Evaluation of a Plant Temperature Based Greenhouse Control Strategy

Abstract

A plant temperature based greenhouse control strategy was evaluated and compared with conventional air temperature based control strategies. These control strategies consisted of 3 temperature integration (TI) regimes with low pre-night temperatures of 17°C and 13°C (PNT17air and PNT13air regimes were controlled based on air temperature, and a PNT13plant regime was controlled based on plant temperature) were applied from 6 pm to 9 pm with 3-days of integration period. Same target 24-h average temperature of 18.46°C for 3 TI regimes was maintained by adjusting temperatures in other periods during a day. A different climate control strategy was adopted for PNT13plant since plant temperature frequently deviate significantly from air temperature. Two infrared sensors/infrared cameras were installed in two compartments with PNT13plant regime and integrated with Argus control system. The TI regimes were implemented using the Argus Smartheat climate control program with actual greenhouse temperature (air or plant temperature measured in preceding days). Lower relative humidity (2-3%), higher leaf to dew point temperature differences (3-4°C), and higher vapor pressure difference (VPDleaf to air) with PNT13 regimes (PNT13plant and PNT13air) in comparison to PNT17air indicated higher potential for lower condensation on the leaf surfaces. There were no significant differences in growth parameters of tomato crop among 3 TI regimes (control strategies). The early yield with PNT13plant was about 12% higher than PNT17air and about 23% higher than PNT13air regime. However, total yield for Big-Dina was slightly higher (2%) with PNT13plant in comparison to PNT17air and PNT13air regimes. The energy consumptions with PNT13plant were about 5-10% lower than PNT13air and PNT17air regimes from March to May. Thus, this research demonstrated that the temperature integration regime with plant temperature based greenhouse control (PNT13plant) showed some potentials in improving energy use efficiency, fruit yield, and microclimate.