Investigations on the Energy Efficiency of Stratified Air Distribution Systems with Different Diffuser Layouts

Abstract

This paper investigated the influence of diffuser layouts on the energy performance of stratified air distribution systems (STRAD). The energy saving potentials of STRAD systems are theoretically analyzed. The cooling coil load of a STRAD system is proportion to the return air temperature, while inversely proportional to the exhaust air temperature. Based on that, numerical studies are conducted for the applications of STRAD systems in three typical building space types. Two evaluation indices are developed to assess the energy performance of STRAD systems. The simulation results demonstrated that further energy saving could be achieved by keeping the exhaust grille at ceiling level and decreasing the height of return grille. Therefore, in order to optimize the energy saving capacity of STRAD systems, the return grille is recommended to be located as low as possible, whilst paying special attention on the "short-circuit" of cold supply air. Furthermore, when the STRAD system is applied in large space buildings with a big horizontal span, supply diffusers should be distributed surrounding the occupied zone as uniformly as possible, while avoiding installing return diffusers at exterior walls.

Effects of Return Air Inlets’ Location on the Control of Fine Particle Transportation in a Simulated Hospital Ward

“…When the height of the return air inlet was 0.3 m, the energy consumption was the lowest. Cheng et al [ 49 ] also had a similar conclusion. Due to the limitation of the experimental chamber conditions, the minimum return air inlet height was 0.7 m. In CFD, the heights of return air vents were calculated at 0.3 m, 0.7 m, 1.2 m, 1.6 m and 2.0 m, to make up for the lack of experiments.…”

“…Cheng et al [ 49 ] suggested that the return air vents in a small space could be located in a lower area to save the energy of the cooling coil. Heidarinejad et al [ 20 ] studied the effects of the heights of the side wall return air inlet and other parameters on the energy consumption, thermal comfort conditions and indoor air quality in UFAS, and found that reducing the height of return air inlet was more energy efficient.…”

Transmission mitigation of COVID-19: Exhaled contaminants removal and energy saving in densely occupied space by impinging jet ventilation

“…For a system with the exhaust/return-split layout ( Fig. 5 ), Q coil is calculated by the following equation [ 75 , 76 ]: where Q spcae is the space cooling load (consisting of heat sources and external heat flux through walls), T e is the exhaust temperature, and T f is the fresh air temperature. The fresh air flow rate equals the exhaust flow rate for airtight spaces.…”

Optimizing the Return Vent Height for Improved Performance in Stratified Air Distribution Systems

“…The exhaust/return-split layout (Figure 1b) can reduce the cooling load further when thermal stratification exists. As explored by Cheng et al [8,9], this strategy involves trapping heat in the upper room area, thereby increasing the temperature of the exhaust air and relieving the cooling load. However, this approach introduces a trade-off: while it reduces energy consumption, it exacerbates vertical temperature gradients, potentially impacting thermal comfort.…”