Geothermal heating comes in two flavours: ground source heat pumps for individual buildings, and deep geothermal for district heating networks. Both provide efficient low carbon heat. This guide covers both.
Two very different scales
| Type | Depth | Application |
|---|---|---|
| Ground source heat pump | Under 200 metres | Individual buildings |
| Deep geothermal | 1 to 3 km | District heating networks |
| Direct use (shallow) | Tens of metres | Greenhouses, aquaculture |
Ground source heat pumps
A ground source heat pump moves heat from the ground into a building in winter and reverses direction in summer. Buried pipes carry heat exchange fluid between the ground and the heat pump. Uses grid electricity to drive the pump but delivers 3 to 5 units of heat per unit of electricity.
Configurations
- Horizontal loop. Trenches 1 to 2 metres deep. Large land requirement.
- Vertical loop. Boreholes 100 to 200 metres deep. Compact.
- Pond loop. Coiled pipe in pond or lake. Cheap if water available.
- Open loop. Draws groundwater directly. Very efficient but requires suitable aquifer.
Deep geothermal for district heating
Wells drilled 1 to 3 km deep tap warm formation water (60 to 100 degrees C). Water is pumped up, heat extracted for district heating, and cooled water reinjected. Used at Paris, Munich, Copenhagen, and Iceland.
Global scale
Efficiency
Ground source heat pumps deliver COP (coefficient of performance) of 3 to 5. This means 3 to 5 units of heat delivered per unit of electricity consumed. Air source heat pumps typically 2 to 3 COP. Deep geothermal district heating has very high thermal efficiency.
Cost economics
| Application | Typical cost installed |
|---|---|
| GSHP home 3 to 5 ton | USD 15,000 to 35,000 |
| GSHP light commercial | USD 60,000 to 300,000 |
| Deep geothermal district | USD 20 to 60 million per project |
Payback
GSHP payback typically 5 to 12 years when replacing electric resistance or oil heat. Longer when replacing natural gas. Deep geothermal district heating pays back 15 to 25 years.
Climate benefits
Ground source heat pumps offer heat with 50 to 70 percent less emissions than gas heating (depending on grid mix). Deep geothermal district heating is essentially zero emissions in operation.
Policy support
US IRA tax credits for GSHP installation. EU Renewable Energy Directive recognises heat pumps. UK Boiler Upgrade Scheme. Various regional incentives.
Notable deep geothermal district heating
- Paris basin: multiple sites at 60 to 80 C.
- Munich: Riem, Sud fields at 90 to 130 C.
- Copenhagen: 76 C from 2.5 km depth.
- Iceland: essentially all district heating.
- Netherlands: several greenhouse and district heating projects.
- New York City: exploring for future.
Contemporary challenges
Where geothermal heating is going
- GSHP scaling with electrification.
- Deep geothermal district heating expanding in Europe.
- Networked geothermal (fifth generation district heating).
- Retrofits of urban heating systems.
- New building code requirements.
Frequently asked questions
What is GSHP?
Ground source heat pump. Moves heat between building and ground.
Is it cheaper than gas?
Higher upfront, lower operating cost.
How efficient?
3 to 5 units heat per unit electricity.
Does it work in cold climates?
Yes very well. Ground temperature stable regardless of air temperature.
How long do systems last?
Ground loop 50+ years. Heat pump 20 to 25 years.
What is deep geothermal heating?
Well systems tapping warm formation water for district heating.
Where does deep geothermal heating work?
Paris, Munich, Copenhagen, Iceland, and increasingly across Europe.
Are there incentives?
Yes in US, EU, and many state programmes.
Can we retrofit an existing home?
Yes but land space for loop is required.
Where can I read more?
IGSHPA, ASHRAE, national heat pump associations.
Summary
Geothermal heating comes in two scales: shallow ground source heat pumps for individual buildings and deep geothermal for district heating. Both deliver highly efficient low carbon heat. GSHPs pay back in 5 to 12 years vs high heating costs. Deep geothermal district heating supplies significant heat in Paris, Munich, Copenhagen, and Iceland. Growing role in decarbonising heating globally.
Next reading
- Geothermal energy explained
- District heating
- How geothermal power plants work
- Browse the UtilityRadar directory
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