design, has created several certification programs and labels for buildings, including the Zero Energy Building (ZEB) certification. NBI, which provides guidance and tools for net-zero buildings, will now act as the lead certification auditor and administrator of the data. Taking it a step further, ILFI also runs a program called the Living Building Challenge, which promotes net-positive buildings that produce 105 percent of the energy use of the building using renewables.
In many parts of the country there are real opportunities for net-zero construction. Areas with abundant sunlight, for instance, should already be prioritizing this kind of construction. As battery technology improves, increasing areas of the country will find this an economically viable alternative to traditional forms of construction, and a pathway to resiliency. Downward pressure on pricing and increasingly accessible technologies will also drive construction in this area.
Megan Saunders is the director for sustainability for PBK Architects (www.pbk.com) with nearly 10 years of experience in green building consulting and sustainability leadership, advocating for high-performance and resilient design for building owners and cities.