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Author: John Ochsendorf
Improving the construction and performance of buildings could lead to huge reductions in carbon emissions.
Buildings account for a higher proportion of greenhouse gas emissions than any other economic sector, and emissions attributable to building construction and operation have been increasing in recent decades. These emissions can primarily be traced back to heating, cooling, and lighting systems, although emissions from embodied materials are also significant.
Major new initiatives are under way to reduce the amount of energy consumed by buildings, but numerous technical, economic, and policy barriers will have to be overcome. This article provides summaries of some key challenges to the design and implementation of low-carbon buildings in the United States and describes the resulting opportunities for the engineering professions.
Although buildings have major environmental impacts in terms of water use, consumption of raw materials, and the depletion of other natural resources, the focus of this article is on reducing greenhouse gas emissions for mitigating climate change. Carbon dioxide equivalence (CO2e) provides a simple metric for determining the environmental performance of buildings, including both embodied emissions and operating emissions.
As the largest source of carbon emissions in the United States, buildings also represent a significant target of opportunity for carbon reductions (Figure 1). In a landmark paper, Pacala and Socolow (2004) identified improvements in building efficiency as one of seven “stabilization wedges” that could help offset global increases in carbon emissions over the next 50 years.
The Intergovernmental Panel on Climate Change has identified buildings as the sector with the greatest potential for carbon reductions, particularly because reductions that result from improved building performance also yield substantial economic benefits (IPCC, 2007). The World Business Council for Sustainable Development has concluded that the energy use of buildings worldwide could be reduced by 60 percent by 2050 using existing technologies (WBCSD, 2009). McKinsey Consulting has identified the building sector as the most cost-effective target for carbon abatement. According to McKinsey’s analyses, carbon reductions for most buildings could be achieved at a negative cost (McKinsey, 2007).
Several current initiatives in the United States have established target levels for improved carbon performance of buildings. The best known initiative is the LEED (leadership in energy and environmental design) rating system developed by the United States Green Building Council. The exponential growth of the LEED system has dramatically increased the market share of green construction over the last decade. However, although the LEED system promotes a variety of environmental improvement strategies for many different types of buildings, it does not explicitly address carbon emissions.
The 2030 Challenge
The 2030 Challenge developed by Architecture2030 establishes rigorous targets for reducing carbon emissions from new buildings, and in the next two decades, these standards will become increasingly stringent (Architecture2030, 2012). The current goal is to design buildings that use 60 percent less annual energy than average for that building type. For example, to satisfy the 2030 Challenge, a new hospital must emit 60 percent lower emissions than the current national average for hospitals. The reduction targets will decrease by 10 percent every five years (e.g., a decrease in emissions of 70 percent by 2015), until, by 2030, new buildings will be carbon neutral.
There are three primary approaches to meeting these design goals: (1) improving design strategies; (2) improving the efficiency of technologies and systems; and (3) using off-site renewables, such as off-shore wind energy (up to a maximum of 20 percent). Although the 2030 Challenge is voluntary at present, many city governments have committed to pursuing its goals, and a number of engineering and architectural firms are already tracking energy consumption and carbon emissions for their new buildings in relation to the 2030 Challenge goals.
National and State Initiatives
Some countries are developing binding legal requirements for dramatic carbon reductions in new buildings in the coming decades. For example, in the United Kingdom (UK), the Climate Change Act of 2008 mandates 80 percent carbon reductions on a 1990 baseline by the year 2050 (Crown, 2008). To help achieve this goal, the target for new residential construction in the UK will be zero carbon emissions by 2016.
The most aggressive legal target for carbon reductions in the United States is California’s Assembly Bill 32 (AB32), which mandates reductions to 1990 emissions levels by 2020 (Assembly Bill 32, 2012). Improved building efficiency is a major component of California’s road map toward lower greenhouse gas emissions.
Improving Building Codes
Other policies, such as more stringent building codes, can be important motivators for engineers and architects and can move markets toward lower carbon buildings. An extensive study by the World Business Council for Sustainability has shown that more stringent building codes are the most effective way to reduce carbon emissions from buildings and to transform the market for a low-carbon future (WBCSD, 2009).
Challenges for Low-Carbon Buildings
The Role of Engineers
Engineers, who are crucial to designing more sustainable buildings, often become involved too late in the design process to make all of the necessary decisions. Many key decisions, such as building orientation, glazing ratio (i.e., area of glass/area of opaque wall), and the overall form of the building are made in the earliest design stages. Once these critical decisions have been made, engineers can attempt to optimize a poor design, but it is difficult at that point to achieve a low-carbon design.
The challenge is to integrate engineering analysis in a way that provides rapid feedback to architects and the rest of the design team early in the process. For this, engineers must be trained as designers, so they can propose multiple solutions to open-ended problems. In short, the design of high-performance buildings requires integrated systems thinking beginning in the earliest conceptual design stage.
