温室における燃焼式蓄熱型二酸化炭素施肥システムの省エネルギー性･環境負荷低減性･経済性評価

This study evaluated three types of combustion type CO2 fertilization systems: The thermal storage type (excess heat energy is stored and used for heating), the heat waste type (excess heat is discharged outdoors), and the diffusion type (excess heat is discharged indoors). We analyzed the validity, energy-conserving, environmental load-reducing, and cost-reducing characteristics of these types, and reached the following conclusions.1)The excess heat generated by combustion type CO2 fertilization accounted for several percentages of the daily cumulative solar irradiation during the intermediate period under the standard condition in this study (amount of CO2 fertilization,48 g (CO2) m-2d-1). The thermal storage type is expected to prevent the aggravation of the thermal/humidity environment in the greenhouse and decrease the efficiency of supplied CO2.2)Using the thermal storage type,a maximal energy conservation of 8% and a reduction in CO2 discharge can be expected in large greenhouses (annual energy consumption in the entire greenhouse, about 3 GWh) under the standard conditions of this study (summer/intermediate period ratio, 0.33; thermal storage/discharge efficiency, 0.8).3)The unit cost of CO2 fertilization using this thermal storage type was about 25 yen kg-1 (during depreciation) and about 12 yen kg-1 (after depreciation) under the standard conditions of this study (summer/intermediate period ratio, 0.33; price of unit quantity of heat, 5.5 yen kWh-1; thermal storage/discharge efficiency, 0.8). To reduce the unit cost of CO2fertilization, improvement in thermal storage/discharge efficiency, a decrease in fuel cost, and an increase in the number of days in operation during the intermediate period are necessary.