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Model development and performance analysis of Novel Shallow Ground Heat Exchangers

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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.

We end May with our 7th General Assembly!

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The GEOFIT consortium successfully held its 7th Virtual General Assembly on May 20 and 21 2021, our first GA for 2021! The meeting was organised online in two intense half-day sessions during which work package leaders where able to present the progress made with the core technologies, demonstration activities and coordination work packages.

Kicking-off our 7th meeting!

The first-day session started with a focus on the state of the art of technical work packages (WP). Lead by our colleagues from IDS Georadar, Groenholland, AIT, and Nuig Galway, we got to review WP2 which focused on-ground research, worksite inspection, and improved drilling technologies, and wrapped up its work last April 2021. The presentations for WP 3, 4, and 5 presented the different advances made with our Shallow Ground Heat Exchangers, Heat Pumps, system integration and efficiency management. After a short coffee break, we had the presentation of the progress of pilot implementation. In this sense, we were celebrating the commissioning of our first pilot site in Perugia, an important milestone for the project! Our Bordeaux pilot has also taken important steps in the past months when it comes to drilling.

The GEOFIT Team

On the second day, we were able to review the advances made on our GeoBIM platform and the standardisation, exploitation, and communication activities and R2M started an open discussion on possible business cases, UNE presented different approaches to the standardisation language including the CWA and COMET updated on the most recent events and the new website design and materials.

The meeting wrapped up with high hopes that next time we might meet again in person and with a clear view of the next steps that will be taken by all partners during the next 6 months.

Structural Building Monitoring in the Drilling Phase

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By Lucia Faravelli – SIART

The EU GEOFIT project comes with the goal, among others, of linking three main characters: the geothermal technology promoter, the excavation and drilling operator and the structural engineer. Within a geothermal based retrofitting of existing buildings, the first actor designs the geothermal system and dictates the main data to the excavation (drilling) works responsible. The latter one relies on earth moving machines that transfer vibrations to the soil and from here to the target building. The third character has the main role of supervisor that no damage affects the building during the plant installation.

The simplest policy would be to instrument the site and the building and to carry out a structural monitoring in the drilling phase. Currently artificial intelligence tools able to detect the incipient damage are not available. In other words, the deployed devices will only be able to detect and locate damage when this has already seriously progressed. The alternative feasible architecture goes across the knowledge of the excitation source, the identification of the vibration propagation across the soil and the understanding of the so-called building signature, i.e., the building own frequencies. The trick is to avoid amplifications in the pattern from the source to the building of those frequencies to which the building is sensitive. Along this path, the role of structural monitoring will simply be that of checking that the recorded (accelerometric) signals will confirm the numerical models.

Fig. 1 – Drilling activities at the Sant Cugat pilot

Knowledge of the excitation source. Figure 1 above, shows the drilling machine of one of the GEOFIT partners. Figure 2 below is the plot of the vertical component of the acceleration as recorded by an accelerometer on the machine. Finally, Figure 3 gives a plot of the same vertical component of the acceleration as recorded by an accelerometer on the soil nearby the machine. It is worth noticing the differences between the two ranges of intensity.

Propagation across the soil interface. The phenomenon is covered by reliable scientific software adopting sound mechanical models [2]. The role of the monitoring is to confirm that the recorded output is consistent with the model. In other words, there should not be amplification in the frequencies to which the building is sensitive. Building signature. This aspect can easily be solved by carrying out the structural monitoring in a pre-drilling stage [3].

Fig. 2 -Vertical component of the acceleration as recorded on the drilling machine (time in
seconds; intensity in V; conversion 1V = (1/2.5)g). Zoom on the right.
Fig. 3 – Vertical component of the acceleration as recorded on the soil near-by the drilling
machine (time in seconds; intensity in V; conversion 1V = (1/2.5)g). Zoom on the right.

References

[1] Casciati S.; Chen, Z., A multi-channel wireless connection system for structural health monitoring applications STRUCTURAL CONTROL & HEALTH MONITORING Volume: 18 Issue: 5 Pages: 588-600 Published: AUG 2011

[2] Casciati, F.; Faravelli, L.Dynamic transient analysis of systems with material nonlinearity: a model order reduction approach SMART STRUCTURES AND SYSTEMS Volume: 18 Issue: 1 Pages: 1-16 Published: JUL 2016

[3] Casciati S., Stiffness identification and damage localization via differential evolution algorithms, STRUCTURAL CONTROL & HEALTH MONITORING Volume: 15 Issue: 3 Pages: 436-449 Published: APR 2008

Novel particle-based drill modelling by LTU

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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.

Marco Calderoni elected as New Chair of the RHC-ETIP

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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.

