In the past few decades, climate change has grown to become a major driver in how we approach the design, construction and operation of buildings. A sustainability movement, propelled forward by certification programs, like LEED, Passive House and the Living Building Challenge, drove manufacturers to innovate more environmentally friendly products and inspired architects and engineers to optimize their designs.
Although progress has been made, the specter of climate change has not subsided. If anything, the threat has grown, the stakes are higher and the time left to act is short. The world just experienced an unusually hot summer, even as the standard of “hot summers” continues to rise. According to the Copernicus Climate Change Service, an agency supported by the European Union, June 2021 was the hottest June on record in North America and the fourth hottest worldwide.
Led by groups, like the American Institute of Architects, the building industry is responding to the severity of the situation, and sustainability has become a greater focus than ever before. The concept of sustainability covers a wide array of strategies and is defined by different people in different ways. Is a sustainable building one that’s built from environmentally friendly materials? Is it one that is energy efficient? Is it a space that is healthy for occupants? It can be all these things and more.
To deal with the core issue at the heart of climate change—the vast accumulation of greenhouse gases (GHGs) in the atmosphere—many designers and building professionals have begun to pursue what’s known as the decarbonization of buildings. It’s the next frontier in the fight against climate change.
“The building and construction industry is responsible for nearly 40 percent of global greenhouse gas emissions,” explains Stacy Smedley, executive director of Building Transparency, a non-profit based in Washington state whose mission is to provide the open-access data and tools necessary to enable broad and swift action addressing embodied carbon’s role in climate change. “It’s critical that we begin to decarbonize the sector by focusing on reducing the two emission types associated with our built spaces: operational carbon and embodied carbon.”
Decarbonization: Why and What
Where it relates to climate change, it’s pretty clear that less carbon is what we want, but what exactly does decarbonization mean? How can greenhouse gases be minimized or removed from the building equation? There are several thoughts and approaches, some focused on operation, others on materials.
“Operational carbon is defined as the greenhouse gases emitted during the use of a building,” Smedley continues. “Embodied carbon encompasses the carbon footprint of construction materials and considers all GHGs emitted throughout a product’s supply chain, manufacture, installation, use, replacement and end-of-life disposal. It’s critical that we reduce both emission types to decarbonize our buildings in our collective fight against climate change.”
“Decarbonizing means reducing the carbon used or embodied in the systems, construction and materials in a building,” adds Katy Flammia, design director of Hudson, N.Y.- based design firm Spacesmith. “This means making decisions from the start of the project to reduce the carbon the project will use. For example, reuse or adapt a building rather than tear it down and start new. Or consider clean energy choices and select materials with a lower carbon footprint.”
“To decarbonize buildings is generally defined as eliminating the direct emissions associated with the building,” says John Sheff, director of public and industry affairs for Danfoss North America. “Direct emissions are those produced onsite at the building, as op- posed to indirect emissions, which are produced upstream of the building by the power plant supplying the building’s electricity. In practice, decarbonizing buildings generally means electrifying its HVAC equipment, since they typically use fossil fuels. This could mean replacing gas-fired water heaters with electric ones or switching out boilers for heat pumps.”
“Some considerations may seem straightforward, like whether residential units will have natural gas or electric ranges, but decarbonization is a broad and holistic approach,” adds Jim Podesky, senior project manager with The Architectural Team, Chelsea, Mass. “It can also mean providing more electric car-charging stations or designing to reduce car trips altogether by offering more bicycle parking. A comprehensive approach will always consider long-term impacts and ongoing usage. Building systems that will be in use for years or decades have the potential to consume a lot of energy, so it’s critical to focus on heating, air conditioning, hot water, ventilation and lighting systems.”
“Decarbonization effectively builds on more traditional ideas of sustainability and green building,” Sheff adds. “Traditional green building tended to think of each part of a building—HVAC, lighting, exterior, water management—as a distinct system. Decarbonization takes those components and allows the building designers and operators to incorporate them into a single system.”
“While historically green- building initiatives and standards might focus on energy, waste and water reductions or operational carbon emissions, decarbonization takes these traditional ideas a step further by including embodied carbon and low-carbon procurement requirements to incentivize carbon reduction across a building’s value chain,” Smedley says.
A significant amount of a building’s energy footprint comes from heating and cooling, so HVAC is a major part of the equation for any building looking to reduce its overall carbon impact. As a large contributor to the energy load of a building, the smallest improvements with HVAC can have a substantial impact.
“In most buildings you can get 20 percent reduction by optimizing the controls, operations, maintenance and behavioral elements,” explains Ian Booth, partner with Buro Happold in New York. “It is not uncommon to see HVAC systems that are 20, 30 or sometimes even 40 percent overdesigned. This results in increased overall energy consumption and drastically reduces comfort. I am an advocate of correctly sizing the systems to ensure maximum comfort and efficiency—and agreeing the design criteria with the clients to avoid oversizing systems for extreme weather events. Part of the journey for us is working to make the systems we design as lean and efficient as possible.”
“The best things you can do are to reuse what you can and create buildings that don’t require a lot of energy use,” Flammia says. “Have an insulated envelope, high-efficiency windows, lighting, heat pumps, and details that reduce thermal bridging and air leaks. These strategies are far superior to building conventionally and buying carbon offsets or having a huge solar field.”