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Heat pump diagram

Heat pump diagram (valigursky, iStockphoto)

STEM in Context

Tapping Underground Energy with Heat Pumps

Lars Rose

Summary

Using the heat of the Earth’s interior, you can heat your home with a ground source heat pump. This kind of heating is cheaper and better for the environment!

How do you heat your home? Maybe you have electric heaters or a furnace. Maybe you even heat your home with a fireplace! But there’s another way to heat your home. You can use ground source heat pumps, or geothermal heat pumps. These are just two long names for a technology that can help people spend way less money on heating. They can also lower the environmental costs of heating. Here’s how ground source heat pumps work. 

What is a ground source heat pump?

The Earth's core is made up of a solid inner core and a liquid outer core. The outer core is liquid because the metals found there are so hot that they've melted. The inner core is solid only because of the huge pressure at the very centre of the Earth.

The Earth’s core is hot. But how hot is it? Scientists have calculated that the Earth's core reaches temperatures of more than 6 000 degrees Celsius. That’s about as hot as the Sun’s surface!

Thankfully, we Earth-dwellers are protected by thousands of kilometers of rock. This rock gradually gets colder closer to the surface of Earth’s crust. Otherwise, we’d get cooked! The rock acts like layers of insulation. Because of this, Earth’s surface is at a temperature where life can exist. But as soon as you start digging down into the Earth, the temperature starts to go up.

Temperatures inside the Earth range from over 6 000°C in the inner core to less than 2 000°C at the crust
Temperatures inside the Earth range from over 6 000°C in the inner core to less than 2 000°C at the crust (source of temperatures) (© 2019 Let’s Talk Science using an image by Original Mats Halldin Vectorization: Chabacano [CC BY-SA 3.0 via Wikimedia Commons).

How does a ground source heat pump work?

Consider how much Canadians spend heating their homes. Now consider the pollution released by power plants and furnaces. The idea of tapping the nearly unlimited source of heat just under our feet is tempting! But how do you get the heat from underground into the cold buildings where it can be used as heating?

This is where ground source heat pumps come into play. To build one, you dig down into the Earth. There, you lay a loop of pipe. You install horizontal loops just below the depth at which frost may occur. This is usually about 2 metres underground. You can also install a vertical loop. It will require a deeper hole. This will be more efficient, but will also cost more. There are often regulations that say where and how deep you can dig. These regulations are in place to avoid damage to water and sewage pipes, for example. Dig deep enough, and you may even need a mining permit!

House with horizontal looping on the left and with a vertical looping pipe on the right
House with horizontal looping on the left and with a vertical looping pipe on the right (© 2019 Let’s Talk Science using images by aurielaki via iStockphoto: left, right).

Next, fill a pipe with heat transfer fluid. That’s a special oil that is pumped through the loop. In particularly cold regions, the fluid may contain an antifreeze. The fluid travels several metres down through the pipes until it absorbs the heat from the earth. The deeper the pipe goes, the hotter the liquid can get. When the liquid completes the loop and flows back into the pipes that circulate through the building, the heat from the pipes can be transferred to the air, as well as to the water you shower and wash your hands with.

As the hot liquid in the pipe transfers heat into your home, it begins to cool. The cooled liquid is then pumped back into the ground for another round of heating. If less heat is required, less liquid is pumped underground.

Did you know?

Ground source heat pumps are by no means new. The first ground source heat pump system was theorized by Lord Kelvin in the 1850s. The first commercial systems were installed in the 1970s.

What are the pros and cons of ground source heat pumps?

Ground source heat pumps require electricity, so the heat energy they supply from the ground is not totally free. But it takes a lot less electricity or fossil fuels to operate ground source heat pumps than traditional electric heating systems or furnaces. This is good for the environment. It’s also good for people’s wallets!

So why aren’t ground source heat pumps more popular? Well, they do have one major con. They can be really expensive to set up. It costs between $20 000 and $30 000 to set up a ground source heat pump. That’s more than many brand-new cars cost! 
However, homeowners and businesses can save a lot of money over time by using this simple technology. 

Where are ground source heat pumps currently used?

Many cities already have buildings that use this environmentally friendly and economically sound technology. For example, Vancouver’s National Research Council buildings have been outfitted with a ground source heat pump. Many Canadian government programs encourage people to start using this type of heating. In some provinces, the government pays part of the costs associated with installing and replacing ground source heat pumps. In other provinces, the government provides loans to help people get set up. 

How are the buildings in your area being heated? Ask around. Maybe some of them are using ground source heat pumps!

Starting Points

Connecting and Relating
  • If you were building a house, would you build it with ground source heating? Why or why not?
  • Besides your home or school, what places would lend themselves to using ground source heating?
  • Do you know of anyone who uses ground source heating? Where do they use it?
     
