age of air

The world has experienced the devastating nature of airborne transmitted diseases through the COVID-19 pandemic. Significant actions were taken in order to reduce the number of new infections, such as quarantines, social distancing, mask wearing, frequent hand washing and surface disinfection. However, all these measures have proven insufficient to eradicate short and long-range infections, confirming the need for engineering tools to control the indoor air quality.

In order to provide patients with a high quality indoor environment and ensure a pleasant working place for medical care personnel, thermal environment and indoor air quality are regarded as two of the most important requirements. 

Total heat recovery type ventilators that are connected to each room with ducts are mainly installed in Korea, but they raise concern over duct pollution. In this study, indoor environments made by thin line type ventilators installed in dwelling units of apartment houses are investigated by CFD. Results show the case that thin line type ventilators installed in each room - including kitchens - make the best indoor environment that maintains air velocity at under 0.25m/s, and evenly distributes the age of air in all areas.

The purpose of this paper is to analyze the indoor thermal environment and ventilation efficiencycreated by various heating and ventilation systems using CFD. In the case of one room, the value ofmean local air exchange efficiency????*1 of breathing zone*2 becomes about 1.0, because fresh airspreads completely in the room when air-conditioners are operated. In contrast, when air-conditionersare not operated, the mean ?? becomes smaller than 1.0, and the area of poor ventilation efficiencybecomes large.

States that it is difficult to achieve good mixing in a large space and that the usual methods to evaluate the ventilation system in such large spaces with the age of air measured by tracer gas is not often practicable. Proposes a new method to evaluate this ventilation, based on the normal step-down or decay method. A small control volume of tracer gas is used as opposed to filling the entire space. the local mean age of air is then measured in a study of the transient decay curve of the tracer gas concentration.

The characteristics of a hybrid air-conditioning system, utilizing natural and mechanical ventilation, is investigated in an office setting. The characteristics of the indoor environment are examined with CFD(Computational fluid Dynamics) simulation under various conditions of incoming outdoor air. The control of the room air conditioning system (VAY system) is included in the calculation through changing the supply air volume to keep the task zone's temperature at a target temperature.