| Abstract |
HT-UTES (High Temperature Underground Thermal Energy Storage) systems are very attractive solutions to match the heat availability from various heat sources (waste, process, solar, district heating network, …) with heat demands. One drawback of these solutions is their inherent heat losses, especially under high temperatures. The BTESmart pilot was developed to tackle this problem. In addition to a standard BTES field, outer (lateral) recovery boreholes are installed at the field periphery to capture heat losses from the field heart. The heat to be stored into the BHE field will come from thermal solar panels. The system will cover the heating needs for the administrative buildings of Storengy main natural gas storage facility located in Chémery (region Centre Val-de-Loire, France), i.e. 211 MWh/year. The BTES will be charged at 40°C through 12 radial lines of 4 boreholes in series. The project should be under construction end 2019 and operations should start in June 2020. For HT-BTES applications, analytical models are more suitable for routine use than fully discretized models. They can run over reasonable time frames, i.e. performing relevant simulations over decades with hourly time step. As this innovative design is not available in the standard modelling suites like TRNSYS, a specific BTES module need to be developed to assess the added value of this innovative design and optimize its operation. As the BTESmart project is not yet in operation, it cannot produce already the necessary monitoring data to validate the developed module. Therefore, a fully discretized numerical model is built in FEFLOW to deliver an independent and relevant set of numerical results to validate the new analytical module. FEFLOW enables to accurately take into account the design of BTESmart and to simulate the complete and detailed temperature field and circulating fluid temperatures. Only the first part of the modelling work and the cross-validation between the fully discretized and the semi-analytical models of a BTES with no active recovery boreholes will be presented here. Several conclusions can however be already listed from the work done: - Analytical approach is definitely the way to go to simulate accurately and rapidly the BTES behavior along several cycles; - Temperatures from the new analytical module are compared to the numerical outputs from FEFLOW and the domain of validity of each model is presented; - The influence of design parameter such as boreholes number, location, and operation strategy over the unloaded energy per volume and BTES efficiency is discussed. Acknowledgement : This work is conducted in the frame of the Geothermica HEATSTORE project which aims at promoting the development of HT-UTES solutions (http://www.geothermica.eu/projects/heatstore/). BTESmart is one of the 6 demonstration sites involved in this project. |