Operation Results of a Closed Sorption Heat Storage Prototype

In the frame of the EU funded project COMTES a closed sorption heat storage demonstrator based on sodium hydroxide as sorbent and water as sorbate, has been developed. The system operates on a hybrid basis. Heat is stored in sensible hot water tanks for diurnal storage and in the sorption system for seasonal storage. The benefits of both systems can be utilised, namely low charging and discharging losses in diurnal storage and low heat losses during storage time in seasonal storage. In the absorption heat storage system the heat and mass exchangers were developed on a tube bundle falling film basis, as is common in absorption chillers. In testing the heating (absorption) process of the sorption system, issues were encountered with tube wetting as well as speed of absorption. It was found that absorption did occur, but much slower then expected. This resulted in a highly reduced increase of temperature and decrease of concentration. It is proposed that novel heat and mass exchanges are requires for absorption heat storage systems.