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Net Zero Facility Uses Solar, Geothermal

April 3, 2013 By Linda Hardesty

In Tallahassee, Fla., the Leon County Cooperative Extension Building was transformed into a net-zero facility in March 2012 with the addition of solar power and a geothermal heating and air system.

One year after its retrofit, data shows the 50-year-old building at 615 Paul Russell Road, also known as the Leon County Sustainable Demonstration Center, is producing renewable energy at a rate equal to or greater than what the building annually consumes.

“In the heat of August or the cold of January, we’ll have bills for those months,” said Maggie Theriot, director of resources stewardship for Leon County. “But over the span of 12 months, it balances out to be zero. We still have to pay basic fees and services” to the City of Tallahassee municipal utility.

The solar is tied into the grid and either draws power or earns credits. The building includes 253 solar photovoltaic cells on a ground-mounted structure, which also doubles as shaded parking. The solar array is sized to a 60-kW system compared to a 5-kW system used in the average home. The solar array supplies about 40 percent of the energy needed to power the 13,000 sq-ft building.

Also, a large portion of the facility’s heating and air system was replaced by a geothermal system, which uses the earth’s relatively stable temperature of approximately 68 degrees to cool or heat the building. This geothermal system is approximately 40 percent more energy efficient than a traditional heating and air system. After the geothermal installation, the building was able to take nine HVAC units offline.

The geothermal system was installed at an adjacent empty lot. “We just dug up that area and returned it to overflow parking at the end of construction,” said Theriot.


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