Video camera calibrations and field experiments have been performed to develop a new method of measuring air change rates using a video imagingjtechnique. Thecalibration of video camera usedifor broadcasting showed good correlation between image signals and luminous reflectance of achromatic color chips. This was achieved by appropriately adjusting the pedestal level of video camera so that the image signals were made equal to zero for the black level of the picture. The 8 mm video camera caused non-linearity at low luminous reflectance due to the narrow dynamic ranges. In the field tests, air change rates in the test house were measured from the decay curves of video image signals obtained by the step down method assuming perfect mixing of tracer particles inside the spaces. The smoke candles were used as tracers, and the mean diameter of the smoke particles ranged from 0.77 μm to 1.06 μm. When adjusting camera f-stops and illuminance for the experimental conditions, it was verified that the digital 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.
