This study proposes a hybrid triple glazing system with CO2 and vacuum gaps and determines its optimum thickness and accompanying heat transmittance (Ug value).The proposed system comprises a typical vacuum section and a CO2 section, utilizing the greenhouse gas to improve building thermal performance. The optimum thickness of the vacuum section was at 6.2 mm from previous studies. To determine the optimum thickness of the CO2 section, the Ug value of 120 combinations of glass thicknesses and CO2 gap were evaluated in 1-mm increments using the THERM & WINDOW programs.

System: The Ug value decreased rapidly with increasing CO2 gap for all glass thicknesses, up to a CO2 gap of 10 mm, after which no change was observed. The Ug value reduction ratio for the 1–10 mm thick glass was 14.11–14.38% when the CO2 gap was increased from 1 to 10 mm, with the 6–7 mm glass thickness exhibiting the greatest reduction ratio of 14.38%. Therefore, the optimum thickness of the proposed hybrid triple glazing system is 22.2–23.2 mm, comprising a 16–17-mm thick CO2 section and 6.2-mm thick vacuum section, with a Ug value of 0.274 W/m2·K. The optimum thickness of the CO2 gap and total thickness of the glazing system and Ug value will need to be slightly adjusted depending on the results of future experiments.