Design Optimization of Proportional Plus Derivative Band Parameters Used in Greenhouse Ventilation by Response Surface Methodology

Abstract

Ventilation is one of the most important factors in greenhouse cultivation because the inside temperature of greenhouses rises rapidly in warm climates, and this high temperature may be detrimental to plant growth. The ventilation system in multi-span greenhouses is often controlled by a proportional algorithm. The relationship between temperature changes in the greenhouse and ventilation is not linear. Conventional ventilation strategies mostly employ a proportional band (P-band) control, which contains various settings related to solar radiation, outside temperature, and wind velocity. In practice, these settings may have a relationship with the set ventilation temperature. However, it is difficult to find optimized settings because they must be changed according to the greenhouse location, shape, and local climate changes. In this study, we attempted to optimize the P-band parameters for outside temperature, solar radiation, and wind speed affecting greenhouse ventilation by surface response analysis. Surface response analysis was used to confirm the quadratic response of the relationship between X and Y, which was designed using the central composite design. A total of 32 experimental factors were designed and the results were analyzed by empirical tests. In addition, derivative calculations were added to respond to rapid changes of temperature in the greenhouse and used for ventilation parameters. The results showed that optimized parameters were successfully applied to temperature control and we obtained better performance than without optimized parameters, with a root mean squared error of +/- 1.25 degrees C. It is anticipated that the study results will be useful in providing the numerical guidelines for the influence factors of the ventilation control settings. The study results will be available immediately for the influence factors of the ventilation control settings.