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 earth stores heat from solar radiation. Although the top 30 feet of earth changes temperature with the seasons, below 30 feet the ground stays fairly stable at the average yearly temperature of the air.

In Maine, for example, the ground remains at a nearly-constant 50ºF. As the earth absorbs the heat from the sun, that heat is transmitted downward to a depth of approximately 500 feet.

The Chewonki Foundation, a Wiscasset, Maine-based nonprofit educational institution and winner of the 2009 Great Nonprofits Green Choice Award, is leveraging this natural phenomenon to lower energy costs and reduce its carbon footprint. The Foundation recently installed a geothermal heating unit that will help heat its largest building on campus – the Center for Environmental Education. The geothermal unit will use heat collected from a deepwater well to warm the building’s radiant floors.

“The geothermal system we installed is expected to be energy efficient,” said Tom Twist, sustainability educator for Chewonki. “In fact, we’ve projected the system will function at one-third the cost of a traditional oil-heat system, and can be expected to pay for itself in three to five years.”

To help verify these claims and determine if geothermal is a viable energy source option to fossil fuels, the Foundation installed a web-based energy logging system from Massachusetts-based Onset to measure the heating system’s performance.



Geothermal Application Diagram

The system, a HOBO U30-ETH, was funded through a grant from the Maine Public Utilities Commission (MPUC), which is interested in verifying that the geothermal system will be a more economical energy source over the traditional oil heat source used previously. If the results look promising, the MPUC may consider incorporating geothermal systems into public housing projects.


The data logging unit, which measures, records, and transmits system performance data to the web, is configured with a number of sensors. Two flow meters connected to the well pump measure BTUs the system is producing and flow rates. A kilowatt sensor measures the electric draw of all the system pumps, including a number of tiny circulating pumps and the larger heat pump itself. Temperature probes measure air temperatures inside and outside of the building, and well temperatures coming in and going out.

A real-time display of the data is transmitted via Ethernet to the web over HOBOlink®, an Onset-hosted server. Twist configured the webpage with a “public access” feature so faculty and students can log on to see the latest measurements, as well as measurements taken over the past week and month.

“The web display of the data is a benefit to us for a number of reasons,” explains Twist. “First, I am not a programmer, and it’s unlikely that I could develop any kind of interesting way to view the data online. Having it published by Onset, using their secure and dedicated server, makes it easy for us to see what we need to see. Second, it makes the data widely accessible, which is great for our students who can log in and see firsthand how the system is performing.”

The Foundation will be collecting data on the geothermal heating system through the fall and winter seasons, and aims to have cumulative data to present to the MPUC in the spring of 2010.

“We should, however, know fairly quickly this fall if the system seems to be reducing energy costs and shrinking our carbon footprint,” said Twist.


Application Story