No abstract

The largest borehole thermal energy storage system in Finland (also one of the largest systems in Europe) is located in Sipoo, Southern Finland. The system produces heating and cooling energy for a large logistics centre and consists of 157 vertical borehole heat exchangers that are grouped into 10 blocks. The temperature of the heat carrier fluid circulated in each block has been monitored since the operation was started. A numerical model of the system was created using the finite element software COMSOL Multiphysics ® in order to simulate the temperature evolution of the system and the surrounding rock mass using the monitoring data as input. Simulation results indicate that the temperature within the rock mass embodying the system has decreased as the system is imbalanced but the decrease is moderate. The temperature disturbance created by the system was found to extend 50 metres from the borehole field. Based on the simulation the shallow geothermal reservoir will suffice for the designed lifetime of the system. Recently, new tools have been introduced for GSHP performance monitoring. Monzo, et al. (2016; 2017) presented a large-scale BTES installation with a carefully designed monitoring system and the first measurements from data collection sensors and distributed temperature sensing (DTS) optical fibre cables. DTS offers detailed information of the vertical variations of the thermal response of the ground. In large BHE fields, differences may also exist between the thermal performances of different parts of the field, for example, between the inner and outer BHEs, or due to varying geological properties of the site. In this paper we present long-term monitoring data and simulated temperature response of one of the largest BTES systems in Europe. The BTES has been in operation since 2012 and the performance of the system has been monitored since the beginning. A numerical model was developed to simulate the temperature response of the BHE field and to evaluate the thermal performance of the system. This BTES system and the monitoring data starting from 2012 will be studied in more detail in further work. This kind of long-term monitoring of BTES operation is called for in order to further improve designing of large-scale systems and enable commercial development.