The top 500 ft of the earth stores heat from solar radiation. While the temperature of the top 30 of those feet changes with the seasons, below 30 ft, ground temperature is fairly stable, staying at the average yearly temperature of the air.

In Maine, for example, ground temperature is a nearly constant 50°F, with heat absorbed from the sun transmitted to a depth of approximately 500 ft.

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

“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,” Tom Twist, sustainability educator for Chewonki, said.

To help verify those projections, the foundation installed a Web-based energy-logging system from Onset to measure performance.

The system, a HOBO U30-ETH, was funded through a grant from the Maine Public Utilities Commission (MPUC), which is looking for verification that geothermal is a more economical energy source than the oil used previously. If the results are promising, the MPUC may incorporate geothermal systems into public housing projects.

The data-logging unit, which measures and records system-performance data and transmits it to the Web, is configured with a number of sensors. Two flow meters connected to the well pump measure British thermal units and flow rates. A kilowatt sensor measures the electric draw of all of the system pumps, including a number of tiny circulating pumps, while temperature probes measure the temperature of air inside and outside of the building and the temperature of water going into and coming out of the well.

Data is transmitted to the Web via Ethernet over HOBOlink, an Onset-hosted server, in real time. Twist configured the Web page with a public-access feature so faculty and students can log on to see the latest measurements, as well as measurements taken over the last week and month.

“The Web display of the data is a benefit to us for a number of reasons,” Twist explained. “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 winter, with plans to have cumulative data to present to the MPUC during the spring of 2010.

“We do not have complete cumulative data yet, but figures that I do have look promising,” Twist said. “The system has produced a total of 4,094,400 Btu this year at a COP (coefficient of performance) of around 3. John Logan of Water Energy Distributors Inc. has predicted … that our heating cost will be reduced to about a third of what it would be if we were heating with No. 2 heating oil. So far, it looks like we're on track.”

Twist added: “We have also purchased electricity from renewable sources for all of our buildings, so the geothermal heat pump should be essentially carbon-neutral.”


Information and graphics courtesy of Onset and The Chewonki Foundation.
Circle 100

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