Experimental evaluation of IDA ICE and COMSOL models for an asymmetric borehole thermal energy storage field in Nordic climate

Abstract

• A large-scale asymmetric borehole field was modelled in IDA ICE and COMSOL. • Simplification of asymmetric borehole field layout was investigated in 3-D model. • Borehole field models were validated by DTS-measured brine temperatures. • Validation of borehole field models showed good agreement. • Simplified-geometry borehole field model can reduce computational work. Appropriate modeling of borehole thermal energy storage (BTES) system is crucial for accurate prediction of BTES-coupled ground source heat pump performance with accessible computational load. This study aims to validate 3-D numerical models developed in IDA ICE 4.8 and COMSOL for a large-scale asymmetric borehole field consisting of 74 groundwater-filled boreholes with average depth of 310 m in Otaniemi, Finland. Comparisons were conducted between the detailed-geometry IDA ICE and COMSOL borehole field models and between the detailed-geometry and simplified-geometry IDA ICE borehole field models. All these models were validated by 1.5-years brine temperatures measured by temperature sensors and a distributed temperature sensing monitoring system. The results show the detailed-geometry IDA ICE model can estimate the BTES inlet and outlet brine temperatures as well as the COMSOL model. The average inlet and outlet brine temperature differences against the measurement data in the detailed-geometry IDA ICE and COMSOL models were both within 1 ℃. The simplified-geometry IDA ICE models can predict the borehole field inlet and outlet brine temperatures with a similar high accuracy (within 1 ℃ against the measurement) and can reduce the computational time by 72 % less than the detailed-geometry IDA ICE model.