Geothermal 101: The Difference Between Open and Closed Loops

November 25, 2013
Ross and Witmer

Geothermal, or ground-source, heat pumps provide energy-efficient heating and cooling for many homes in the Charlotte area. These systems use the constant ground temperature several feet below the surface as a source of heat during cold weather and a heat sink (a place to dispose of heat) during warm weather.

The heat pump gains access to this constant geothermal energy via liquids pumped through loops of pipe buried underground or submerged in a lake. These systems can use closed loops that circulate water or antifreeze inside a completely closed system or open loops that draw water in from a well or lake and discharge it into a second well or back into the lake after it has run through the system. Here are some of the advantages and disadvantages of each system.

Cost of Installation

An open loop is cheaper to install than a closed loop. Because they rely entirely on natural groundwater or lake water supplies, open loops do not have to be leak-proof. Closed loops often carry potentially hazardous antifreeze chemicals, so building them to ensure environmental safety adds cost to the project.

Changes in Constant Temperature

A closed loop can lose efficiency over time, because the circulation of the heat transfer fluid can influence the temperature of the soil near the loop. This problem does not occur in an open loop, because the source water is never mixed with the discharge water, so the original source temperature stays constant.

Maintenance Costs

Open loops can be more expensive to maintain than closed loops. Open loops depend on an adequate supply of incoming water and adequate disposal capacity for outgoing water, so changes in well deliverability can be a problem. Open loops can have problems with scale buildup and bacteria growth that inhibit water flow. A closed loop does not have any of these problems, because the same fluid is constantly recirculated inside the system with no possibility of outside contamination.

Contact Ross & Witmer if you are considering a geothermal heat pump for your Charlotte-area home. We can help with design, installation and maintenance of all types of heating and cooling systems.

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