Simultaneous heating and cooling systems are advantageous when heating and cooling loads occur at the same time in a building. However, the usage of auxiliary heat sources is inevitable because of the variable occurrence of the loads. As the auxiliary heat source has a lower coefficient of performance than the simultaneous heating and cooling system, when removing the same amount of load more energy is required. To reduce energy, the usage of simultaneous heating and cooling systems and auxiliary heat sources must be increased and decreased, respectively. In this study, the Load Reset Control (LRC) that can set heating temperature in real time was proposed to increase the usage of the simultaneous heating and cooling system for buildings when the cooling load exceeds the heating load. The process determines the temperature for the next point using the heating temperature of the previous point and the energy inside the tank. To analyze the energy saving rate of the LRC method, it was compared with the conventional constant temperature control method in three cases with different cooling and heating load ratios. The static calculation and dynamic results were also compared. The results of the analysis show that in all three cases, temperatures close to the comfort range can be achieved while saving energy compared to the conventional method.