Michael Holigan: Because the earth absorbs and stores much of the energy it receives from the sun as heat, underground temperatures below the frost line remain constant at a point between 42 and 77 degrees Fahrenheit year round depending on where you live. Geothermal systems can use this energy source to economically heat and cool almost any kind of home. In its simplest form, a geothermal system is made up of three components - a heat pump, or geothermal unit, a duct distribution system to channel the heated or cool air to the indoors and an underground heat exchanger made up of small diameter pipe.
Van Bourn: In the winter time we're extracting that natural heat out of the earth. It's being processed, taken into the home in a very comfortable temperature. In the summertime, we're actually reversing it. We're gathering up the heat from the house and injecting that to the natural coolness of the earth. Overall, makes the system extremely efficient.
M.H.: To heat your home, the geothermal unit compresses heat it receives from the earth raising it to a higher temperature and then distributes heated air throughout your home. When you switch to cooling, the unit simply absorbs heat from your home and transfers it through a loop to the cooler earth. These days most underground heat exchangers are closed loop systems. A continuous underground pipe is connected to the heat pump at both of its ends forming a sealed closed loop. Water circulates through the loop to transfer heat between the heat pump and the earth. In an open loop system, ground water is pumped from an aquifer, passes through the geothermal unit where heat is added to it or extracted from it and then it's discharged back to the aquifer, or a lake or stream. But because of the filtering requirements and environmental concerns, open loop systems are becoming less common. The pipes of a closed loop system can be placed in a horizontal trench dug below the frost line. To minimize the amount of trenching that needs to be done, slinky coils can be used to increase the pipe surface area. And that increases the amount of heat exchange per foot of trench. Wherever space prevents installing a horizontal loop, the pipes can be installed vertically in holes that are drilled into the earth. They can be drilled with an existing landscaping, under driveways and sidewalks or even beneath the home itself. How many loops do you need to heat and cool the house?
V.B.: Rules of thumb, in a vertical loop it's about 200 feet of bore per ton of equipment. In the Midwest it might be 150. Some areas it might be even a little less. So typically somewhere between 150 and 200 to 250.
M.H.: The polyethylene pipe being placed here in the ground at our high-tech house is guaranteed to last at least 50 years. Anywhere two pieces of pipe join, they're permanently fused together in a heat process.
Steve Lauten: We take one piece of pipe and put it on one side of the iron and take the other piece on the other side of the iron and leave them on there long enough for them to heat up. Then you'll see we'll pull them off the iron, slide them together and the joints are actually stronger than the pipe is by itself. If you cut a piece of pipe apart and look inside of the pipe, it is actually melted to the point where it's one piece now. It's a much stronger joint than you can get with any type of glues that many pipes use. So we rarely, if ever, have leaks on our pipes in the earth because of the strong joints we're able to make.
V.B.: We think the loop system itself is going to last as long as the house or longer. The equipment itself, they projected it right at 20 years of life expectancy.
M.H.: It doesn't have any big wear with running all summer and all winter?
V.B.: Not really, because it's not working very hard. It's kind of like a refrigerator and you know when you buy a refrigerator, you really think about that lasting until you want to give it to your kids.
Geothermal
Heatpump Consortium - 1-888-333-GHPC (4472)
Steve Lauten of Total Heat and Air - 972-881-0020
Tom Damiani of Texas Geothermal - 972-724-1584
Episode 48 1996 - 97 Season
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