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 is among the technologies that can negate the need for natural gas, but it 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.
Glessner House, completed in 1887, was a radical departure from 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 otherwise posh neighborhood only obtained the necessary infrastructure to connect it to the grid shortly before the Chicago World’s 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 doing 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.
“But what we’re seeing now, because gas prices are going back up and generally speaking, the overall cost for [geothermal systems] are going down, there’s more people doing it,” Nussbaum said.
Geothermal systems take advantage of solar 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 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 a geothermal system needs two pipes — one to handle hot water and the other for cold water.
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.
“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 where they 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 landmark restrictions can also pose a challenge, but Nussbaum said these can be overcome — although not without making sometimes difficult tradeoffs.
“There’s 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’s maybe some performance downsides. But I won’t have to touch nearly as much as your building to do that.’
“There’s never been somebody who told me, ‘Please tear the heck out of my building.’ But I tell ’em that just because they have to understand [the circumstances]. Most engineers are unwilling to design something that is not 100% perfect. I take the other approach. The building has value [as well],” Nussbaum said.
While performance issues are a valid consideration, geothermal systems can be advantageous for historic structures like Glessner House, largely because much of their infrastructure is below ground and out of sight, according to Bonnie McDonald, president and CEO of Landmarks Illinois, based in Chicago.
“That’s an incredible opportunity for the construction industry [and] for the design industry to look at the opportunity around helping homeowners and property owners make these buildings more sustainable in ways that also celebrate the historic features in the building,” McDonald said.
In the case of Glessner House, budgetary constraints presented more hurdles than logistical or technological or even landmark status considerations. The initial project budget did not allow the entire geothermal system to be installed at once. Installing the system in phases allowed the project to move forward while allowing for contingencies that would accommodate additional phases as more funds became available.
“At Glessner House, they [initially] didn’t have the money after we got it designed to bid to do the whole project. … They could only afford one unit. But the way it worked out, they got a big grant that allowed us to put the majority of the rest of the system in,” Nussbaum said.
A similar phased approach lies behind installing networked geothermal systems for multiple buildings. Within a networked geothermal system, accommodations can be made to address variations from building to building, or even within a single building, according to Zeyneb Magavi, co-executive director of the nonprofit HEET, based in Cambridge, Massachusetts.
“[Within] the network, you can make choices between how much efficiency and weatherization that building takes on and how much you simply provide more energy. And that gives you flexibility to really address the older building stock in a way that’s really quite challenging in a building-by-building approach,” Magavi said.
Networked geothermal systems have the potential to overcome the hurdle of upfront investment by leveraging economies of scale enjoyed by legacy utilities, which could also assure that less affluent communities are not left with the financial burden of the natural gas system, Magavi said.
However, configuring a workable ownership model and management system remains one of the major unanswered questions regarding networked geothermal systems, Magavi said.
“While we are moving forward with the gas utility to geo utility transition model, the other ownership models on the table are municipal or community-owned district network grants,” Magavi said.
Economies of scale
Networked geothermal systems are already in place on a number of college campuses. Scaling up from a college campus to a municipality or utility-scale system presents legal and administrative rather than logistical challenges. Most likely, the solution will require adopting a public-private model, according to Sachin Anand, a mechanical design engineer and principal at dbHMS in Chicago.
“It is definitely feasible. I think the difference between a city and a campus is [that] on a campus, all the buildings are owned by a single ownership entity, whereas in a city, there’s different ownership entities. So, some other third party would have to come in and invest into that infrastructure and then sell that as a utility and recoup that cost over a period of time.
“Drilling those wells and installing those wells is expensive, but if there were more people in the market, it could get much cheaper to do that. The private sector’s not going to put money into it because they don’t see immediate returns. It’s no different than when we got the internet or electricity a hundred years or so ago. You really have to plant that seed with public funding. That’s the only way to do that,” Anand said.
Ultimately, utility-scale geothermal systems could operate on a billing model much like today’s electricity or natural gas companies, according to Magavi.
“So instead of feeding natural gas into these buildings, we could feed geothermal water. And then we could meter that and sell that. It’s no different than when you pay your water bill, ” Magavi said.
Geothermal installations on existing buildings can be combined with existing gas or other heating and cooling systems to form hybrid systems to ensure reliable heating and cooling during a transitional period away from carbon-based fuels, much like hybrid vehicles, Nussbaum said.
“The way that heat and cooling works is I have to provide enough heat in the building for the coldest day of the year. The typical load is well within the reach of a geothermal system. … We [just] have to have that capacity there for those cold days, but that represents just a small piece,” Nussbaum said.
‘What we need now is totally different’
As the effects of climate change manifest themselves in more extreme weather events, the need to move away from carbon-based heating and cooling systems has become increasingly urgent. Innovative solutions like networked geothermal systems reflect the same type of forward looking thinking that motivated the implementation of indoor comfort systems presently in place, Magavi said.
“We put in the gas infrastructure starting in the 1800s. And whoever did that had a lot of vision and probably didn’t imagine it would be this big or last this long. It’s quite stunning.
“And what we need now is totally different. We now know very different things we didn’t know necessarily or many of us didn’t. And so now we have to have the vision to imagine a different energy infrastructure and meet all the needs, including the needs of the gas workforce, including the needs of our existing economic system. … We have to work with where we are at and imagine something that meets all the core needs and allows us to move forward,” Magavi said.