In what geothermal system is the refrigerant used in the ground heat exchanger instead of an antifreeze solution?

• A. DX system
• B. Closed-loop system
• C. Open-loop system
• D. Hybrid system

Answer: (A)

Direct exchange geothermal systems place the refrigerant directly in the buried ground loop to absorb and release heat. Because the refrigerant itself circulates through the underground coil, no separate heat-transfer fluid such as water or antifreeze is used in the ground. This can improve efficiency by reducing thermal resistance between the ground and the refrigerant. In a closed-loop system, the loop is filled with water or a water–antifreeze mixture that carries heat to the refrigerant in the indoor unit, so antifreeze—not refrigerant—is in the ground. Open-loop systems use groundwater directly as the heat-transfer fluid, and hybrid systems mix approaches but still involve a primary fluid in part of the system. So, using refrigerant in the ground loop corresponds to a direct exchange geothermal setup.