Model development and performance analysis of Novel Shallow Ground Heat Exchangers

by Henk Witte – Groenholland

One of the key aspects of the EU GEOFIT project is the development of integrated engineering design tools for different types of ground heat exchangers. This toolkit provides design methodologies for vertical borehole heat exchangers, shallow horizontal and slinky type heat exchangers, and earth basket (spiral) heat exchangers.

Ground heat exchangers (GHEX) are used to provide a heat source or heat sink used for heating or cooling a building. They are typically constructed of plastic pipes installed in different configurations in the ground. A fluid is circulated in the pipes and the GHEX extracts heat from the ground (heating operation) or rejects heat to the ground (cooling operation).

For the validation of the analytical solutions used in the integrated engineering design toolkit, especially the new finite line source solutions developed for earth basket (spiral) heat exchangers laboratory experiments (figure 1) and detailed numerical simulations (figure 2) have been performed.

Figure 1. Experimental sandbox setup for earth basket (spiral) heat exchanger characterisation (foto: AIT)

The performance of a ground heat exchanger can be summarized to two key parameters:

  1. Pressure drop: A measure of the pump energy needed to move the fluid through the heat exchanger.
  2. Thermal resistance between fluid and ground: A measure of the thermal performance of the GHEX.
Figure 2. CFD simulation of earth basket (spiral) heat exchanger (foto: AIT).

The goal of the performance analysis is to identify key-design parameters affecting the overall system performance. Parameters investigated include:

  • Diameter of the earth basket (spiral) heat exchanger
  • Pipe diameter in relation to flow rate and pressure drop
  • Distance between adjacent rings in relation to total length and buried depth
  • Soil thermal parameters

Evaluation of the results of the performance analysis should take into account the actual effect on system performance. As an example, it can be attempted to reduce the thermal resistance in all cases as much as possible. However, the effect on performance is related to the actual heat rate of the system (figure 3). It is clear that with a low heat rate (5 W/m) the thermal resistance can be allowed to be high without affecting performance. These results will have implications for operating these systems during part-load conditions, which is important in view of the application of frequency-controlled compressors in the heat pumps. In this way, the results of the GEOFIT project not only provide designers with the tools to evaluate different types of ground heat exchangers in one integrated tool but also allows optimization of actual system operational control.

Figure 3. Relation between thermal resistance (fluid to ground) and energy performance degradation for different specific heat rates.


Meeng, C.L (2020). Development of an engineering tool for the design of novel shallow ground heat exchangers – GEOFIT. MSc Thesis TU Eindhoven.

Dörr, C.J. (2020). CFD Analysis of Ground Heat Exchangers. MSc Thesis Montan Universität Leoben, Austrian Institute of Technology.

Kling, S. (2020). Experimental characterization of Helix-Type Ground Source Heat Exchangers Configurations for Developing a Standardized Design Tool. MSc Thesis FH Burgenland University of Applied Sciences, Austrian Institute of Technology.

Marco Calderoni elected as New Chair of the RHC-ETIP

GEOFIT project coordinator, Marco Calderoni, was elected as new chair of the RHC-ETIP, the European Technology and Innovation Platform on Renewable Heating and Cooling. His mandate started on the 1st January 2021 and will run until the end of 2021. The RHC-ETIP represents stakeholders from the biomass, geothermal, solar thermal sectors, heat pumps, district heating and cooling, thermal storage and hybrid systems. It is, therefore, a unique ETIP covering all the renewable heating and cooling technologies.

Marco Calderoni takes over for Javier Urchueguía, RHC-ETIP Chairman in 2020. As key takeaways from his presidency period, Dr.Urchueguía pointed out the influential role of the RHC-ETIP to tip the balance of the budgetary distribution towards renewable heating and cooling. During his first meeting as Chairman of the RHC-ETIP, Marco Calderoni highlighted the potential positive impact of new alliances formed in 2020, such as the one with ETIP SNET and the Clean Energy Transition Partnership.

GEOFIT is already part of their project database and is now closer to the RHC Platform that it has been so far. Thus we can indirectly contribute to their work of maximising synergies and strengthening efforts towards research, development and technological innovation of Geothermal Energy within the European Union.