To ensure that engineers with the necessary skills are available, more of them must be trained in building science and sustainable design. However, most engineering schools do not directly address the design and operation of buildings, because sustainable building design involves aspects of mechanical engineering, civil engineering, and architecture.
The few existing programs in architectural engineering are turning out graduates, but in numbers far below those of traditional engineering disciplines. Thus, despite the dramatic economic and environmental impacts of buildings and the growing need for engineers in this field, the engineering of sustainable buildings is not being taught in most schools of engineering in the United States.
Funding for Research
Finally, there is an acute lack of spending on research and development (R&D) for sustainable buildings. It has been estimated that only 0.25 percent of gross sales in construction are spent on R&D in the United States, much less than is spent by industries in other economic sectors, such as the automobile and electronics industries (Gould and Lemer, 1994). Furthermore, only 0.2 percent of federal research funding is spent on topics related to green buildings (USGBC, 2008).
The scarcity of research funding means that fewer researchers are working on this vital topic, despite the urgency of climate change and the favorable economics for carbon reductions through improved buildings. Increased research funding would not only attract more students, but would also attract leading engineers to this important field.
Opportunities for Low-Carbon Buildings
More efficient building design is one of the most cost-effective opportunities for large-scale reductions in carbon dioxide emissions on a national and global scale. Thus more emphasis on integrated building design for the full life cycle of a building can lead to dramatic improvements in building performance. The key is to incorporate systems thinking at the conceptual design stage, taking into account climate-specific factors and regional climate.
The choice of materials for a building can not only determine the embodied carbon of a building, but also has implications for the carbon emissions from building operations, through thermal mass and improved day-lighting. For example, appropriate building materials can moderate diurnal temperature swings or help to distribute daylight deeper into interior spaces. In addition, decisions about building orientation, façades, heating and cooling strategies, and glazing ratios, which must be made early in the design process, are crucial factors in the final energy performance of a building.
New Design Tools
Most traditional architectural design software does not have the capacity to analyze energy or environmental performance in the conceptual design phase. How-ever, in the last decade, several tools have been developed to assist architects and engineers by providing architects with rapid feedback on environmental performance.
For example, the MIT Design Advisor enables the rapid estimation of building energy use based on massing, orientation, climate, glazing ratios, and other factors (Design Advisor, 2012). More recently, the DIVA platform has been developed to enable architects to run basic performance simulations in the early design stage using existing architectural design software (DIVA, 2012). Although such programs are being developed quickly, there is still an urgent need for improvement, as well as for engineers capable of systems-level building design.
Educating Architectural Engineers
A multidisciplinary education focused on sustainable design can attract a new generation of engineers to the profession. In addition to expertise in heat transfer, thermal science, materials engineering, and other traditional building sciences, sustainable buildings require expertise in design thinking and creative problem solving.
There is also a strong demand in the market for increased literacy in rigorous sustainability metrics and for expertise in the life-cycle environmental and economic performance of buildings. Integrated graduate education in the built environment, such as the Solving Urbanization Challenges by Design, a program at Columbia University, combine engineering, architecture, and planning to provide a broad-based education for sustainable building designers and researchers (IGERT, 2012).
Funding for Research and Development
Increasing funding for R&D on sustainable buildings will require new partnerships among industry, academia, and government. Some current examples are (1) the Greater Philadelphia Innovation Cluster for Energy Efficient Buildings supported by the U.S. Department of Energy (DOE) and numerous academic and industry partners (GPIC 2012); (2) the Center for Architecture Science and Ecology supported by Rensselaer Polytechnic Institute and Skidmore Owings and Merrill (CASE 2012); and (3) the Advanced Building Systems Integration Consortium at Car-negie Mellon University (ABSIC, 2012).
Increased federal funding could be provided by the National Science Foundation and the DOE, both of which are appropriate agencies for promoting research on sustainable buildings. In addition, new graduate research fellowships for students working in building science would help attract more researchers to the field.
Many low-carbon buildings constructed in recent years can serve as models to inspire engineers, architects, building owners, and policy makers. Note-worthy examples of a residential building development, a school, an office building, and a cultural building are described below.
BedZED, Beddington, England, 2002
The Beddington Zero Energy Development, known as “BedZED,” is a pioneering low-carbon residential development outside London, England, made up of 99 homes of various sizes (BedZED, 2012). Opened in 2002 and designed by a team of architects, engineers, and developers, these low-rise buildings have passive heating, cooling, and lighting strategies that dramatically reduce residential energy requirements (Figure 2).
However, the BedZED concept goes beyond the design of buildings to include transportation, food production, and other holistic urban-design strategies. For example, photovoltaic arrays and biofuel incinerators are designed to generate 100 percent of on-site electricity demand.
