Experimental and numerical investigations on heating load reduction of a fan-coil window during heating season

Reducing the heat loss through glass envelopes is essential for achieving efficient heating in winter. The double skin façade (DSF) performs well in specific scenarios but has a limited ability to dynamically adjust thermal performance to adapt to variable outdoor conditions. To actively regulate the thermal performance of glass envelopes, this paper proposes a fan-coil window (FCW) system that combines fan coil units that use low-grade energy with a double-glazed shading window. A numerical model and experimental platform for the FCW are established, and the performance of the FCW system under more than 80 operating conditions during heating season is measured or simulated. The results indicate that as the supply water temperature varies between 8℃ and 20℃, FCW can effectively achieve heating load interception and has a high coefficient of performance (COP). The heat flux of the internal glass can be reduced from 35.1 W/m² to 5.3 W/m² at an ambient temperature of -10℃. Moreover, by altering water temperature and air velocity in cavity, the U-value of FCW varies in the range of 0.2–1.6 W/(m²·K), and the average energy utilization rate exceeds 40%, with a maximum heating load reduction rate and COP of 84.8% and 32.6, respectively. Additionally, approximately 40% of common operating conditions exhibits heating load reduction rate exceeding 35%, with average value of 26.0%, and COP of 68% operating conditions exceeds 12, with average value of 14.0 In conclusion, the proposed window system shows great potential as an energy-saving solution for glass-based building envelopes.