Research on Optimization Combination of Heat Transfer Coefficient and Solar Heat Gain Coefficient of Plastic Doors and Windows in Frigid Regions and Carbon Reduction Pathways under the Target of Ultra-Low Energy Consumption

In ultra-low energy buildings in frigid regions, plastic doors and windows must simultaneously reduce heat transfer coefficients and optimize solar heat gain coefficients to balance heating demand and carbon reduction objectives. Since solar radiation is fundamentally governed by electromagnetic wave transmission and energy conversion processes, optimizing envelope parameters for efficient electromagnetic energy utilization has become increasingly important in sustainable building engineering. To address the conflict between energy consumption and carbon reduction, this paper constructs an optimal combination of U-value and solar heat gain coefficient together with a carbon reduction pathway. A coupled calculation model of door and window heat transfer and solar heat gain is established using meteorological annual data and an indoor heating setpoint of 20 ◦C. A two-dimensional parametric grid with U ranging from 0.60 to 1.20 W/(m2·K) and SHGC ranging from 0.30 to 0.60 is evaluated through dynamic load calculations, while life-cycle carbon emissions are incorporated into a multi-objective optimization framework using a genetic algorithm and weighted entropy method. The results indicate that the optimal interval is U = 0.70–0.80 W/(m2·K) and SHGC = 0. 45–0.50, reducing life-cycle carbon emissions from 24.8 to 19.9 kgCOe/(m2·a) and peak heating load from 38.4 to 31.6 W/m2. The proposed approach provides practical guidance for ultra-low energy building design and electromagnetic radiation-aware solar energy utilization.