Experimental and theoretical investigations are carried out to study the heating of a 302 x 302 x 55 mm test box of steel containing a sodium acetate water mixture. A thermostatic bath has been set up to control the charging and discharging of the steel box. The charging and discharging has been investigated experimentally by measuring surface temperatures of the box as well as the internal temperature of the sodium acetate water mixture through a probe located in the center of the steel box. The temperature developments on the outer surfaces of the steel box are used as input parameters for a Computational Fluid Dynamics (CFD) model. The CFD calculated temperatures are compared to measured temperatures internally in the box to validate the CFD model. Four cases are investigated; heating the test module with the sodium acetate water mixture in solid phase from ambient temperature to 52oC; heating the module starting with the salt water mixture in liquid phase from 72oC to 95oC; heating up the module from ambient temperature with the salt water mixture in solid phase, going through melting, ending in liquid phase at 78oC/82oC; and discharging the test module from liquid phase at 82oC, going through the crystallization, ending at ambient temperature with the sodium acetate water mixture in solid phase. Comparisons have shown reasonable good agreement between experimental measurements and theoretical simulation results for the investigated scenarios.