Potentials of energy-active windows with integrated airflow geometries for improved thermal comfort and energy efficiency

Abstract

Optimizing building envelope systems is essential for improving energy efficiency and indoor thermal comfort, especially in hot climates with high cooling demand. This study evaluates the performance of an Energy-Active Window (EAW) system enhanced with internal airflow-modifying elements. Return air temperature (outflow), outflow–inflow temperature difference (ΔT), and inner glazing temperature were extracted from CFD steady-state simulations, while whole-building energy demand and occupant comfort were assessed via EnergyPlus using the Fanger PMV model. Optimized EAW configurations were compared to a base case and conventional glazing systems, including double, triple, and Low-E glazing. The square bar design (SA₂), with three bars spaced 0.1 m apart in the outflow slot, showed the best performance, achieving a return air temperature of 39.04 °C and a ΔT of 16.06 °C. Reducing bar spacing to 0.05 m further improved ΔT to 16.45 °C, lowered the inner glazing temperature to 23.3 °C, and reduced the U-value to 0.12 W/m²·K. The optimized EAW reduced cooling demand by 24 % compared to double glazing, 18 % versus triple glazing, 14 % versus double Low-E, and 11 % versus triple Low-E, and 6.16 % over its base case. Comfort analysis confirmed better PMV values (–0.10, 0.07, 0.53) compared to more negative values (–1.46 in double glazing and –1.44 in triple glazing) in conventional systems. These findings identify the SA₂ configuration as a promising strategy for enhancing both energy performance and thermal comfort in energy-active window systems, while demonstrating a competitive advantage over conventional and Low-E glazing technologies.