Investigation of a household-scale open sorption energy storage system based on the Zeolite 13X/water reacting pair

Sorption thermal energy storage is a promising concept for seasonal heat storage. Advantages of sorption heat storage are high energy storage density (compared to sensible and phase change heat storage) and negligible energy losses during storage over long time periods. In order to investigate the potential of sorption thermal energy storage, a high power open sorption heat storage system has been designed and built for household space heating applications. In this paper, the characteristics of the open zeolite 13X/water sorption energy storage system will be presented. The setup consists of four segments with a total capacity of 250 L of zeolite. A segmented reactor has been designed to reduce the pressure drop over the system, which results in less required fan power. This configuration also decreases the response time and makes the system scalable. Dehydration of the reactor is performed by supplying hot air to the zeolite bed. Hydration is performed by supplying humidified air to the bed. In all the segments, the pressure drop, temperature, and humidity are monitored. Furthermore, inside one of the reactor segments, the temperature is monitored at different locations in the zeolite bed. Several tests, using different mass flow rates, have been performed. During the tests, a maximum temperature step of 24 °C was realized. The maximum delivered power was 4.4 kW and the obtained storage capacity was 52 kWh. The reactor efficiency was 76% taking into consideration the conductive heat losses through the reactor wall and the sensible heat taken up by the thermal mass of the solids. Furthermore, it has been noticed that the flow through the bed was not completely uniform. This has a negative influence on the performance of the system.