Why New Isn't Always Better
Architects and preservationists have long tried to make the case for the cultural and sustainable value inherent in retrofitting existing buildings rather than replacing them. This case was made in person last week at UN HQ Report: The Carbon Case for Retrofits.
A new study, led by Michael Adlerstein, Assistant Secretary-General and Executive Director for the UN Capital Master Plan, and prepared by Vidaris, Inc. with Syska Hennessy Group, analyzes the renovation of the UN Campus and confirms what we have suspected – existing buildings have embodied value in terms of carbon and energy that would take decades to recoup.
Fundamental to the project approach was the decision to renovate the existing campus as opposed to demolishing the complex and building anew. Limiting carbon emissions—not just reducing energy—was an early driver in this decision-making process, according to the team. To make case for retaining as much of the original UN structures as possible, they set out to quantify the value of the existing building elements.
The findings of this report were presented in last week’s presentation, which included Adlerstein; John Amatruda (Vidaris); Kris Baker (Syska Hennessy); and moderator Ellen Honigstock (Urban Green).
There were two particularly interesting takeaways from this discussion. First, the team showed how they managed to bring efficiency to a building that was originally built with little consideration of energy conservation. Second, the team explained how they created an equitable way to compare the retrofitted building with a potential replacement.
Creative Solutions to Increase Efficiency
The UN campus is a complex of six buildings comprising 2.6 million square feet of meeting and office space. The iconic Secretariat building, completed in 1952, was innovative for its time. It included one of the first installations of a glass curtain wall on a tower, and it used river water to provide cooling. Baker described the condition of the original façade as "so degraded that the exterior hanging scaffolds were actually blown around from the interior – air infiltrating and exfiltrating through the façade." Some original innovations were kept in place, such as the river-water cooling and the radiant heating system at the north and south limestone façades.
Given this situation, the team found some traditional and some not-so-traditional ways to achieve their energy goals:
- They expanded the thermal comfort range so that the interior rooms were cooler in the winter and warmer in the summer than is typical. Thermostat settings were adjusted to reflect use patterns, and the UN also implemented a climate responsive dress code.
- Since the building has unforgiving east and west glass exposures, the blinds were installed with automated daylight controls to avoid unnecessary heat gain.
- The curtain wall was retrofitted with high-performance components to retain its original character while allowing improved control.
- As in most existing buildings, the team found it difficult to insulate as much as they wanted to, but they increased insulation where they could.
- The pre-computer age buildings benefited from a newly centralized, dedicated data center that aggregated the server rooms, which were previously distributed throughout the UN campus.
- The lighting and controls were upgraded (although much of the renovation was completed pre-LED technology).
- Many HVAC improvements were made, including installing new high-efficiency electric chillers, air-side economizers, VAV boxes, demand-controlled ventilation and a BMS system.
Retrofit vs. Replace: Measuring the Savings
A large part of making their case was to demonstrate that the retrofitted campus would, in fact, reduce carbon and energy “costs.” The comparative study considered two aspects of carbon reduction: Embodied (the carbon associated with building construction) and Operational (carbon emitted during the life of the building).
Looking at the embodied carbon, Life Cycle Analysis (LCA) impacts were studied using the Athena Impact Estimator LCA software. The team analyzed all the building elements to be retained, including the reinforced concrete walls and slabs. Retained elements were measured and modeled to quantify their embedded carbon. The team also factored in potential additional impacts associated with their removal and replacement.
To calculate operational emissions, the team first calculated that the retrofitted project would result in a 50 percent reduction in energy consumption and a 65 percent reduction in operational carbon emissions. The team then determined, through additional energy modeling and other evaluations, that a new construction project with matching programmatic parameters would be 5 percent to 10 percent more energy efficient.
When taken together, the study notes that if the campus were demolished and reconstructed, it would take 35-70 years before the operational efficiencies gained by the new construction would offset the initial outlays of embodied carbon. Since climate change imperatives are not limited to concerns about operational emissions, the total quantity of carbon released must also be considered. Because carbon dioxide is not quickly purged from the atmosphere, the carbon burden embedded in the original UN construction, although 65 years ago, still contributes to the current CO2 intensity.
More than just preserving an important modern cultural landmark, the renovation provided an opportunity for the UN to demonstrate to the world their commitment to addressing climate change by using modern building technologies and techniques. This study goes a long way to advocate for a better understanding and accounting of the true cost of demolition and makes a strong case for retrofits and renovations.