aerosol

Ultraviolet germicidal irradiation (UVGI) inactivates viral aerosols in indoor environments. Upper room UVGI systems use wall or ceiling mounted fixtures to create a disinfection zone above the occupied zone. The performance of upper room UVGI systems varies with indoor airflow induced by mechanical ventilation and thermal plumes from occupants, which carries contaminated air into the disinfection zone where viral aerosols are partially inactivated before circulating back into the breathing zone.

For years, ventilation and air-conditioning systems have played an increasingly important role in ensuring sufficient air exchange in buildings. With time buildings are becoming more and more airtight to avoid energy losses through uncontrolled air leakage and mechanical ventilation systems are installed to ensure a good indoor air quality. What is a good approach in theory can fail in practice due to leaky ductwork.

This paper describes two recent applications of aerosol sealing techniques in buildings for improving indoor air quality and reducing energy required for heating, cooling, and ventilation. One application applies a commercially-available duct sealing technology, which has typically been used in single-family applications, to large-building exhaust systems. The initial leakage rates, percent leakage sealed, and issues encountered are presented for several large buildings.

Indoor aerosol particles, their concentration and deposition in displacement, their movements in two ventilated rooms are compared numerically. For the simulation of particle tracks, the discrete trajectory model is adopted whereas the Eularian method is used for solving the continuous fluid flow.

We conducted an on-site test of air-conditioning systems in a hotel in Changsha, Hunan, China in the summer of 2003. And indoor particulate matters, bioaerosols were the main pollutants sampled from indoor spaces and three air-conditioning systems, one of which serves the lobby of the hotel, with the other two supply fresh air to the cook room and dinning-rooms. Short-term and long-term sampling of deposited particles in the air-conditioning systems was carried out and their size distribution was tested by Optical Particle Counters (OPCs).

The quantitative knowledge gained from the assessment of particle deposition in ducts is importantto study, for example, the elimination of air leakage from duct systems with aerosolized sealant particles or to implement strategies of cleanliness of air ventilation systems. The study of particle deposition on the components of ventilation systems contributes also significantly to a better understanding of human exposure to particulate pollution. In this work we investigate deposition of aerosol particles in bifurcating ducts with a curved inlet segment.

Samples near a frying pan, grill plate or deep fryer were taken in 10 kitchens in order to determine the composition of aerosol and vapours in the surrouding air. The main components are aerosols and low molecular aldehydes. Up to 90% of the aerosols consist of triglycerides and fatty acids. An aerosol concentration of 1.5 to 2 mg/m3 can be used as a guideline value to design the ventilation system.

When a person works facing a local exhaust ventilation (LEV) hood, it may be possible to obtain higher concentrations of aerosols in the breathing zone (BZ) than without the hood because recirculating eddies form downstream of the body. These eddies shed periodically in an alternating pattern called vortex shedding, which is thought to be a primary determinant of contaminant transport in and out of the breathing zone (1, 2, 3). Previous computational fluid dynamics (CFD) studies have explored the effect of timedependent airflow on occupational exposure to gaseous contaminants (2, 3).

Preliminary numerical simulations of human exposure to paint-spray aerosols demonstrate the ability of computational fluid dynamic (CFD) software to discriminate between two different orientations of spraying a flat plate in a cross-flow ventilated spray booth. To conduct exposure-scenario simulations using CPD, a conceptual model of reality must be created that is compatible with the computer code. If this conceptual model is not a sufficient representation of reality with regard to the desired outcome, then no matter how accurate the simulation, the results will be of limited value.