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How heat pumps work for geothermal heating and cooling?

In our blog post ‘About Geothermal Heating and Air’ in May we explained the three major components of a Geothermal System: The earth loop which warms water in heating mode and cools down in cooling mode, the air duct system in the house to blow warm or cool air into the house and the unit in between, the heat pump. Today we want to try and explain in layman terms, how such a heat pump works.

To start we need to remember, that heat flows naturally along the temperature gradient, from hot to cold. So a heat pump must overcome physics and transport heat from cold to hot.

Heat pumps accomplish this by using physics again: When a gas is liquified, lots of energy is stored in the then liquid and this energy is being released as thermal energy when the liquid is allowed to evaporate into the gaseous state. In heat pumps these gases/liquids are called refrigerants.

From here let’s quote a section of Wikipedia about mechanical heat pumps, paragraph Principle of Operation (modified/shortened for the purposes of this blog post)

Mechanical heat pumps exploit the physical properties of a volatile evaporating and condensing fluid known as a refrigerant. The heat pump does work on the refrigerant to make it hotter on the side to be warmed, than at the cold side where heat is absorbed.

The working fluid, in its gaseous state, is pressurized and circulated through the system by a compressor (4). On the discharge side of the compressor, the now hot and highly pressurized vapor is cooled in a heat exchanger, called a condenser (1), until it condenses into a high pressure, moderate temperature liquid. The condensed refrigerant then passes through a pressure-lowering device, the expansion valve (2). The low pressure liquid refrigerant then enters another heat exchanger, the evaporator (3), in which the fluid boils, evaporates and absorbs heat. The refrigerant then returns to the compressor and the cycle is repeated.

Pricipal function of Heat Pumps - Source: WikipediaA simple stylized diagram of a heat pump’s vapor-compression refrigeration cycle: 1) condenser, 2) expansion valve, 3) evaporator, 4) compressor.

In such a system the temperature properties of the refrigerant are extremely important as the compressed refrigerant in the condenser must be hot enough to heat and it must be cold enough after expansion to again absorb heat.

For the purpose of a geothermal heat pump the above process is designed reversible to allow for:

  • heating mode, absorb heat from the earth loop (evaporator) and make this heat available to heat the house (condenser),
  • and cooling mode, absorb the heat from the air in the house and dispose off in the earth loop.

Now we understand the principle of a heat pump, no miracle, just physics and a great design by the manufacturer to provide us the effectiveness we expect.

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