Energy performance of diaphragm walls used as heat exchangers

Abstract

The possibility of equipping diaphragm walls as ground heat exchangers to meet the full or partial heating and cooling demands of overlying or adjacent buildings has been explored in recent years. In this paper, the factors affecting the energy performance of diaphragm walls equipped as heat exchangers are investigated through finite element modelling. The numerical approach employed is first validated using available experimental data and then applied to perform parametric analyses. Parameters considered in the analysis include panel width, the ratio between the wall and excavation depths, heat transfer pipe spacing, concrete cover, heat-carrier fluid velocity, concrete thermal properties and the temperature difference between the air within the excavation and the soil behind the wall. The results indicate that increasing the number of pipes by reducing their spacing is the primary route to increasing energy efficiency in the short term. However, the thermal properties of the wall concrete and the temperature excess within the excavation space are also important, with the latter becoming the most significant in the medium to long term. This confirms the benefits of exploiting the retaining walls installed for railway tunnels and metro stations where additional sources of heat are available.

Thermo-hydro-mechanical coupling analysis of a thermo-active diaphragm wall

“…Amis (2011) reported a rise of 20% in thermal resistance as well as a 13% reduction in the thermal conductivity value. In addition, some other research were performed to investigate on the factors affecting the energy performance of thermo-active diaphragm walls (Xia et al, 2012;Donna et al 2016). Stewart et al (2014) used an analytical model to evaluate the effect of incorporating heat exchangers into a geosynthetic-reinforced retaining wall.…”

A Model of a Diaphragm Wall Ground Heat Exchanger

“…A coupled thermo-mechanical analysis was employed by Coletto and Sterpi [17] to investigate how the heat transfer affects the soil temperatures, the wall internal actions, and the soil-structure interaction. Di Donna et al [18] detailed the key parameters controlling the energy efficiency in DWHEs through numerical investigations and statistical analysis.…”

On the performance of energy walls by monitoring assessment and numerical modelling: a case in Italy

“…As far as diaphragm walls analyses are regarded, they are often based on simplifying assumptions, concerning for instance the geometry, the soil thermal properties, the thermal boundary conditions and their time-dependence. From monitored case studies and numerical investigations on the energy performance and on the geotechnical and structural response of energy walls (Xia et al 2012, Bourne-Webb et al 2016a, Di Donna et al 2016a, Sterpi et al 2017, it can be inferred that the thermal boundary conditions and the heating/cooling input, related to the building energy demand, play a relevant role in the overall behaviour. Moreover, Accepted manuscript doi: 10.1680/jenge.18.00037 methods conventionally adopted for the heat transfer analysis in borehole heat exchangers or in energy piles do not apply to walls, due to their specific features, and purposely conceived methods should be considered in this case (Kürten et al 2015, Sun et al 2013.…”