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.
Tracer gases are commonly used to evaluate the performance of ventilation systems. One way to reduce the time, complexity, and cost of such experiments is to use the carbon dioxide generated by occupants as a tracer gas. In this paper, a method for using the carbon dioxide generated by occupants as a tracer gas for determining the effective supply air flow rate to a zone or the relative air-change effectiveness of a zone is described. The approach is to make use of a model of the accumulation dynamics and a model of the way that occupants generate carbon dioxide.
The common way to determine air infiltration, exfiltration and interzonal flows from tracer gas measurements in multizoned buildings is to rely upon the standard single or multizone model, Vc(t) = Qc(t)+p(t) . Here c, p are zonal tracer concentrations and injections, t is time and V, Q are the sought volumes and flows. This model may work well provided that all zones are sufficiently well mixed and all flows really are constant during the measurements. The latter can be doubtful in naturally ventilated buildings, especially as the measurements may require several hours.
The use of local exhaust is considered to be the most effective way to control pollutant dispersion from intense sources, such as in kitchens, in toilets, as well as in copy machine rooms. The optimum air exhaust rate required to prevent pollutants from escaping into the major occupant areas very much depends on the natural air exchange rate(AER) between the hooded room and the major room space. This paper presents a mathematical model and a test procedure of using tracer gas technique to quantify the AER.
The work presented in this paper is aimed at the definition of tracer gas experimental procedures for measuring the air change rate, the age of air and the air change efficiency in real buildings under mechanical ventilation conditions. The measurement procedures, based on the decay method, were validated in a special experimental chamber and implemented in two rooms of a building under real operating conditions. Measurements of volumetric flow rate through the air ducts of two buildings, performed by means of the constant emission rate method, will be shown and commented.
One of the main aspects determining the thermal behaviour of buildings concerns the distribution and circulation of air. Experimentation was undertaken in the context of the investigation of a method of measurement of the natural ventilation of large rooms. The first objective was to endeavour to characterise the atmospheric conditions around the building, namely, conditions related to wind factors, but also those concerned with the location of the building in relation to neighbouring obstacles (other buildings, relief of the ground, etc).
The study concerns the ventilation of a parallelepiped shape room by means of several systems whose supplying and extracting methods differ, so the different thermic conditions applied to limits. To qualify the efficiency of each of these systems in relation with the various current criteria, we carried out measurements by means of a tracer gas, both with a transitory and a permanent flow. At the same time, numerical simulations were carried out by means of a CFD code which solves the equations of the fluids mechanic, material and heat transfers associated with flows.
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