A high-temperature environment is one of the most important factors limiting the growth of crops in Chinese solar greenhouses during summer. To reduce the substrate temperature of summer plant cultivation in a Chinese solar greenhouse, we proposed a water-circulating tomato-root zone-substrate-cooling system (WCTRZSCS). The system used water as the circulating medium, a chiller as the cooling source, and polyethylene raised temperature resistance (PE-RT) pipes laid in the substrate as the cooling component. The greenhouse was divided into test area TS₁ (one PE-RT pipe), TS₂ (two PE-RT pipes), and a control area CK (no PE-RT pipe) for the root-zone substrate-cooling test. The results demonstrated that (1) in the summer, WCTRZSCS can effectively reduce the substrate temperature, and (2) WCTRZSCS improves the temperature conditions for tomato vegetative growth. There were significant differences in plant height, stem diameter, dry weight, fresh weight, leaf area, net photosynthetic rate, total root length, and total root projection area between tomatoes in the test and control areas (p < 0.05). The TS₁ and TS₂ growth rates were 60.2% and 81.2% higher than CK, respectively, and the light-utilization efficiency was 56.3% and 81.3% higher than CK. (3) The system’s cooling energy consumption per unit ground area was 35.2~67.5 W·m⁻², and the coefficient of performance (COP) was 5.3~8.7. Hence, WCTRZSCS can effectively reduce the substrate temperature in the root zone, but the profit by tomato cannot offset the cost of using WCTRZSCS. Through the optimization of and improvement in the system, its economy may be further improved, and it is expected to be applied in practical production.

Solar greenhouse is extensively used in horticultural production in China. Natural ventilation is one of the key technological means to adjust the inside environment of greenhouse, while the effects of window opening styles on the inside environment are still not well understood. In the present study, the temperature and air flow field of five operation styles, namely back roof central opening style (G1), back roof evenly spaced opening style (G2), top roof full opening style (G3), style of G1+G3, and style of G2+G3 were simulated using the CFD method. The results indicated that: (1) the simulated and measured results exhibited favorable agreement, with relative errors within 5%; (2) In the case of the windows opening area was the same and only single ventilation style was applied, back roof full opening style exhibited the best cooling effect. The inside average temperature of the greenhouse with G1 style decreased by 0.5 degrees C and 1.6 degrees C respectively compared with those of greenhouses with G2 and G3. (3) The cooling effect of the style of G2+G3 was more favorable than that of the style of G1+G3. The style of G2+G3 exhibited better cooling effect than the single ventilation styles, with the lowest temperature (27.5 degrees C) and temperature uniformity coefficient (0.36).

Plant height and leaf area index (LAI) are crucial growth indicators that reflect the growth status of tomatoes in greenhouses, enabling accurate determinations to effectively estimate crop transpiration and formulate irrigation strategies for reducing agricultural water waste. There is a need for the increased application of related models to simulate tomato growth indices in the traditional greenhouse production in China. This study proposes a nondestructive, real-time monitoring and simulation device for measuring tomato plant height and leaf area index. The weight of aboveground tomatoes was obtained by suspending tomato plants on dynamometers, while the total weight of stem and leaf organs was determined using a distribution coefficient simulation model. The R² value between the measurements from the electronic scale and those from the aboveground fresh weight device for tomatoes was 0.937, with an RMSE value of 0.05 kg. The monitoring device did not affect the average tomato growth during operation. The device will not affect the growth of tomatoes during monitoring. A multiple linear regression was used to compare the measured and simulated values of the plant height and leaf area index of various types of greenhouse tomatoes cultivated in different greenhouse types. The average R² value for simulating plant height was 0.817 with an RMSE of 10.81 cm. The average R² value for the leaf area index was 0.854, with an RMSE of 0.55 m²·m⁻². The simulated values for plant height and leaf area index closely matched the measured values, indicating that the model has high accuracy and applicability in traditional Chinese greenhouses (solar greenhouses and insulated plastic greenhouses). However, further optimization is required for commercially produced, continuous plastic greenhouses equipped with greenhouse environmental control equipment.

The internal air temperature of Chinese solar greenhouse (CSG) has the problem of uneven spatial and temporal distribution. To determine temperature distribution at different locations, we designed a greenhouse temperature real-time monitoring system based on virtual local area network (VLAN) and estimate, including interpolation estimation module, data acquisition, and transmission module. The temperature data were obtained from 24 sensors, and the Ordinary Kriging algorithm estimated the temperature distribution of the whole plane according to the data. The results showed that the real-time temperature distribution monitoring method established was fast and robust. In addition, data validity rate for VLAN technology deployed for data transmission was 2.64% higher than that of cellular network technology. The following results are obtained by interpolation estimation of temperature data using gaussian model. The average relative error (ARE) of estimate, mean absolute error (MAE), root mean square error (RMSE), and determination coefficient (R²) were −0.12 °C, 0.42 °C, 0.56 °C, and 0.9964, respectively. After simple optimization of the number of sensors, the following conclusions are drawn. When the number of sensors were decreased to 12~16, MAE, RMSE, and R² were 0.40~0.60 °C, 0.60~0.80 °C, and >0.99, respectively. Furthermore, temperature distribution in the greenhouse varied in the east–west and north–south directions and had strong regularity. The calculation speed of estimate interpolation algorithm was 50~150 ms, and greenhouse Temperature Distribution Real-time Monitoring System (TDRMS) realized simultaneous acquisition, processing, and fast estimate.

Carbon dioxide (CO₂) is one of the important factors affecting vegetable yield in controlled environments. This study used cucumber as an experimental material to investigate the effects of hanging different amounts of CO₂ generation bags (CGBs) on the growth of temperature-loving vegetables under facility soil cultivation. CGBs of three different densities were set up: no application (TC), eight bags/265 m² (T1), and sixteen bags/265 m² (T2). The results showed the following: (1) Hanging CGBs at different densities significantly impacted indoor CO₂ concentration. Light, temperature, and humidity also affected CO₂ concentration to a certain extent. (2) The application of CGBs improved cucumber growth, photosynthesis, and quality-related indexes, resulting in a 28.9% increased yield compared to the control group. (3) The economic benefits of CGB application in each group were analyzed, revealing the economic benefits of high-density CGB cultivation on solar greenhouse cucumber. This study explored a low-cost and effective CO₂ generation application mode.

The thermophysical properties of a working-fluid play an important role in the process of stirring-heating. The heating process of stirring is accompanied by two processes: the friction between the solid mechanism and the working-fluid and the viscous dissipation of the working liquid. Traditionally, the sensible heat of water-based working-fluids is low, while that of oil-based working-fluids is higher, but the load capacity is relatively low. In order to find a balance between the two, an optimal stirring working-fluid should be selected. In this study, an experimental method was used to study the heating process of 30 kinds of working-fluids. The numerical evaluation model of the effects of thermophysical properties on the comprehensive evaluation index of heat (CEIH) was established by multiple linear regression methods, and a computational fluid dynamics (CFD) tool was used to analyze the heat generation and flow field of different working-fluids in the stirring-heating device. The results show that viscous dissipation is the most important way of stirring-heating. CFD can completely replace the experiment to study the heating effect of stirring. The thermophysical properties of the working-fluid affect the upper circulation and the overall velocity of the double circulation flow. The experimental results and regression model analysis show that specific heat capacity has the greatest effect on the heating effect, but density will also play a positive role in the stirring-heating. Water-based salt solutions such as KCl can achieve a better heating effect, and oil-based working-fluids are not always the best choice.