Decoupling exhaust and return vents of supply momentum-driven stratified thermal environment with reinforced supply air jet entrainment from occupied zone

The supply momentum-driven stratified thermal environment created by advanced air distribution is a promising solution for sustainable and livable indoor environments. This study proposes a strategy to decouple the exhaust and return air for the supply momentum-driven stratified thermal environment. Experimentally validated Computational Fluid Dynamics simulations are used to verify the effectiveness of the strategy regarding energy efficiency improvement in a stratum-ventilated office. The proposed decoupled strategy positions the return vent below the exhaust vent and above the supply vent. The proposed decoupled strategy has two mechanisms for energy efficiency improvement, i.e., 1) reducing the cooling load of return air by lowering return air temperature relative to exhaust air temperature, and 2) advancing the airflow pattern with improved cooling efficiency of the occupied zone by reinforcing and suppressing the entrainments of the supply air jet from the occupied zone and the upper zone, respectively. The advanced airflow pattern reduces the cooling loads of both return air and fresh outdoor air and increases the Coefficient of Performance. Decreasing the height of the return vent strengthens Mechanism 1, but nonmonotonically affects Mechanism 2. By properly determining the height of the return vent, results show that the proposed decoupled strategy saves energy by 13.5% and 11.9% in thermally neutral and slightly warm environments, respectively. This study contributes to advancing air distribution for energy saving with thermal comfort.