Graphical Presentation of Area Measurements
By measuring the concentration of an air contaminant at the same time in several points with the help of a real-time monitoring instrument it is possible to visualize its spatial distribution by making a graphical presentation of data. If the measurements for example are made at a constant distance from the floor and at regularly placed measuring points in a grid, it is easy to produce a 3D graph illustrating how the contaminant concentrations are distributed.11 A grid with 3 x 3 points may be enough to give a rough view, but a slightly denser grid with 5 x 5 measuring points may be preferable. Experience shows that it is possible to col lect data manually within a few minutes for a denser grid. By manual collection of data it is therefore possible to visualize the spatiai distribution if the situation is mainly stable within the time limits for collection of data.
Many different standard software packages for computers may be used tor the processing of data to a.3D graph. Figure 12.8 illustrates such a grid map produced from data from a.5 x.5 points measuring grid. By also superimposing the graph over a perspective drawing of the measured area, the result will very effectively visualize how, tor example, contaminants are leaking out from a machine and in what direction the contaminants are transported. By making a series of such measurements and graphical presentations it is possible to visualize the effect of changes such as alterations in the ventilation system.
To produce this kind of grid map by quickly measuring the concentrations at some points for immediate processing and graphical presentation is a simple and often effective way to communicate the results to persons who are not trained to analyze primary results of measurements. The method must, how ever, be used with care since there is a risk that the sampling of data itself may affect the airflow in the studied area. The equipment needed is relatively expensive, and the method is therefore of interest when the prerequisites are already available for other reasons.
It is of course also possible to arrange so that the measurements are made at every point with a fixed instrument and the data transferred to a computer equipped with suitable software to produce the grid map, all in real time. If the graph is also superimposed on a video picture from the measured area, the result will be a video, visualizing the spatial distribution in real time.
In a factory hall.
A similar graphical presentation of the spatial distribution of a tracer gas or a real contaminant and thereby to some extent the airflow in the studied area is based on the use of computed tomography and optical remote sensing.121′ IR beams are sent out horizontally and reflected back to an IR analytical instrument, analyzing the average concentration of the contaminant along the IR beam. By combining data from several measured lines it is possible ro present data in a similar way to Fig. 12.8. Those methods presuppose access to an expensive and complicated sampling/data processing system.
Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK