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The most common geothermal system uses vertical wells. Another option is the use of horizontal trenches, but due to the prohibitive amount of land area required, we’ll focus on vertical systems here. Vertical systems can either be closed- or open-loop, the difference being that closed loop systems do not use groundwater while open loop systems do.
Closed loop systems consist of a loop grouted in the well and a fluid, either water or a mixture of water and an environmentally friendly antifreeze, is circulated through the loop. This fluid absorbs heat from, and releases heat to, the surrounding underground formation. A heat exchanger in the building transfers heat between the refrigerant in the heat pump and the solution in the loop.
Open loop systems use the groundwater as the heat transfer medium and consist of two pipes in the well. One pipe holds a pump that pulls water from the upper zone of the water column while the second (return line) pipe discharges the conditioned water back deeper into the ground. Natural groundwater attenuation and the flow of water from the top of the water column to the bottom allows the water to return to its ambient state.
Costs and Efficiency
Note though that the cost of installing a geothermal system is higher than installing a traditional furnace and air conditioning system. However, the greatly increased energy efficiency results in savings on heating and cooling bills that allow the system to pay for itself within five to 10 years. Geothermal heat pumps are:
• 40% more efficient than air source heat pumps;
• 48% more efficient than gas furnaces; and
• 75% more energy efficient than oil furnaces.
When a geothermal system is installed during new construction, no chimney or flue is required to vent by-products from burning fossil fuels. There is also no need for an outside mechanical area and the size of the required inside mechanical area can be reduced by up to 50%. Also, air purification and humidity control measures are incorporated into the system itself. Additionally, radiant heat, air conditioning, and snowmelt systems can be added to the system far more cost effectively than with a fossil fuel system.
Notes about Geothermal Systems:
• Geothermal systems do not lose efficiency when the temperature of the outdoor air drops below freezing, like with air-source heat pumps.
• Geothermal heating systems are different from geothermal generating facilities, which tap underground steam reservoirs to produce electricity.
• Geothermal wells do not need to make water. The design of the well is determined by the size of the building.
• Geothermal systems do not need to “bleed” any water.
Geothermal systems are becoming far more common with more and more states adopting increased energy efficiency and Net Zero goals for their new and retrofit building codes. More than one million geothermal heating systems have been installed in the U.S., and it’s estimated that these systems have saved eight billion kwh of electricity and reduced the amount of CO2 released to the atmosphere by almost six million metric tons. This monumental impact is equivalent to taking 1.3 million cars off the road or planting more than 385 million trees!
