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Understanding Geothermal Energy

Understanding Geothermal Energy. Dr. Michael Shepard Department of Geography and Geosciences. A GEOTHERMAL SYSTEM is a type of HEAT PUMP. Typical Heat Pump Operation. In winter , a heat pump extracts heat f rom the outside air. The colder it is o utside, the harder the system has to

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Understanding Geothermal Energy

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  1. UnderstandingGeothermalEnergy Dr. Michael Shepard Department of Geography and Geosciences

  2. A GEOTHERMAL SYSTEM is a type of HEAT PUMP. Typical Heat Pump Operation In winter, a heat pump extracts heat from the outside air. Thecolder it is outside, the harder the system has to work. In summer, a heat pump dumps heat from the home. Thehotter it is outside, the harder the system has to work Image courtesy: http://www.srpnet.com/energy/pumpworks.aspx

  3. Just a few feet down, the Earth maintains a constant temperatureof ~50°F (10°C) year round. Geothermal heat pumps use the ground (geo) as a heat exchanger (thermal) INSTEAD of air like the more typical heat pump. • In the winter… • They extract heat from the Earth to heat your home. • It’s FAR more efficient to extract heat from a 50°F ground source than much colder outside air. • In the summer… • They dump heat from your home to cool it. • It’s FAR more efficient to dump heat to a 50°F ground sink than to much hotter outside air.

  4. Typical Setup -Wells are dug. -Plastic piping goes from unit into and out of the wells. -Piping is filled with antifreeze; often water mixed with alcohol. -Piping can also be horizontal, or placed in a pond, etc.

  5. In summer, heat from home is dumped into the Earth; Another way to think about it: cold water from the Earth is used to cool the home. In winter, heat from the Earth is used to heat the home; Another way to think about it: heat is extracted from the water coming from the Earth, and colder water is returned. Image courtesy: http://mvgeothermal.com/faq.php

  6. Advantages • Heat pump is inside and very quiet. • Most units also provide domestic hot water. • Not subject to wild swings in oil/gas prices. • Few moving parts and low maintenance. • System life 25+ years; 50+ years for the loop. • Very high energy efficiency (300%-600%, EPA). • Payback in 5-10 yrs over a conventional system. • One-time tax break of 30% of unit cost.

  7. Personal experience • System added in June 2008 • Replaced an older oil-burning forced-air furnace and exterior air-conditioner (HVAC). • Cost of the unit was similar to a new high-efficiency gas or oil furnace. • Extra cost of $7,500 was incurred to dig 3 wells (each 150 ft deep) and lay tubing in my suburban front-yard.

  8. Costs to date…. Summer Cooling • Sum of June-Sept 2007 Electric Bill: $595 • Sum of June-Sept 2008 Electric Bill: $585 Difference: - $10 Winter Heating • Sum of Nov 2007-Feb 2008 Electric Bill: $528 • Sum of Nov 2008-Feb 2009 Electric Bill: $740 Difference: $212

  9. Comparison of Costs • Cooling costs during the summer – negligible • Heating costs/month with oil: $275 • Heating costs/month with geothermal: $53 • Estimated payback time:3-10 yrs (depends on price of heating oil)

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