A new technique for measuring air change rates in indoor spaces using the step down method of video image signals

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Video camera calibrations, wind tunnel experiments and field experiments have been performed to develop a new method of measuring air change rates using a video imaging technique. The camera calibrations showed good correlation between image signals and luminous reflectance of achromatic color chips. This was achieved by appropriately adjusting the pedestal level of the video camera so that the image signals were made equal to zero for the black level of the picture. In the wind tunnel experiments, air obtained by the step down method assuming perfect mixing of tracer mists inside the spaces. The video image method could measure air change rates with an error of less than 9% of those by the tracer gas procedure using a high-speed hydrocarbon analyzer. In the field tests, air change rates in the test house with test space were also measured using smoke candles as tracers. It was verified that the video method could measure air change rates with virtually the same precision as derived from the decay curves of smoke particle concentrations using an aerosol monitor.