Investigation on the thermal comfort and energy efficiency of stratified air distribution systems

A stratified air distribution (STRAD) system is a feasible air conditioning design for large space buildings that satisfies the energy conservation and thermal comfort requirements. In this paper, a novel energy efficiency index for STRAD systems is developed using theoretical analysis to properly evaluate the system's energy saving potential. Using a validated numerical model, two typical stratified air distribution designs in a hypothetical terminal building are evaluated based on thermal comfort and energy savings. The influence of supply and return diffuser distributions on the ventilation performance of these two ventilation designs is studied. When the air is supplied at mid-height, the local thermal comfort is greatly improved without sacrificing the energy efficiency due to additional return grilles located at exterior walls. When the air is supplied at floor level, installing additional return grilles at exterior walls slightly alleviates the local draft risk, but doing so largely impairs the energy saving capacity of the ventilation system. To achieve better thermal comfort and higher energy efficiency, a more uniform distribution of supply diffusers surrounding the occupied zone is suggested. When the air is supplied at the floor level, increases in solar radiation intensity can be mitigated by utilizing external shading designs, which are particularly important in preventing too large of a temperature gradient in the region exposed directly to the solar radiation.