The planning of our communities also has a large impact on carbon dioxide emissions. Dense cities with good public transit have lower per-capita emissions because of the relative efficiency of multifamily housing and fewer individually owned automobiles as compared to low-rise suburban types of communities with few options for public transportation and mostly single-family housing.
Embodied Emissions Due to Buildings
In the recent past, architects, engineers, and building owners focused almost exclusively on operations and energy efficiency (operational carbon emissions). Less well understood is the large impact buildings have on carbon dioxide emissions during construction due to the emissions associated with mining, manufacturing, and the transportation of building materials, as well as the construction process. This is referred to as embodied carbon. Embodied carbon has come to the fore because of the urgency of reducing greenhouse gas emissions. Although reducing embodied carbon in buildings will have only a short-term impact, given the urgency of the problem, it needs to be a key focus because embodied carbon contributes about 50 percent of a building’s carbon emissions during its first 15 or so years of occupancy, as illustrated in Figure 2.
Keep Existing Buildings
Tearing down old buildings and building new ones severely and negatively affects climate change. Historic preservationists have gotten it “right” for decades when they have advised saving old buildings is not just good for preserving history and culture; it’s good for the environment. A great deal of carbon is sequestered in existing buildings. When they are torn down, the carbon embodied in them is gone. Replacing them simply adds to the carbon emissions problem. As illustrated in Figure 3, refurbishment reduces carbon emissions throughout a building’s life.
Building Materials and Embodied Carbon
According to Architecture 2030, “Just three materials—concrete, steel, and aluminum—are responsible for 23 percent of total global CO2 emissions (most from the built environment). There is an incredible opportunity for embodied carbon reduction in these high-impact materials through policy, design, material selection, and specification.”
Therefore, a focus on these materials and the reuse of existing buildings will have the greatest short-term impact on emissions in buildings. Together with reductions in operational carbon, the building sector can significantly reduce emissions related to climate change and global warming.
The following examples illustrate the potential for reducing carbon dioxide emissions in large and complex buildings as well as the benefits of using an integrative design process. This process helps the design team move beyond first-cost thinking to maximizing efficiency while minimizing costs.
The Empire State Building
An inspiring example of the reuse of an existing building while reducing operational energy is the retrofit of the Empire State Building. ESB case study (rmi.org); Alejandro de la Garza, The Empire State Building’s Green Retrofit Was a Success. Will Other Buildings Follow Suit?, Time (May 10, 2021, 2:22 PM EDT).
The owners of the Empire State Building were planning to replace their chillers and do some retrofits, so it was a perfect time to review the entire project and determine how to best maximize energy savings and comfort while minimizing costs. Rocky Mountain Institute helped the owner and design team use an integrative design approach to do this. When all the system upgrades and savings were taken together as a whole package and not piecemeal, the overall first-cost savings were huge and long-term energy savings were maximized. According to the Empire State Building owners, even after retrofitting all the windows in the building, upgrading lighting, adding insulation, and doing more, they achieved approximately a three-year payback. These measures reduced heating and cooling requirements, allowing the old chiller plant to be renovated rather than replaced. This process is referred to as “tunneling through the cost barrier.” Most owners and designers find “tunneling through the cost barrier” to be challenging because it requires a very integrated approach to design, requiring most of the design team and the owner to be closely involved in the new building or renovation from the beginning. In the author’s experience, it is by far the best way to achieve maximum savings.
Sarah E. Goode STEM Academy
A project for which the author provided sustainability consulting services is the Sarah E. Goode STEM Academy, a new 200,000-square-foot LEED Platinum high school on Chicago’s southwest side. This project also used an integrative design approach to reduce building costs and embodied carbon while maximizing energy efficiency. (LEED is a green building rating system created by the US Green Building Council and stands for Leadership in Energy and Environmental Design.)
Common to both of these project examples and to all high-performance projects is the use of an eco-charrette early in the design process to identify opportunities and potential system synergies that could lead to improved energy efficiency and reduced first costs. The cost to build Goode was less than another prototype high school with the same floor plan (but with a different building envelope design, structural system, and HVAC systems). Because of its less expensive and more efficient HVAC system, the building height was reduced. Yet the energy consumption by Goode was significantly lower than the consumption by the other school, which achieved LEED Gold. In addition, by reducing the building height and using a more effective structural system, the embodied carbon was also reduced.
The thought process that goes into these projects is as follows: First, use passive strategies such as good orientation and appropriate windows for daylight and views, and avoid building orientation that increases heating and cooling requirements. Then consider how to reduce building loads by providing good window and wall insulation and high-quality efficient lighting, and reduce plug loads (through efficiency and realistic assumptions). Plug loads refer to equipment plugged into the wall, such as computers, coffeemakers, and task lights. Next, consider the most effective HVAC systems. In the case of Goode, a ground source heat pump system was used, which significantly reduced the size of ducts and allowed the building height to be reduced. Once the building is as efficient as possible, consider the addition of renewable energy. Goode uses solar water heating for heating indoor water, including a swimming pool.
New Considerations for Embodied Carbon and Life Cycle Analysis
The building industry has only recently begun to focus on embodied carbon. Figure 4 from the New Buildings Institute illustrates embodied vs. operational carbon in a building’s life cycle.
Life cycle analysis is regularly used for analyzing which building materials will be most effective in reducing embodied carbon. In LEED, life cycle analysis is used to study the structural elements and building envelope. For structure, comparisons are most often made among concrete, steel, and wood (mass timber), and include how those products were manufactured and sourced. For instance, there are several ways to make steel, including electric arc and the basic oxygen process (BOP). An electric arc can use much more recycled content material than BOP can use and therefore has lower embodied carbon. There are also different ways to make concrete, some with carbon dioxide(!). Some ways use more recycled content materials than others. For the building envelope, there are many potential materials, such as glass, masonry, and precast concrete. To best understand trade-offs, it is important to compare how these materials work based on both embodied carbon and operational carbon (primarily energy use). Ideally, there should be no new buildings, just the reuse of existing ones. Clearly, this will not be effective in many situations. Life cycle analysis can illustrate the benefits of reuse.
Buildings are large contributors to global warming. Now is the time to step up the effort with all buildings, new and existing, to reduce both operational and embodied carbon. All professionals in the real estate industry have parts to play.