A 5th generation district heating cooling network integrated with a phase change material thermal energy storage: A dynamic thermoeconomic analysis

Abstract

This research proposes a novel layout of a 5th generation district heating and cooling network, integrated with a thermal energy storage consisting of phase change materials. The proposed layout includes two neutral rings, heat pumps and a photovoltaic solar field and its operation is based on an effective power to thermal strategy. The proposed system supplies energy to a huge mall located in Leganes near Madrid. One of the main novelties consisting in the use of a hybrid storage strategy. The excess renewable electricity is first used to charge a system of lithium-ion batteries. Then, additional excess renewable electricity is supplied to the heat pumps, producing thermal or cooling energy suitably stored in the novel thermal storage system based on phase change materials, according to the developed power to thermal strategy. This hybrid strategy allows one to maximize the self-consumption of renewable electricity. The simulation model is developed in TRNSYS environment, mimicking the yearly dynamic real operation of the system, based on hourly weather data. The developed model includes detailed dynamic models for all the components included in the system. In this framework, a novel model for the phase change material storage was suitably implemented in the overall simulation model. The developed dynamic model also includes an efficient control strategy to manage the plurality of components included in the system. Finally, a suitable thermoeconomic is included in the model aiming at calculating capital costs, operating costs and economic profitability indexes for the proposed system. In this analysis, the effect of a carbon tax policy for the proposed system is also considered. The proposed system achieves interesting results: renewable energy matches almost 88 % of the load of the mall. On the other hand, the high capital costs determine a poor economic profitability is poor, with a payback period of 19 years. However, this result can be significantly enhanced in case of carbon taxes: in fact for carbon tax value greater than 0.21 €/kgCO_2,eq the simple payback period is lower than 10 years.