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.

REFERENCES

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.

Novel particle-based drill modelling by LTU

Using numerical modelling for simulating manufacturing processes and predicting final properties is more or less mandatory in many industries. However, it is barely used within the rock drilling market despite being a powerful and cost-efficient method.

This is why GEOFIT will introduce a novel particle-based finite element method for modelling the drilling and excavation process. With this new approach, we aim to assist operators in choosing optimum drilling parameters and tools to reduce wear These simualtions will then be validated by comparing the outcome with the data from some of the pilots.

They key strength behind these simulations is their potential to simulate the rock fragmentation processes. The rock material will be mechanically characterized and finally the numerical approach will be validated by comparing the outcome with the data from some of the pilots.

In this video below you can see some of the numerical simulations developed up to date by the group at the Division of Mechanics of Solid Materials of Lulea University of Technology (LTU) for the GEOFIT project.

Still curious about our drilling innovations? Make sure to read EURECAT’s article on their work on Drilling Bit Materials for an Improved Performance.

Completion of Civil Works at Perugia

Civil works began on December 3rd, 2020 at the Perugia Pilot. At that time, partner IDSGEORADAR performed a ground-penetrating radar measurements survey. Meanwhile, partner R2M operated UAV flights with and without a thermal camera. And all throughout the drilling phase, partner UNIPG completed the Structural Health Monitoring (SHM).

After one week, the works completed the shallow excavations of up to 2.5 meters deep. This meant the area was ready for the 50 centimeters of the sand bed that increases the conductivity on the ground.

Later, on January 11th, the company in charge of the fieldwork started the installation of the slinky GHEXs that go 2 meters deep. It considers 5 parallel trenches, with 1.35 m of mutual distance, 24 meters of average trench length, and 53 rings for each trench.

After the GHEXs installation, on January 18th, GROENHOLLAND came to the Perugia Pilot to install the fiber optic cable (FOC) monitoring. This technology has a particular approach that allows remote checking of the new system’s performance while matting underground temperature.

To increase the innovative aspects and the scientific relevance, UNIPG installed on the first two trenches, two parallel tubes of a drip plant that allows experimental evaluations and comparisons that consider different boundary conditions and configurations, such as with varying ground hydration content.

Drip plant in the first two trenches.

Finally, civil works were completed on January 28th as soon as all the excavated area was backfilled with an additional 50 cm of sand. Also, the ground excavated material was reused on-site.

Backfilling the area with other 50 cm of sand.

Furthermore, all the heating/cooling system components: heat pumps, boilers, tanks, are available on-site. And today, FAHRENHEIT’s chiller also arrived at Perugia!

Presently, UNIPG is working to complete the whole installation by the end of March and to move forward with the commissioning of the system.

The GEOBIM Platform

In the GEOFIT project, heating and cooling components design and integration are developed for the different layouts and demo-sites and comprise a detailed design and description of the different subsystems or components to form a complete system.

Key elements and components, as well as their specifications, are being developed and inventoried as part of the GEOFIT project activities. As in previous work, the deployment of low-invasive risk assessment, site-inspection, and worksite-building monitoring techniques extend its use as a monitoring tool for geothermal based retrofitting operations and deploy novel tools enabling the view of assets in a cartographic or a geographical environment and comparing with the information stored into GIS collectors and the Web Map Services (WMS).

A common data environment containing GIS/BIM models/sensor data allows users to locate, map, update and share objects and subsurface utility information simultaneously, contributing to the realization of a new “GEOBIM platform”. The objective of the GEOBIM platform is to assess and verify the integration of the GEOFIT solutions in specific cases developing the respective different BIM models over a geographical information layer, aiming at replication and modularity of the solutions, outputs for exploitation, impact assessment, and dissemination of the results.

The implementation of the previously defined system is addressed for buildings with different typologies and energy demands. Then, integration of the conditions and the building’s engineering specifications are defined within the GEOBIM platform.

The GEOBIM platform considers the scalability and flexibility of the data integration and analysis tools development to support interoperability among the elements installed. The design inputs come from:

  1. Boreholes and ground excavations information
  2. Geothermal heat exchangers designs
  3. Ground source heat pumps designs
  4. Heat pumps designs
  5. Heating and cooling systems designs
  6. Sensors information
  7. Simulations data

By covering the 7 dimensions of the #BIM approach, the GEOBIM platform implements the following functions:

  • Project visualization
  • Data management
  • Demo-site analysis functions
  • Geothermal performance
  • Heating/Cooling performance
  • GEOFIT assets management
  • CAPEX
  • The lifecycle of systems and assets

Within the GEOBIM platform development (understood as a common data environment), model-based cooperation is the advanced portrayal of the general GEOFIT development process. This portrayal is made in collaboration with the different partners involved in the design, modeling, construction/fabrication, installation, and commissioning, who utilize different CAD-based tools. The Common Data Environment (CDE) is characterized as a typical advanced task space, which gives very much characterized collaborative territory to the undertaking partners joined with clear status definitions and a strong work process portrayal for sharing and endorsement forms and objects data.

Written by Sergio Velasquez, from IDP

Want to learn more?

Click on this link to have a look a the 10 Geobim videos posted on the project’s Youtube channel and thank you for watching!

Videos produced by COMET

Ground Penetrating Radar Analysis at Perugia

On the 6th of October, IDS GeoRadar was at the pilot in Perugia to perform a Ground Penetrating Radar (GPR) survey over the area where excavation works will be executed. 

Nowadays, GPR is commonly used to detect both metallic and nonmetallic underground objects, as well as providing 3D location, reporting depth, and “X,Y” location.  

However, this technology has some drawbacks. Mainly, that it requires an expert, typically a trained geophysicist, to interpret the scans. In GEOFIT this issue was addressed and an algorithm, capable of detecting most of the buried utilities, has been developed. 

At Perugia, IDS GeoRadar used a recently developed compact GPR array solution designed to provide a 3D mapping of underground utilities. This is called STREAM C and uses a massive antenna array with two polarizations that provide a huge amount of data, thus dramatically increasing the detection performance and the level of accuracy of the survey.  

The analysis of the collected data will therefore allow avoiding damages to the buried infrastructures when performing the excavation for the heat-exchanger installation.