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Direct Exchange Geothermal (DX Geothermal)

What is direct exchange geothermal?

DX geothermal is a type of closed loop, ground source heat pump system. To capture the ground’s heat, DX systems circulate refrigerant through copper tubing installed in the ground.

How do DX geothermal systems operate differently from standard geothermal systems?

DX and standard geothermal systems both use the ground as an energy source, but they differ in how that energy is transferred into the home.

How do standard geothermal systems work?

Standard closed loop geothermal systems absorb heat by continuously circulating a mixture of water and non-toxic antifreeze through buried or submerged plastic pipes.

The water-based mixture is carried into a heat exchanger where it exchanges its heat with refrigerant. The refrigerant is boiled, vaporized, and compressed before entering a second heat exchanger. Here, the hot refrigerant gas exchanges its heat with air, which is then distributed through the home’s ductwork.

How do DX geothermal systems work?

DX geothermal systems absorb heat by continuously circulating refrigerant through buried copper pipes. Copper is a highly conductive material, so it easily transfers the ground’s heat to the refrigerant.

The warm refrigerant enters the heat pump where it is boiled, vaporized, and compressed before entering a heat exchanger. As with standard geothermal systems, the hot refrigerant exchanges its heat with the air before it’s distributed through the home’s ductwork.

What are the downsides of DX geothermal?

Pipe Corrosion:

DX geothermal is good in theory but often disappointing in practice. Although DX systems have the potential to be more efficient than standard geothermal systems, they often aren’t because copper piping corrodes far more easily than plastic. When copper corrodes, it can lead to catastrophic system failure.

Oil Pooling:

It occurs when the refrigerant piping isn’t sized properly (velocity is too low and it falls out of suspension in the refrigerant).

Geothermal systems use a small amount of oil to keep the compressor lubricated. When that oil doesn’t return to the compressor the compressor’s temperature increases, which can damage the compressor.