With the cathedral remaining open throughout construction to accommodate community members and 18 masses every week and given the complexity of designing and installing a geothermal system in a historic structure with such a high intensity of use, an experienced team of collaborators was key to the project’s success. As design team leader, MBB enlisted a top-tier group of experts, including geothermal plant designer Landmark Facilities Group, Norwalk, Conn.; well-drilling consultant P.W. Grosser Consulting Inc., Bohemia, N.Y.; structural engineer Silman, New York; and geotechnical engineer Langan Engineering, Parsippany, N.J., who collaborated with Zubatkin Owner Representation LLC, New York, and construction manager Structure Tone to conceptualize and design the geothermal system.
The geothermal system itself comprises 10 wells in terraces flanking the north and south sides of the cathedral; Samuel Stothoff Co., Flemington, N.J., drilled 9-inch-diameter boreholes through dense Manhattan schist at a depth of up to 2,250 feet through bedrock. Pumps and compressors were located in a former boiler room in the basement, controlled by a building management system that determines whether and how much to heat or cool based on thermostats set around the cathedral, heating or cooling different zones independently.
Producing air conditioning and heating for the entire campus, the system is capable of generating 2.9 million Btus per hour of air conditioning and 3.2 million Btus per hour of heat when operating at full capacity. To increase durability and mitigate corrosion, stainless-steel pumps and an HDPE ground loop were used. To increase resiliency, the project team included gas-fired boilers and an evaporative fluid cooler to back up the primary system by adding extra cooling or heating to the wells at peak demand, if required. The geothermal plant itself was designed for longevity and ease of maintenance with durable titanium plate modular heat exchangers and other modular, small-scale elements. The modular design enables single wells to be taken offline to work on component parts.
Throughout the installation process, careful staging and an interim building system helped enlighten visitors about the work’s scope and impact, even during presidential and papal visits. Construction sequencing minimized disruption to cathedral operations; for example, a rolling scaffold supported work on ducts and restoration of stained glass and the ceiling, keeping the cathedral open and its nave clear—and avoiding the cost of scaffolding the full interior. Respecting existing historic structures, geothermal system wells are piped through the undercroft and unused crawl space, increasing their utility and mitigating needs to build externally.
The project team’s thoughtful approach emphasizes seamless integration of new HVAC elements, and the attention to detail is apparent throughout the renovated cathedral. New air-handling units were ducted to custom grilles fitted to the ribs of the triforium. Fan-coil units were built into millwork during the restoration, preserving the cathedral’s original detailing, and piping was run in the undercroft, reducing run length and keeping them out of sight. This leveraging of existing space served preservation and environmental goals of the project team.
The choice of a no-bleed geothermal system represents a significant reduction of water use. A comparably sized cooling tower would have required 3.8 million gallons of makeup water annually and bleeding the geothermal system would have used 1.3 million gallons, but the system that was designed and installed at St. Patrick’s uses only 300 gallons per year. Furthermore, the condensate losses inherent in district steam are eliminated by switching over to ground-source heat.
Installing the geothermal well field required removal of two planting areas marked by compacted soils and dense ivy mattings. This presented a further opportunity to improve the cathedral site’s appearance, sustainability and functionality. With the geothermal system in place, the project team recreated planting areas, using absorbent soils and native plantings and trees. Consistent with local hydrologies, the new flora helps absorb runoff from adjacent hardscape and requires minimal irrigation. A 600-square-foot green roof covering the new secure vehicle entry further improves stormwater management while new soils and a native plant palette attract birds, squirrels, and other animal and insect life. New bluestone walkways and curbs aid pedestrian access.
A remarkable success story, since the geothermal system launched in 2017, it has provided all of the cathedral’s heatingand cooling, without the need to engage the backup system. Post-occupancy performance includes the cathedral’s largest attendance ever, visits by heads of state, and expanded programming while maintaining stable environmental control and energy-use reductions equivalent to 772,211 kilograms of CO2. Based on working environment metrics—temperature and ventilation control, acoustics, lighting and visitor response—cathedral staff report high levels of satisfaction in operations, and New York City Mayor Bill de Blasio has lauded its decreased emissions and support for a greener community.
The highly public modernization, which created national awareness of cuttingedge sustainability solutions, points in new and promising directions for retooling historically significant architecture and conserving natural resources. Ready to serve the public for generations to come, St. Patrick’s Cathedral now shines as an example to other world-class organizations of how institutional leadership can harness technology to take a long-term, sustainable approach to architectural stewardship.
Bleed Versus No-bleed Geothermal
BLEED is the mechanism by which open-loop geothermal systems help keep maximum and minimum temperatures within operating range. It can be thought of as a “relief valve”, which is accomplished by diverting some water to the sewer system and allowing “fresh” groundwater to enter the loop through the wells. Because St. Patrick’s Cathedral’s geothermal system was designed to operate without relying on bleed, New York-based MBB was able to avoid the associated water waste.
ARCHITECT: MBB (Murphy Burnham & Buttrick Architects), New York
CONSTRUCTION MANAGER: Structure Tone Inc., New York
GEOTHERMAL PLANT DESIGNER: Landmark Facilities Group, Norwalk, Conn.
WELL-DRILLING CONSULTANT: P.W. Grosser Consulting Inc., Bohemia, N.Y.
WELL DRILLING: Samuel Stothoff Co., Flemington, N.J.
STRUCTURAL ENGINEER: Silman, New York
GEOTECHNICAL ENGINEER: Langan Engineering, Parsippany, N.J.
OWNER REPRESENTATIVE: Zubatkin Owner Representation LLC, New York
SPRINKLER SYSTEM: ABCO Peerless Sprinkler Corp.
GLASS DOORS AND WALLS: Seele Glass
HEAT-RECOVERY CHILLER: Multistack
CIRCULATOR PUMPS: Bell & Gossett Ecocirc
HEAT EXCHANGER: Alfa Laval (titanium plate)
BUILDING AUTOMATION SYSTEM: Niagara
ENTRANCE DOORS: Narthex with Invisible Wall System by Vitrocsa USA
CHAPEL ENCLOSURE DOORS: CRL Jackson 900 Series Spring-powered Recess Floor Mounted Door Closer by C.R. Laurence Co. Inc.