|Cornell University partnered with Verizon on this project, which researchers hope can be replicated elsewhere. Source: Koenraad Beckers|
Where a typical installation calls for just three to four boreholes, this one involved almost a dozen of them, equipped with 70 sensors that monitor the system’s performance and impact on ground temperatures.
It’s all part of an innovative experiment born of a partnership between Verizon and Cornell University, one focused on creating a ground-source cooling system for a cellular tower equipment shelter located near the school’s campus.
“We’ve done a lot of these over the years, but what was unique about this site was the amount of control work that went into it,” says Lesperance, whose Rochester, N.Y.-based contracting company managed the installation of this complex geothermal system.
Normally, Verizon relies on conventional air conditioning units to cool the equipment shelters that sit next to its cellular towers. This project, however, has the potential to bring significant gains in terms of sustainability and energy efficiency.
A Unique Partnership
The project was first discussed about five years ago, when Cornell University alum and Verizon CEO Lowell McAdam visited the school with an interest in exploring how to implement sustainable technologies at his company.
“The Atkinson Center for a Sustainable Future organized a roundtable with faculty who did research relating to energy sustainability,” says Abby Westervelt, director of corporate relations for Cornell. “Through those discussions, we identified some areas of interest, and one key idea was the concept of geothermal cooling for cell towers.”
In 2009, the Verizon Foundation started providing funding to this and three other graduate research projects focused on energy sustainability. While Cornell faculty and graduate students are responsible for the research and design of this innovative project, Westervelt emphasizes the leading role Verizon played in helping make the project a success.
“Verizon has been a fantastic partner. They’ve really opened up all the resources and information our students needed to apply themselves to the project,” she says. “This is a prime example of a great partnership between our facilities group, our researchers and our outside partners.”
Exploring the Idea
Leading the research side of the project is Professor Jeff Tester, the Croll Professor of Sustainable Energy Systems and director of the Cornell Energy Institute. Before construction started, his group investigated how they could design a system capable of providing the data needed to apply their concept across regions with varying conditions.
“We looked carefully at what was known with various geothermal heat pump organizations, talked to a lot of manufacturers and people who drill these holes,” says Tester. “We quickly came to the conclusion that the kind of data we need isn’t normally taken at all.”
Tester points out that while most heat pump systems have both a heating and cooling cycle—transferring heat underground in summer and cycling it upwards in winter—the project they were proposing would be used strictly to cool the cell tower shelter.
“This is a cooling-only application, so you’re constantly heating the ground. It’s why we’ve had to study the subsurface much more carefully,” he says.
Brandon LaBrozzi, a student of Tester’s who graduated in 2010, first mapped out the space, bringing together geological data, seasonal temperatures and system design options to get a sense of cost variability across the country. With this information, LaBrozzi was able to develop specific guidelines for selecting sites where the company would be able to recoup its investment faster.
Koenraad Beckers, another graduate student of Tester’s, is now taking a leading role in the project, helping design the system and build the data model that will ultimately determine the feasibility of installing similar systems in other parts of the country.
Building the System
During the construction phase of the project, Beckers led several other students in conducting a seismic survey of the site. The team also collected and analyzed rock cuttings from one of the boreholes at 20-foot intervals in order to better understand the site’s stratigraphy.
Lesperance describes the significant amount of work that went into constructing the system.
“Normally where we might have had three or four boreholes, Verizon had us put 11 holes in the ground,” he says. Eight of these were drilled at a depth of 265 feet, with three drilled to 385 feet.
Between 100 and 130 feet, the drillers encountered a porous rock layer that was causing the boreholes to fill with slurry, which ultimately led them to line each hole to that depth.
According to Lesperance, 10 of the 11 boreholes that comprise the system are equipped with heat exchangers, with one well dedicated exclusively to monitoring. Each well is separately controlled with its own pump, giving operators maximum control over the system.
“We can flow some wells part of the time, and let them recharge by keeping them idle for other parts of the time. In addition, during the winter months we can actively recharge by injecting chilled water obtained by heat exchange with the cold ambient air,” says Tester.
Sensors distributed at regular intervals collect data on subsurface temperatures as well as the performance of the heat pumps themselves, including the flow rate of each heat exchanger and power consumption.
Of course, installing dozens of temperature sensors wasn’t totally straightforward.
“It was challenging to get them down in the ground and sending a signal back,” says Lesperance. “We had to secure them, epoxy them and wrap them to get them to stay in place when we pushed the tubes into the ground.”
In the end, putting all the pieces in place required a substantial investment from Verizon, something that made a real impression on Lesperance.
“Verizon deserves a pat on the back for stepping up and investing that kind of money,” he says.
Looking to the Future
While the project has serious potential in terms of advancing energy efficiency technology, Tester is quick to emphasize that this is just the beginning of the experiment. Usable insights into the technology’s viability for other sites will only be available once researchers have the chance to collect and analyze enough data on how the system performs as a whole.
“We want to validate some of our models that we’re collecting data on to try to predict what the subsurface field does over time—how it heats up, how we recharge it in the winter,” he says. “Ultimately we’d be turning over a model that people could use with very few measurements, that they could be confident they’re getting the right results.”
Verizon leaders are also looking forward to seeing the outcome of this innovative project. Michael Gray, network operations manager for Verizon and coordinator of the project’s installation, highlights the benefits of leveraging the expertise available at Cornell.
“They’ll help us determine the overall ROI [return on investment] over the life of the system. We really want to be thinking about the long term, since it’s an important part of our network and how we provide service to our customers,” he says. “This equipment will be there for a good long time.”
But Verizon isn’t just focused on the financial and operational benefits this type of technological advancement could potentially provide. The company is also interested in energy-efficient cooling options as a way to achieve publicly stated sustainability goals.
“We’re really committed to using technology to help solve these types of environmental sustainability issues,” says Gray.
Regardless of the outcome, the project is a worthwhile experiment for all parties. This is especially true for the students involved, who are benefitting from being able to apply the research expertise at Cornell to real-world sustainability problems.
“It’s exactly what we hoped for,” says Westervelt. “It’s a real living laboratory for students.”