Geothermal 101: Energy-efficient heating and cooling

| by Teena Hammond
Geothermal 101: Energy-efficient heating and cooling

One of the hottest topics of the green movement is geothermal. Homeowners and professionals alike are becoming increasingly interested in learning more about geothermal heating and cooling technology.

However, despite the current buzz, it's not a new technology. Geothermal has been around for more than 50 years although it's significantly improved over the decades. Right now, more than one million geothermal systems have been installed in the United States in both residential and commercial applications.

Many people considering adding geothermal to their home have questions. And many of the queries are similar: How much does it cost, how much savings will result, and will it work in a particular geographic region. Although every situation is unique, it is easier to understand all of the variables that can take place once someone has a basic understanding of how geothermal works.

Geothermal 101

The technology is simple. A geothermal system uses the heat stored below the surface in the ground, which is essentially solar energy since the earth is heated by the sun, to provide heating, cooling and hot-water assistance.

Outdoor air temperatures fluctuate from season to season, but ground temperatures are constant throughout the year, approximately 50 to 55 degrees Fahrenheit on average, depending on the region. The geothermal system transfers heat from the ground to the house in the winter, and transfers heat from the house to the ground in the summer.

A geothermal system is also known as a ground-source heat pump and typically consists of a geothermal heat pump with a compressor, evaporator, coaxial coil, variable speed blower, auxiliary heater and control board; ground loops of polyethylene pipe buried nearby either horizontally or vertically; a heat exchanger; and HVAC ductwork inside the home. A mixture of water and antifreeze circulates through the ground loops to absorb heat from or relinquish heat to the earth.

Geothermal details

Jeff Hammond, vice president of marketing and product development for Greenville, Ill.-based Enertech Global LLC, which manufactures geothermal systems, gives a detailed explanation of how geothermal works by comparing it to an air conditioner.

"You take a typical air conditioner. You know when you go outside you feel warm air coming from the unit. That kind of gives homeowners a feel for what that particular device is doing. Take a geothermal heat pump. It still has a compressor. It's still a refrigeration device. But instead of a fan we have a small little pump. We're circulating water through a little pumping system that's buried in the ground," Hammond said.

"The same thing applies with the geothermal heat pump. Now we're taking heat out of the ground. There's still a compressor and we're pumping that heat exchange between the water heating through the ground loop ... to the refrigeration circuits. We blow air across the coils and we're getting warm air through the refrigeration circuit. We're using the ground as a heat source."

Hammond said an analogy is that of a refrigerator. "You know it's cold inside but you feel heat coming off the back or the bottom. That's a heat pump as well." Hammond continued, "Same situation there. If the inside of the refrigerator was your house, you'd be cooling your house but you'd be rejecting that heat to the outside."

"The key really is the simplicity of it. Another concern that comes up a lot is the piping in the ground. People ask is it going to last a long time," he said.

"The pipe itself is high density polyethylene. If you have cereal in the morning, that's the same material on your milk jug. But the thickness is really thin on a milk jug. If you have a pipe wall thickness, that's a pretty strong piece of pipe," he said.

The pipe is extremely flexible, so while an earthquake might be a problem, with anything else you'd have to directly strike the pipe with a backhoe or shovel in order to damage it, he said.

Instead of using any mechanical fittings underground, all joints and fittings are heat fused so that everything underground is a solid piece of plastic.

Horizontal vs. vertical ground loop

Many people also want to know if the installation of the ground loop portion of the geothermal system will kill their trees. The answer is simple — the system is customized for each installation.

"The pipe is a closed system. It doesn't care if it's going vertical or horizontal or a circle or a loop. It's customized to every property. If we have a lot of space it's usually less expensive to bring out a backhoe or a trencher and do it horizontally. We can go around trees and stay clear of nice landscaping," he explained.

"In a suburban or urban setting we drill straight down. There is more cost to go vertical but it can be put in almost any lot. With a vertical loop you're down in very constant temperatures. Once you get below 8-10 feet it's very constant. With a vertical loop you need less pipe, but it does react quicker in the seasons."

A horizontal loop is buried between 5-8 feet, depending on the region and the ground temperatures. Since the pipe is closer to the surface, it takes a longer length of pipe to allow for the heat exchange to take place, he said.

More pipe is required for horizontal installations, but pipe is inexpensive compared to the excavation costs of deep vertical installations. There is, however, a little more thermal storage in a horizontal loop than a vertical loop.

