According to the researchers, underground climate change poses a silent danger in Chicago and other cities

As the planet warms from global warming for much of the past century, the spaces below the Loop have too. That’s a cause for concern about the impact on buildings, according to new research from Northwestern University, although it also presents an opportunity to reuse that heat.

Building basements, subways, parking lots, and other underground areas generate a lot of heat. This, combined with the warmer air on the surface, has made the underground significantly warmer, something old cities around the world experience.

So Alessandro Rotta Loria, an assistant professor of civil and environmental engineering, set out to find out how hot it is under Chicago’s Loop, how it affects the soil, and what that means in terms of potential damage to building foundations. After installing more than 150 temperature sensors in the center’s underground spaces, he found wide variations.

The undisturbed ground temperature in the Chicago area is about 52 degrees Fahrenheit, Rotta Loria said in an interview. In the heart of the Loop, we measured a ground temperature of over 70 degrees. In some underground structures we measured more than 97 degrees.

He called those warmer areas significant drivers of underground climate change. That excessive heat causes soil layers to expand or contract and cause the soil to swell. As a result, the foundations of buildings sink slowly.

Next, Rotta Loria created computer models to see how this will continue to affect buildings and other structures over the next 30 years.

The ground is deforming, Rotta Loria said. No existing civil structure or infrastructure is designed to withstand these changes.

The impact poses a silent threat to the operational performance of civilian infrastructure in Chicago and potentially other cities around the world, Rotta Lorias’ team concluded.

Their research is published in the journal Communications Engineering, an affiliate of the London science journal Nature.

Rotta Loria points out that there is no imminent threat of collapsing buildings or similar dangers.

Of course, displacement, sinking and swelling are not desirable. It can create cracks in the foundation.

The good news is that the heat that escapes from the boiler systems of large buildings and the inefficient designs of the city’s first skyscrapers can be captured and reused as heat, space heating and water in downtown buildings.

More research is needed, and this idea that a potential problem can be turned into an energy resource can be applied to other cities, the team found. The findings can be used to further study a way to capture underground heat throughout Chicago as well, potentially providing heat energy to neighborhoods, Rotta Loria said.

The Loop was studied for its density of buildings, second only to Manhattan in the United States. It also has many very old structures. There are more than 300 historic landmark buildings in the Loop built before 1940, according to the city.

One morning in May, Rotta Loria swept through the lower levels of the nearly 100-year-old Union League Club building at 65 West Jackson Blvd., which includes a massive boiler system that extends deep beneath the street. After a ride, it’s easy to see that such an antiquated system would release a lot of excess heat into the surrounding area.

Rotta Loria calls these hot spots underground heat islands.

Born and raised in Turin, Italy, he received his PhD in Switzerland and joined Northwestern four years ago. The son of an artist and an anthropologist, Rotta Loria, 33, sees further sustainability opportunities by studying underground heat and its impact.

Fortunately, we are able to transform this undesirable phenomenon into a significant opportunity for all cities in the world, said Rotta Loria.

He added that the finding could inform Chicago officials to take action.

First, they would have to determine which buildings or groups of buildings contribute the most to underground heat, then decide which of those buildings could be made more energy efficient to prevent so much heat from escaping, he said.

There should also be an assessment of the buildings to see if there are any foundations or other structural problems around the heat impact, Rotta Loria said.

Amy Masters, director of government and external affairs for the Building Owners and Managers Association of Chicago, said the research presents promising opportunities for the center.

We need to find more creative and innovative solutions for energy use, he added.

Brett Chases’ environmental and public health reporting is made possible by a grant from the Chicago Community Trust.