Reusing buildings rather than constructing new ones is clearly beneficial to society in terms of reduced resource consumption and waste, assuming that the new and renovated buildings operate with similar efficiencies. But how much is the benefit? A new study from the Preservation Green Lab delves into this question.
The study, which considered buildings from across the U.S., used different scales to measure climate change, resource depletion, human health, and ecosystem quality. Researchers found that reusing buildings has positive impacts ranging between 4 and 44 percent. Even larger effects (5-46 percent) accrue when the new and renovated buildings are assumed to operate 30 percent more efficiently than average.
However, the study falls short of evaluating the impact of deep energy retrofits, such as the 50 recent projects that achieved 30-80 percent energy cost savings analyzed in a BetterBricks report, and instead calls for further research to “clarify how impacts are altered if a new or existing building can be brought to a net-zero level using various technologies, including renewable energy.”
Net-zero is a term used in the buildings industry for super-efficient buildings that use on-site renewable energy to produce as much energy as they consume each year.
But let’s put net-zero terminology aside and say more broadly that, because buildings use 42 percent of the nation’s energy—and much more than 30 percent of that is wasted through inefficient design and operation—deep energy retrofits are needed in order to transform our buildings from energy hogs to more comfortable, liveable, and workable spaces that can help usher in an efficient and renewable energy era.
Many will assume that such large savings would require a complete “gut” of the building, resulting in environmental impact similar to new construction. But that’s not necessarily the case.
Let’s take a quick look at the groundbreaking Empire State Building deep energy retrofit.
The business-as-usual plan for this building was to spend about $93 million for improvements that would impact but not optimize energy use—measures common to large commercial buildings, ranging from a new chiller to resealing windows. Instead of implementing the typical measures, a team was formed—including Clinton Global Initiative, Jones Lang LaSalle, Johnson Controls and Rocky Mountain Institute—to complete a deep energy retrofit to analyze the building for better ways to spend the money. The result was 38 percent energy savings for only $13 million extra cost and a three-year payback.
Now let’s think of this project not in terms of dollars, but environmental and human health impact. We’ll find that as a result of rearranging, altering, and adding to the business-as-usual measures, the external impact was minimized much like the capital cost.
The business-as-usual plan for the Empire State Building was to reseal the 6,514 windows. Instead, the team replaced the windows to save much more cooling load and energy. To reduce the cost and external impact of the window replacement, the original glazing and frames (dating to 1990) were salvaged and remanufactured. The total embodied carbon footprint saved by reusing the glass and frames is about 2,000 metric tons of carbon equivalent. It’s reasonable to assume that about 15 percent of these savings was used for a plastic film suspended between the two glass panes, metallic “low-e” coatings on the glass and plastic to reflect heat, and the energy needed to remanufacture the components into a new window. The new windows also received krypton and argon gas during the remanufacture to further improve the insulation (effectively making it very difficult for heat to travel through the glass), which totaled about 3,400 metric tons of embodied carbon.
Hence, the total embodied carbon footprint for the new windows was 3,700 metric tons.
In addition to the new windows, more than 6,000 insulated reflective barriers were installed behind radiator units located on the perimeter of the building. The external impact created by these barriers was about 20 metric tons of carbon.
In addition, direct digital controls were added, creating another 20 metric tons. New windows, a reflective barrier, and controls helped reduce the cooling load by 1,600 cooling tons (a unit of power, not to be confused with the unit of weight), which enabled the team to avoid having to add cooling capacity—thus saving the external impact from manufacturing a new chiller, about 40 metric tons.
The deep energy retrofit also had an effect on the air-handling units. Originally, the plan was to replace all 485 constant-air-volume units one-for-one over the next several years. Instead, the team needed only 240 units and upgraded them to a more efficient variable-air-volume type—avoiding 2,400 metric tons.
Thus, achieving deep energy savings through a deep energy retrofit added only 1,300 metric tons of carbon equivalent to the business-as-usual case. This initial carbon “expenditure” will be paid back 100 times over the next 15 years, because the Empire State Building is now much more operationally efficient.
Conducting a full assessment on individual projects typically costs too much or takes too much time, which is why Preservation Green Lab has called for further studies to produce high-level information. However, on a project level the publically available EcoCalculator from the Athena Sustainable Materials Institute enables quick structural and envelope assembly comparisons. In addition, Green Footstep from Rocky Mountain Institute helps decision-makers visualize over time the carbon expenditure and payback resulting from a building project.
Historically considered negligible or unknown, external impact from building construction will likely become a greater concern to decision makers as our buildings become more operationally efficient. The result will be buildings that are elegantly frugal in material as well as operation, and the building materials will be manufactured, transported, and recycled using much smaller amounts of energy.