Energy Quay Walls (EQWs) are innovative energy geostructures with the unique capability to exchange heat with both soil and open water. Although previous laboratory testing demonstrated a promising energy efficiency for this type of system, its novelty necessitated thorough research to advance comprehension of its thermal behaviour and optimise energy efficiency. This paper conducts an in-depth examination of EQWs, employing numerical models validated against real data from a full scale test in Delft, The Netherlands.

Two Finite Element numerical models were developed to (i) reconstruct the undisturbed (i.e. pre-geothermal activation) temperature profile within the soil and (ii) conduct a comprehensive (3D) analysis of heat exchange processes in an EQW application (i.e. during geothermal activation), calibrating relevant parameters with field test data, providing valuable insights into its energy efficiency. Following validation, the geothermal activation model was employed to assess the impact of the flow regime within the heat exchanger pipes and the velocity of the open water on the energy efficiency of the EQW system. Additionally, the contributions of soil, water, and air to the energy gain are investigated. The results indicate that the primary source of energy gain is from open water, and the dominance of this contribution is further increased by the presence of turbulent flow within the heat exchanger pipes. However, the soil can play a key role in short term energy delivery. Furthermore, this study emphasises the importance of the open water movement, revealing a 48% reduction in energy extraction for fully stationary water scenarios.

Energy Quay Walls (EQWs) are innovative energy geostructures which exchange thermal energy with both soil and open water while providing a structural function. A full-scale EQW with thermally activated sheet piles was tested, measuring 8.4 m in length along a 1.75m deep canal, with the sheet piles embedded 13m into the underlying soil. Two different length heat exchangers were used: shallow (3 m length) loops primarily extracting thermal energy from the open water, and deep (15 m length) loops extracting energy also from the soil. The shallow loops demonstrated a high heat extraction rate per activated surface area (∼200 W/m2 at 8 °C water temperature, compared with ∼60 W/m2 for the deep loops), with their performance closely linked to the open water temperature. The shallow loops did not require time to restore surrounding temperatures, indicating stable long-term performance, yet can extract the least energy at the coldest time periods. In contrast, the deeper loops exhibit greater stability across varying open water temperatures and achieve the highest total energy extraction per quay wall length (∼900 W/m at 8 °C water temperature, compared with ∼600 W/m for the shallow loops). Realistic operation of the deep loops lowered the soil temperature by ∼2 °C.

The Cutter Soil Mix (CSM) energy wall represents a novel type of energy geostructure, merging the environmental and cost benefits of the CSM technique with ground source heat pump technology. This innovation necessitated comprehensive research to understand the thermal, physical and mechanical characteristics of the material, and optimise energy performance of the CSM energy wall. Laboratory tests and finite element numerical modelling, replicating a full-scale CSM test site in Amstelveen (the Netherlands), were employed to evaluate energy performance under varying demand scenarios: heating only, and combined heating and cooling. Key aspects examined include the influence of horizontal connection pipes on energy extraction and injection, and the impact of U-loop configuration on heat exchange rates over short and long terms. Findings indicate that energy demand significantly affects system performance, with combined heating and cooling demands enhancing long-term heat exchange rates compared to heating-only scenarios. The study demonstrates that non-insulated connection pipes increase overall heat exchange rates, especially under heating-only conditions, while reducing the number of U-loops decreases thermal interaction and enhances energy extraction rates per activated area.