Evaluation of diaphragm wall heat exchanger potential

Abstract

Diaphragm wall foundations adapted for use as ground heat exchangers are an attractive proposition to achieve low-carbon heating and cooling with heat pumps in larger non-domestic buildings. As the extent of a diaphragm wall installation is driven by geotechnical questions and the number of storeys, key system design considerations are the peak and seasonal capacity of the ground heat exchanger and the proportion of the building demands that can be satisfied. Dynamic simulations of prototypical office buildings in a range of climatic conditions have been used to analyse heat exchange potentials using a Dynamic Thermal Network (DTN) heat exchanger model. Systematic evaluations of the time-dependent heat fluxes between three boundaries (heat exchanger, basement, ground surface) have been made to maximize heat exchange potentials and overall system efficiency given temperature constraints over 20 years operation. This has allowed maximum heat exchange potentials to be evaluated for a range of design parameters and climates to enable preliminary design of diaphragm wall heat exchanger systems and assessment of hybridized solutions. Considering short timescale dynamic effects suggests peak heat exchange rates higher than previously reported. In some climates seasonal operation is found to be constrained by temperature limits according to ground thermal properties.