Configurations for multiple thermal energy storages in thermal networks

In practice, there are some conditions, depending on space availability, economics, project requirements, insulation, storing media type and other issues, for which it may be advantageous to utilize several thermal energy storages (TESs) instead of one in thermal networks like district energy systems. Here, various configurations for multiple TESs are proposed and investigated. Significant parameters for a TES, or a set of TESs, include discharging temperature and recovered energy. First, one TES is investigated to determine the final temperature and energy recovery. Next, characteristics for various configurations of multiple TESs are developed as functions of TES characteristics (e.g., charging and discharging temperatures and energy quantities). Series, parallel and general grid (simultaneous series and parallel) TES configurations are considered. In the parallel configuration, the TESs behave independently. This suggests that with the TES can consist of different storage media types and sizes, and that there is no restriction on initial temperature of the TES. In the series configuration, the situation is different because the TESs are connected directly or indirectly through a heat exchanger. If there is no heat exchanger between the TESs, the TES storage media should be the same, because the outlet of one TES is the inlet to the next one in the series. The initial temperature of the second TES must be smaller than the discharge temperature of the first. There is no restriction on the TES size for series configurations. The general grid configuration is observed to exhibit characteristics of both series and parallel configurations.