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Geological project could lead to more efficient geothermal systems

Tuesday, October 4, 2011 - 8:10 am

Hidden beneath the surface of Allen County lay soils that can radically vary from one mile to the next, creating a perfect laboratory for an Indiana Geological Survey project.

Allen County is an area where the Wabash and the Fort Wayne moraines – an accumulation of boulders, stones and other debris carried and deposited by a glacier – come within a few miles of each other. The moraines were formed 12,000 to 15,000 years ago, which from a geologist's perspective is fairly recent. It's because of this glacial activity that there is so much variety in the soil.

Shawn Naylor, a research hydrogeologist and director at Indiana University, has received a $69,000 grant from the U.S. Department of Energy to set up six test sites around the state. The data he gathers will be used to help engineers design more efficient geothermal heating and cooling systems for homes. The idea is based on knowing how well a certain type of soil absorbs water, heats up and cools down; that way, new geothermal systems can be specifically designed to target each type of soil.

There are two types of geothermal systems on the market. One type runs close to the surface horizontally; the other runs vertically into the ground, sometimes as deep as 150 feet.

Although more space efficient, the vertical system is more expensive to install. Naylor hopes that the data he collects will help designers plan shorter and more efficient horizontal systems that homeowners with less space would use.

Naylor is installing two sub-surface testing sites in Allen County. Those will have multiple sensors that will collect data on soil moisture, temperature and matric potential (how water moves through the soil). The sensors are buried beneath the surface.

An above-ground control box contains a hard drive to store the data and a modem to send the information that can be triggered by a computer in Bloomington. Above the box are sensors that measure wind speed, rainfall, humidity, temperature and solar conditions. The system is powered by a small solar panel.

Larry Yoder's farm in northwest Allen County was selected for one of the test sites. Yoder's farm is a hive of activity in the spring, when area schoolchildren come out to watch the making of maple syrup. On Wednesday the peaceful calm of an early autumn morning was broken by the sound of a backhoe moving dirt. The soil on Yoder's farm is relatively sandy, but just a hop across Chapman Road, barely a mile away, is the Acres Land Trust's Dustin Nature Preserve. The soil there is totally different, thick and dense with clay. That is the location for the second testing site.

To install just one of these test sites takes about 10 hours. Naylor and his two geology interns arrived Tuesday and were just finishing the first site Wednesday morning. They will move across the road to the Dustin Nature Preserve later Wednesday and should be finishing up their work Thursday.

Stations are being installed around the Indianapolis area; one is south of the city, two are east and one to the north. The idea is to put them close to the two largest urban areas in the state, areas where new homes are being built and homeowners will potentially be interested in geothermal options.

The grant provides enough money to set up the six sites and collect the data for two years. Naylor hopes to continue collecting data as long as the sites are functioning, possibly six or seven years.