Geothermal installation updates New York City’s historic St. Patrick’s Cathedral.
By William Wagner
For John Rhyner, it was the thrill of a lifetime to help retrofit New York City’s St. Patrick’s Cathedral with a geothermal heating and cooling system. Not only was the job an epic challenge, but it was also of historical significance.
“Fitting an old, iconic structure with a heating and cooling system that’s totally new and cutting edge, and not impacting this historic structure in the least because everything is underground and out of sight, was unique,” says Rhyner, vice president, geothermal services of P.W. Grosser Consulting in Bohemia, New York, the firm that designed and oversaw the construction of the system. “It was really gratifying.”
The geothermal system, part of a $177 million restoration of the nearly 150-year-old cathedral, officially went online in February 2017, and it is everything Rhyner and his coworkers could have imagined. For one, it matches the vision of a certain high-placed member of the Catholic Church, one Pope Francis, whose agenda includes returning the environment to a more pristine state.
The heating/cooling plant at St. Patrick’s certainly does its part in achieving that goal: The annual CO2 emissions are approximately 94,000 kilograms lower than those of a conventional plant. The new setup is also a model of frugality, with energy costs that should be 25% lower per year than those of a standard system.
“The old equipment was from the 1960s,” Rhyner says. “It really had reached the end of its lifespan, at least the cooling system had. And the heating system was also antiquated. They were relying on steam heat, which is expensive.”
P.W. Grosser Consulting was invited to participate in a feasibility study for the cathedral’s renovation in 2009. A number of heating/cooling options were considered at that point, such as building a conventional plant or tapping into the Rockefeller Center facility on the other side of Fifth Avenue. In the end,
geothermal was deemed to be the most cost-effective and eco-friendly route. And thanks to its stellar track record in geothermal, P.W. Grosser Consulting was awarded the gig.
“We’ve done other geothermal projects in the city,” says Rhyner. “One was the General Theological Seminary. They informed (St. Patrick’s Cathedral) that we had worked for them very successfully as consultants on that project. We’re a pretty recognized name in the geothermal industry in the city. There are very few (geothermal companies in New York City). You can almost count them on one hand, especially if you’ve lost a couple fingers along the way.”
The work began in earnest in 2013, and P.W. Grosser Consulting’s mission was to design a standing column well system. Ten wells were dug into the bedrock around the cathedral’s perimeter, ranging in depth from 800 to 2200 feet.
Says Rhyner, “The depths vary based on conditions we found at each location and the proximity to neighborhood buildings that we couldn’t encroach on beneath.”
Each well starts with 12-inch-diameter steel piping that runs from near-grade to 50 feet into bedrock. Below that, the well drops to 9 inches in diameter and is self-supported bedrock to the bottom. Each well is fitted with a 6-inch pipe, like a straw extending to the bottom of the well.
A submersible pump is set into the straw at the top of the standing-water column in the well to circulate the groundwater between the well and a geothermal plant beneath the church. Each well has its own plate-frame heat exchanger to separate the groundwater from the heat-recovery chillers that deliver the heating or cooling to the premises.
Generating 2.9 million BTUs of air conditioning and 3.2 million BTUs of heating per hour, the system is the largest of its kind in New York City. Best of all, at least for those who visit or work at the cathedral, the complex infrastructure is virtually invisible since it’s underground. “That was another reason geothermal won out,” Rhyner adds.
Not surprisingly, a project of such magnitude came with several challenges. Chief among those was determining where to drill, which created some tricky and cumbersome logistics.
“To keep the drilling work to the cathedral’s property, rather than drilling through the adjoining sidewalks, we had to work on the terrace level on
either side of the cathedral,” Rhyner says. “The terrace level is about 6 feet above the sidewalk level. To get the rigs up on those terrace levels, we had to shut down Fifth Avenue. And we built special ramps that the rigs could drive up over the front steps of the cathedral onto the terrace level. They worked up there for several months.”
The piping situation beneath the cathedral added another element to the project’s complexity.
“We had to route the piping from the south side of the cathedral to the plant, which is on the north side, under the church,” Rhyner says. “So we had to drill over a dozen holes through the foundation of the cathedral. It was just a massive slab of rock that was put into place there. So that was quite an ordeal.”
And, of course, there were the regulatory issues that go with doing a major construction project in New York.
“Regulatory approvals are a challenge for these types of projects in the city,” Rhyner says. “And the New York State Department of Environmental Conservation has very strict requirements for drilling wells that are deeper than 500 feet. We had to monitor the drift of the drill bit. As you drill, you can’t go straight no matter how hard you try. The DEC requires you to monitor the hole drift every 100 feet to ensure you don’t violate any property boundary limits. That is time-consuming and breaks up the driller’s routine. We requested and fortunately were issued a variance to reduce the frequency of monitoring to every 300 feet.”
Along the way, there were also some surprises. For instance, the bedrock didn’t turn out to be what the team had envisioned.
“We were anticipating solid, crystalline bedrock, such as what you find all over the city,” Rhyner says. “But we found a very large fracture network that we weren’t anticipating, between 800 and 900 feet down. We encountered a lot more water in this rock. That was something we had to manage, the extra water.”
In the end, however, the entire restoration—including the work of P.W. Grosser Consulting—was nothing short of a marvel.
“It was great to be part of the process of bringing this cathedral back to its original grandeur,” Rhyner says. “The exterior and interior were totally restored. It’s now as beautiful as I imagine it was in the 1800s when it was built.”
The ultimate reward occurred when Pope Francis visited St. Patrick’s Cathedral in 2015. P.W. Grosser Consulting was on hand, as were workers from the other trades that had been contributing to the massive project.
“The construction teams got special invites, so we were standing on the front steps and were greeted by the pope,” Rhyner says. “That was a memorable experience.”
William Wagner is an award-wining writer, editor, and project manager for Wagner Communications. He has written for magazines, newspapers, books, and websites. He lives in the Chicago area