Impact of Window Size Modification on Energy Consumption in UK Residential Buildings: A Feasibility and Simulation Study

This study investigates window renovation strategies for a detached building in Belper, UK, analyzing double- and triple-glazed, vacuum, and low-E vacuum windows with varying gas fillings, pillar radii, and spacing. The results reveal that increasing glass layers reduces energy consumption, while a larger pillar radius decreases efficiency. More pillars improve window performance. For windows with the same U-value, a higher SHGC enhances energy efficiency by maximizing solar heat gain, particularly in colder climates. Conversely, reducing the U-value while maintaining a constant SHGC enhances insulation and minimizes heat loss. The study emphasizes the necessity of balancing U-value and SHGC for optimal window performance in different climates. The most effective strategy involves using a low-E vacuum window with a 0.25 mm pillar radius and 40 mm spacing while doubling the south-facing window area, leading to a 7.01 GJ heating load reduction—a 27.9% improvement over modifying the window type alone. Additionally, a key ratio, SHGC/(Uwindow − Uwall), is introduced to assess window size modifications. The results indicate that enlarging windows is beneficial when solar heat gain surpasses additional heat loss, underscoring the importance of balancing heat conduction and solar energy utilization in energy-efficient building design.