Geothermal Heat Pump: How Does It Work

Today, geothermal energy is probably one of the least talked about forms of renewable energy. And yet, we have utilized it to power everyday operations since the 1940’s [1]. Geothermal energy uses the earth’s high temperatures for heat particularly during winter and it can also use the earth as a heat sink for cooling in the summer [2].

Apart from it being a tried and tested technology, it is much more efficient compared to other forms of renewable energy. Specifically, geothermal heat pumps can provide clean heating and cooling without producing any noise or disrupting the landscape and also cut your energy bills by up to 70 percent [3].

It therefore makes sense that geothermal energy is used in all 50 States in the United States, with 80,000 units installed each year. About 27,000 units are installed in Sweden every year and geothermal heat pumps were the heating system of choice for new houses in Finland, their market share exceeding 40 percent between 2006 and 2011 [2].

How does a geothermal heat pump work?

A geothermal heat pump, otherwise known as a ground source heat pump, uses the heat that is found underground by pumping water through it. Depending on your geographical location, ground temperatures will range from 7 to 21 degrees Celsius (45 to 70 degrees Fahrenheit). Just like a cave, this (under)ground temperature is warmer than the air above it during the colder months and then cooler during the summer months [1].

The heat pump can then increase the temperature and use it to heat your home or water. It runs on electricity but it uses much less electricity compared to what is needed to produce that heat. It works very much like a boiler but the heat pump uses air from the ground rather than burning fuel to generate heat.

In terms of energy use though, a heat pump with mid-range efficiency uses only a third of the energy needed by a boiler to produce the same amount of heat [4].

Geothermal system components

A geothermal heat pump includes the following components: what is called a “ground loop” which is essentially a set of interlinked water pipes which are buried underground and a heat pump which is installed at ground level. Some space is needed to install this technology; this must also include a way for digging machinery to access this space.

The size of the ground loop depends on the size of your house as well as how much heat you will need. The greater the size of the loop, the more space the heat pump requires, so that is a further consideration you need to take into account if you are considering whether to install a geothermal heat pump [5].

Components of a geothermal heat pump

The heat pump consists of:

• an evaporator
• a compressor
• a condenser

A mixture of water and anti-freeze is pumped though the ground loop network of water pipes which are underground. The heat pump then pumps out this water mixture and extracts the heat from it so it can be transferred to your home heating system, at the same time increasing the temperature.

What is great about a geothermal pump is that it can increase the temperature quite substantially – between 1.5 and 4 times. This means that if the water extracted from the ground is 12 degrees Celsius (54 degrees Fahrenheit), this can reach anywhere between 18 and 48 degrees Celsius (64 to 118 degrees Fahrenheit) [5]. The water can then be used for taking hot showers and baths while the heat can be sent to radiators.

The leftover heat can be stored in hot water cylinders and used later on [5]. The direction of the water mixture determines whether the heat is moving into the house or being pulled out of it to lower temperatures [3].

Advantages of geothermal heating pump system for your home

A geothermal heating pump system can be a great solution for keeping your house warm during the winter months but also cooling it down during the summer. It has a low carbon impact, uses a natural source of heat and can help lower your energy bills.

So if you are still a bit skeptical about whether installing a geothermal heating pump system is worth investing in, here are some advantages that might help you make up your mind!

#1 Geothermal heating pumps save money

By installing a geothermal heating pump you can save money. Getting a geothermal heating pump will cost you around $15,000–$20,000, including installation costs, ground loops, heat pump, and controls [3].

#2 Governmental incentives

While this is a substantial upfront investment, most countries provide incentives to make it easier for citizens to install such heating pumps.

For example, in Canada there is a $3,500 federal grant, in the U.K. the government has put in place a “Renewable Heat Incentive” scheme which provides payments between £2,500-4,000 to households opting for heat pumps.

In the United States, there is a standard federal tax credit [3].

#3 Return on investment

Even without those government incentives, you can see a return on your investment quite swiftly. A study conducted by the Air Force Institute of Technology estimated that it takes 7-8 years to recoup costs [3].

