TL;DR
- Geothermal power can be used to create electricity to heat homes, but here we are specifically talking about systems that directly use underground temperature to heat and cool buildings.
- Residential geothermal heating and cooling systems can have high up-front installation costs but offer a reliable and emissions-free alternative to fossil fuel-based systems that will eventually pay for itself.
- TL;DR
- HVAC energy demands
- Geothermal heating/cooling
- Components
- Cost for homeowners
- Challenges
- Opportunities
- Resources
HVAC energy demands
Half of all energy consumption in the EU goes towards heating and cooling buildings, and at the household level, 79% of total energy is used toward heating and hot water.
In the US, 51% of home energy costs are related to heating and cooling (70% if you add in hot water). The annual energy spending towards space heating by commercial buildings in the US is more than $27 billion. Most of this energy comes from natural gas, resulting in 161 million tonnes of CO2 emissions yearly (likely more today, as this data is from 2010).
Geothermal heating/cooling
Temperature varies widely from day to day, depending on the season and where you are in the world, but if you dig a few meters into the ground the temperature there is relatively stable. This is because soil slows down the movement of heat. So as the northern hemisphere moves into winter, the ground is still being heated by the summer, and as we move into the summer it is still being cooled by the winter.
With geothermal heating systems, we can tap into the stable underground temperature to essentially equalize building temperatures. This is done by digging into the ground to bury pipes containing fluid that absorbs the underground temperature and circulates it into the connected building above. According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps can be used by all building types and are “the most energy-efficient, environmentally clean, and cost-effective systems for heating and cooling buildings.” This is because geothermal heat pumps do not generate heat, they only harvest it.
The size of the system is very important because if the ground system is too small, it will likely fail, and if it is too large, will be unnecessarily expensive and less efficient. The size and depth of the borehole required will depend on factors like average ground temperature, heating requirements, and soil depth.
Geothermal systems can also be set up to heat multiple homes and buildings, this is called geothermal district heating. District heating uses a distribution network of pipes to provide heating and cooling to a large area, up to entire cities.
Reykjavik, Iceland, has the largest municipal geothermal district heating system in the world.
Components
- Geothermal loop: The underground pipes that carry fluid to the building.
- Open system: Pulls water from groundwater, cycles it through, and pumps it back into the aquifer. There are risks of contaminating the aquifer or having buildup from the aquifer entering the heating system.
- Closed system: Repeatedly cycles its own water (or some other liquid) through the system, removing the risk of contamination.
- Geothermal heat pump: This is what replaces a traditional furnace. Instead of producing the heat itself, this is moving heat from one place to another. Larger buildings will need multiple heat pumps (one per “zone”).
- Distribution system: Geothermal is compatible with forced air and radiators.
- Desuperheater: Not necessary for basic functioning. This is only if you also want to use geothermal with a water heater.
Cost for homeowners
Here are a few examples of the cost associated with installing geothermal heating for a family home. The price will depend on: location, size of the home, type of system, soil conditions, current home heating system, and accessibility of the location.
- US: $10,000-$45,000 (average = $25,000)
- The Inflation Reduction Act has extended tax credits available in the US for geothermal heat pump projects. If installed before 2033, a 30% credit applies. Homeowners are also eligible for energy efficiency rebates.
- UK: £24,000-£49,000
- The Boiler Upgrade Scheme launched in 2022 provides £6,000 off cost and installation of ground source heat pumps.
- Sweden: €15,000-€24,000 (€14,000-€21,000 after incentives)
Challenges
- High upfront costs: While ground-source heat pumps have lower operating costs, they require a larger initial investment than fossil fuel-based systems.
- Location issues: Some areas are too hot or cold for geothermal heat pumps to regulate building temperature, and the shallow subsurface temperature in urban areas may be higher due to the urban heat island effect. This can be a benefit during cold seasons but may make cooling in the warm ones more difficult.
Opportunities
- Financing: Geothermal represents a significant investment, and so there are opportunities to help facilitate the market and help homeowners secure financing, navigate tax credits, and even lease geothermal systems.
- Deeper drilling: When there is limited space for geothermal systems (like in urban areas), you can drill deeper into the ground.
- Building envelope optimization: Any form of heating will only perform well if the building is properly insulated.
Resources
- [VIDEO] Is Geothermal Heating and Cooling Worth the Cost? Heat Pumps Explained (Undecided with Matt Ferrell, Mar 2021)
- [VIDEO] Thermal response of borehole heat exchangers: modeling and experimental analysis - Mid-term seminar (Willem Mazzotti Pallard, Apr 2020)
- The heat beneath our feet (CTVC, Sep 2022)
- Geothermal energy at different depths for district heating and cooling of existing and future building stock (Romanov & Leiss, 2022)
- Long-term performance evaluation for deep borehole heat exchanger array under different soil thermal properties and system layouts (Cai et al, 2022)
- State of the Art, Perspective and Obstacles of Ground-Source Heat Pump Technology in the European Building Sector: A Review (Menegazzo et al., 2022)
- Ground source heat pump: Costs, plus all questions answered (Homebuilding & Renovating, Aug 2022)
- Don't look up? Look down. Geothermal could help curb climate change (wbur, Jun 2022)
- Use of energy explained: Energy use in homes (US Energy Information Administration, Jun 2021)
- How Much Does a Geothermal Heating System Cost? (Fixr, updated: May 2022)
- Geothermal heat pumps are among the most earth-friendly home energy sources, experts say (The Washington Post, Mar 2022)
- Performance evaluation of enhanced geothermal‑based desiccant cooling and heating systems for an office building (Hassanpour et al., 2021)
- The Earth itself could provide carbon-free heat for buildings (Vox, Nov 2020)
- Retrofit solutions for an historic building integrated with geothermal heat pumps (Carnieletto et al., 2019)
- Deep Boreholes for Ground-Source Heat Pump (Swedish Energy Agency, Dec 2018)
- Advances in Ground-Source Heat Pump Systems (2016)
- Chapter 2: Vertical borehole ground heat exchanger design methods (Spitler & Bernier, 2016)
- The ABC’s of Geothermal Heat Pumps (Nordic GHP, Jul 2015)
- Heating and cooling (European Commission)
- Renewable Space Heating (US EPA)
Last updated: Nov 2022