Keep Cool Primer #0001: Geothermal Energy and Heat Pumps

Geothermal energy and heat pumps

If you dug a hole deep underground, you would find that it’s pretty hot . Even if you dug just a few feet underground, temperatures start to get much less variable than above ground. Where does this heat come from? I hadn’t thought about it in a while either, but the Earth’s core is as hot as the sun. It’s a renewable energy source just like wind and solar. It’s just hard to harness at scale. If we could harness even a fraction of the energy produced underground, the Earth’s core, like the sun, would produce far more than enough power for than we could regularly use.

While we’re a long ways away from being able to harness even a tiny fraction of the Earth’s geothermal energy, there are systems that can both produce electricity from geothermal and leverage the reserve of heat that exists underground. Some countries like Iceland are blessed with highly specific geology (e.g. hot hydrothermal water sources) that can be used to generate electricity in 
‘traditional’ geothermal energy plants. Icelanders generate about a quarter of all their electricity from them.

Meanwhile, the most common geothermal systems in use today don’t produce electricity. Instead, they pump heat from underground into buildings, or pump heat out of buildings into the ground (for cooling). In fact, geothermal heat pumps have been in use 
since World War II

How do geothermal heat pumps work? If you recall your high school physics class, heat wants to move ‘downhill’; if it’s hotter in one place than another, the heat will move towards the colder area. Heat pumps take advantage of this dynamic to transfer heat around. To dig a step deeper, they use 
ground loops, i.e. series of pipes underground where the temperature is constant. The ground loops circulate water to absorb heat from the ground and move it.

While not the talk of the town, geothermal heat pumps can be more efficient than other heating and cooling appliances. This efficiency is good for the grid, and can also help cut down on emissions from electricity generation. Perhaps more impactfully, it’s also certainly a greener way to heat your home than burning fossil fuels. These systems don’t produce energy; they’re still connected to the grid, and aren’t 100% emissions free until the grid itself is. 

Geothermal heat pumps can be used in a variety of different types of buildings. Residential is the low-hanging fruit so-to-speak, but heat pumps can be scaled to service commercial buildings, and 
even high-rises. This does come with another caveat; the larger the building, the more important the energy mix that powers the heat pumps. If the electricity used to power the pumps isn’t ‘green’, the emissions intensity of heating and cooling the entire building can add up quickly and start to rival those of other heating and cooling systems.

Beyond heat pumps, you can explore more on the different types of geothermal energy systems in this 
video (h/t to Mehrad for the source).

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