Geothermal heating and cooling
Geothermal heating and cooling

Geothermal heating and cooling

Tags

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.

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.

Source:
Source: Now You Know, Aug 2020

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.

Source:
Source: Energy.gov

Reykjavik, Iceland, has the largest municipal geothermal district heating system in the world.

⚠️
In July 2022, the US Department of Energy announced it will award $300,000-$13M in funding for up to 10 projects that can expand community-scale district heating and cooling.

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.
      • Source:
      Source: energy.gov
  • 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.

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

Last updated: Nov 2022