Selective temperature and humidity control strategy for a chinese solar greenhouse with an event-based approach

This paper introduces an application of a selective temperature and humidity control scheme for chinese solar greenhouses, which are the most widely used in the northern provinces of China. Firstly, a PI controller for temperature is studied with an event-based approach. After the evaluation of different event-generator thresholds, an optimum value is selected which significantly reduces the number of vent movements by 43.8%, while only increasing the temperature error by 1.13%. Secondly, a controller for relative humidity and another controller for absolute humidity were implemented. The results show that the controller for relative humidity performs adequately when the set-point is not high. However, the control action is deteriorated when the set-point is over 70%. The absolute humidity control allows to regulate the humidity for references of any value, but with less control precision. Finally, through a simulation study, the effectiveness is demonstrated for a selective temperature control strategy with a humidity priority control scheme. This control strategy keeps the relative humidity below 80% while controlling the temperature to the set-point, preventing high humidity from damaging the crop.