Analytical Investigations into Thermal Resistance of Diaphragm Wall Heat Exchangers

Geothermal energy is a promising and sustainable source that can reduce current dependence on conventional fuels for thermal energy production. To exploit this source of energy complex thermo-active geostructures such as diaphragm wall heat exchangers are being investigated theoretically as well as experimentally. These geostructures are composed of concrete panels embedded with reinforcement cages fitted with absorber pipes. The thermal boundary surfaces are applied at surfaces representing the adjacent ground and the exposed concrete surface in addition to the pipe surface. An effective and optimised design for such geostructures is fundamental to efficient energy production. In the present study the thermal resistance of such complex thermo-active substructures are quantified using boundary collocation least squares method. To that end, steady state temperature distribution in a two dimensional cross section of a diaphragm wall heat exchanger is investigated. Design parameters including pipe and heat exchanger fluid specifications, pipe embedded section geometry and convective boundary conditions representing the fluid and the ground are used as model inputs. Thermal resistances are investigated for varying design parameters over a range of thermal properties of the ground and the concrete.