Ting Yao

Evaluation of thermal comfort conditions in a classroom with three ventilation methods.

UNLABELLEDnThermal sensation is studied experimentally under mixing ventilation, displacement ventilation, and stratum ventilation in an environmental chamber. Forty-eight subjects participated in all tests under the same boundary conditions but different ventilation methods in the classroom. Thermal comfort analysis was carried out according to the designated supply airflow rate, room temperature, and relative humidity for the three ventilation methods. The thermal neutral temperature under stratum ventilation is approximately 2.5 °C higher than that under mixing ventilation and 2.0 °C higher than that under displacement ventilation. This result indicates that stratum ventilation could provide satisfactory thermal comfort level to rooms of temperature up to 27 °C. The energy saving attributable to less ventilation load alone is around 12% compared with mixing ventilation and 9% compared with displacement ventilation.nnnPRACTICAL IMPLICATIONSnThe confirmation of the significantly elevated thermal neutral temperature can have a number of implications for both thermal comfort in an air-conditioned room and energy consumption of the associate air-conditioning system. With respect to the former, it provides scientific basis for the feasibility of elevated room temperatures, and with respect to the latter, it reveals considerable potentials for energy saving.

Uniformity of stratum-ventilated thermal environment and thermal sensation

Three human test series were conducted to evaluate the uniformity of the thermal environments in a stratum-ventilated chamber with dimensions of 8.8xa0m (L)xa0×xa05.1xa0m (W)xa0×xa02.4xa0m (H). In all, nineteen conditions were generated by adjusting the room temperature, supply airflow rate, and supply terminal type. An air diffuser performance index (ADPI) of at least 80% was achieved for most cases. This result shows that the air velocity and temperature in the occupied zone are reasonably uniform. Subjective assessments using the ASHRAE 7-point scale indicate that the thermal sensations of the subjects in stratum ventilation are also uniform. This study examines the applicability of the predicted mean vote (PMV) model for evaluating stratum ventilation. When compared to the actual mean thermal sensation votes (ATS), the PMV values are acceptable. The PMV results at a height of 1.1xa0m above the floor show better agreement with the ATS than at a height of 0.1xa0m.

Numerical comparison of dispersion of human exhaled droplets under different ventilation methods

Stratum ventilation has been proposed to accommodate elevated room temperatures recommended by several governments in East Asia for energy saving. One key issue in evaluating the performance of stratum ventilation is whether this air distribution method performs significantly different in person to person infectious diseases transmissions. Particle dispersion in a classroom under mixing ventilation, displacement ventilation and stratum ventilation respectively are investigated by numerical simulation. The drift-flux model based on an Eulerian-Eulerian approach is adopted to simulate the particle movement in a room. The results show that the flow patterns created by different ventilation methods have great influence on the particle fates. The particle concentrations for the breathing zone under stratum ventilation are significantly lower than that under mixing ventilation and/or that under displacement ventilation, which imply that the risk of pathogen inhalation under stratum ventilation is lower than that under mixing ventilation and/or displacement ventilation.

A Case Study of the Energy Saving Potential of Stratum Ventilation

Abstract Stratum ventilation is a recently proposed air distribution system. It works by creating a layer of fresher air in the occupants breathing zone. This is achieved by placing large supply inlets along the side-walls of the room just above the height of the occupants. Fresh air is emitted into the room and gradually loses momentum. The supply velocity is sufficiently strong to provide fresh air directly to the occupants without space mixing. This technique has been proposed as a method to cope with elevated indoor temperatures in summer, which is required by several governments in East Asia for carbon reduction. Previous studies have shown that stratum ventilation provides good indoor air quality (IAQ) and thermal comfort. This paper is intended to demonstrate the energy saving potential of stratum ventilation by comparing its energy performance with that of displacement ventilation. A typical classroom is used as an example. Computational fluid dynamics (CFD) simulations were conducted to study airflow and pollutant transport in the classroom. The air quality and comfort performance (PPD, PD and local mean air age in the occupied zone) of the stratum case were found to be comparable to those of displacement ventilation. In addition, energy saving of the stratum ventilation case, under the current set-up, was found to be significant.