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This study aims at analyzing carbon dioxide changes in urban-type plant factory systems, which are capable of producing plants with surplus carbon dioxide in urban areas. The system consisted of plant module and human module of 32 ㎥ each, and was designed to use the carbon dioxide from human module for plant growth and to return the cleaned air to human module. Time constant, presenting controlled characteristics of the system, was 3.5 min. Ventilation numbers were 0.407 hr^(-1) with air circulation and 0.086 hr^(-1) without air circulation in two modules. The time taken for carbon dioxide concentrations of two modules to be equal could be controlled by the air exchange rate between two modules. Carbon dioxide concentrations of plant module without plants were 800-1100 μ㏖·㏖^(-1) and 900-1400 μ㏖·㏖^(-1) for one and two persons´ stay in the human module, respectively. With 150 lettuce plants, carbon dioxide concentrations of plant module were 600700 μ㏖·㏖^(-1) at 130 g of average leaf weight and 900-1100 μ㏖·㏖^(-1) at 75 g of average leaf weight for one and two persons´ stay in the human module, respectively. Moreover, 0.15% of oxygen increment was observed in plant module caused by photosynthesis at 85 g of average leaf weight. From the results, the urban-type plant factory was proved to satisfy the needs of carbon dioxide for plant production and to reduce the accumulation of carbon dioxide in the urban area.
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