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Do-Over for a Critical Geothermal Heating and Cooling System

In June 2011, the geothermal (earth-coupled) heating and cooling system started to fail in the emergency operations center for Sussex County, Delaware, even though the $13 million building had only been built in 2008.

The 18,000-square foot facility in Georgetown, Delaware contains $4 million worth of electronics equipment to process 911 calls. The building was designed to withstand winds up to 120 miles per hour and serve the region during disasters. But it also has heavy cooling loads, thanks to all that equipment.

To supply that cooling (and heating during the winter), the green building was fitted with a closed-loop geothermal system, to take advantage of the natural temperature gradient beneath the structure. The system essentially works like a refrigerator, only instead of exchanging heat with the air, it exchanges it from fluid in 24 closed, 600-foot-deep wells, the temperature of which was expected to range from 60 to 70 degrees Fahrenheit.

However, in the summer of 2011, the fluid in the system’s wells ranged from 80 to 85 degrees. It reached 95 degrees more than once. If it had reached 100 to 105 degrees, the system’s 110-ton air conditioning system would have totally failed, putting the expensive equipment at risk.

As an emergency measure, the facility brought in a temporary cooling tower , but the bills started adding up.

County officials also looked for outside help, and they called Jay Egg, a geothermal heating and cooling expert with decades of experience in the field, classroom, and boardroom. Jay and I recently co-wrote the book Geothermal HVAC.

Hot Ground

Jay told the frustrated officials that the ground around the emergency facility could absorb no more heat. He said he has been seeing this “thermal retention” problem for years, especially in warmer climates like Florida, where he lives with his family.

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Sussex County's director of engineering, Steve Hudson, poses with Jay Egg (right) at the center. (Photograph courtesy Jay Egg)

Instead, Jay is a big proponent of open-loop geothermal systems, in what’s called pump and injection. In this method, groundwater is pumped over a heat exchanger and injected back into the aquifer from which it came. In the case of most aquifers, this provides a steady source of cool water that is able to efficiently carry away the heat once it is warmed.

Unfortunately, it’s going to cost Sussex County about a quarter of a million dollars to redo the geothermal system to pump and injection, but Jay is confident the long-term stability and savings will be worth it.

Jay says, “The fact is, a properly engineered pump and injection geothermal system will cost one third that of a closed loop system; it will use almost no space, and the performance will improve.”

It’s Not Pump and Dump

One of the reasons pump and injection is less well known among installers is because it is often confused with something called “pump and dump,” which has a bad reputation. Before engineers started routing warmed (or cooled) water back into the aquifer whence it came, they used to let that water spill onto the ground or into a lake or pond.

Trouble is, that water often wouldn’t make its way back into an aquifer, at least in a reasonable period of time. It would often evaporate or end up causing a mess on someone’s property. In a world with rising water shortages, this is a problem.

Some people also worry that pump and injection could somehow pollute the groundwater, but this should not be the case, because it passes over what should be a clean heat exchanger. Nothing is added or taken out of that water.

Historically, some local governments prohibited open-loop systems out of concerns over groundwater, but as the safety and effectiveness of new systems is demonstrated, a lot of these guidelines are getting rewritten.

As Jay and I discovered when we researched Geothermal HVAC, the key is properly sized and engineered systems, correctly installed. The right geothermal technology can definitely slash a building’s energy use for heating and cooling, and provide many years of exceptionally stable, reliable service. And Jay thinks open loops may be especially powerful for cooling-dominant areas and buildings.

Brian Clark Howard wrote Geothermal HVAC with Jay Egg.