Load aggregation for thermal interactions between boreholes

A load aggregation method is proposed for efficient simulations with multiple boreholes using network-based simulation methods. The method splits fast and slow dynamics. Fast dynamics, i.e., the impact of boreholes on themselves, are solved every timestep using available load aggregation methods. Slow dynamics, i.e., heat interactions between heat sources, are solved at a lower frequency by introducing a time delay in the update of their calculation. A first order correction term is proposed to estimate the variation of temperatures in-between updates. The error caused by the delayed update depends on the distance between the boreholes and the frequency of updates; more distanced boreholes can use a lower frequency of updates to achieve acceptable accuracy. A 20-year hourly simulation of two interacting bore fields showed that a maximum error of 0.003°C on the inlet fluid temperatures can be obtained while decreasing the calculation time from 275s to 26.2s.