Shallow geothermal systems: how to exchange heat with the ground?

Shallow geothermal systems

Several technological solutions called Ground Source Heat Pumps (GSHPs) are available for shallow geothermal systems. What do they do? Most of all, they transfer heat between underground and residential, industrial or commercial buildings.

Since GSHPs are conceived to extract and/or inject heat from/into the ground during winter and/or summer, several technological solutions exist. As a result, two main categories of GSHPs are commonly adopted, the so-called open loop and closed-loop systems.

Open loop systems consist of using groundwater as heat carrier fluid. At first, extraction of water from the ground occurs. Then, the fluid reaches directly the heat pump remaining in contact with the surrounding environment. Closed loop systems, instead, use water or a mix of water and antifreeze as heat carrier medium. This medium circulates inside borehole heat exchangers (BHEs) or collectors, so it is physically separated from the surrounding rock/soil/groundwater.

Ground Source Heat Pumps, open loop, closed loop

Ground source heat pumps system: an overview (modified by VIGOR Project )

Generally GSHPs consist of three main parts the heat exchanger, the heat pump unit and the heat distribution system.

The first is for extracting heat from the ground towards the heat pump unit. Then the second raise the temperature of the fluid circulating in the pipes, transferring heat between ground and building. Finally, the third distributes the heat inside the building.

Here you can find a short video created under the European project ReGeoCities and the initiative The Heat Under Your Feet ().

It is really well done and summarizes what is a shallow geothermal systems!


Closed loop systems

Closed loop systems are divided in vertical and horizontal systems.

The former, called also borehole heat exchangers (BHEs), is generally used up to hundreds of meters deep. In this case, the available installation area is reduced and low landscape disturbance is required. However, the installation costs for drilling operation are quite expensive. The latter, instead, preferred when the area at disposal is consistent, is economically advantageous. In fact the costs for trenching are definitively lower than for drilling. Several configuration for horizontal heat collectors includes plain and spiral collectors, used generally between 1 to 2 meter deep. However, the special forms (i.e. heat basket, helix systems etc…), are able to reach also a maximum depth of about 10 meter.

The horizontal closed loop systems exploit the very shallow geothermal energy resources. As clarified by ThermoMap Project, solar radiation, annual air temperature variation and ground thermal properties directly influences these resources.


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