Energy Performances of Open Sorption Reactor with Ultra-Low Grade Heat Upgrading for Thermochemical Energy Storage Applications

The work discusses a problem of harvesting and upgrading of ultra-low grade heat with thermochemical energy storage technology for space and domestic water heating in residential area. The laboratory scale prototype, operating on the principle of an open packed bed sorption reactor and using moist air as a heat/mass transfer fluid, is experimented. The range of experimental air temperature was set to 17-40 °C, which corresponds to the typical range of domestic waste thermal energy. The tested sorbent was a salt-in-matrix composite material composed of a silica gel containing 43 wt.% of calcium chloride (CaCl2) salt. Hygrothermal behavior and energy performances of the prototype control volume filled with 245 g of material, representing the reactive front of a thermal wave, were analyzed at constant inlet hydration conditions (water vapor pressure of 12.5 mbar). The average temperature lift was recorded as 9-13 °C, representing the amplification of a supplied heat on 23% - 75% depending on the inlet temperature. The average specific thermal power inside the material bed was measured to be 168-267 W kg-1. The apparent energy density, based on the prototype control volume, ranged between 1.0 and 1.6 GJ m-3. Taking into account the heat of water vaporization, the coefficient of performance of the process was determined to be 0.96-1.57.