Geothermal HVAC and Power

Before we dig into the pros and cons of Geothermal Energy, we have to understand a little bit about geothermal power. Geothermal Energy is using the energy in the ground to heat, cool or create electricity for our homes and businesses. It is a renewable resource – there is, effectively, unlimited energy stored within the ground we stand on. We harness this energy through steam turbines to produce electricity, or through heat pumps to heat and cool.

Geothermal Power for electricity production is done in one of a few ways. In rare situations (where there are naturally occurring geysers), the Earth is producing steam close enough to the surface that we can take that steam, run it through a turbine, and return the condensation to the ground.  This “dry steam” geothermal system is rare, since it is rare to have that hot steam close to the surface!

A much more common system for geothermal electricity production uses relatively hot groundwater – water which isn’t naturally steam – to produce electricity. The hot water is brought to the surface and de-pressurized, which causes it to “flash” into steam. That steam is run through a turbine and the condensate is returned to the ground. 

 

Geothermal Power to Electricity 

 

 

The third method of geothermal power to electricity is to use lower groundwater temperatures, and using a heat exchanger to convert that heat to another fluid with a low boiling temperature, creating a gas that can be run through a turbine and returned to the heat exchanger! The groundwater is returned to the ground.

On a smaller scale, individual buildings and neighborhoods can use geothermal energy to create domestic hot water, and to heat and cool their living and working spaces! These geothermal HVAC systems use some electricity to operate a “ground source heat pump”, where the heat from the Earth’s surface is multiplied to add heat to the building or used as a dumping ground for heat from the building. Using this heat pump cycle can create efficiencies of up to 500% – meaning you put in 1 kW of electricity and get 5 kW of heating or cooling. 

 

Who is using Geothermal Energy?

The most common use of geothermal energy currently is in “ground source heat pumps”, where a building will heat and cool their building with a geothermal HVAC system. These can be found in buildings all around the world, although due to their cost, they are more common in wealthier countries. 

For electricity production, there are large scale geothermal power plants used to create grid-scale electricity. These are generally used by utilities and power generation companies – and the USA is the largest Geothermal Power Producer in the world, followed by Indonesia and the Philippines. Smaller systems are in development for use in rural areas.

 

How does Geothermal Energy Affect the Environment

And how does Geothermal Energy compare to Fossil Fuels

 

 

Once operating, geothermal electricity production produces no greenhouse gases and uses minimal water compared to fossil fuel energy production. However, creating a geothermal electricity generation station can release some trapped greenhouse gases due to the drilling process (often drilling miles into the Earth), and can increase the risk of earthquakes nearby. 

This, along with the cost per kilowatt-hour of up to twice as much as coal, are disadvantages of geothermal electricity production. Compared to fossil fuels, geothermal energy has a very minimal effect on the environment – including harmful emissions, earthquake risk and future cost to our planet. So, although creating a geothermal electricity plant does cause some pollution, it is minimal compared to fossil fuels.

Geothermal HVAC has almost no disadvantages compared to fossil fuels except for first cost – a fossil fuel system will be 2-3 times less expensive up front than a geothermal system, but will likely cost less to operate. 

Both Geothermal Power for electricity generation and HVAC can have a long-term risk of over-cooling the part of the ground they are in, although most systems manage this risk through design.

 

What are the 3 main disadvantages of Geothermal Power

• First Cost! 
  • Whether we’re discussing geothermal power for electricity generation or geothermal heat pumps, these systems tend to be quite expensive compared to their traditional fossil fuel counterparts. Operating costs are much lower, so there is a payback, but it does require a significant investment up front.
• Emissions at Installation
  • Nothing is perfectly carbon-neutral, and that includes geothermal power. There are emissions produced in creating the concrete, pipes and metals used to build the systems. In electricity producing geothermal plants, some harmful gasses are released during drilling. However, compared to their traditional fossil fuel counterparts, geothermal energy produces far less emissions over the lifetime of the system.
• Earthquake Risk
  • This disadvantage only applies to geothermal electricity production, there is a heightened risk of earthquakes around the installation of a power plant. These are typically not particularly large earthquakes but can cause damage. Of course, compared to fracking natural gas, the earthquake risk is similar.

 

What are the 3 biggest advantages of Geothermal Power

• Operating Cost!
  • Although first cost is a disadvantage, these geothermal power plants and geothermal HVAC systems operate at a very low annual cost and per kWh cost, meaning there is almost always a payback on installing one!
• Lifetime Emissions
  • Harmful emissions may be released at start-up, but compared to the lifetime emissions, geothermal energy is a huge winner when compared to fossil fuels, especially if combined with generation from a renewable source such as solar power.
• Reliability
  • Geothermal heat pumps for HVAC and geothermal power plants tend to be incredibly reliable and long lasting – meaning less downtime, lower replacement rates and happier users.

 

Geothermal Conclusions

Geothermal energy definitely has some downsides – mostly related to first cost! However, long term, geothermal power for heating, cooling, electricity generation and even domestic hot water is a sustainable and reliable source of energy for our growing energy needs.

If a household or building pairs a geothermal HVAC system with a solar generation system, their entire building can be heated and cooled reliably without using any fossil fuel power!

 

Resources

1. https://www.nrel.gov/research/re-geo-elec-production.html
2. https://www.renewableenergyworld.com/types-of-renewable-energy/tech-3/geoelectricity/
3. https://www.renewableenergyworld.com/baseload/the-hidden-genius-of-geothermal-hvac-systems/
4. https://people.uwec.edu/piercech/210webs/renewable/geothermal.htm