page_title: Direct exchange geothermal heat pump
section_title: Operation Principles
hierarchical_section_title: Direct exchange geothermal heat pump / Operation Principles
caption_attribution_description: English: Vapor Compression Cycle in DX Geothermal
context_page_description: A direct exchange geothermal heat pump is a type of geothermal heat pump in which refrigerant circulates through copper tubing placed in the ground. It is a closed-loop, refrigerant-based geothermal system.
  Direct exchange geothermal heat pumps function similarly to air source heat pumps, according to the principles of vapor compression refrigeration, except they take advantage of the relatively constant ground temperatures, which are less variable than outdoor air temperatures. Ground temperature is cooler than the outdoor air temperature in summer – making for a better heat sink – and warmer in the winter – making for a better heat source. Direct exchange geothermal heat pumps are therefore more efficient than air source heat pumps. They are also quieter, more durable and require less maintenance since they don’t have any outdoor fan or outdoor coil. Furthermore, the uniformity of the underground temperature compared to the outdoor air translates into less stress on the systems.
  In direct exchange systems, the refrigerant exchanges heat directly with the soil through the copper tubing.
context_section_description: Direct exchange heat pumps are closed-loop geothermal systems which rely on small copper pipes (¼” to 1-1/8”) to exchange heat with the earth. The copper pipes are placed in the ground and form a ground loop – sometimes also referred to as earth loop or refrigerant loop - where the circulating refrigerant undergoes phase transition by exchanging heat with the ground: in heating mode it absorbs heat and changes from liquid to gas (evaporation), while in cooling mode it gives heat off and changes from gas to liquid (condensation).
  A direct exchange geothermal heat pump is a type of central heating and cooling system that functions similarly to a standard heat pump, according to the vapor-compression cycle.
  In the heating mode the ground serves as the evaporator. Liquid refrigerant coming - through the liquid line- from the heat pump’s indoor coil (serving as the condenser) is expanded and enters the smaller diameter tube of the ground loop. Heat is then transferred from the warmer ground to the ground loop. This leads to the refrigerant boiling to a vapor (evaporation) as it progresses through the loop. The refrigerant vapor then exits the ground loop and is returned -through the vapor line- to the compressor unit. Once in the compressor, the refrigerant is compressed to a higher pressure and temperature. The hot, superheated refrigerant vapor is now delivered to the indoor coil (condenser) where it gives off heat to the cooler building’s final delivery fluid with the assistance of the indoor circulator. As the refrigerant vapor gives off heat, it gradually condenses back to the liquid state.
  In the cooling mode the ground serves as a condenser. Superheated vapor refrigerant from the heat pump’s compressor is pumped -through the vapor line- into the larger diameter tube of the ground loop. Heat is then transferred from the ground loop to the cooler ground. This leads to the refrigerant condensing to a full liquid as it progresses through the loop, as shown in Figure 12. The refrigerant liquid then exits the ground loop and is returned -through the liquid line- to the indoor coil to be re-expanded to a lower pressure and temperature. This will enable it to absorb heat from the space to condition with the assistance of the indoor circulator. It will also enable it to dehumidify thanks to the indoor coil (evaporator) temperature being lower than the room temperature dew point. As the refrigerant absorbs heat while passing through the indoor coil (evaporator), the refrigerant evaporates and exits as a saturated vapor towards the heat pump’s compressor.
caption: Vapor Compression Cycle in DX Geothermal
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