Overall performance evaluation of underfloor air distribution system with different heights of return vents

Numerical Study on Effects of Air Return Height on Performance of an Underfloor Air Distribution System for Heating and Cooling

“…Different experiments were conducted with air being exhausted from vents that were located in the ceiling and floor, respectively. Table 2 briefly introduced the experimental conditions and more details can be found in [16]. Figure 3 shows a general agreement between the numerical results and experimental data [29], both in the shape and magnitude of the velocity and temperature.…”

“…Apparently, most of the studies demonstrated that the optimum height of return vent in a small space was around 1.3 m in order to maintain a balance between the thermal comfort and energy saving [14,15]. Furthermore, in our previous research [16], a series of numerical computations with various height positions (Z = 0.8 m-2.6 m) of the return vents were conducted in order to comprehensively evaluate the effects of the height of return vents on thermal comfort, contaminant removal, and energy efficiency. The results revealed that positing a return vent at a lower level was beneficial for saving energy and a lower CO 2 concentration, but it resulted in another larger mean air age (MAA).…”

“…A room model, which was similar to that of our previous study [16], was built as the computational domain for a comparative study on the heating performance and the cooling one of system. In addition, Park and Chang [17] reported that the UFAD system was ineffective for heating when the large downdraught from the exterior windows could block the buoyancy force above the occupant and stagnant air would occur.…”

“…For example, Cheng et al [11] proposed a numerical procedure for predicting the thermal comfort and energy saving for stratified air distribution systems in a large terraced classroom. They revealed that the cooling coil load reduction could be as large as 16.5% of the total space cooling load with separated locations of return and exhaust vents. A numerical study [12] was further performed to investigate the impact of the return vents height (4.8 m-2.3 m) on the energy efficiency of the system in the same classroom.…”

“…The main reason was that the lack of detail and quantitative information of these systems for heating mode. Therefore, a validated CFD model was employed in this study to investigate the effect of the location height of return vents on the energy consumption, indoor thermal comfort, and air quality in the previous domain [16] for heating mode. The objective of this study is to find the optimum height of return vent of an UFAD system for both cooling and heating.…”