Dynamic model and performance evaluation of a thermochemical storage system for residential heat demand

The present study proposed a thermochemical storage system based on absorption/desorption of ammonia in Strontium-Chloride salt. The storage is charged by transferring heat from an energy resource to the reactor, where the heat leads to desorption of ammonia. The ammonia is then compressed and stored at ambient temperatures. This preserves the chemical potential without energy losses for an unlimited period. During the discharging process, the ammonia is throttled to the reactor pressure and absorbed by the salt. The released absorption heat can then be used for space heating or domestic hot water supply in the building and the proposed thermal energy storage system can be optimized to outbalance mismatches between energy supply (availability\price) and the heat demand of building.
A dynamic model of the system was implemented in Modelica to assess the dynamic response of the system during charging and discharging. Further, the influence of ambient temperature and charging temperature on the system performance was assessed. The round trip efficiency of the system was about 55 % to 60 %. The major energy losses were identified to be the heat rejected from the condenser and heat losses from the storage tank and reactor. The effective storage capacity decreased considerably for low ambient temperatures due to reduced pressure of the storage tank. This effect could be reduced by avoiding keeping the system in direct thermal contact with the ambient.