Tapping underground energy with heat pumps

Lars Rose
9 June 2014

Above: Heat pump diagram (© istockphoto.com/valigursky)

Ground source heat pump and geothermal heat pump are two excessively long names for a nifty technology that can greatly reduce the financial and environmental costs of heating homes and businesses. Sound good?

Did you know? Scientists have calculated that the Earth’s core reaches temperatures of almost approximately 6300 degrees Kelvin, or more than 6000 degrees Celsius. That’s as hot as the surface of the sun.

Here’s how ground source heat pumps work. The Earth’s core is hot. How hot is it? It’s so hot that all the rocks and metals found there are mixed together in a continuously glowing glob. The core remains solid only because it is under immense pressure.

Thankfully, we surface dwellers are protected by thousands of kilometers of rock that gradually gets colder as you move toward the Earth’s crust. Otherwise, we’d get cooked. These layers of insulation are thick enough to cool the surface down to a temperature where life can exist. However, as soon as you start digging down into the Earth, you immediately encounter a rise in temperature.

When you consider how much Canadians spend heating their homes and 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’s needed?

This is where ground source heat pumps come into play. Essentially, you dig down into the Earth and lay a loop of pipe. Horizontal loops are installed just below the depth at which frost may occur (usually 2 metres). In the case of vertical loops, a deeper hole means more efficiency but also more cost. Furthermore, there are often regulations governing where and how deep you can dig, to avoid damage to water and sewage pipes, for example. Dig deep enough, and you may even need a mining permit!

Did you know? Temperatures can vary greatly in mines, from balmy warm near the surface to sauna hot deep underground. In South Africa’s Mponeng Mine, air temperatures can reach 66 degrees Celsius at a depth of 3400 metres.

Next, the pipe is filled with a special oil, called heat transfer fluid, which is pumped through the loop. The fluid takes the heat from the ground and moves it into the building. In particularly cold areas, it may contain an antifreeze, such as ethanol, methanol, ethylene glycol, propylene glycol, or calcium chloride. Several metres down, the liquid begins to get heated by the Earth. The deeper it goes, the hotter it gets. When it completes the loop and comes back into the building, it can be used to heat the air as well as the water you shower and wash your hands with.

As it transfers the heat it collected underground, the liquid in the loop cools. It’s then pumped back into the ground for another round of heating. If less heat is required, less liquid is pumped underground.

Ground source heat pumps are by no means new. The Ground Source Heat Pump Association claims that the first system was installed by Lord Kelvin in the 1850s. The first commercial systems were installed in the 1970s, with continuous improvements in efficiency ever since.

Did you know? Under the right circumstances, heat can be extracted from the air. Air source heat pumps can operate in temperatures as low as -25 degrees Celsius!Today, high initial set-up costs are one important factor in why heat pumps are not more popular. However, it is important to remember that this simple technology can provide homeowners and businesses with significant savings over time.

Many cities already have buildings that use this environmentally friendly and economically sound technology. In Vancouver, for example, the National Research Council buildings have been outfitted with a ground source heat pump. Government incentives, such as the LiveSmart BC program, which pays part of the costs associated with installing and replacing heat pumps, help encourage adoption.

Ground source heat pumps require electricity to operate, so the heat energy they supply from the ground is not totally free. However, the amount of electricity or fossil fuels required is much lower than with traditional electric heat or furnaces, which is good for both the environment and homeowners’ wallets.


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.

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