A thermodynamic model of a “heat wave” phase shifter operating with phase change material (PCM) has been developed and experimentally investigated. The work started by building a physical model and developing numerical algorithms constructed to simulate its thermal behavior. Parameter studies reveal its operation characteristics and demonstrate a remaining potential for further improvements. This new phase shifter is a short term PCM heat storage device which uses the daily variation of the outside air temperature to indirectly cool the interior of a building. Besides sensible heat storage and phase shifting an important influence of the latent heat of the PCM is observed that originates from the high latent heat thermal inertia of the PCM. This latent heat greatly increases the heat storage capacity and, as a consequence, the phase shift of the “heat wave”, compared to a device working solely with a material showing only a sensible heat capacity. To maximize the phase shifters efficiency it is important to operate the PCM in its full range between the solid (cold) and the liquid (hot) phase. Finally, a 45 % increase of the phase shift compared to only sensible heat storage could be achieved. In this article the derivation of this and similar results are outlined in detail.