Referring Seasonal Energy Efficiency Ratio（SEER）——a method for seasonal performance evaluation of room air conditioners in GB 7725, the Seasonal Temperature Effectiveness was proposed to evaluate thermal seasonal performance of a heat pipe heat recovery unit based on the annual operation data in a shopping mall. And its calculation formula was deduced thereafter. With the case study, it was indicated that seasonal temperature effectiveness of the unit was 66.08% in the winter and 55.43% in the summer, which meant that the system was efficient.