Richard A. Sileo, P.E., may have caught some divine intervention in the heart of midtown Manhattan.

The senior engineer with Norwalk, Connecticut, engineering firm Landmark Facilities Group had the rare opportunity to design a massive geothermal heating system in New York City.

On top of that, the project was for the Roman Catholic Archdiocese of New York at its St. Patrick’s Cathedral, which reportedly receives more than 5 million visitors per year and is the home of Archbishop Cardinal Timothy Michael Dolan.

“It was a true privilege,” Sileo says. “As we visit a jobsite, things start to become very commonplace, and you get acclimated. Yet with this jobsite, especially inside the cathedral, you’re in awe. It’s such an impressive and inspiring structure — every time I stepped inside, I was amazed.”

Sileo notes that geothermal systems in the heart of New York City are unusual because the majority of buildings do not have the real estate to house all the needed components. It was possible at St. Patrick’s because the church and its connected buildings cover an entire New York City block.

“The restoration started with the rectory building on the northeast corner,” Sileo says of the midtown-Manhattan church on 5^th Ave. between 50^th and 51^st streets.

The campus has four buildings: the more than 76,000-square-foot cathedral, the rectory where the priests live, a residence building for the cardinal and a parish facility with offices for the support staff.

Building in protection

A project of St. Patrick’s Cathedral’s undertaking requires some redundancy, and LFG provided it with a backup boiler plant on the premises. The boiler plant was designed in the event the standing column wells are unable to meet demand. The plant features a Triangle Tube Prestige 399 Cascade system in a compact boiler room located in a cellar space on the church’s campus.

The Cascade features a common-vent system that saves space in the mechanical room by combining multiple vents into one. Sileo notes the system is a hybrid that can reject heat with a Baltimore Aircoil cooling tower located in the mechanical room.

“So far, through one heating and cooling season, neither the boiler plant nor the cooling tower has been needed,” Sileo states. “They are standing by in case the standing column wells can’t keep up with demand.”

If the boilers need to turn on, they will be enabled by a signal when the hot-water loop supply temperature falls below the set point. In this scenario, the boilers will inject water into the load-side hot-water loop to supplement the heat extracted from the wells.

Sileo appreciated the support provided by Triangle Tube in coordinating the design and installation of the boiler plant at St. Patrick’s.

“The polypropylene vent kit worked out nicely,” he says. “The length allowance for the vent and combustion air was generous.”

Sileo notes the piping design for the boiler plant was innovative because the pipes ran out of the bottom of the boilers. This allowed for Sileo and his team to create a pump rack about 3 feet out from the boilers. With that space savings, there was room for a service corridor in the small mechanical room.

A decade in the making

Sileo notes the St. Patrick’s Cathedral restoration spanned nearly a decade; LFG’s work on the geothermal system design and construction took nearly two years. The church never closed, and work had to be performed around the mass schedules, which includes one at noon. Sileo notes that during drilling of standing column wells, sound blankets were erected to mitigate noise.

Sileo explains each of the rectories was converted off steam heating to hot water via International Environmental single-pipe hydronic fan-coil units. The other small campus buildings use a traditional two-pipe system.

“When we went the fan-coil route, we had a vision of a geothermal system, but it was yet to be formally approved,” he says. “Also, we knew that we were marching forward with a system that would be compatible with a geothermal system.”

The 10 standing column wells are of various depths with the deepest reaching 2,200 feet. LFG worked with John Rhyner, a geotechnical consultant with Bohemia, New York-based P.W. Grosser Consulting. Rhyner provided water- quality testing and found the groundwater on the St. Patrick’s campus had high chlorination and other chemistry concerns that prompted Sileo to make changes to the design.

Sileo says when the standing column well drilling started, they hit bedrock after about five feet, which was ideal. The strong bedrock avoids any risk the wells will collapse or cave in over time.

Additionally, the system at St. Patrick’s does not mix water from well to well, Sileo says. The system is comprised of 10 independent circuits where water comes out of the standing column well, passes through an Alfa Laval titanium plate-frame heat exchanger, and returns to its respective well.

“Normally, you’d use a stainless steel plate-frame heat exchanger,” Sileo says. “But with the water chemistry results we got back from the lab, we knew stainless steel could be under attack from the chlorides in the water. The titanium plate-frame exchanger will stand up against the aggressive quality of the groundwater.”

The pulse

Sileo says the “heart of the system” is the Multistack dedicated heat-recovery chiller with a proprietary feature called “virtual movable endcap.” He says there are eight modules, each the size of two refrigerators back-to-back, where the units can be in heating or cooling mode at any time. This was needed because the demands of a 76,000-square-foot cathedral might not be in line with other buildings on the campus.

“The heat-recovery chiller uses two position-motorized valves to allow one unit to go from heating to cooling or vice versa over the course of a day,” Sileo says. “While we don’t simultaneously heat and cool within a building, we know all these buildings are unique enough that one may want cooling while the other is in heating mode.”

Hot and chilled water is circulated around the St. Patrick’s campus and runs using a primary/secondary piping system featuring large Bell & Gossett base-mounted pumps in the mechanical plant. Within each building, there also are Bell & Gossett secondary circulator pumps distributing the hot and chilled water.

With the large number of moving pieces, a DDC control system was installed so LFG can keep a close eye on the system’s overall performance, including how many Btu/h are exchanged with the earth or, more specifically, how much is being deposited back into the earth compared with what is being taken out.

“We remotely monitor things such as pressure drop across the heat exchangers,” Sileo says. “We want to see if they are fouling or if there is an indication of material accumulating on the plates.

“If we find the system is heating-dominant and we’re extracting a lot of energy out of the earth, then we know there will be a point in time we’re going to need to enable the boilers to maintain an energy balance with the earth.”

Other challenges LFG overcame included the underground piping network at St. Patrick’s, which runs through small crawlspaces underneath the cathedral and connect the buildings. The 3- and 4-inch pipes ran through the undercroft and created a challenge for the mechanical contractor, according to Sileo. Additionally, the former steam radiator enclosures in the cathedral varied in construction material from stone to wood.

“We had to do some surgery on them,” Sileo says. “We had to remove the radiators to install the hot-water fan-coil units. Now, we have to provide service access for filter maintenance. This was done in a way to respect the enclosure construction. Anyone who visited the church prior to construction and upon completion wouldn’t even realize the radiators were replaced.”

Sileo understands the St. Patrick’s Cathedral project is a once-in-a-lifetime opportunity. He knows the church will be happy for years to come and that LFG secured a strong future for this historic house of worship.

“It was a privilege to work on a team that was committed to respecting this landmark and put in a system that will give the Archdiocese decades’ worth of sustainable, reliable operation,” he says.

“We’ve done right by the building.”