You can now read the full press release from RHC-ETIP here.

SIART and IDSGEORADAR Perform Structural Monitoring at Sant Cugat Pilot

From 27th to 31st July, SIART and IDSGEORADAR were at Sant Cugat pilot for structural monitoring, during the same week drilling works started. The goal was to perform structural monitoring before and during drilling, and see any impact in the school buildings.

IDSGEORADAR installed a Hydra-G system which monitored real-time measurements of sub-millimetric displacements in the administrative building and in the primary school. This system provides the high-accuracy and resolution radar technology. The system was accompanied by an optical and infrared HD camera providing real- time visual inspection of monitored area, draping radar data on a 3D model of the scene created using the radar system.

On the other hand, SIART installed several accelerometers in both buildings, administrative and primary school, to monitor vibrations before and during the first drilling carried out on 31st July. The goal of monitoring before drilling works is to know the building frequency, and see, once the drilling starts, if it has changed due to the vibrations propagation throughout the terrain. Once data has been captured, SIART will analyze them and present some results.

On the left: one of the accelerometers installed by SIART; On the right: Hydra-G system and camera installed by IDSGEORADAR.

Drilling Works Have Started at the Sant Cugat Pilot Site

On 31st July, Catalana De Perforacions (CDP) started the drilling works at the Sant Cugat demo site. The design of the geothermal field consists of 12 boreholes up to 120m deep and one Horizontal Directional Drilling (HDD).

Image 1: location of the 12 boreholes.

While drilling the first well, some problems with the ground material, mainly clays, and the groundwater level at depths beyond around 60 meters were faced. The borehole heat exchangers are double U PERC 100 SDR 11 PN16, with a diameter of 32mm.

On the other hand, on 3rd of August, the works related to the horizontal connection between the collection chamber and the plant room where the Ground Source Heat Pump (GSHP) will be installed, also started.

These works, including the geothermal field and the horizontal connection between the chamber and the plant room, should be completed on 31st August according to schedule.


Image 2: the second borehole drilled


Image 3: excavation of the collection chamber of the pipes coming from the 12 boreholes


GEOFIT: Stakeholders and Markets, a Commercial Approach

The stakeholders in a building retrofit project often are unfamiliar with shallow geothermal energy (SGE) technology and potentially have conflicting requirements [MUSE, 2019]. The following table shows the influence and interest of (in)directly involved stakeholders of typical SGE for building retrofit projects, in the framework of suggested management principles.

GEOFIT stakeholder matrix
Table 1. Preliminary GEOFIT stakeholder matrix

Building upon results of ‘sister projects’ such as the aforementioned MUSE, as well as GEO4CIVHIC and GRETA among others, GEOFIT takes a close look at the wide spectrum of SGE stakeholders in order to develop commercial-ready solutions. In order to gage SGE for building retrofit viability in Europe from a commercial standpoint, the typology of existing building stock is a critical factor. Therefore, one of the key images for this purpose comes from the Buildings Performance Institute Europe [1], shown below:

European Buildings at a glance

Another focus of GEOFIT Market Analysis is the sizing of market opportunities, defined by the specific technologies or ‘markets’ that together make up the full GEOFIT solution set. Initially investigated ‘markets’ include ground source heat pumps, heat exchangers, structural health monitoring,  geographic information systems, building information modelling, building energy management systems, architecture, engineering, and construction, horizontal directional drilling, project management software and services, heating, ventilation, and air-conditioning, and drones.


New Stakeholder Workshop in Austria – 8 May 2019

Stakeholder workshop
Geothermal Energy and Ground Source Heat Pumps In Austria:
‘The Geofit solution’

Join us for an open panel discussion on the status of geothermal energy in context with ground source heat pumps and how the GEOFIT project is using the latest geo technologies for energy and cost efficient building retrofitting.

  • Date: Wednesday 8th May 2019
  • Time: 17:00 – 18:30 Uhr
  • Venue: Giefinggasse 2, 1210 Vienna