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Here’s a model for bringing geothermal to urban areas

This story was first published by the Energy News Network.

The United States’ existing stock of 111 million buildings — roughly two-thirds of which will still be standing in 2040 — pose a daunting challenge to decarbonization efforts. 

Geothermal cooling and heating are among the technologies that can negate the need for natural gas, but they can prove costly and complex in dense urban areas. A historic home on Chicago’s Near South Side, however, provides a blueprint for how it can be done. 

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Glessner House, completed in 1887, was a radical departure from the ornate Gilded Age mansions of the era with its relatively simple exterior design. Its utilities were also advanced: The house was fully wired for electricity, although the posh neighborhood didn’t obtain the necessary infrastructure to connect to the grid until shortly before the Chicago World Fair in 1893

Today, Glessner House continues to employ forward-looking technology in its utilities with an ongoing conversion to a geothermal heating and cooling system.

Mark Nussbaum, owner and principal of Architectural Consulting Engineers in Oak Park, Illinois, the architectural firm carrying out the conversion, has created a niche for himself and his company by specializing in sustainable systems design for historic buildings in and around Chicago.

Nussbaum says the higher costs of geothermal energy remain a deterrent. 

Because gas prices are going back up and, generally speaking, the overall cost for [geothermal systems] are going down, there are more people doing it,” Nussbaum said.

Getting creative

Geothermal systems take advantage of energy stored in the earth, acting as a heat sink in the summer and a source of warmth in the winter. The systems harness this resource by pumping fluid through loop fields in the ground, and they can be fully carbon-free if powered by renewable energy.

While installing geothermal systems in new construction is often relatively simple, retrofitting geothermal systems into existing buildings frequently proves to be a challenge. For example, in many urban areas, much of the building stock is heated by steam radiators using a single pipe. That’s problematic for geothermal systems because they require two pipes. 

Similarly, the ground-source heat pump for a geothermal system cannot produce steam, and radiators can’t cool. In most cases, a complete conversion is needed, although in some cases a forced-air system for cooling can be added to supplement existing boilers for cooling functions. Either scenario can be very costly, Nussbaum said.

An open storage cabinet with a black and silver mechanical device installed inside
A ground-source heat pump installed in the storage area below the main stairs in the Glessner House (Audrey Henderson)

Geothermal likes to have both heating and cooling, because the ground loop absorbs energy in the summer and releases energy in the winter. Otherwise, if I’m only taking energy out of the ground to heat, it makes the system not work well,” Nussbaum said. 

Geothermal systems also need a certain amount of real estate to install the necessary piping below the surface of the ground, known as the loop field, and open space is often limited in densely populated urban areas. But Nussbaum noted that the infrastructure could be spread across multiple locations or installed in phases. 

So it’s through creative thinking that you can make those types of systems work really well. There are currently lots of buildings that use water-source heat pumps, and they use the boiler and a cooling tower instead of a ground loop. At any point, you could add a ground loop to that and start taking load off those other two pieces of equipment. So it’s a really flexible system,” Nussbaum said.

Historic restrictions

Historic landmark restrictions can also pose a challenge, but Nussbaum said these can be overcome — although not without making sometimes difficult trade-offs.

There are two ways we can approach this. The typical engineering approach would be, I will tear the heck out of your building to put the system in exactly the way it needs to be to guarantee you that it’s going to perform perfectly without exception,’ or, I’ll do the best I can. It’ll be good almost all the time, but there are maybe some performance downsides. But I won’t have to touch nearly as much as your building to do that.’” 

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