5/11/2006 by Jay Moynihan

As the cost of heating and cooling buildings and homes rockets, one energy alternative is quietly going mainstream: geothermal. Ask Mark Gutteter, owner/operator of restaurants in Ashland, Ironwood, Rhinelander, Superior and Woodruff.

“Originally, I went geothermal for return on investment reasons, and to be environmentally friendly,” Gutteter said about the new home he finished a year and a half ago. “With fuel prices going up, though, you are going to see a lot of these.”

Gutteter said his 6,000 square-foot home has 80 windows. The house, a pool, jacuzzi and two-story heated garage all use a horizontal coiled loop geothermal system for heating and cooling. How is it doing?

“Wonderful,” Gutteter said. “In-floor heat . . . air conditioning in the summer, it’s great. My total heating and cooling bill runs $100 to $150 a month.”

Geothermal technology cuts heating and cooling costs by about 70 percent using the simple rule of geophysics: At a certain distance into the ground, there’s a layer of year-round constant temperature, about 48 degrees Fahrenheit. In the Twin Cities, that point is about 15 feet down; in northern Wisconsin and northern Minnesota, it is at a shallower 12 feet.

That constant temperature can be effectively concentrated by geothermal technology to heat or cool without burning fuel or using excessive electricity. The main workhorse is a geothermal, or ground source, heat pump that uses a compressor and heat exchanger coils to transfer heat from the ground to the house ductwork or radiant floor tubing system. The heat pump operates on the principle that you can move heat from a warm place to a cool one.

“The reason geothermal is so efficient is that it is based on refrigeration technology,” said Mark Sakry, president of Northern GroundSource Inc. in Brimson, north of Two Harbors. “A heat pump moves heat instead of making it.”

Sakry designed and installed Gutteter’s system. He designs and installs geothermal systems for all types of buildings in extreme northern climates. “The technology originated in southern states, for cooling.

Over the last 20 years it has migrated north to both heat and cool. We now have a mature technology, fitted for the north, with correct depths, antifreezes, and loop field capacity,” he said.

The systems can be built horizontally, vertically, or by using ponds. Horizontal design is most common. Here’s how it works.

Buried in the ground is a “loop field” comprised of coiled, “slinky” polyethylene pipe, filled with 25 percent alcohol and 75 percent water.

“You take the heat from the ground via the fluid, energizing the refrigerant on its way back to a compressor. The compressor actually makes the heat. In summer you run it the other way, and the refrigerant takes the heat out of the building and loses it in the ground phase.

The compressor runs on electricity. The cost of running the compressor and circulating pumps is your heating and cooling bill,” Sakry said.

“Horizontal slinky systems are buried at six- to eight-foot depths so they don’t compete with encroaching winter frost, but close enough to the surface so they benefit from the seasonal dynamics of direct sunlight and rain,” he said.

Determining building needs

How do you determine a building’s heating and cooling requirements?

“We figure that using formulas (based upon) BTUs,” British Thermal Units, a measure commonly used in energy calculations, he said.It takes 12,000 BTU’s to melt one ton of ice in 24 hours, a sum called a ton. Essentially, you take thetotal net heat loss on a structure during the coldest day of the year and divide that by 12,000 BTUs. That yields the “tonnage” requirement of a building for energy purposes.

For example, the average Minnesota home is a 5 BTU-ton structure.

“From that we can calculate the size of the coil field, and what pump and compressor units are necessary,” Sakry said. He said Gutteter’s house is a 11-ton home.

The cost of a ground source heat pump system runs about $2,500 to $3,500 per ton. The larger the system, the smaller the per ton cost. This cost generally does not include ductwork, plumbing or electrical. But it does replace the furnace, boiler and air conditioners.

“We design for 100 percent geothermal,” Sakry said. “The extra initial cost is recouped in five to seven years. If your furnace and central air cost about $5,000 to install, it would cost you about $8000 to $10,000 more to upgrade to geothermal. You would be spending that anyway over the next few years on energy bills. So you may as well do the geothermal, save the money in the long run, and increase the home’s equity and sale value,” he said.

Many utilities provide a $100 to $200 per ton rebate for a geothermal system. Sakry also performs design and installation consulting with other contractors and engineers. The systems are going into homes, public buildings, hotels, restaurants, stores, and industrial buildings.

“The sustainable development and environmental folks have not really entered the geothermal market as strongly,” Sakry said. “Ninety-five percent of the market is strictly economically driven.”

Among the market-driven converts are President Bush and Vice President Cheney: Each has closed loop systems in their private homes, Sakry said. “It is comfortable. Radiant heat in the floor, and forced air, water heating, and air conditioning,” he said.

While horizontal loop systems are most common, there are other designs.

“If you are limited for yard space, you can do a vertical bore system, 200 feet in depth per BTU ton,” he said.

Sakry also designs and installs “pond” systems. “You put the coils in a more compact form about eight feet down in the water. You need a body of water with 3,000 square feet of surface area per ton. Up here, when you get about eight feet down in the water, its 39 degrees.

“A pond system has nearly zero environmental impact. The effect of the temperature transfer is slight, kind of like trying to heat a sidewalk with your thumb,” he said.

Useful Link:

Directions to Northern GroundSource Inc.

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