The tool is described as providing an inexpensive way of carrying out full lifecycle analysis (LCA) of design choices while buildings are still being planned, rather than waiting until the end of the design – by which time it may be too late to make significant changes. The aim is to make lifecycle analysis an integral part of the design process from the beginning.
It is currently a standalone tool for use in designing single-family homes, but the aim is for it to be available as a plug-in for commercial software packages and for its scope to be widened to include much bigger residential and commercial buildings.
The new process is described in the journal Building & Environment in a paper by MIT researchers Jeremy Gregory, Franz-Josef Ulm and Randolph Kirchain, and recent graduate Joshua Hester. It is said to be simple enough that it could be integrated into the software already used by building designers so that it becomes a seamless addition to their design process.
Ulm, a professor of civil and environmental engineering and director of MIT’s Concrete Sustainability Hub (CSH), said that typically LCA is applied “only when a building is fully designed, so it is rather a post-mortem tool but not an actual design tool.”
That’s what the team set out to correct. “We wanted to address how to bridge that gap between using LCA at the end of the process and getting architects and engineers to use it as a design tool,” he said. The big question was whether it would be possible to incorporate LCA evaluations into the design process without having it impose too many restrictions on the design choices, thus making it unappealing to the building designers. Ulm wondered, “How much does the LCA restrict the flexibility of the design?”
The team had to come up with a process of measuring the flexibility of design choices in a quantitative way. They settled on a measure they call “entropy,” analogous to the use of that term in physics. In physics, a system with greater entropy is “hotter,” with its molecules moving around rapidly. In the team’s use of the term, higher entropy represents a greater variety of available choices at a given point, while lower entropy represents a more restricted range of choices.
To the researchers’ surprise, they found use of their LCA system had very little impact on reducing the range of design choices. “That’s the most remarkable result,” Ulm said. When introducing the LCA into the early stages of the design process, “you barely touch the design flexibility,” he said. He was convinced there would be a compromise, where design flexibility would have to be limited in order to gain better lifecycle performance. “But in fact, the results proved me wrong,” he said.
The system looks at the full range of climate impacts from a new structure, including all three phases: construction, operation and the final dismantling and disposal, or repurposing of the structure, at the end of its service.
To evaluate the lifecycle impact of design choices requires looking at a wide range of factors. These include: the location’s climate (for their research, they chose Arizona and New England as two very different cases of U.S. climate); the building’s dimensions and orientation; the ratio of walls to windows on each side; the materials used for walls, foundations, and roofing; the type of heating and cooling systems used; and so on. As each of these factors gets decided, the range of possibilities for the building get narrower and narrower — but not much more so than in any conventional design process.
At any point, the program “would also provide information about a lot of the things that are not yet defined,” essentially offering a menu of choices that could lead to a more environmentally friendly design, says Kirchain, who is a principal research scientist at MIT and co-director of the CSH, which supported the project.
While designed particularly for reducing the climate impact of a building, the same tool could also be used to optimize a building for other criteria, such as simply to minimize cost, the researchers say.
By comparing the design process with and without the use of such tools, the researchers found that the overall greenhouse gas emissions associated with a building could be reduced by 75% “without a reduction in the flexibility of the design process,” Ulm said.
While the program is currently designed to evaluate relatively simple single-family, the team hopes to expand it to be able to work on much bigger residential or commercial buildings as well.
At this point, the software the team designed is a standalone package, so “one of our tasks going forward is to actually transition to making it a plug-in to some of the software tools that are out there” for architectural design, said Kirchain.