Geothermal energy piles design, sizing and modelling

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School of Engineering | Doctoral thesis (article-based) | Defence date: 2025-11-20
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Authors

Date

2025

Department

Rakennustekniikan laitos
Department of Civil Engineering

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Mcode

Degree programme

Language

en

Pages

135 + app. 88

Series

Aalto University publication series Doctoral Theses, 228/2025, TALLINN UNIVERSITY OF TECHNOLOGY DOCTORAL THESIS, 81/2025

Abstract

This thesis addresses the challenges associated with the design, sizing, and modelling of geothermal energy piles (GEPs), the lack of validated methods for their use as a renewable heating and cooling solution for nearly zero-energy buildings (NZEBs). GEPs provide both load-bearing and ground heat exchange functions, making them well-suited for use with ground source heat pumps (GSHPs). However, their designs have often relied on assumptions originating from borehole heat exchangers (BHEs), which differ considerably from GEPs in geometry, thermal boundary conditions, and placement, as the layout of GEPs is dictated by the building’s foundation plan. This research aimed to develop and validate a modelling method for assessing the performance of GEPs with thermal storage coupled with a detailed whole building simulation model for a parametric study. The method was developed in IDA ICE and validated using COMSOL Multiphysics and realworld measurement data. The research methodology combined a systematic literature review, model development, validation, and demonstration of the modelling method’s performance using an as-built calibrated model with measured performance data from a commercial NZEB in Finland for energy analysis. A parametric study was conducted to support the development of a tabulated GEPs sizing method for early-stage design, considering factors such as heat pump sizing power, pile spacing and depth, soil type, and the presence of a thermal storage. The findings confirmed that conventional BHE-based modelling approaches are unsuitable for GEP systems due to major differences in thermal boundary conditions, particularly the influence of building floor slabs on ground temperature distribution. The validated GEP modelling method, implemented in IDA ICE and verified with COMSOL simulations, accurately captured these effects and showed strong agreement with measured data from a monitored NZEB in Finland. The model calibration procedure revealed unexpected plant operation due to improper control algorithms, highlighting the importance of monitoring and logging systems in buildings with unconventional plant designs to ensure proper operation and maintain long-term efficiency. According to parametric study results, seasonal thermal storage demonstrated notable improvements in energy efficiency and enabled a reduction in required pile length by over 50% in a specific case. A tabulated GEP sizing guide was developed to support early-stage design, enabling engineers to estimate system configurations effectively without relying on complex simulation tools. The method demonstrated in this thesis can be extended to any climate region and building type.

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Supervising professor

Salonen, Heidi, Prof., Aalto University, Department of Civil Engineering, Finland

Thesis advisor

Kurnitski, Jarek, Prof., Aalto University, Department of Civil Engineering, Finland
Pikas, Ergo, Prof., Tallinn University of Technology, Estonia
Ferrantelli, Andrea, Prof., Tallinn University of Technology, Estonia

Keywords

activated pile foundations, seasonal thermal storage, GSHP, GEP sizing guide

Other note

Parts

  • [Publication 1]: Fadejev J, Simson R, Kurnitski J, Haghighat F. A review on energy piles design, sizing and modelling. Energy, Volume 122, pp.390-407, January 2017.
    DOI: 10.1016/j.energy.2017.01.097 View at publisher
  • [Publication 2]: Fadejev J, Kurnitski J. Geothermal energy piles and boreholes design with heat pump in a whole building simulation software. Energy and Buildings, Volume 106, pp.23-34, June 2015.
    DOI: 10.1016/j.enbuild.2015.06.014 View at publisher
  • [Publication 3]: Ferrantelli A, Fadejev J, Kurnitski J. Energy pile field simulation in large buildings: Validation of surface boundary assumptions. Energies, Volume 12, Art.No. 770, pp.1-20, February 2019.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-201904022511
    DOI: 10.3390/en12050770 View at publisher
  • [Publication 4]: Fadejev J, Simson R, Kesti J, Kurnitski J. Measured and simulated energy performance of OLK NZEB with heat pump and energy piles in Hämeenlinna. E3S Web of Conferences, NSB 2020 – 12th Nordic Symposium on Building Physics, Volume 172, Art.No. 16012, pp.1-11, June 2020.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202008124699
    DOI: 10.1051/e3sconf/202017216012 View at publisher
  • [Publication 5]: Ferrantelli A, Fadejev J, Kurnitski J. A tabulated sizing method for the early stage design of geothermal energy piles including thermal storage. Energy and Buildings, Volume 223, Art.No. 110178, pp.1-16, June 2020.
    Full text in Acris/Aaltodoc: https://urn.fi/URN:NBN:fi:aalto-202006254075
    DOI: 10.1016/j.enbuild.2020.110178 View at publisher

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https://urn.fi/URN:ISBN:978-952-64-2828-4

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[diss] Insinööritieteiden korkeakoulu / ENG