Elsevier

Renewable Energy

Volume 154, July 2020, Pages 476-487
Renewable Energy

Energy diaphragm wall thermal design: The effects of pipe configuration and spacing

https://doi.org/10.1016/j.renene.2020.02.112Get rights and content

Highlights

  • The retaining wall depth is critical to the thermal performance of energy walls.

  • Larger pipe spacings result in more cost-effective energy diaphragm wall designs.

  • The site material thermal conductivities do not affect the choice of pipe spacing.

  • Vertical and horizontal pipe configurations result in similar thermal performance.

  • Vertical configurations may result in construction delays based on splicing numbers.

Abstract

Energy geo-structures utilise underground structures primarily designed for structural and geo-mechanical stability to also provide renewable geothermal energy for heating and cooling purposes. Piping is incorporated in the structures to exchange heat with the ground via a carrier (water) and connected to a ground-coupled heat pump on the building side. This work focuses on energy diaphragm walls, expanding on the limited available knowledge and undertaking a comprehensive parametric analysis using experimentally validated numerical modelling. Focus is put on the wall pipe configuration and spacing, which are parameters the geothermal design can directly control, however, the effects of ground thermal conductivity and wall depth are also considered. The wall depth is shown as a critical factor to the thermal performance and low thermal conductivity material sites might require deep energy walls for a cost-effective design. Larger pipe spacing (≥500 mm) appears preferable, despite less piping being placed, since small spacing leads to increased costs but insignificant thermal performance gains. Comparing the horizontal and vertical pipe configurations, relatively small temperature differences of less than 1 °C are found. Moreover, the former can be less expensive for multiple-section deeper walls, while the latter for shorter walls or when construction delays are non-critical.

Section snippets

Geothermal energy diaphragm walls

Shallow geothermal systems are utilised around the globe to provide renewable energy for heating and cooling buildings, contributing towards tackling the critical global problems of increasing energy demand, depleting natural resources and the effect of greenhouse gas emissions. These systems transfer heat between the building and the ground, utilising the latter as a heat source or sink. Ground-source heat pumps (GSHPs, either one or several) are connected to the building heating/cooling

Methodology

This work aims to provide a further understanding on the geothermal design of energy diaphragm retaining walls and determine the impact of factors such as the pipe configuration, site location (i.e., ground thermal properties), and geo-structure geometry (i.e., wall depth, thickness). Detailed finite element numerical modelling is utilised throughout to simulate the thermal performance of the system under a range of different conditions. A parametric analysis is presented to identify how

Results & discussion

This section presents and discusses the results of the various investigations on energy diaphragm walls. An example case is firstly shown, for fixed values of most parameters in Table 2, discussing GSHP design practices and serving as an introduction to the more wholistic analyses. Section 3.2 is the most comprehensive one, providing a number of analyses on the thermal performance of these structures. Amongst the key aims of this research is to identify the importance of pipe spacing as well as

Summary and conclusions

This work investigated the potential of energy diaphragm walls as energy geo-structures, utilising an experimentally validated finite element modelling methodology. A large-scale parametric study was undertaken, using data from a total of 480 25-year long simulations, focusing on the thermal performance of the energy geo-structures and the impact of key design parameters on this performance. The study focuses mainly on the effects of the pipe configuration and spacing, which in the case of

CRediT authorship contribution statement

Nikolas Makasis: Conceptualization, Data curation, Methodology, Software, Formal analysis, Investigation, Visualization, Writing - original draft. Guillermo A. Narsilio: Conceptualization, Formal analysis, Visualization, Writing - review & editing, Supervision, Funding acquisition.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Funding from the Australian Research Council (ARC) FT140100227, The University of Melbourne, the Melbourne Metro Rail Authority and the Victorian Government is much appreciated.

References (39)

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