Although the initial cost of construction was slightly higher than for conventional construction, occupants are realizing substantial annual energy savings, and the resale value of homes has exceeded the local average housing market by 10 to 20 percent (BedZED Toolkit II, 2003). Now 10 years old, BedZED continues to set an international standard for developers and designers to learn from and emulate.
Richardsville Elementary School, Richardsville, Kentucky, 2010
Richardsville Elementary School is an 82,000 square foot net-zero-energy educational building for 600 students (Sherman, 2012). Like other low-carbon buildings, Richardsville’s initial design was significantly more efficient than the design of typical school buildings (Figure 3). For example, annual energy demands are only 5.3 kilowatt hours per square foot per year (kWh/ft2/yr), about 75 percent lower than the national standard for elementary schools. In addition, a 348 kW photovoltaic array generates on-site renewable energy to meet this demand.
At a cost of approximately $190 per square foot, the school’s construction costs are competitive with those of other schools around the country. Insulated concrete form (ICF) construction provides improved insulation and reduces air infiltration through the exterior envelope of the building, and geothermal technology generates heating, cooling, and hot water. Overall, Richardsville has dramatically lower annual operating costs than traditional school buildings, resulting in equally dramatic reductions in life-cycle economic costs.
Advanced building technology in schools also has pedagogical benefits. For example, it can motivate students to learn about green building design and construction. Students and teachers also actively monitor the energy performance of the building, and green technologies are incorporated into lesson plans. Richardsville is an example of how an integrated design team can dramatically reduce the energy demands of a building to achieve a zero-energy school.
Research Support Facility, National Renewable Energy Laboratory, Golden, Colorado, 2010
The Research Support Facility of the National Renewable Energy Laboratory is a 222,000 square foot, net-zero-energy office building located at an altitude of 5,300 feet in the Rocky Mountains of Colorado (NREL, 2012). Home to 800 employees, this federal office building is both a showcase for low-energy building technology and a living laboratory for ongoing research and for monitoring the performance of green technologies (Figure 4).
Equipped with day-lighting and passive heating and cooling strategies, the building requires only 10.3 kWh/ft2/yr, which is 50 percent less than the national standard for office buildings. The energy demand is met by an on-site 1.6 megawatt photovoltaic array, which also helps power an on-site energy-intensive data center. Even at an altitude of one mile above sea level, the building does not require conventional heating. Instead, it is warmed by the data center and by transpired solar collectors, which were originally developed at NREL.
Interpretive Centre, Mapungubwe National Park, South Africa, 2009
The Mapungubwe National Park Interpretive Centre is both a museum and a visitor’s center at a World Heritage site in a remote area of northeast South Africa (Figure 5). The client for the project, South Africa National Parks, required a building with minimal environmental impact to be built, as much as possible, with local materials and labor. In this harsh climate, where daytime summer temperatures can reach 110°F, the design team was determined to use passive strategies to maintain a comfortable interior temperature.
Using on-site soil and stones, the advanced structural design of the building consists of massive masonry walls and load-bearing vaults that increase thermal mass. The soil-cement vaults were built with minimal formwork and no interior steel reinforcements, thus reducing the amount of embodied carbon in the building materials by approximately 80 percent compared to conventional steel and concrete construction (Ramage et al., 2010).
Because of the remote location, on-site energy demands were kept to a minimum, and daylighting is the primary lighting source. For its radical approach to design and construction with local materials, the building was honored as the 2009 World Building of the Year at the World Architecture Festival.
In these and most other low-carbon buildings, the crucial design strategies were developed by collaborative teams of architects and engineers early in the design process. In addition, owners or clients often played a central role in establishing a vision for each project, essentially setting a challenge for the design team to meet. By setting clear targets for energy consumption, these designs were achieved at costs similar to those of conventional construction. However, as a result of reduced operating energy requirements, they have significant life-cycle economic benefits. These and other projects clearly show that the carbon intensity of new buildings can be dramatically reduced using existing technologies.
Buildings are widely recognized as the most significant opportunity for cost-effective carbon reductions in the United States and around the world. To take advantage of these opportunities, engineers must continue to play a vital role in transforming the built environment for a low-carbon future.
Numerous areas for improvement remain. An intensive emphasis on conceptual design, life-cycle thinking, and innovative research partnerships will be necessary to advance the field, reduce carbon emissions, and train a new generation of engineers. We now know from experience that dramatic improvements in the design and operation of buildings are possible. Our hope is that well trained engineers will provide leadership for the United States and the carbon-constrained world of the future.
ABSIC (Advanced Building Systems Integration Consortium). 2012. Advanced Building Systems Integration Consortium, Carnegie Mellon University. Available online at http://www.cmu.edu/architecture/research/cbpd/absic-cbpd. html.
Assembly Bill 32. 2012. California Global Warming Solutions Act. Available online at www.arb.ca.gov/cc/ab32/ab32.htm.
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