The pipe-embedded building envelope is heavyweight thermally activated building systems (TABS) that has its pipe circuits inside building envelopes, but it has been seldom done in existing buildings. In this context, the concept of thermo-activated phase change material composite wall (TAPCW) is proposed to address the retrofitting challenges facing existing buildings, that is to substitute the pipe-embedded interlayer with macro-encapsulated PCM panel and relocate it to the exterior of the load-bearing layer. This work aims to investigate the thermal and energy saving performances of TAPCW under the winter climate conditions of northern China (i.e, Tianjin city) through a validated numerical model. Furthermore, performances of TAPCW are examined for some key factors, including the pipe spacing, PCM thickness, and orientation. The comparative study of three cases (case 1: TAPCW; case 2: normal wall integrated with PCM; and case 3: normal wall) verifies the effectiveness of TAPCW, and the daily heat loss (Groom), primary energy consumption (PE) and operation cost (C) can be reduced by 105.5％, 14.07％, and 56.03％, respectively. The parametric study shows that the pipe spacing has a more obvious influence than the PCM thickness, and the case 100/30 could be used as an optimum value for thermal barrier function, while the case 75/30 could provide a more efficient supplementary heating. Results also show that the TAPCW applied in the north orientation is more effective, which has the highest value of interior temperature increase (1.8 ℃), effective PCM utilization ratio (14.14％), reduction size of PE (64.98％) and reduction size of C (34.43％). Overall, the proposed TAPCW presents a satisfactory thermal behavior in the heating season and could contribute to the progress of energy saving retrofit in the vast existing buildings.