Geothermal Heating and Cooling Systems Are a Viable Alternative to Traditional HVAC

Geothermal systems, which use the relatively stable and moderate temperature of the ground as an energy source, are piquing the interest of green-minded builders as an efficient and clean alternative to conventional heating and cooling systems.

Geothermal heat pumps (GHPs) accounted for about 50,000 residential and (mostly) commercial installations nationwide in 2006. That’s less than 1% of the overall heating and cooling equipment market, according to a recent report issued by the Freedonia Group, a Cleveland-based research firm. GHPs work typically by exchanging or transferring heat via liquid-filled tubing loops that run between the house and the ground or a nearby body of water. That same report, though, forecasts 6.5% annual growth for the technology through 2011, setting a new bar of 70,000 installations that year. By 2016, the report predicts nearly 100,000 geothermal heat pumps will be put in place per year.

“The growth is exponential,” says Eric Dickie, president of Delta Geothermal, a distributor and installer in Lake Country, British Columbia. “For every geothermal heat pump system we sell, it generates two more sales.”

And why not? Geothermal (also called geoexchange, earth-coupled, or ground-source) offers some pretty attractive benefits, from far superior heating and cooling efficiencies compared to even the highest-rated furnaces and air conditioners, to the use of a free, nontoxic resource of ground temperature.

“Simply, you’re moving energy from one place to another versus spending money and resources to create it,” explains Cary Smith, president of Sound Geothermal Corp., a ground-source system designer in Sandy, Utah.

In addition, a geothermal heat pump is a heating and cooling machine-in-one, eliminating the outdoor air conditioning or air-to-air heat pump compressor from the spec sheet. Fitted with a standard blower and filter, it leverages the same distribution network of ducts and supply/return registers as any other air-forced system.

GHPs also mitigate seasonal fluctuations in performance (unlike air-source heat pumps), run on about half the amount of electricity of a conventional system, deliver effective humidity control, and can be specified within the same unit footprint to heat the home’s water supply, in-floor radiant heating system, and swimming pool.

And while builders will need an excavation or drilling crew and likely a certified installer to trench and hook up the underground loop of circulation tubes that feed the system, any HVAC contractor worth his sheet metal can connect the rest of the equipment. The systems are generally applicable in almost any climate, thanks to the consistent temperature of the ground of around 70 degrees F, at about 8 feet below the surface, whether you’re in Scottsdale or Scarsdale.

What to Watch For

There are caveats, of course, chief among them an installed cost that’s about two to three times that of a conventional system, primarily to excavate for and install the underground loop of high-density polyethylene tubing.

For a new home, the straight return on an upfront investment of about $2,500 per ton of capacity plus perhaps another $5,000-plus to install a closed-loop, ground-source system (see “How It Works,” below) is at least four years and probably more, even in the most expensive utility markets. Some of that premium might be recouped from local utility rebates, state-sponsored grants, and federal tax credits, though it may require proof of a system that meets minimum performance standards and certified installation to qualify.

But, amortized within a fixed-rate, 30-year mortgage, the per-month payback for a geothermal system is almost immediate thanks to energy use that even the EPA says can be 50% less than a furnace and air-conditioning system.

The effectiveness of a geothermal heat pump also relies on a well-built and insulated shell. “If the [building] envelope is not designed for high-efficiency equipment, a ground-source heat pump won’t do you any good” in terms of significant energy and cost savings, says Phillip Russell, a Pensacola, Fla.–based custom builder. Russell’s first house 28 years ago featured an open-loop geothermal system, and he’s installed variations of the technology in about 75% of his homes to date.

The performance of the system also requires a more deliberate calculation of the home’s heating and cooling needs than what’s typically conducted for a traditional HVAC system. “If you oversize a gas furnace, it’s not a huge deal,” says Dickie. “If you oversize a geothermal heat pump, you increase the cost of the equipment and the infrastructure.”

Dickie recommends a thorough heat-loss and heat-gain analysis and calculation for the home, which determines the capacity of the system that, in turn, dictates the design and extent of the ground or water-source loop.

Defining Efficiency

If you check the spec sheet of a geothermal heat pump system, you’ll notice two distinct ratings regarding its efficiency: COP (coefficient of performance, for heating efficiency) and EER (energy efficiency ratio, for cooling performance). In both cases, the higher the rating, the better the energy performance.

These two ratios should be used as a relative gauge among geothermal systems—and within that, similar types of GHPs such as open- vs. closed-loop—and reflect a “steady-state,” or factory-tested, performance rather than what’s likely to be found in the field. The ratings are similar, but not directly comparable, to efficiency ratios calculated for conventional HVAC equipment. That being said, GHPs are typically three to four times as efficient in heating mode and at least 50% better in cooling mode than a furnace and air conditioner, respectively.

