Contributor: Brian Urlaub
Photo caption: The Eversource Geothermal Pilot Project in Framingham (MA) will be the first utility-driven networked geothermal system serving an existing mixed-use neighborhood in the U.S. Credit: Wangkun Jia / Alamy Stock Photo

Ground Source Heat Exchange (GSHE) systems are well established as a basis for thermal system electrification and realizing associated decarbonization and operation cost benefits. With a maturing public understanding and the broader application of geo-source technologies in general, the industry is poised to introduce to the market the still-greater efficiencies of GSHE in a networked ambient loop system. Salas O’Brien’s 5G thermal energy network experience ranges from multi-block urban mixed-use developments, to commercial campuses, to community-scale single-family home developments.

The prior generations of district thermal systems began with coal-fired steam in the 1880s (many of which remain in operation), successively improving in efficiency by transitioning from steam to hot water and then incrementally lowering water temperatures. Beginning around 2000, the fourth generation integrated high percentages of renewable energy accessed via GSHE systems, enabling yet lower operating temperatures. Today’s nascent fifth generation improves GSHE efficiency with energy sharing and distributed energy sources, lowering operating temperatures further still.

GSHE thermal energy networks, to date

A conventional GSHE system serving a building consists of a central heat exchanger source, principally vertical bores drilled 300-800 feet in unoccupied land near the building. Each bore contains a pipe loop through which a fluid circulates, accessing the ground’s year-round constant temperature (determined by location) in a two-pipe supply and return cycle as an energy source (or sink) to cool or heat the building relative to the surface temperature.

The concept of one central heat exchanger and a two-pipe system represents the design historically implemented by district thermal energy networks as well. However, the unoccupied land and infrastructure space necessary to accommodate the aggregate heating and cooling loads and two-pipe distribution can limit the viability of implementation.

A look at 2-pipe and 1-pipe thermal energy networks

Common Two-Pipe Geothermal HX System

Networked ground source heat exchange systems initially applied single-building heating and cooling concepts to multiple freestanding buildings using a two-pipe supply and return distribution system.

One-Pipe Ambient Loop Geothermal System

An ambient loop thermal energy network utilizes a single pipe to interconnect buildings with distributed vertical ground loop heat exchangers as the energy source.

The heart of the 5G thermal energy network: single-pipe ambient thermal loop GSHE

A GSHE system integrated with a single-pipe ambient loop circulates fluid at a consistent temperature  from multiple sources (±5° between sources) to multiple buildings around the loop in a shared distribution system that lowers capital expenditures as well as operating costs. This approach eliminates the space and proximity requirements of a single centralized heat exchanger and reduces infrastructure space needed, simplifying installation of distribution piping – while matching the heating and cooling performance of a traditional two-pipe system.

Where the GSHE in a two-pipe system connects directly to individual buildings, the GSHE in a single-pipe ambient system connects to the buildings collectively, via the shared ambient loop. The loop acts as a mediating component, interconnecting the buildings to share thermal energy among them.

A temperature profile for the loop is determined by changes in heating and cooling loads within individual buildings, and how the net thermal load is imposed on the ambient loop and mixed with the passing fluid. The net thermal load is based on conditions created by shifts in internal occupancy and human interaction, determined by comfort and daily routines. Planning and design for this diversity allows for lower coincident peak heating and cooling loads, resulting in smaller sizing of the GSHE, potentially reducing upfront costs and establishing a basis for balanced system performance to maintain capacity without exceeding the system’s design parameters.

Compounding benefits in a 5G thermal energy network

The single distribution pipe typically requires less space than a two-pipe system, even less by eliminating the return crossovers necessary in a two-pipe system. The smaller GSHE requirement facilitates distribution of GSHEs in small groups around the loop to create a series of load -to- energy source/sink sequences, maintaining the ambient loop at +/- 5 degrees F. Every building thereby receives approximately the same temperature fluid as the other buildings, effectively providing each owner with the same efficiency. By only needing to maintain the fluid temperature difference between each ground heat exchanger injection point and not between a “first building” and a “last building” as in a two-pipe system, the flow rate decreases. With the lower flow rate, the pipe size can be decreased, also reducing the pump energy needed to circulate the fluid. In addition to multiple GSHEs and pump stations, bypass loops mitigate any risk of failure to operate the loop as a whole.

The Berczy Glen residential community in Markham, Ontario, is the first thermal energy network in North America that has all its thermal assets and ambient thermal loop contained within the right of way of the neighborhood’s street.

Two landmark networked ambient loop GSHE systems – both Salas O’Brien projects – have been completed or are beginning construction in North America. In operation since 2022, Salas O’Brien’s Berczy Glen residential community project in Metro Toronto is the first thermal energy network in North America that has all its thermal assets and ambient thermal loop contained within the right of way of the neighborhood’s streets. The development consists of 312 houses averaging 1500 sq ft; the geo-exchange system is comprised of 144 vertical loop boreholes, 850 feet deep, grouped in eleven pods that are connected by the two-mile single pipe ambient water loop connecting the heat pumps of each home. Circulation pumps serving individual pods and the loop are housed in sub-grade vaults eliminating visible infrastructure.

Construction of the Eversource Geothermal Pilot Project in Framingham, MA, began in summer 2023 to establish a networked ambient loop geothermal system as a viable, affordable clean energy option to delivered fuels and natural gas service for heating and cooling homes and businesses. On completion, it will be the first-of-its-kind utility-driven networked geothermal system serving an existing mixed-use neighborhood in the U.S. The loop will connect 140 customers in 37 building – 32 residential and five commercial – to three bore fields distributed around the loop.

Like any district heating and cooling system, Berczy Glen and the Eversource Geothermal Pilot project are subject to regulations, codes, and other legalities applying to owning and operating an infrastructure network – including maintenance and service – whether within the right of way of community streets, on private lots, or both. Prior planning and design experience is instrumental to effectively executing these logistics; identifying community champions is essential to successful implementation. Early engagement with stakeholders to coordinate space for the infrastructure, establish access to assets after installation, and determine demarcation points within the system for installation and repairs, can elevate a district GSHE system project into a collaborative community enterprise.

How Salas O’Brien can help clients with a 5G thermal energy network

Salas O’Brien is a leader in networked ambient loop GSHE systems with experience that ranges from multi-block urban mixed-use developments, to higher education and commercial campuses, to community-scale single-family home developments. Reach out to Brian Urlaub below to discuss your project.


Brian Urlaub

Brian Urlaub

As head of Salas O’Brien’s mixed-use and residential district energy system practice, Brian Urlaub is part of a leadership group that has completed more than 400 geothermal projects to date, providing over 84,000 tons of system capacity. Urlaub is a member of the board of directors of IGSHPA, serving as vice chairman, and is past president of the Wisconsin Geothermal Association, past member of the Board of Directors of the Minnesota Geothermal Heat Pump Association, and past Advisory Council member of IGHSPA. Brian serves as Vice President, Director of Geothermal Operations for Salas O’Brien. Contact him at a href=”mailto:[email protected]?subject=Inquiry about article”[email protected]

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