Cooling performance for tomato root zone with intelligent ecological planting matrix temperature control system driven by photovoltaic in greenhouse

Short-term or continuous high-temperature conditions usually occur during summer greenhouse production. However, the existing cooling measures either fail to achieve effective cooling effects or consume excessive energy. In order to better realize the annual output of the greenhouse, this study used an ecological intelligent planting matrix temperature control system to cool more efficiently in the summer. The system combined control strategies with ecological intelligence to study the safe production of tomato under high temperature conditions. It was driven by photovoltaics, and the excess power was stored in the battery to maintain the system's operation under adverse weather. The system controlled the temperature of the plant root zone not over 33℃during the day and around 22℃at night. When the system needed to cool down, the DC water pump in the water tank was turned on to drive the water to cool the root zone of the plant through the pipes in the thermal planting groove of the experimental group, and at the same time, the heat exchange with the phase change material was realized by the heat exchanger in the water tank. The matrix temperature at different depths of the substrate in experimental group and control group was compared to evaluate cooling performance of the system. The results showed that it was necessary to cool down twice to reach the appropriate temperature, and it took one hour each time on sunny day in the summer. It took only one time to cool down on cloudy or rainy day. Compared with the control group under the experimental conditions, the average matrix temperatures of experimental group were reduced by 8.65, 11.38, 11.47 ℃ respectively on sunny (2018-07-18), cloudy (2018-06-30) and rainy (2018-07-01) days. The data of the average temperature of the three weathers were calculated by taking the data of sunny, cloudy and rainy days for three consecutive days. The average maximum temperatures at the D8 of the experimental group were 31.26, 29.92, and 27.89 ℃, respectively, which were 6.51, 5.76, and 6.0 ℃ lower than the control group. The root zone temperature of tomato in experimental group was always lower than the highest tolerance temperature (33 ℃) of tomato root during the day, and kept the optimum temperature (20-23 ℃) throughout the night. All tomato plants in the control group died on the 17th day of the experiment, while plants in the experimental group still grew well and after that they even blossomed and bore fruit. Under this test condition, it took 4.41×106 J energy to run the system at a time, and the cooling power per unit area of the thermal planting groove was 510.42 W/m2, as the average matrix temperature was reduced by 9.03 ℃. It was far less than the energy consumption required for cooling the entire greenhouse air, and it could meet the high demand for precise temperature control of greenhouses in humid and high-temperature environments. In conclusion, in the case of ultra-low energy consumption, the temperature control method of the ecological intelligent planting matrix temperature control system could be used to solve the problems of high temperature tolerance and safe production of greenhouse tomato planting.