Trouble shooting air distribution problems in mechanically ventilated offices often has to be carriedout in limited "after hours" periods. The method of applying a pulse of tracer to the fresh air supplyhas been found to be too time consuming to map the local mean age of air over complex floor plans.In response an automated gas chromatograph has been developed to make air change efficiencymeasurements in real time using the method of homogeneous emission.
The effects of different kinds of room ventilation were evaluated in an experimental chamber and in kitchens of four residences in Beijing. Carbon monoxide was used as a tracer gas in the chamber, and this together with nitric oxide and nitrogen dioxide concentrations from the gas appliances were measured in the chamber and the kitchens. The ventilation styles evaluated were natural ventilation, an exhaust fan and a kitchen range hood.
The concept of ventilation effectiveness for mechanical ventilation of an airspace is reviewed and associated parameters for describing the performance of ventilation systems are described. The idea is applied to a study of the thermal environment in the waiting hall of a railway station. Two ventilation schemes: one with a ventilation system only and the other with an air-conditioning system were considered. The proposed air-conditioning system would provide air at a temperature only 5 °C below the ambient but with a higher air circulation rate.
The first part of the paper will show some aspects of experimental research on air distribution in ventilated rooms. The study has been carried out to get an understanding of the air movement and the ventilation effectiveness by means of tracer gas measurements. It has been investigated the velocity and the distribution of the concentration in a two-dimensional isothermal flow issue of a linear supply opening. The second part of the paper will describe a proposed zonal model in 9 zones.
The effectiveness of a ventilation system in terms of the age of air and its ability to remove contaminants will be significantly affected if part of the exhaust air is recirculated. In this paper the consequences of recirculation of air in mechanical ventilation systems on ventilation effectiveness parameters is examined. Two alternative methods of establishing ventilation effectiveness parameters relating to air change efficiency and contaminant removal effectiveness when recirculation of air is present are presented.
A high resolution particle-imaging velocimetry has been developed and applied to study full-scale room air flows. The system is designed to study local field quantities in occupied zones (microclimate), ventilation effectiveness, and airborne pollutant transport in the indoor environment. The system can be applied to evaluate indoor environment in typical commercial and residential settings. The technique and instrumentation have been applied successfully to study localized air flow patterns and particle concentration distribution in the indoor environment.
In order that sampling points may be strategically located, it is desirable to have knowledge of the spatial variation of ventilation eflectiveness parameters prior to measuring them using tracer gas sampling techniques. The research described in this paper is being carried out to establish a tracer gas sampling strategy as well as to facilitate the prediction of ventilation effectiveness parameters. The procedure developed requires the division of the internal space into a large number of cells and, by the application of CFD, the mass flow rates between adjacent cells to be established.
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