Continuing Education: Net-Zero Retrofits
“Energy” is often used as a proxy for “emissions,” but, when it comes to climate-friendly design, the distinction between them matters. Energy use itself isn’t what’s fueling the climate crisis; the problem is the greenhouse gas emissions that energy use generates. This distinction is especially important when it comes to retrofitting existing buildings. It can mean the difference between a zero-carbon retrofit that’s prohibitively expensive and one that a client can afford.
Even after minimizing a building’s energy consumption, meeting remaining needs from carbon-free sources on-site (net zero energy) is typically far more expensive than purchasing carbon-free energy from a utility that’s in the business of producing it. Yet the two approaches are equally successful in eliminating emissions—and that, from a climate perspective, is what counts. The less expensive approach is just that much more likely to happen. Going further, a focus on emissions logically extends to embodied as well as operating carbon, and so can lead to a total carbon takedown.
Demonstrating how the distinction between energy and emissions plays out in practice are three recent renovations of 20th-century office buildings that have achieved carbon-free benchmarks (carbon-free meaning the net amount of greenhouse gas they generate is zero) on constrained budgets. The AIA’s overhaul of its seven-story, 148,000-square-foot headquarters, in Washington, D.C., is set for completion in June of this year. Originally built in 1973, the renovated building—to be renamed the AIA Global Campus for Art & Design—aims to achieve net zero embodied carbon and to leapfrog the AIA 2030 Commitment’s phased reductions in operating emissions by five years. The repositioning and expansion of the 1974 Silvio J. Mollo Federal Building, a 10-story, 160,000-square-foot property located in Lower Manhattan and owned by the U.S. General Services Administration (GSA), is targeting the International Living Future Institute’s (ILFI) Zero Carbon Certification. And the recently renamed Arthur Erickson Place, a 26-story, 363,000-square-foot heritage office tower designed by Erickson and built in 1968 in Vancouver, last year was certified under the Canada Green Building Council’s Zero Carbon Building-Performance Standard. With over 80 percent of 2050’s buildings already standing, reducing existing structures’ greenhouse-gas output may well be the architecture and construction sector’s most effective strategy for mitigating climate change.
The AIA’s transformation of its 50-year-old Brutalist building is helping to set new standards for zero-carbon renovations. And yet, without a paradigm shift at the outset, “to start with carbon as the framing, not energy,” the achievement wouldn’t have been possible, says Brad Jacobson, a principal at architecture firm EHDD. Preliminary studies indicated that a strategy of intensive energy-use reduction combined with on-site renewables to meet all the building’s energy needs would have exceeded the AIA’s budget, while still leaving the renovation’s embodied carbon unmitigated. Instead, the project team adopted a five-step decarbonization strategy that takes account of total carbon load at a budget-compliant price.
The first step consisted of measures to improve energy performance as much as the $60 million budget would bear. These included replacing single glazing with thermally broken double glazing, adding insulation to the walls, upgrading HVAC components, and improving the energy performance of lighting and domestic hot water systems. External shade canopies of fritted glass, with integrated photovoltaics (PVs) above south- and west-facing ribbon windows, reduce cooling loads and improve daylighting, while also expressing the AIA’s performance goals and design values. Together, these improvements are expected to reduce the campus’s energy use by about 30 percent.
Courtesy EHDD, click to enlarge.
Second, the renovation eliminated fossil fuels, replacing the original gas boiler with six air-source heat pumps on the roof. “Heat pumps are electric heating done efficiently,” says Peter Rumsey, founder of Point Energy Innovations, the project’s m/e/p, energy, and decarbonization consultant. “They are a critical part of electrifying buildings.” With a coefficient of performance (the ratio of the energy they need to run to the useful energy they put out) typically between 2 and 3, heat pumps use about a third of the power a boiler or an electric resistance heater would use to supply the same amount of heat. They can also provide cooling, pumping heat out of a building. The technology has been around for decades, but its widespread adoption for commercial buildings is relatively new, Rumsey says.
With the Global Campus design fully electrified, the next step was to source its power from carbon-free renewables. The PVs integrated into the shade canopies, and others installed on the roof, account for about 10 percent of the building’s needs. For the remainder, the AIA will purchase zero-carbon electricity from D.C.’s grid. This energy will have full additionality, meaning new PVs will be added to the grid to provide it, just as if the AIA had installed them at its Global Campus, but without the organization’s having to find the space and up-front capital. Operational emissions: net zero.
The fourth step focused on embodied emissions, the ones that resulted from producing the renovation’s materials, products, and furnishings and installing them on-site. A life-cycle carbon calculator, EPIC (developed by EHDD and available free online as c.scale), helped to establish an embodied-emissions budget for the project. What followed was a rigorous, iterative approach to identifying low-carbon options for each building system and product, including a manufacturers’ questionnaire to verify product performance, and resulting in a low-carbon specification and procurement. These efforts reduced embodied emissions by 55 percent compared to a baseline new building, including a 26 percent savings from the reuse of the existing structure.
