To improve the utilization of excess energy, a heat storage system was developed, which is composed of a combined heat and power unit (CHP) with an integrated long-term heat storage. For economic reasons, a CHP unit is operated at optimum efficiency throughout the year. So the heat energy should be stored during summer in order to use it during the heating season. In this case, a binary system comprising a modified zeolite 5A and ammonia is used as a heat storage system. The final design of this system shows that it can be used as short- and long-term heat storage in buildings.