The paper deals with the comparison of the one-dimensional (1D) and three-dimensional (3D) models of a thermally activated wall panel with a microencapsulated phase change material. The 3D model was created in the off-the-shelf simulation tool COMSOL Multiphysics. The 1D model was an in-house developed TRNSYS type. The main advantage of the 1D model is the short computation time but it comes at the expense of lower accuracy and less detailed results. In most building performance simulations, however, detailed knowledge of the temperature distribution over the surface of a wall is not important. For this reason, the results of both models were compared in terms of the mean surface temperature of the wall panels, the outlet water temperature, and the overall heating and cooling capacity of the panels. The two models provided very similar results for the practical range of water flow rates. The mass flow rate of water had a relatively small influence on the mean surface temperature and the heating and cooling capacity of the panels. For the one-tube mass flow rates of water between 0.25 and 2 g/s, the mean surface temperature was in the range of 28–29.5C in the heating scenario and 21–21.5C in the cooling scenario, with the heating and cooling capacity ranges of 65 W/m² to 75 W/m² and 35 W/m² to 40 W/m², respectively.