Courtesy EHDD, click to enlarge.
Offsetting the remaining embodied carbon led to one of the most innovative aspects of the project. Working with Habitat for Humanity, the AIA purchased rooftop PVs for 70 households in a nearby affordable-housing development. In addition to cutting power bills for low-income residents (a demographic that has been disproportionately affected by climate and environmental impacts), the fully additional, emissions-free energy from the panels will offset the renovation’s embodied carbon, with most of the mitigation occurring during the first 15 years. Expanding the view of the project to include all of its net emissions, even when they’re generated or mitigated beyond its lot lines, “is a much more pragmatic view of how we actually address climate change with the proper scale and speed,” says Jacobson. Global warming, he points out, “doesn’t actually care about where, but it does care about when.”
Nothing says scale like the GSA, the largest landlord in the U.S., with some 8,800 owned or leased assets totaling about 370 million square feet (though the future of that portfolio is uncertain with the current administration’s goal of shrinking the agency’s holdings). The planned modernization of one GSA property, the Silvio J. Mollo Federal Building, which is home to the U.S. Attorney’s Office for the Southern District of New York, has multiple goals. Slated for completion in 2026, it will increase the building’s square footage (by hanging a new facade outboard of the structure and infilling the floor slab), visually associate the building with the nearby courthouse (rather than with the nearby prison it was originally paired with), improve its entry sequence and relation to the plaza on which it fronts, and upgrade its accessibility. On top of that, the project is intended to serve as a model for decarbonizing the GSA’s entire portfolio, says Gabriel Wilcox, director of sustainable design at Krueck Sexton Partners, the project’s architect, “so this has huge scalable impact.”
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The 1974 Mollo Federal Building (1), in Lower Manhattan, is planned to be retrofit (2) to achieve ILFI zero-carbon certification. Images courtesy Krueck Sexton Partners (1), Image courtesy Filippo Bolognese Images (2).
As with the AIA Global Campus, the key to decarbonizing the Mollo Building is electrification. Helping to do that as efficiently as possible (with a 75 percent reduction in energy use compared to a baseline building), the new facade is designed to optimize such factors as the window-to-wall ratio, the U-value of the wall, the solar-heating coefficient of the glazing, and external shading. Also helping are improvements to the air-handling system’s heat recovery and distribution efficiency, balancing loads as evenly as possible and avoiding peaks for either heating or cooling. “In the olden days, to oversize a boiler for a couple of peaking hours cost you almost nothing,” says Nico Kienzl, senior executive director in the New York office of Atelier Ten, the project’s sustainability consultant, “but if you do this electrically, additional heat pumps are proportionately more expensive. So, you really need to get the overall building right.”
Relying on heat pumps for both heating and cooling will allow the project to eliminate an entire subsystem. Even though cooling towers and chillers would have provided more energy-efficient cooling by a factor of 1 or 2 percent, not installing them will save almost a million dollars in first costs, with additional savings on maintenance (predicted to exceed the value of the 1 or 2 percent energy savings). Add in the reduction in embodied emissions from less equipment, and the savings of about 400,000 gallons of water per year that the cooling towers would have needed, and heat pumps are the clear winner on cost, carbon, and water conservation. Plus, in the roof space that a separate cooling system would have needed, there’s now room for PVs. “So this is really a super-holistic view,” Kienzl says, “not just chasing one metric.”
On-site PVs, integrated into shade fins as well as positioned on the roof, are expected to provide about 10 percent of the building’s energy (a real achievement, given the small footprint-to-volume ratio, Wilcox notes). For the remainder, the GSA plans to purchase clean power from the grid, which it has historically done; in this case, a longer-than-usual 15-year contract will meet ILFI’s Zero Carbon Certification requirements.
After bringing operational emissions to net zero, the Mollo design prioritized materials with low embodied carbon. The facade, for example, consists of zinc panels, which have “far and away” fewer embodied emissions, Kienzl says, compared to stainless steel or, in this case, even stone (for which security considerations would have mandated a carbon-intensive steel backing). As with the cooling towers and chillers, materials were eliminated whenever possible; rather than installing ceilings throughout, for example, the design takes opportunities to expose the existing waffle slabs. Bio-based elements such as wood doors, handrails, and ceilings (where they were preferred) were selected both to complement the concrete and to sequester carbon. Salvaged materials were used as much as possible, especially in the landscape.
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Image courtesy Krueck Sexton Partners, click to enlarge.
A one-time carbon offset to mitigate inevitable embodied emissions has been estimated in the range of $56,000. (The price of offsets varies with type and market timing.) The architects have provided the GSA with research for an alternate pathway: investing in additional renewables on one of its other buildings.
