In its 75-year history, modern ground source geothermal energy (GSGE) has flown so far under the radar, it might as well lie in your granddad's root cellar. But unlike root cellars, built as crude geothermal systems to preserve perishables in a static environment, a ground source geothermal heat pump (GSGHP) can deliver a dynamic and effective heating or cooling system.

In winter, GSGE extracts heat from the constant temperature reservoir provided by the earth’s underground geothermal gradient.  Then in summer, the cycle is reversed and GSGHPs reject heat back into the ground.

GSGHPs currently make up some 5 percent of the total heating, ventilation and air conditioning (HVAC) market.  In the U.S., an estimated 100,000 residential and commercial GSGHP units are installed annually, with the current market fairly evenly distributed between residential and commercial sectors. 

“Ground source geothermal energy is one of the best renewables, even though it took a while for people to consider it a renewable energy source,” said Garen Ewbank, an industrial engineer and the owner of Ewbank Geo Testing in Fairview, Oklahoma.  “It’s renewable because of the constant temperature due to the earth’s geothermal gradient.  About 1 percent actually comes from solar; the rest is geothermal.”

The key to it all is sheer geothermal underground dynamics.  A couple of dozen feet under, temperatures remain the same almost year-round.  As Ewbank notes, ground source temperatures tend to vary from 49 degrees in Toronto to 72 degrees in the Florida Keys, which he says represents a surprisingly narrow range for such a wide geographic area. 

GSGE taps into this constant energy gradient in both winter and summer to heat and cool homes, businesses, schools, hospitals, retail stores, hotels, ski resorts, even the Statue of Liberty gift shop.  But the residential market arguably could offer the GSGE industry the most potential growth. 

A typical closed-loop installation involves three vertical 250 ft. deep bore holes which are, in turn, loaded with high density polyethylene pipe to circulate water from the indoor heat pump throughout a continuous pressurized loop. 

Using a fan, compressor and indoor heat pump, the GSGHP system extracts heat from this constant ground source and during winter compresses it to higher temperatures.  During summer, the system simply reverses.  The most commonly used GSGHP setup uses a closed-loop heat exchanger, water and underground piping to either extract or reject the heat.

As Ewbank explains, the whole point of the ground source heat pump is to transfer heat against the direction it would naturally go. 

Even so, electricity, water and refrigerant are still needed to run the system, which is typically four times as efficient as a conventional HVAC.

The first GSGHP systems in the U.S. were installed in the late 1930s, but fizzled out in the early 1950s due to construction and design issues.  But the industry got a reboot in the late 1970s; about a decade after air source heat pumps became common in the U.S. 

“Instead of exchanging energy from the environment where you have a refrigerant to air heat exchanger, GSGHPs have a refrigerant to water heat exchanger,” said Jeff Spitler, a mechanical engineer at Oklahoma State University in Stillwater. 

A fan and duct system then circulates the hot or cold air from the heat exchanger to points throughout the home or business.

But to install and equip a three bedroom house with a GSGHP, count on costs that are roughly double that of a conventional heating and cooling system.  However, with tax credits for installation, homeowners can expect to recoup their investment within five years.

“The market is still maturing because there are still places where you can’t find a competitive bid on this kind of technology,” said Spitler.  “And as you go farther south, it’s less likely to be economically feasible.”  

Spitler notes ideal GSGE locations are regions with big temperature swings like Oklahoma.

Ewbank says that in Oklahoma, with brutal 115 degree summers and 0 degree winters, GSGHPs can tap into a constant deep earth temperature of about 64 degrees.  The end result is that ground source energy can be pumped in and out of houses or businesses, using less refrigerant and less power than conventional HVAC systems.

“Ground Source Geothermal is a more reliable and efficient way of doing air conditioning,” said Eric Woodroof, the Kentucky-based CEO of Profitable Green Solutions, an energy efficiency consultancy.  “It’s easier to reject heat to 60 degrees than it is to 100.  And in the winter, it’s a heck of a lot easier to absorb energy from 60 degrees than 32 degrees.”

But with new home construction still in a slump and existing homeowners already looking to cut corners, intital costs are holding many homeowners back from taking the plunge into GSGHP.

“The first cost needs to be at the utility scale,” said Ewbank.  “Let the utilities install and finance them, then the homeowner could choose a very efficient system and not be subject to the first cost.” 

The idea is that utilities could then just bill their GSGE customers for BTUs of geo-cooling or heating rather than in kilowatt-hours.

Ewbank says an electric utility would gain winter load since customers wouldn’t shift from electricity to fossil fuels to heat their homes.  And, in turn, gas utilities would gain summer load, since homes cooled by gas-driven heat pumps are the rare exception. 

Ewbank says that, in essence, GSGHPs are no different than any other energy production facility.  The difference is that competing energy technologies’ higher “first costs” are usually borne by either the public at large or utilities involved in financing such projects.

Thus, Ewbank says, the challenge is to make sure that when future new homeowners argue over whether to forego Ground Source heat pumps in favor of granite kitchen countertops, they will understand that they have options to have both. 

How can that happen? 

“We’ve got to shift the first costs of installation,” said Ewbank. 

In the meanwhile, Spitler says that newer, less expensive drilling techniques and improved heat exchangers would help make GSGE more attractive to both new homeowners and potential commercial users.  But as Spitler points out, it’s likely that the average U.S. homeowner, school or business doesn’t realize that Ground Source Geothermal is a viable heating and cooling option.

However, Doug Dougherty, the president and CEO of the Geothermal Exchange Organization in Washington D.C., says that although new marketing efforts should help bolster GSGE’s prospects, he doesn’t foresee a significant increase in market-share until new home construction returns to pre-recession levels.  

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Lead image: Geothermal heat pump diagram via Shutterstock