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 geo-thermal 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 degrees 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. (C) 2020 Elsevier Ltd. All rights reserved.