Adjustable window–Trombe wall composite envelope for solar heating: An experimental study of thermal performance under different operating conditions

The thermal performance of building envelopes is important for effective passive solar heating, particularly in solar enrichment zones such as the Qinghai–Tibet Plateau. Large fluctuations in temperature and solar radiation pose significant challenges for passive solar heating. Therefore, building envelopes must simultaneously satisfy conflicting daytime and nighttime thermal requirements, a condition that is difficult to achieve with conventional envelopes exhibiting static thermal performance. To address this challenge, this study proposes an adjustable window-Trombe wall composite envelope (AWT). The envelope integrates a vertically slidable window for adjustable insulation/heat gain performance and a Trombe wall incorporating rotatable multilayer PCM-insulation louvers for adjustable thermal storage performance. By adjusting the slidable window to strengthen nighttime thermal insulation while remaining daytime solar heat gain. By rotating the PCM-insulation louvers within the Trombe wall to enhance solar heat absorption during daytime and release stored heat indoor at night. The experiments were conducted in artificial controlled environment with different operating conditions to investigate the dynamic thermal performance of AWT. Compared with the non-adjusted condition, heat loss of the transparent part was reduced by 53.2% at night, while the heat loss of the opaque part was reduced by 85.6% and the indoor heat gain was improved by 1268.6 kJ·m-2 during nighttime. Overall, the solar heating efficiency increased from 22.7% to 72.6%. This study provides evidence for the application of adjustable building envelopes for passive solar heating in solar enrichment zone.