In a geothermal heating system heat is taken out from underneath the earth surface from the soil or ground water or sometimes surface water. This heat is then compressed and pumped into your house via air heating or underfloor heating.
Pipes are installed underground to capture a near constant temperature underneath the ground. The pipes are filled with a refrigeration liquid, that once it heats up becomes a gas and is then pumped into the heat pump. The heat pump further compresses the hot gas, making it even hotter. The heat can then be either blown into the house via air or be transferred to water and pumped around the house via a central underfloor heating system. Geothermal systems are more efficient than your regular outdoor unit heat pump, but they are also more expensive. The reason they are more efficient is that they capture warmer temperatures during winter times.
In the central underfloor heating system of geothermal heating the heat of the gas is now transferred into the heating system.
The reason for an underfloor heating system used with water is simple: the heat generated from below the earth and compressed gas does not heat water to the required 55 or more degrees Celsius required for convector or radiator heaters to heat your home. Instead, it is closer to heat the water to the about 38 degrees Celsius which are warm enough in a large area as in underfloor heating to heat your home, but not too hot for you to burn your feet as you walk barefoot on a warm floor.
You might be able to secure funding towards your heating system in New Zealand. Check the below link for free to access your eligibility.
Advantages of geothermal heating:
A free and renewable resource is used to heat the home, as it is a heat transfer from the earth to your home
It is the most reliable source of renewable energy, having no outages or shortages
The operating cost is very low
No large outdoor unit like in an air heat pump as the condense water is under ground
Hot water tanks can be also connected to geothermal, utilising free energy
Disadvantages of geothermal heating:
Though it runs incredibly cheap, the set up costs tend to be higher than other systems once pipes are included
An outdoor area is required that has the right size to get enough heat out for you- otherwise you will need a backup system
The compressor housing and often even the pipes are made of plastics, sadly not recycled resources which could be done
Electricity for pumps, controller and compressor is still required