Similarly, the UK’s Energy Saving Trust calculated that a geothermal heating pump, or a ground source heat pump as it is also known, can help you save between £410 and £2,000 each year, depending on which existing heating system you would be replacing [4].

If you want to find out how quickly you will be able to make up for your investment, speak to an experienced installer who can conduct a more expert calculation based on your heating system, energy needs, geology and other parameters.

#4 High efficiency of geothermal heat pumps

Geothermal energy heat pumps are also considered a more efficient way to heat your home. Even though you still need to use some electricity to power your ground source heat pump, you get a lot more energy for every of unit of electricity you pay for – specifically you can get up to four unit of heat more compared too other ways of heating [4].

This brings about an up to 70 percent decrease in your heating and cooling bills [3].

#5 Efficient cooling of your house

A geothermal pump is also more efficient when it comes to cooling your home too. An air-source heat pump takes the heat from your home and transfers it outside, but when the air is hot outside this becomes more difficult. So at the time when the air-source heat pump needs to perform at its best to cool your house effectively, it is much less efficient.

A geothermal pump however relies on underground temperatures which are cooler compared to ambient air during the summer months [6].

The geothermal heat pump delivers a more efficient heating and cooling system while eliminating noisy outdoor compressors and fans.

#6 Low greenhouse gas emissions

Lastly, but certainly most importantly, a ground source heat pump emits much less CO₂ compared to conventional heating systems. This is because they rely on ground temperatures, require less electricity and are an efficient heating and cooling system [4].

The pros and cons of geothermal heating on the environment

• Sustainable and renewable source of energy

Geothermal energy is entirely sustainable and steady. Wind and solar can both be finicky, changing with the seasons or even day to day. Geothermal doesn’t do that. It stays consistent no matter what the weather is doing, which is a huge factor when it comes to supplying the energy needs of an entire nation.

The only things that will change our ability to generate geothermal energy is when the earth shifts. We can account for minor shifts, like settling, better than we can for weather changes.

• Reliable and accessible for many

You might not be able to put a geothermal plant in your house, depending on where you live, but you can probably get one in your area. If you live in an area where you’re able to dig down into the ground, you can use geothermal.

Hot spots like in the Midwest have geothermal springs and steam beds closer to the surface, which makes it easier for companies and individuals to reach them.

In those areas, geothermal has been put to a variety of uses. Homeowners are offered incentives, including up to a 30 percent tax credit for installing geothermal in their homes. Some cities are pioneering it to melt ice and snow off pavements, making travel safer during the winter and reducing the need for salt and soot, which can be harmful to the environment.

• Requires excavation

One big issue with geothermal is that it’s not readily available like wind or solar. You have to dig down and find it, and that makes it harder and more cost prohibitive than others. Many homes can do it because they’re built on solid ground, but the project is expensive and not easy to do.

Creating a geothermal plant is much more efficient since you can disrupt one area to generate substantial amounts of power.

• Uses up local water resources

One of the primary methods of using geothermal energy is to run water underground and let it heat up, then use that increased energy to generate power. The other way is to tap into underground reservoirs of heated water or steam.

In either situation, the power generation is coming from water. Estimates have put geothermal plants as using between 1,700 and 4,000 gallons of water to produce one-megawatt hour of electricity. With dwindling water supplies, that’s an issue.

• Region prohibitive

Geothermal energy is more accessible in some areas than it is in others. If you live near Yellowstone National Park, you won’t have to work too hard to get plenty of geothermal energy, and nothing you or your family do will use it up. Out on the East coast in, say, Manhattan, you’ll have to do a lot more work.

Not only is the water level much higher, making it difficult to go deep enough to reach the heat source, but the structure of the city means you just can’t do it. Everywhere in the city, you have subways and sewers, and even they are already below the water table.

The solution is to have enough geothermal plants that the energy can be created in those zone specific areas and moved around the country. That requires an extensive network that we don’t have, and it would take years to set it up.