Development of strategies for model-based control of CO2 supplement in greenhouse

초록

Supplement of carbon dioxide (CO₂) positively improves leaf photosynthesis and thus productivity for greenhouse crops. However, cost-efficient control of CO₂ supplies is necessary since it is expensive. This study aimed to develop strategies for model-based control of CO₂ supplement. The control strategies are based on the prediction of the amount of CO₂ taken up by the crop and ventilated CO₂ loss. Equations have been employed to estimate photosynthetic rate, ventilation rate, ventilated CO₂ loss, and current internal CO₂ concentration. Strategies for model-based control of CO₂ supplement are as follows: i) a step to set the target CO₂ concentration (Cg), ii) a step to input predicted values (PV) of leaf temperature (LT), greenhouse air temperature (DT), relative humidity (RH), and measured internal radiation (IR) and CO₂ concentration (Ci) prior to the first supplement of the day to estimate net assimilate rate, ventilation rate, and ventilated CO₂ loss, iii) a step to calculate the first amount of supplemental CO₂ from the PPFD level higher than 400 µmol m-2 s-1 level, and to supply the first CO₂ fertilization (if the Ci is lower than Cg, the CO₂ is supplied, or if it is higher than the Cg, the CO₂ is not supplied), iv) a step to predict current CO₂ concentration (Ct) inside greenhouse after t time (after calculating the net assimilate rate and ventilated CO₂ loss from the first supplement of the day, the CO₂ concentration become the Ct), v) a step to decide a further supplement (if Ct is lower than Cg, the CO₂ is supplied, or if it is higher than the Cg, the CO₂ is not supplied). The validation experiment performed to compare the calculated with measured Ct showed a correlation coefficient of r2=0.82 (n=98). A future study will implement the algorithm into a commercial integrated environmental control system. © 2025 International Society for Horticultural Science. All rights reserved.

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