Geothermal Heat Pump Case Study
Geothermal systems are not only cost-effective, but good for the environment, according to the Department of Energy and the Environmental Protection Agency.
“With fluctuating gas prices, an increasing number of institutions have taken advantage of high-efficiency geothermal heat pump technology, which can both heat and cool facilities,” says OPPD Account Executive Jim Krist. “It was natural that Bellevue Public Schools followed suit.”
OPPD recently designed and installed a 117-ton-capacity geothermal heat pump system in the Bellevue Schools' Lied Activity Center and an 87-ton unit in the Welcome Center.
“Anytime OPPD has advised us, we’ve saved money.”
-Dr. John Deegan, superintendent, Bellevue Public Schools
The $8.3 million Lifelong Learning Center is “an unprecedented partnership between the community and the school district,” according to Dr. John Deegan, superintendent, Bellevue Public Schools. Bellevue Schools shares the Welcome Center, a 27,000-square-foot L-shaped building, with Offutt Air Force Base. The facility houses the school’s administrative offices, a technology training center, a professional library, a childhood center and a center to welcome new military personnel and their families to the community.
The 44,000-square-foot Bellevue Public Schools Lied Activity Center embodies a state-of-art center for students and a fitness center for community members
“The geothermal systems have a payback period of seven years,” said Dr. Deegan. “In the future, we will save even more money.”
Digging Deep for Savings
Geothermal systems can save nearly 40 percent of building energy costs compared to a conventional HVAC system, according to an OPPD study. The systems are economical because they take advantage of the earth’s constant temperature below the frost line and use it for comfort conditioning inside the buildings. The systems simply transfer the heat to and from the earth, tapping a regenerative energy supply.
For these systems to use the earth’s abundant free energy, a geothermal loop system -- underground piping systems made up of vertical loops -- was constructed below the surface and connected via horizontal piping to the heating and cooling systems inside the buildings. Typical vertical pipe loop depths range from 150 to 300 feet below the surface.
During the winter, a water-based heat-transfer solution circulates through the piping systems, allowing heat to be transferred to those parts of the buildings where it is needed.
In addition, the systems move excess heat from lights, computers and people in the core areas of the buildings, and circulate it through the loops to provide heat for the perimeter areas of the buildings. During the summer, the systems remove heat from inside the buildings and discharge it into the earth. Because of their efficiency, the systems are very cost-effective.
Testing Makes Sure
The process began with a geothermal conductivity test to accurately determine the properties of the soil, and the depth and number of boreholes needed for the project.
“Geothermal conductivity testing makes the project more economical, as it can accurately size the number of loops and the amount of piping needed for the heat pump system,” said OPPD Energy Solutions Engineer Kirk Estee. “The geothermal loop heat exchangers for the two Bellevue facilities combined consist of 252 loops with more than eight miles of vertical piping.”
This project was partially financed by the U.S. Department of Energy through a Special Projects grant awarded to the Nebraska Energy Office from the State Energy Program. Any opinions, findings, conclusions or recommendations are those of the author(s) and do not necessarily reflect the views of the Department of Energy or the Nebraska Energy Office.
For more information on geothermal heat pump systems, please call an energy management engineer in OPPD’s Business Energy Solutions & Technology Divistion, (402) 636-3536.
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