Connecting and Relating
  • If you were building a house, would you build it with ground source heating? Why or why not?
  • Besides your home or school, what places would lend themselves to using ground source heating?
  • Do you know of anyone who uses ground source heating? Where do they use it?
     
Relating Science and Technology to Society and the Environment
  • How is ground source heating better for the environment than other methods of home heating? Explain.
  • What infrastructure challenges would installing a ground source heating system present?
  • Currently, installing ground source heating is much more costly than traditional heating sources. Should governments provide funding to make this technology more affordable? Why or why not?
     
Relating Science and Technology to Society and the Environment
  • How is ground source heating better for the environment than other methods of home heating? Explain.
  • What infrastructure challenges would installing a ground source heating system present?
  • Currently, installing ground source heating is much more costly than traditional heating sources. Should governments provide funding to make this technology more affordable? Why or why not?
     
Exploring Concepts
  • What type(s) of heat transfer is/are used in ground source heat pumps?
  • What would be the most important characteristics of the heat transfer fluid that is used inside the underground loop?
  • What geological features must people be aware of when digging wells for geothermal heating?
     
Exploring Concepts
  • What type(s) of heat transfer is/are used in ground source heat pumps?
  • What would be the most important characteristics of the heat transfer fluid that is used inside the underground loop?
  • What geological features must people be aware of when digging wells for geothermal heating?
     
Media Literacy
  • Do you think ground source heating companies can compete with oil, natural gas and hydroelectricity in terms of advertising? Explain.
     
Media Literacy
  • Do you think ground source heating companies can compete with oil, natural gas and hydroelectricity in terms of advertising? Explain.
     
Teaching Suggestions
  • This article can be used for Earth & Environment and Engineering & Technology teaching and learning related to Earth’s interior and heat transfer. Concepts introduced include ground source heat pump, Earth’s core, Earth’s crust, insulation and heat transfer systems. 
  • After reading this article, teachers could have student do a Concept Definition Web learning strategy for the concept of ground source heat pump. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [PDF] formats. 
  • To consider the STSE issues connected with this topic, teachers could have students consider the positive and negative aspects of using ground source heat pumps with a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 
  • To go further, teacher could have student use the Consequence Mapping learning strategy with the key question, “What would be the consequences over the next 100 years if every house in Canada received heating from heat pumps today?” Ready-to-use Consequence Mapping reproducibles are available in [Google doc] and [PDF] formats.
     
Teaching Suggestions
  • This article can be used for Earth & Environment and Engineering & Technology teaching and learning related to Earth’s interior and heat transfer. Concepts introduced include ground source heat pump, Earth’s core, Earth’s crust, insulation and heat transfer systems. 
  • After reading this article, teachers could have student do a Concept Definition Web learning strategy for the concept of ground source heat pump. Ready-to-use Concept Definition Web reproducibles are available in [Google doc] and [PDF] formats. 
  • To consider the STSE issues connected with this topic, teachers could have students consider the positive and negative aspects of using ground source heat pumps with a Pros & Cons Organizer learning strategy. Ready-to-use Pros & Cons Organizer reproducibles are available in [Google doc] and [PDF] formats. 
  • To go further, teacher could have student use the Consequence Mapping learning strategy with the key question, “What would be the consequences over the next 100 years if every house in Canada received heating from heat pumps today?” Ready-to-use Consequence Mapping reproducibles are available in [Google doc] and [PDF] formats.
     

Learn more

The Engineering Challenges of Renewable Energy: Crash Course #30 (2019)

This video (11:31 min.) from CrashCourse explores hydropower, wind, geothermal, and solar power, including their challenges, as well as how engineers are working to make their use more widespread.

The Core of the Earth (2014)

This video (2:38 min.) from the Science Channel, with host Bill Nye, examines the Earth's inner and outer core.

Infographic: The World's Deepest Gold Mine (2016)

This is visual from The Money Project looks at the geological and economic issues involved in operating the world's deepest mine.

References

Natural Resources Canada. (2017, March 27). Ground-source heat pumps (Earth-energy systems).

Renewable Energy World. (2008, September 9). Geothermal heat pumps.

Lars Rose

Lars Rose is a PhD candidate in high temperature Solid Oxide Fuel Cell research (that is sustainable energies), at the Department of Materials Engineering in the Faculty of Applied Science at the University of British Columbia (UBC), and at the National Research Council Canada, Institute for Fuel Cell Innovation (NRC-IFCI). He enjoys teaching fun stuff and is the current Media Relations and Human Resources coordinator of the outreach program Let's Talk Science at UBC. He enjoys writing science in a fun way for CurioCity, UBC Terry, the Science Creative Quarterly, Fuel Cell Today and Ubyssey.