Although the facade retrofits on the AIA Global Campus and the Mollo Federal Building helped to make their electrification more energy efficient, the Arthur Erickson Place (AEP) retrofit proves that it is in fact entirely possible to decarbonize a building without touching its facade. “The green-building industry has historically been dominated by new construction,” says Brad White, president of SES Consulting, the mechanical consultant for AEP’s zero-carbon achievement, “so there’s almost a bias there about how important the envelope is.” That mindset needs to change, he says. “Especially around retrofits, if the goal is carbon, then you shouldn’t really be thinking about the envelope too much.”
Arthur Erickson Place in Vancouver has been decarbonized without any alterations to its heritage facade. Photo © Hariri Pontarini Architects
Even with its original single glazing, the Erickson retrofit, completing in May 2026, has dropped the building’s operating carbon by 97 percent (with the remaining 3 percent a function of an almost but not perfectly clean grid). Embodied carbon was limited to the mechanical equipment and the process of installing it. But the cost difference between electrifying with or without engaging the facade was an order of magnitude that dictated whether the retrofit would move forward at all. “I might be able to fix the mechanical systems and fully electrify for $10 million, but to redo the facade would probably be $100 million,” says Joe Brown, vice president for building technology and decarbonization lead at KingSett Capital, a private equity real-estate investment firm that, with Crestpoint Real Estate Investments, co-owns the building. And that’s not even considering the disruption to tenants or the need for approvals to modify a heritage building.
The first step in bringing Erickson Place to zero carbon operations was to make refinements to the existing environmental systems—things like fan upgrades, new motors, improved controls, and reconnecting a disused perimeter distribution system. These reduced natural gas use (and therefore emissions) by about 20 percent, with an additional 10 percent savings in electricity. The owner then ran the building through a winter, and SES used the resulting performance data as the basis for sizing the equipment for the retrofit. Without that data, the design would have had to rely on energy modeling, White says: “We’d have to be much more conservative, and it would probably have cost a lot more.”
The new system draws thermal energy from three sources. Recovering heat from interior zones (which require year-round cooling) and transferring it to perimeter zones where it’s needed accounts for about half of the building’s heating load over the course of the year. Then there are new air-source heat pumps that take atmospheric heat and put it in the building (or vice-versa). Third, a backup electric boiler handles peak loads (about 10 to 15 percent of the total annual load). White estimates that including a backup boiler cut the required number of heat pumps by one-third or even half. “In a new building, with the best possible envelope, it’s a little more practical to use only heat pumps,” he says, “but in retrofitting older buildings, we look much more to these hybrid solutions.” (The Mollo retrofit also includes an electric boiler to assist if, for example, heat pumps need to cycle through a defrost mode during a prolonged cold snap.)
For a building in KingSett’s portfolio to become a candidate for electrification requires a combination of three factors, Brown says. Mechanical systems need to be reaching their end of life, so that the capital project is already on the books, and it’s just a question of the incremental cost to electrify. Second, the building needs to be connected to a grid that’s clean. “Otherwise, you might as well heat by burning the gas in the building rather than burn gas or coal at a plant, convert it to electricity, and then convert it back to heat at the building,” he says. Third, “we need to make a business case to get these projects pushed over the finish line.” Electricity is more expensive than fossil fuel, and heat pumps are more expensive than boilers, so even with more efficient operation, he says, the economics are often pretty much a wash. “Incentive programs can really help make the numbers work,” he says.
Does decarbonization itself have business value? “We believe it does,” Brown says, noting that across North America—despite what government changes may come and regardless of whether it’s a federal, state, provincial, or city government that makes the environmental push—in major urban centers, one of those levels of government will probably be requiring improved carbon performance for existing buildings. Lenders are starting to get there as well, he says, and tenants are demanding it: “This is where the real-estate industry is going.”
Continuing Education
To earn one AIA learning unit (LU), including one hour of health, safety, and welfare (HSW) credit, read the article above and ““A rational Approach to Large Building Decarbonization: Lessons from New York’s Empire Building Challenge,” by Jared Rodriguez, Mayra Lujan, Brett Bridgeland, and Michel Beguin, Building Energy: The Magazine of the Northeast Sustainable Energy Association (NESEA), Vol. 40, No. 1, 2021, pages 20-23. Then complete the quiz.
Upon passing the quiz, you will receive a certificate of completion, and your credit will be automatically reported to the AIA. Additional information regarding credit-reporting and continuing-education requirements can be found at continuingeducation.bnpmedia.com.
Learning Objectives
- Explain the distinction between energy use and emissions.
- Outline the steps that the teams behind the three profiled retrofit projects took to achieve net zero carbon.
- Describe the strategies used by these projects to address both operational and embodied carbon.
- Discuss the role of electrification in these projects.
AIA/CES Course #K2503A
