| Title | Performance Evaluation of Borehole Thermal Energy Storage Systems Through Energy and Exergy Analysis |
|---|---|
| Authors | Alberto LAZZAROTTO, Willem MAZZOTTI PALLARD, Mohammad ABUASBEH, José ACUÑA |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | borehole thermal energy storage, performance, exergy analysis |
| Abstract | The use of densely populated fields of borehole heat exchangers is a viable solution for seasonal thermal energy storage and has great potential to increase the share of renewable energy and reduce the use of fossil fuels. A proper evaluation of borehole storage performance is necessary in order to evaluate benefits of candidate design configurations or to compare borehole storage system with other thermal energy storage options. Performance of borehole heat storage are often presented in literature in terms of energy performance. Another significant performance figure that is considered (although less frequently) is exergy. Exergy has the benefits of taking into account both the quantity of the heat exchanged as well as the temperature at which this heat is exchanged. In this paper we investigate a viable methodology for the analysis of performance of borehole thermal energy storage systems. The method considers as relevant parameters for the analysis energy as well as temperature and exergy. These parameters are evaluated at the interface of the storage, e.g. inlet and outlet quantities, but also within the storage volume. An analytical model based on the line source is utilized to describe the heat transfer within the ground. The model provides the temperature field within the ground volume as a function of time and enables monitoring how the energy stored looses quality, i.e. exergy, as the difference between a given time of interest and the time of injection increases. The analysis proposed aims at breaking down the storage process in the borehole and evaluate how a variety of parameters in the configuration and operation of the system affect the processes of injection, storage and extraction of thermal energy. A set of test cases where a number of design and operational parameters are investigated is presented to illustrate the benefit and insight provided by the analysis.​ |