Assessment of Double-Glazing Performance on HVAC Energy Demand Using the HAP Simulation

Abstract

Windows are a major source of heat loss and a significant contributor to solar heat gain in residential buildings, particularly in cold-dominated climates. In Kabul, Afghanistan, where winter heating demand is high, improving window thermal performance can significantly reduce HVAC energy consumption. This study evaluates the impact of double-glazed windows on heating and cooling loads in a typical mid-rise residential building using the Hourly Analysis Program (HAP). Two scenarios were simulated: single-glazed windows as the baseline and double-glazed windows (3 mm glass + 6 mm air gap) as the improved case, with all other building and operational parameters held constant. Results indicate that double glazing reduces the peak heating load by 14.9% and the cooling load by 6.2%, demonstrating improved thermal resistance, lower U-value, and reduced solar heat gain. These findings highlight double glazing as an effective and practical strategy for enhancing energy efficiency and indoor comfort in residential buildings in Kabul and similar cold and semi-cold climates.