湿帘风机安装高度对Venlo温室降温效果分析

针对大型玻璃连栋温室（Venlo温室）在夏季湿帘-风机联合机械降温过程中出现的温度垂直梯度大、降温不充分、冷量浪费的问题，该研究设计并优化了不同湿帘和风机的安装高度（即设备距离地面的最低高度），分析其对温室降温效果的影响。采用试验和仿真相结合方法，通过与试验温室对比验证仿真模型准确性，并以仿真的方式设计不同的安装高度方案。结果表明，在3.2 m安装高度内，当湿帘安装高度为0.8 m，风机安装高度为3.2 m时降温效果最明显，温室平均温度降低了2.1℃；湿帘安装高度为3.2 m，风机安装高度为3.2 m时温度垂直梯度最小，温室平均温度的垂直梯度降低了5.8℃。湿帘和风机安装高度的变化对Venlo温室的综合降温效果影响较大，适当的降低湿帘安装高度和提高风机安装高度，可以加强温室流场换热过程，进一步强化温室湿冷空气流场的流动均匀性。该研究为温室湿帘和风机降温系统设计提供了进一步优化的理论依据。

Analysis of cooling effect on the Venlo greenhouse depending on the installation height of wet curtain and fan

Abstract: As an indispensable design parameter in the large glass greenhouse complex (Venlo greenhouse), the installation height (minimum distance from the ground) of the wet curtain and fan in the mechanical cooling system plays a significant role in greenhouse performance. In order to address the issues of large vertical temperature difference, insufficient cooling, and insufficient cooling consumption that occur in the process of mechanical cooling of the wet curtain and fan of Venlo greenhouse in summer, the influence of different installation heights of the wet curtain and fan on the cooling effect of the greenhouse was analyzed using the method of combining experiment with numerical calculation in this paper. The experimental greenhouse was analyzed through a two-factor, four-level simulation design and range analysis of the different installation heights of the wet curtain and fan. The experimental method involved measuring data from the experimental greenhouse. The greenhouse is a butterfly-shaped glass greenhouse located in Kemulang, Tianhe District, Guangzhou, which was newly built in 2019 in the Demonstration Base of Guangdong Agricultural Technology Extension Center, and equipped with a mechanical cooling system, including wet curtains, fans, and environmental data collectors. The experimental data was collected in August 2021, and the numerical calculation method was based on CFD. 16 different combinations of the installation heights of the wet curtain and fan were simulated for the greenhouse. The installation heights were 0.8, 1.6, 2.4, and 3.2 m. Data was processed by using the range analysis method, with the average temperature of each installation height serving as the evaluation standard for the cooling effect. The simulation method was verified, with an average temperature error of 1.5?℃ for the simulation model. The simulation model was also verified for cell independence, with an average error of 1.8?℃ when the number of cells increased and an average error of 0.9?℃ when the number of cells decreased. The results showed that within the 3.2?m installation height: Simulation program 4, that was when the wet curtain installation height was 0.8?m and the fan installation height was 3.2?m, had the most obvious cooling effect, with the average temperature of the greenhouse reduced by 2.1?℃; the maximum temperature vertical gradient in the greenhouse was 8.1?℃, which was 6.4?℃ lower than that in the experimental greenhouse; the average temperature vertical gradient was 7.1?℃, which was 4.3?℃ lower than that in the experimental greenhouse; when the wet curtain installation height was 3.2?m and the fan installation height was 3.2?m, the temperature vertical gradient was the smallest, and the average temperature vertical gradient of the greenhouse was reduced by 5.8?℃. It can be seen through the analysis that raising the installation height of the wet curtain and fan can cause the flow field of the wet and cool air to flow towards relatively higher positions in the greenhouse, providing better cooling for higher crops in the greenhouse. However, due to the characteristic of the downward flow of wet and cool air, the upward flow of the flow field is relatively limited, and the enhanced cooling effect is limited. Compared with the experimental greenhouse, the change in the installation height of the wet curtain and fan does indeed affect the overall cooling effect of the Venlo greenhouse. Properly reducing the installation height of the wet curtain and increasing the installation height of the fan can allow the flow field of wet and cool air in the greenhouse to flow and diffuse more thoroughly, so as to strengthen the heat exchange process; however, the impact of flow field changes on wind speed, humidity, and other factors still needs to be considered.