How can combined heating and cooling networks benefit from thermal energy storage? Minimizing lifetime cost for different scenarios

The concept of smart thermal grid argues in favor of integrated heating and cooling networks to benefit from potential synergies and renewable energy sources. We developed a method showing how thermal energy storage (TES), coupled with heat pumps, contributes to reduce the total cost of a thermal grid. An optimization model is introduced, based on an energy hub including fuel boilers, electric heaters and chillers. For different loads, thermal grids integrating heat pumps alone, TES alone or a combination of both are compared to a reference hub. It was found that the inclusion of both TES and heat pumps simultaneously is more beneficial than when they are used separately, extending the synergic use of the heat pumps to satisfy both heating and cooling loads. With maximal loads, the total cost was reduced respectively by 0.48%, 6.37%, and 7.25% with the addition of only TES, only heat pumps, and both. Furthermore, the benefit of TES when components of the system (chiller or boiler) are under-sized is assessed. TES can compensate the lack of capacity, but there is a limit of chiller under-sizing that it can accommodate. The results are useful to design or operate smart thermal grids.