Abstract
The purpose of this research is to study security of $CO_2$ exhaust at night in indoor air quality purifying system using plants. For this purpose, two same units for experiment were built, and difference of $CO_2$ exhaust by existence and nonexistence of plantation were measured. To reduce error by entrance of people, automatic measurement system were developed and used. At first, baseline were measured to check standard value, and next, $CO_2$ exhaust by plantation were measured. As a result, in baseline experiment, values of all spaces were steady as 400~500 ppm. When plantation was set-up, value of $CO_2$ at night was measured high as 150 ppm, and maximum value was around 600 ppm. This result is a lot lower than maximum standard of $CO_2$, 1000 ppm.