Quantifying the Thermal and Energy Impacts of Air Infiltration in a Hot-Humid Educational Building: A Sensitivity Analysis Using a Field-Evaluated EnergyPlus Model

Air infiltration is a highly uncertain input in building energy simulation, yet its effects on cooling-dominated educational buildings remain poorly quantified. This study quantified infiltration sensitivity in a 34,168 m2 university building in hot-humid Jazan, Saudi Arabia, using an EnergyPlus model developed in a companion field study. The infiltration rate of all 31 zones was varied from 0 to 1.0 air changes per hour (ACH) in annual simulations under conditioned (Ideal Loads Air System, 22.5 °C, 60% relative humidity) and free-running operation. Each 0.1 ACH increased the annual thermal cooling requirement by 1766 MWh, 72% of which was latent. At the commonly assumed rate of 0.8 ACH, infiltration accounted for 84% of the annual requirement. With a coefficient of performance of 3.0, reducing infiltration from 0.8 to 0.3 ACH would save about 2950 MWh of electricity, USD 251,000, and 1670 t CO2 per year. Raising the setpoint to 24 °C kept the predicted mean vote within ISO 7730 Categories I–II and reduced the cooling requirement by 10–12%, but the infiltration penalty remained 1540 MWh per 0.1 ACH. In free-running operation, infiltration lowered indoor air temperature by 4.2–6.6 °C, yet operative temperatures still exceeded adaptive comfort limits. For educational buildings in hot-humid climates, airtightness combined with controlled, dehumidified ventilation should therefore be treated as a primary design and retrofit parameter.