Comparison Of Indoor Thermal Comfort And Pollutant Distributions With Different Air Supply Modes

Indoor air environment has become more and more important than ever before in current days because people spend most of their time in the indoor environment. Studies showed that a thermally comfortable environment and indoor air quality are the most important attributes of a inclosed space, they are related to the pollutant sources and HVAC systems used in the buildings. Therefore study on ventilation strategies has been paided extensive attention.The mixing ventilation system currently used provides a uniform air temperature distribution and dilutes pollutant. However, the mixing ventilation system could spread infectious airborne diseases through the pollutant transportation. With the increasing demand on air quality and energy saving, the mode of displacement ventilation, underfloor ventilation and impinging jet ventilation, are gradually applied. Despite the displacement ventilation is widely used as a mean of ventilation to provide good indoor air and save energy, it has some shortcomings due to the low momentum supply, i.e., poor ventilation efficiency in some zones of the room and the fact that it can only be operated in a cooling mode. In comparison to the displacement ventilation system, underfloor air distribution system deliver air through floor diffusers with higher supply air velocities, increasing the amount of mixing. There is a shortcoming that heat supply is poor. A wholly new system called impinging jet ventilation system, claimed to have advantages of both mixing ventilation and displacement ventilation system, i.e., energy saving and good indoor air quality. At the same time it can be used under heating scenarios.To compare the indoor temperature distribution, airflow and thermal comfort environment with the four air supply modes mentioned above, indoor temperature and air velocity were measured under real heat resource condition as well as prosthesis heat resource. Carbon dioxide from human emission was used as pollutant. Pollutant concentrations were measured to analyze and compare the indoor air quality with different air supply modes.The results showed that the temperature gradients are similar in the steady state under the two types of heat resource condition. The temperature distributed more uniform and PD values are slightly smaller in the room with prosthesis heat resource than that of the real heat resource condition. Therefore prosthesis heat resource can be applied for experimental study of indoor thermal environment and air quality. Concentration stratifications were presented in displacement ventilation, underfloor ventilation and impinging jet ventilation systems. While the CO2concentration for the mixing ventilation is more uniform that of the other three systems. In this paper, the results show that the impinging jet ventilation system presents slightly better temperature distribution and velocity field.