Evaluating the effectiveness of transom window in reducing cooling energy use in high-rise residential buildings in Hong Kong

Abstract Transom window (TW) has been demonstrated to be effective in enhancing natural ventilation in high-rise residential buildings in tropical climates. However, virtually no work has been done to investigate whether a naturally-ventilated hybrid system (using enhanced ventilation created by TW supplemented with air-conditioning (AC)) is effective in reducing cooling energy consumption and providing the desired thermal comfort. For this purpose, cooling energy usage of an AC only system is compared with that of a hybrid system for achieving the same thermal comfort in high-rise residential buildings in Hong Kong. In this study, a carefully-designed methodology which involves the use of market survey, statistical analyses, site measurements, and integration of CFD and EnergyPlus simulations was adopted. Market surveys and statistical analyses were used to provide reliable input data for simulations. Site measurements of ventilation were used to assess the uncertainty of CFD simulation results. The integration of CFD and EnergyPlus simulations were for accurate predictions of natural ventilation performance (ACH) and air velocities achieved with TWs, hour-by-hour air temperatures, and hour-by-hour cooling energy use of the hybrid and the AC only systems. The simulated air velocities and temperatures were used for thermal acceptability analysis. It was found that depending on the TW design, average improvement in ACH ranges from 117 % to 190%, and the associated cooling energy saving from hybrid system ranges from 22.2% to 22.7%. The results confirm the effective use of TW in reducing cooling energy use and providing thermal comfort in high-rise residential buildings in Hong Kong.