Impact of window performance on the thermal comfort and energy consumption in the building equipped with internal daylighting louvers

This study investigates the impact of internal daylighting louvers on energy consumption and thermal comfort, considering variations in window thermal performance. A 22.8 m² office space with a south-facing window with internal daylighting louvers was modeled using DesignBuilder.

To examine various combination of window and internal daylighting louvers, parametric simulations were performed for 277 window configurations with U-values ranging from 0.70 W/m²K to 5.9 W/m²K, solar heat gain coefficients (SHGC) from 0.19 to 0.9, and visible light transmittance (VLT) values from 0.09 to 0.91. These configurations included 151 single-layer windows, 114 double-layer windows, and 12 triple-layer windows. Four louver configurations were tested: baseline (fully folded), fully closed, fully open, and half-open.

The results indicated that implementing louvers increased lighting and heating energy consumption, while reducing cooling energy consumption, because the solar heat transmission was reduced by internal daylighting louvers. The most significant impact on energy consumption was observed in single-layer windows, while discomfort time was most affected by the triple-layer louver configurations.

The variation rate of total energy saving was -33.0 % ~ 35.1 % with fully closed, -19% ~ 15 % with fully open, and -28.5% ~ 22.5 % with half open louvers. The maximum energy savings, averaging 9.2%, were achieved with single-layer windows. When the SHGC increased, the energy-saving rate demonstrated a high R² value above 0.9, regardless of the louver configuration.

The VLT value greater than 0.7 showed effective energy savings, particularly with a half-open louver configuration, regardless of the window layer. These findings suggest that operating indoor daylighting louvers in a half-open configuration in windows with higher SHGC value and VLT values above 0.7 with half-open louvers can enhance energy efficiency and reduce discomfort time.

The results of this study highlight the significant impact of louvers, influenced by the SHGC and VLT of windows, on both energy consumption and thermal comfort. Therefore, it is essential to consider window performance and louver configuration together to achieve optimal energy efficiency and thermal comfort.