Heat Transfer and Thermodynamic Analyses of a Novel Solid-Gas Thermochemical Strontium Chloride-Ammonia Thermal Energy Storage System

A novel solid-gas thermochemical sorption thermal energy storage (TES) system for solar heating and cooling applications operating on four steady-state flow devices and with two transient storage tanks is proposed. The TES system stores solar or waste thermal energy in the form of chemical bonds as the working gas is desorbed from the solid. Strontium chloride-ammonia is the working solid-gas couple in the thermochemical sorption TES system. Strontium chloride-ammonia has a moderate working temperature range that is appropriate for building heating and cooling applications. The steady-state devices in the system are simulated using Aspen Plus, and the two transient components are simulated using the ENGINEERING EQUATION SOLVER (EES) package. Multiple cases are examined of different heat and cold production temperatures for both heating and cooling applications for a constant thermal energy input temperature. Energy and exergy analyses are performed on the system for all simulated cases. The maximum energy and exergy efficiencies for heating applications are 65.4% and 50.8%, respectively, when the heat is generated at a temperature of 87 degrees C. The maximum energy and exergy efficiencies for cooling applications are 29.3% when the cold production temperature is 0 degrees C and 22.9% when it is -35 degrees C, respectively. The maximum heat produced per mass of the ammonia produced, for 100% conversion of the reactants in the chemical reaction, is 2010 kJ/kg at a heat production temperature of 87 degrees C, and the maximum cold energy generated is 902 kJ/kg at a temperature of 0 degrees C. Finally, the system is modified to operate as a heat pump, and energy and exergy analyses are performed on the thermochemical heat pump. It is found that the maximum energy and exergy coefficients of performance (COP) achieved by upgrading heat from 87 degrees C to 96 degrees C are 1.4 and 3.6, respectively, and the maximum energy and exergy efficiencies are 56.4% and 79.0%, respectively.