Geothermal cost and tax credits

The federal Residential Renewable Energy Tax Credit is a strong incentive to install geothermal. The 30 percent tax credit is for residential installations between Jan. 1, 2009 and Dec. 31, 2016. Geothermal systems installed between Jan. 1, 2006 and Dec. 31, 2008 were given a maximum $2,000 tax credit, so the 30 percent credit on the entire installation cost is a substantial benefit.

In addition, there are local and state rebates and credits available in various locales. A good resource for available incentives is www.dsireusa.org, a website run by the U.S. Department of Energy.

The price of a geothermal heat pump is similar to a high-efficiency gas furnace and high-efficiency air conditioner, but the ground loop is the cost difference. There are some variations, but the ground loop makes the total installed cost about two to three times the cost of an installed HVAC unit, Hammond said.

It is less expensive to operate a geothermal system in some environments, but since natural gas is currently fairly inexpensive, there is only a slight savings over traditional HVAC units that run on natural gas. But there is a significant savings over HVAC units that run on propane or electricity, with a 70-75 percent savings using geothermal compared to those operating costs, Hammond said.

"On new construction that changes the complexion a little because you typically finance the heating and cooling system with the house, so geothermal doesn't cost you anything because the savings you realize offsets the additional payment. If you're going to buy with cash, then depending on the fuel you're looking at, the savings will change a little," he said.

"Normally we see versus propane or electric we're typically at a 3-5 year payback on a cash purchase. If we're comparing to natural gas it's a 10-12 year payback," Hammond said.

Mike Ryan, co-founder of PanTerra Energy, a geothermal solutions provider based in Colorado that focuses on residential, commercial and municipal applications, said that he likes to compare the cost of a geothermal system to a 95-percent efficient traditional HVAC system.

"Geothermal systems do use a small amount of electricity to operate. But typically, with a 95-percent efficient furnace and air conditioner, for every dollar of energy that you're buying you're using it for 95 cents worth of heating and cooling. With geothermal, for every dollar that you spend on energy, you're getting $5 in return," Ryan said. "That's a substantial difference."

Pond loops and open systems

Two other geothermal variations are pond loops, if someone has a pond on their property, and an open system. But Hammond said he doesn't talk about those as much.

"With an open system, essentially you're taking water out of the ground, running it through the heat pump, and discharging it somewhere. It's a lot of water usage. We kind of discourage that. As a closed loop, you just don't have any of those problems," he said.

Builders turning to geothermal

In Asheville, N.C., builders Jason Brownlee and Will Evert, partners in Evert and Brownlee Inc., are building a model house to LEED gold standards in order to show potential homeowners how geothermal works in a smaller footprint home.

"We've built this house as a model home so that we can provide tours for people can come in and view the mechanical room," Brownlee said. "We are creating a mechanical room where people can view the statistical data that we will have on the wall representing the monthly energy bills for the house."

The house is a 1,700-square-foot house on a slab, and will target the aging baby boomer market with a tight building envelope.

"We're really into the geothermal technology. The operating costs are so low and we feel that people are really going to appreciate that in the future as utility costs rise," Brownlee said.

Evert said that there has been misinformation about open geothermal systems from the 1980's, so part of their job is to educate the public about the high-efficiency model that they are installing.

Future of geothermal

With rising energy costs a key concern, the future of geothermal is strong in both commercial and residential applications.

A compounded 8.9 percent annual growth rate is predicted for commercial installations across the world through 2017. This growth will continue to educate the public about the value of the eco-friendly alternative to traditional heating and cooling, said Georgina Benedetti, senior industry analyst for Frost & Sullivan and the author of the Global Geothermal Power Market report that came out in November 2011.

The Geothermal Energy Association has projected that geothermal power production will triple in the U.S by 2035, with its growth outpacing the renewable power average.

Each year in the U.S., approximately 50,000-plus residential geothermal systems are installed in addition to the more than one million units already operating in residential and commercial venues. With rising energy costs and increased global warming, the demand for geothermal is expected to grow.

Read more about geothermal systems and energy-efficient heating and cooling.


Topics: Geothermal Heating & Cooling, Heating & Cooling, Rebates / Tax Credits

Companies: Enertech Global, LLC



Teena Hammond
Teena Hammond has published more than 2,000 articles in People and W magazines, Women's Wear Daily, and in dozens of newspapers and books. She also wrote a home improvement, remodeling and decor column that ran in Gannett newspapers nationwide. She's interested in all things green and would love to hear from you with your story ideas.

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