To ensure consistency, the ratings were standardized for the industry in 2000. The Air-Conditioning and Refrigeration Institute regulates them, mitigating discrepancies in what manufacturers include in their energy-use calculations to arrive at the ratios.

And, relative to conventional HVAC equipment, which also is tested and rated in a steady state, GHPs are clearly—and in some cases dramatically—more energy efficient.

Demand Drivers

Though suitable for almost any climate and scalable to any building size, geothermal isn’t for everyone.

Bob Schmitt Homes in North Ridgeville, Ohio, for example, installed about 85 geothermal heat pumps in the late 1990s, but stopped doing so eight years ago after financial incentives and other support provided by the local electrical utility vanished. “If there’s an easy way to get it installed, it’s a nice system,” says executive vice president Scott Kubit, noting that the tight-lot suburban land plans the company develops are less accommodating to geothermal than wide-open rural lots.

But some builders may not have much of a choice. Economic and environmental factors are both coming on strong as demand drivers among consumers. “Ninety five percent of the inquiries we get for residential systems are homeowner-driven,” says designer Smith. “The builder can embrace it and learn about it or resist it,” perhaps at his peril.

Smith also points out that contractors are being held more accountable by building codes for energy performance, specifically higher standards for the thermal envelope. “If you’re forced to make that investment, these systems make a lot more sense,” he says.

A complex combination of environmental and economic factors is conspiring to drive a cottage technology that’s been in use since the 1940s, and especially since the first “energy crisis” of the early 1970s, into the mainstream.

“Interest right now is off the charts,” says Thomas Ross, vice president of marketing and sales for manufacturer Northern Heat Pump. “I call it a 30-year overnight success.”

How It Works

All heat pumps, whether air-to-air or ground-source, work by exchanging heat from one place (the equipment) to another (the house). In a geothermal setup, the “equipment” is the relatively stable and moderate temperature of the ground at about 8 feet below the surface, a storehouse of heat derived primarily from solar radiation. In a GHP, the heat is carried through a closed loop of high-density polyethylene tubes filled with a heat transfer agent, usually a nontoxic antifreeze solution.

There are, however, variations on that basic model. Among closed-loop systems, the network of tubing can be installed horizontally or vertically, usually depending on site conditions and available land around or even under the building footprint, as well as the comparative costs of trenching (for horizontal) or drilling (for vertical). Closed-loop systems also can tap the heat stored in a water well or nearby pond, which is called a water-to-water system.

Lastly, an open-loop (or ground-water) GHP eliminates the antifreeze carrier, instead using the solar-heated water of a pond or well. The heat is then exchanged at the pump inside the house, as with a closed-loop system, or used directly for hydronic space (and perhaps water) heating. For various reasons, some municipalities regulate the drilling for and discharge water of open-loop systems, especially large-scale installations far exceeding those of an individual home. For open-loop systems, especially, consult the local building department and other appropriate regulatory agencies about what is allowed and how to best handle the discharge of water that’s been through the heat exchanger.

Once the heat from the ground or water source makes it to the heat pump inside the house, the system works the same as any forced-air system. In cooling modes, the process is reversed, with the heat pump taking hot air out of the house and exchanging it with the ground temperature—which, in the summer, is far cooler than the outside air—and using an ozone-safe refrigerant to cool it further and distribute it throughout the house.

Resources

Air-Conditioning and Refrigeration Institute (ARI): Regulates and rates geothermal heat pumps for their relative performance efficiencies, specifically COP and EER, among other HVAC equipment; publishes a semi-annual directory of certified products, which is also available online. www.ari.org

U.S. Department of Energy (DOE): In addition to the federal Energy Star program (www.energystar.gov), which qualifies and lists GHPs among several other product categories, the DOE offers additional information via its Energy Efficiency and Renewable Energy resource. www.eere.energy.gov/consumer/your_home/ (search “space heating”)

NAHB Research Center: The center’s online Toolbase of various construction-related topics includes a section on geothermal heating and cooling.
www.toolbase.org/Technology-Inventory/HVAC/geothermal-heat-pumps

The International Ground Source Heat Pump Association (IGSHPA): In addition to providing a wealth of information on GHPs, the association’s Web site offers a directory of accredited installers. www.igshpa.okstate.edu

Geothermal Heat Pump Consortium: A storehouse of GHP information, including a directory of local contractors and access to financial and other incentives provided (or not) by each state. http://geoexchange.us

Rich Binsacca is a freelance writer in Boise, Idaho.