This spring, Chewonki has installed a geothermal unit that will help heat our largest building, the Center for Environmental Education. The geothermal unit will use heat collected from a deepwater well to warm the radiant floor of Chapin Hall.

Listen to our Geothermal Podcast. . .

The geothermal system is very energy efficient. For every one unit of energy you put in, you get three to five units of energy out. These additional units of energy come from underground. We use the constant and relatively warm temperature of the ground as the source for heating our building.

It is projected that our geothermal system will function at one-third the cost of a traditional oil-heat system, and can be expected to pay for itself in 3-5 years. Because we have totally switched over to buying green electricity, or Renewable Energy Credits, the heating of Chapin Hall will be totally carbon-neutral.

Our geothermal system is used for both reducing our carbon footprint and for educating both students and adults about this type of renewable energy. Click here to learn more about our teacher resources and tours . . .

We have recently installed a HOBO Link data logger on our geothermal system, which will give instantaneous feedback on how our unit is performing. Having this knowledge helps us with troubleshooting, efficiency data, and giving our students and the public an inside look at how geothermal units actually work.

 

 

Click here to see Real-Time data on Chewonki's Geothermal System. . .

 

 

 

How to interpret our Real-Time data stream. . .

 

How does a geothermal system work?

The word geothermal literally means “earth heat.” We can capture the heat that is stored in the earth and use it to heat our buildings. The top 500 feet of the earth stores heat from solar radiation. Although the top 30 feet of the earth changes temperature with the seasons, below 30 feet, the ground stays pretty stable at the average yearly temperature of the air. For example, in Maine, the ground stays about 50 degrees Fahrenheit. As the earth absorbs the heat from the sun, that heat is transmitted downward to a depth of about 500 feet. Below this depth, the earth gets even hotter, but that heat is as a result of radioactive decay in the mantle and core of the planet.

In Maine, there are no places where this deep heat comes to the surface through springs or vents. This type of geothermal activity and the heat that goes with it is much more common in the mountains of the western United States and other places with active tectonic boundaries.

Nevertheless, many people in Maine can access geothermal heat through their wells. If a building has a well, the temperature in that well is about 50 degrees Fahrenheit all the time. This heat can be pumped up from the well, and concentrated to heat buildings. This concentration uses a heat pump similar to the heat pump that keeps a refrigerator cold. In the case of a refrigerator, the heat pump works by pumping heat out of the fridge to the coils on the back or underneath. In a geothermal heat pump, the heat from the well water is taken and passed onto other water, reaching temperatures of up to 120 degrees. This water is then pumped around to heat the building. In the summer, the process can be reversed to cool spaces by taking the heat out and depositing it in water which goes back to the well. Additionally, the excess heat from the pump can be captured to heat water for domestic use. This actually improves the efficiency of the heat pump.

Geothermal heating systems are a great way to heat our buildings and water in winter and cool them in summer. However, this technology, like all renewable energy sources, has its limitations. The greenhouse gases associated with this heating system come from the electricity needed to run the pumps. This problem could be solved by using another renewable source to generate this electricity. Geothermal heating systems are highly cost effective, if there is already a suitable well on site, they can pay for themselves in two to five years.

More. . .

 

(Geothermal graphics courtesy of onset.com, tricountyarie.com, hvce.com, and oee.hrcan.gc.ca. Many thanks!)