24 June 2014


Circular borehole field geometries are sometimes preferred when designing
borehole thermal energy storage systems, including controlled radial temperature gradients from the center and across the borehole field. A numerical model has been described in this paper in order to study the influence of connecting boreholes in radial zones with different thermal loads. The studied geometry consists of 3 concentric rings having 6, 12, and 18 boreholes, and the boundary condition at the wall of all boreholes can be flexibly changed. In this case, a realistic quasi-uniform temperature condition, observed using distributed
temperature measurements, was applied at the borehole wall, giving a temperature gradient of 1 K from bottom to top in all boreholes. The boreholes are thermally connected with each other. Thermally connecting the boreholes is one of the alternatives of the Superposition Borehole Model (SBM). A few control strategies for using the circular borehole field are
studied, both for balanced and unbalanced thermal load cases.