What is shallow geothermal energy and why should you use it

Interest in renewable energy sources, green buildings and the reduction of greenhouse gases has been growing rapidly in recent years. And that’s great news!

One of such energy sources is shallow geothermal energy and it deserves more attention. It is a virtually unlimited source of energy-efficient heating and cooling that can be used by any building, regardless of its purpose.

It also has a whole bunch of other benefits, but let’s start at the beginning.

What is shallow geothermal energy and how does it work?

Shallow geothermal energy is one of the most convenient renewable energy sources, which is present almost everywhere in Europe.

Shallow geothermal energy is essentially the warmth of the Earth’s crust – from 1.5 meters deep all the way down to 300 or 400 meters deep. The heat originates from the earth’s core and is therefore the cleanest and practically inexhaustible source of energy.

The use of shallow geothermal energy relies on the constant temperature of the Earth’s crust. It doesn’t matter if it’s a freezing winter or a scorching summer outdoors, a wide layer of the Earth’s crust always has a temperature of around 13 °C. You have probably noticed this phenomenon when you went to the basement or into a cave – it is pleasantly cold in the summer and warmer than you’d expect in the winter. This layer of constant temperature starts around the depth of 3 meters. If we go deeper, the Earth gradually warms up and reaches 20 to 25 °C at a depth of 400 meters.

This difference between the outdoor temperature and Earth’s crust temperature is exploited by shallow geothermal systems. These systems, to put it very simply, “pump” the heat from the ground in winter and return cold to it, and vice versa in summer. Don’t worry, we’ll talk more about that soon.

But first, let’s take look at why you should think about taking advantage of shallow geothermal energy.

What are the advantages of using shallow geothermal energy?

1. A clean and renewable energy source

Shallow geothermal systems do not produce carbon dioxide emissions. This means that over the course of a year an average residential house reduces enough carbon emissions to equal removing two cars from the road. The impact is even bigger when it comes to larger buildings.

 

2. A reliable and safe source of energy

Shallow geothermal energy is independent of sun, wind or weather conditions and is available all year round. This is a huge advantage, as reliability is a burning issue when it comes to the use of some other renewable sources, such as the sun or the wind. Shallow geothermal systems are also safe, as there is no risk of carbon monoxide leakage or explosion.

 

3. Energy that cools and heats

Although shallow geothermal energy is usually associated with heating, hybrid systems make good use of it for heating as well as cooling. This results in significant savings throughout the year.

 

4. Efficiency and savings

Shallow geothermal heat pumps and hybrid systems typically consume 25% to 50% less electricity than most conventional heating and cooling systems. Not just that, their hardware is quite small, so they should also save you some space – especially if you install it in a larger building. 

Although installation costs are slightly higher, monthly heating and cooling bills are 40% to 50% lower (on average). When we combine these savings with our next point, it is clear that it is an investment that pays off.

 

5. Low maintenance and long service life

Shallow geothermal pumps and hybrid devices do not have many moving parts and are located inside the building, which means that problems and failures are very rare. Pumps typically last at least 20 years, and pipes often have a warranty of 25 to 50 years.

Hybrid devices are often automated to switch between winter, summer, and transition mode at the right conditions or time of the year.

Shallow geothermal energy potential of Europe

The ThermoMap below estimates the very shallow geothermal potential in terms of heat conductivity of unconsolidated underground up to 10m depth.

EU map of thermal conductivity (Source: Thermomap.eu, 2020)

As you can see most of Europe has quite high shallow geothermal potential. The deployment of shallow geothermal systems is thus mainly restricted by water protection regulations, not by its natural potential.  

Depending on parameters such as grain size distribution and humidity, the highest very shallow geothermal potentials were found in Liechtenstein, Finland, Iceland, and Norway. With over 50% of the respective country affected, Andorra, Montenegro and Slovenia have the highest values assigned with a limitation for very shallow geothermal exploitation. 

However, potential is now everything. Switzerland is one of the leading international players in shallow geothermal energy technology despite its fairly average potential. We can contribute the widespread geothermal heat pump installations in Switzerland to their geothermal awareness and extensive know-how.

How does a shallow geothermal energy heat pump work?

When using a shallow geothermal heat pump, you should use a system that is capable of:

• Heating by drawing the heat from below the Earth’s surface and distributing it throughout the building, while transferring the cold below the surface.
• Cooling by transferring and distributing the cold from below the earth’s surface throughout the building, while sending heat below the earth’s surface.
• Achieving optimal regeneration of the renewable source, which is especially important when it comes to larger heat consumption.

 

Each such system generally consists of three main parts:

• Collectors that use a heat transfer medium (e.g. water) to obtain energy below the earth’s surface. There are several different types of collectors that we’ll take a look at soon.
• A heat pump or a hybrid system to which collectors send the medium and where its energy is converted into usable energy that heats or cools the building.
• A distribution system which ensures that the building is evenly heated or cooled.

Shallow Geothermal Energy – Geothermal Heat Pump and Chiller + Energy Module and Hydraulic Module

Depending on the method of energy collection, we divide shallow geothermal energy heat pumps into closed and open systems.

Which system is the right choice for you depends on the composition of the soil, the presence of groundwater, substances in groundwater and more.

 

Open systems use groundwater as a medium and a heat source at the same time. They release the water back into the ground to the same water layer after they extract heat or cold from it. This allows an open system to utilize a powerful energy source for a low cost. 

However, the use of groundwater requires a source of groundwater, a suitable chemical composition of water (low iron content) and a well that reaches that water source. Therefore an open system requires more maintenance than a closed system. Groundwater suitable for heat pump use has between 3 and 14 °C – the closer to the golden mean the better.

In closed systems, the heat transfer medium circulates in a closed circuit and has no direct contact with the outside world. The medium is heated or cooled in collectors below the Earth’s surface and this energy is then transferred to the heat pump or a hybrid device. Closed systems can be horizontal or vertical.

 

Horizontal systems are the easiest to install, as the collectors are laid shallowly below the surface – they can be as shallow as 1.5 meters. The pipes are laid in parallel or spiral formation or in layers. Horizontal systems require a fairly large area, so they are only suitable for situations when there’s plenty of land around the building. This ground should not be covered by anything, as the solar heat that heats the ground is an important source of energy for horizontal collectors.

Vertical systems exploit the constant temperature of Earth’s crust we’ve talked about. They are usually at a depth of 15 to 180 meters. The temperature of the soil heats or cools the medium in the pipes, and the medium transfers this energy to the heat pump or a hybrid device. These systems are suitable for more densely populated areas, as they require very little space.

 

This is just the introduction to our series of articles on the use of shallow geothermal energy. We hope you can see why you should consider using it. Next month we will take a closer look at how heat pumps and hybrid systems work and compare water-air and water-water heat pumps.