How Modular Construction Was Used in a Geo-Exchange System
As part of its goal to achieve carbon neutrality by 2046, Princeton University sought to utilize geo-exchange technology. Beginning in 2012, the university started assessing its facilities and how to reduce its carbon footprint.
Following a study was a master plan to upgrade Princeton's systems, improve reliability and resiliency, replace aging equipment, and help reach carbon neutrality, according to Justin Grissom, department manager of Burns & McDonnell. "This includes a full campus conversion to hot water, a new satellite plant with fully electrified heating and cooling, and new thermal energy storage, both hot and cold," says Grissom.
This massive undertaking is a collaborative effort of engineering consulting firms Salas O’Brien and Burns & McDonnell, and construction management company Whiting-Turner. Systecon provided an indoor, modular central plant to meet this effort.
"We are installing one of the largest closed-loop geo-exchange systems in the United States,” says Princeton energy plant director Ted Borer.
How Geo-Exchange Works
Geo-Exchange uses the ground (geo) as a renewable heat source in winter and heat sink in summer (exchange). Borer describes the concept, using canning as a relatable metaphor: "You take ripe fruit, make jam, put it in jars, and then store it in the basement. When there's no fruit to be had, you can bring it up from the basement and enjoy it when needed." In a similar concept, "We will recover heat from the buildings during the summer and store it in thousands of holes that have been drilled to a depth of about 850 feet. When winter comes, this energy will be used to heat the buildings and produce domestic hot water," says Borer.
Geo-Exchange Projects
Investing in projects to create and convert systems to geo-exchange technology with enough capacity to support the entire campus will bring Princeton closer to NetZero. Such projects include drilling geo-exchange bore holes, new buildings to house the heat pumps and electrical equipment, converting to district hot water, and converting their cogeneration plant and building systems.
Integrated into the Princeton campus, a new satellite plant a.k.a. TIGER (Thermally Integrated Geo-Exchange Resource) and TIGER-CUB (Central Utility Building), are new buildings that will house the heat pumps and electrical equipment needed to expand geo-exchange heating and cooling systems. Two thermal energy storage (TES) tanks will store hot and chilled water nearby.
"Systecon is involved in an important piece of a very large effort; basically building the TIGER plant offsite and delivering it to a building built to house it," says Grissom.
Systecon supplied two large heat pumps as part of the geo-exchange system, each with a cooling capacity of 1750 tons and 28,120 MBH heating capacity. The design allows for the ability to add two heat pumps as the campus grows.
Systecon provided performance testing of the large water pumping systems for verification and baseline energy efficiency for long-term comparison through the plant's life cycle.
To convert from steam to hot water heat, the university is installing over 13 miles of new underground hot water distribution pipes. The new hot water pipes and systems will eventually enable each campus building to utilize geo-exchange heating and cooling.
"All the traditional assets, the boilers and chillers, and eventually the cogeneration system will be converted to a system very similar to TIGER," says Grissom. Princeton will convert their Cogen Plant from a chilled water plant and combined heat and power (CHP) steam plant to one with hot water geo-exchange technology. After conversion, the plant will operate with TIGER to meet the campus heating, cooling, and partial electric load needs economically and thermally. The two plants will also be interconnected to partially backup each other for campus heating and cooling.
The process of converting heating and cooling systems in existing campus buildings to geo-exchange technology will take many years and when fully converted, the geo-exchange systems will heat and cool over 180 buildings.
As part of their Solar Expansion project, Princeton is installing new solar panels above their parking lots, garages, and in fields, adding solar photo-voltaic (PV) panels to meet campus electrical needs through solar power. Their onsite energy production for sustainable electricity for TIGER-CUB is essential for resiliency and limiting carbon emissions from generation.
Modular Construction
The engineering team initially thought they would go the usual route of fabricating the plant on-site, recalls Grissom. In thinking of other ways of delivering the project however, they saw an opportunity to utilize modular construction. While it would be their first experience with a modular plant, the construction management company had previously worked with Systecon.
Bringing its expertise in modular design packages, Systecon transitioned the initial field-built design into shippable modules and manufactured this essential component of the geo-exchange system in their factory.
Modular construction with Systecon allowed for advanced design development for critical elements of the plant, including equipment selections and piping arrangements. In a cohesive effort between the engineering teams and Systecon, equipment selections could be reviewed and compared for optimum pairing and efficiency. Manufactured piping modules reduce field work and allow for more certainty in flow and pressure loss for the long-term life cycle of the plant.
Systecon's factory-built plants are tested and provide highly functional, proven packages. That, along with reducing on-site labor and on-site commissioning time and providing a higher factory quality than a field-built system are among the benefits of modular construction.