Completion of Civil Works at Perugia

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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.

  • Excavated Area – 50 cm of sand bed on the bottom of the excavated area to increase conductivity.

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.

  • Slinky GHEXs installation and FOC monitoring.

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.

On Wednesday and Thursday 4th & 5th November, We Held Our GA#6!

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The GEOFIT consortium successfully held our 6th General Assembly (GA) on November 4th and 5th, 2020, hosted remotely by R2M Solution. Important progress has been carried concerning the design of the GEOFIT systems to be installed in each of our five pilots. And although we are facing some delays during this installation phase due to the COVID-19 sanitary situation, the geothermal field in the school of Sant Cugat has been completed during the summer and installation at other pilots is planned to start before the end of the year.

Drilling and civil works for the horizontal connection to the plant room in Sant Cugat pilot (AJSC)

During the two-day meeting, we discussed the progress of our work and individual Work Packages, putting special focus on the pilots’ progress. The project moves in the right direction and the work is getting more advanced.

Among the progress included in the partners’ presentations, overviews on the last decisions made regarding the Bordeaux and Galway pilots were shown by NUI GALWAY and NOBATEK, progress on the engineering design tool for ground heat exchangers was shown by GROENHOLLAND, as well as how the GeoBIM platform is being implemented by IDP in the more advanced demo-sites, Sant Cugat and Perugia.

Two workshops were also organized during the GA, the first one to discuss the life cycle approach within the project context, led by EURECAT, and the second one to start analyzing the pilot business cases and discuss why Geothermal is an appealing technology for building retrofitting, led by R2M.

The meeting closed by setting up the next steps and plans for the upcoming six months.

Ground Penetrating Radar Analysis at Perugia

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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. 

GEOFIT at Sustainable Places 2020

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On Day 3 of the 4-day virtual Sustainable Places 2020 (SP2020) conference, Thursday 29th October from 14.00 – 17.00 CET, Marco Calderoni from GEOFIT contributed to the “Renewable Heating and Cooling Solutions for Buildings and Industry Workshop”, and the presentations and video recordings are publicly accessible.

Banner for “Renewable Heating and cooling solutions for Buidlings and Industry” at SP2020

The workshop brought together a selection of H2020 EU-funded projects involving experts from the biomass, geothermal, solar thermal and heat pump sectors to discuss a common strategy for increasing the use of renewable energy technologies for heating and cooling for buildings and industry. Renewable energy technologies for heating and cooling are safe, clean, efficient and increasingly cost-competitive. The workshop comprised four thematic sessions, namely “RHC for industrial applications”, “Storage solutions for RHC support in buildings”, “Innovative solutions for RHC deployment in buildings”, and finally the one that GEOFIT presented in called “Demonstration actions for RHC in buildings”.

Marco Calderoni from R2M Solution presented the GEOFIT project and highlighted first lessons learnt based on experience at the five demonstration sites.

R2M Solution organizes the annual international Sustainable Places conference, and the recent 8th as usual focused on the built environment at building, district, and urban scales to include our transport and energy infrastructures. Renowned for showcasing results coming out of the EU Horizon 2020 Framework Programme via the participation of cutting-edge research and innovation projects, the scope of Sustainable Places is captured directly in its name. It involves designing, building and retrofitting the places we live and work in a more sustainable way.

A GEOFIT poster was also displayed in the virtual room of Sustainable Places 2020.

Participating projects were: SWS-Heating – HYBUILD – CREATE – TRI-HP – HYCOOL – SHIP2FAIR – SUNHORIZON – Heat4Cool – GEOFIT – SCORES – Innova microSolar – Hybrid BioVGE – RES4BUILD – SolBioRev – FRIENDSHIP

Chair of the workshop: Andrea Frazzica (CNR ITAE) – partner of GEOFIT

Geothermal Catchment Field Completed at the Sant Cugat Pilot

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We have finished the geothermal catchment field in Pins del Vallès School in Sant Cugat, one of our five Geofit pilots. It consists of twelve 120 m deep vertical boreholes and one horizontal directional drilling.

Works carried out during the month of August include, on the one hand, drilling, installation of geothermal heat exchangers and pressure tests, and on the other hand, all civil and installation works related to the horizontal connection between wells and the plant room where the ground-source heat pump will be installed.

The next steps to be taken in our Spanish pilot include the installation of the passive cooling in the administrative building designed by Uponor and the installation of the new electrically-driven heat pump provided by Ochsner and currently under tests at AIT Austrian Institute of Technology GmbH laboratory.

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This project has received funding from the European Union’s H2020 programme under Grant Agreement No. 792210.

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