An Efficicent Strategy For The Operation Of An Integrated Thermal Energy Storage Facility And CHP/DH Plant
Combined Heat and Power (CHP) systems are of interest for District Heating (DH) networks due to their high conversion efficiency. The main challenge in implementing CHP/DH systems is in matching the inherent dynamic demand of residential thermal demand. In fact, the large mismatch between production and consumption profiles is issue of concern. Thermal Energy Storage (TES) can be used to cope with this issue. The operational strategy of an integrated CHP with TES plays a significant role in profitability of the whole plant and, as such, necessitates precise study. In this paper, different options for the operation of an integrated CHP/DH with TES are investigated, all based on the same concept, sending a constant hourly amount of energy to the TES/DH. In order to find the best constant flow rate, the performance of the TES facility has been investigated numerically. To find the best operation strategy, the objective function in simulations was to minimize thermal energy dumping due to the following sources: thermal energy degradation in the thermocline hot water storage tank and/or thermal energy dumping due to uncertainty of thermal demand. In all scenarios, hourly thermal energy supply is set at a constant average value for each month, but is varied from one month to another. Moreover, the amount of supplied energy varies between design options as it only covers a certain percentage of the thermal demand. Based on the proposed method of operation, the hourly full load operation mode is dictated to the CHP plant. This has been shown to allow CHP to have its best energetic performance in all scenarios. The results show that the best constant hourly thermal energy that should be supplied to the TES/DH should be equal to the monthly average of the maximum thermal demand. Furthermore, policies with fewer mismatches have resulted in better thermal performance of TES. Since all alternatives have been compared based on the same TES capacity, the best energetic scenario also represents the best economically one.
Keywordsó Combined Heat and Power, Thermal Energy Storage, District Heating, Operation Strategy, Numerical simulations.