Window design is a critical factor significantly influencing building aesthetics, daylighting performance, visual comfort, and energy consumption. Conventional energy-saving strategies often rely on reducing window area, which negatively impacts architectural aesthetics and user satisfaction. This study proposes a novel form-oriented design approach that enhances energy efficiency while maintaining the window area. Four window geometries—flat, polygonal, protruded, and curved—were compared under identical area and material conditions. Key performance indicators included U-value, Solar Heat Gain Coefficient (SHGC), cooling and heating loads, and daylighting performance. The analysis revealed that curved windows achieved the highest cooling performance with an 18.2% reduction in cooling load but exhibited a significant drawback with an 8.2% increase in heating load, indicating substantial winter heat loss. Protruded windows showed a minimal cooling load reduction of only 0.3% and a 3.6% increase in heating load. Polygonal windows demonstrated the most balanced performance, with a 7.1% reduction in cooling load and a 3.8% increase in heating load. These results suggest that in a cold climate like Pyongyang, winter heating performance has a greater impact on annual energy consumption than summer cooling performance, implying that window form selection should not be based solely on summer performance.