Choosing Tips for Windmill and Wet Baffle in Greenhouses

The wet-baffle cooling system for fans is widely used in greenhouses. How can you choose a cooling system more skillfully to allow your plants to breathe more freely? Shandong Jeno Temperature Control technicians offer you the following reference principles:

Principles of Selection

The selection principle for the dimension of wet pads is to ensure the system achieves good performance. Typically, in horticultural greenhouses, fiber-based wet pads measuring 10 cm or 15 cm in thickness are commonly used. A 10 cm thick fiber-based wet pad performs well at an air velocity of 76 meters per minute through the pad. A 15 cm thick paper-based wet pad, however, requires an air velocity of 122 meters per minute.

When selecting the thickness of a wet pad, in addition to considering the local geographic location and climate conditions, one should also take into account the distance between the wet pad and the fan within the greenhouse, as well as the degree of temperature tolerance of the flower crops. If the distance between the fan and the wet pad is greater than 32 meters, a 15 cm thick wet pad is recommended; if the cultivated flowers have poor tolerance to the greenhouse temperature and high temperatures, a 15 cm thick wet pad is also suggested. Conversely, if the distance between the wet pad and the fan within the greenhouse is shorter or the flowers have lower temperature sensitivity, a 10 cm thick wet pad can be used.

From an economic perspective, a 10 cm thick wet curtain is less expensive than a 15 cm thick one, costing only two-thirds of the latter's price.

Additionally, the intake size of the wet curtain should be as large as possible. A smaller intake size increases static pressure, which significantly reduces the fan's efficiency and increases energy consumption.

Methods for Estimating Traditional Greenhouse Cooling Equipment

1. The necessary ventilation volume for a greenhouse = greenhouse length x width x 8 cfm (Note: cfm stands for cubic feet per minute, the unit of air flow). The ventilation volume per unit area of the ground should be adjusted according to altitude and light intensity, etc.

2. Estimate the required area of the wet pad. If a 10 cm thick wet pad is chosen, the wet pad area = greenhouse necessary ventilation volume / wind speed x 250. If a 15 cm thick wet pad is used, the wet pad area = greenhouse necessary ventilation volume / wind speed x 400. Divide the calculated wet pad area by the length of the ventilation wall covered by the wet pad to determine the wet pad height. In humid climates, increase the fan airflow and wet pad size by 20%. According to the principle that hot air rises and cold air sinks, the fan and wet pad should be installed above the greenhouse, as is the case with early-built greenhouses.

However, in recent years, there has been a trend of lowering the installation position of fans and wet curtains in greenhouse potted plants. Currently, during the construction of greenhouses, it is common to install the fans at a height of 1/3 below the seedling beds and 2/3 above the bed surface. The wet curtains are installed starting 30 centimeters above the ground. This installation is primarily designed based on the actual temperature felt by the crops on the bed surface. Since the temperature at the top of the greenhouse is quite high, but the plant leaves do not sense it, there is no need to consume unnecessary energy to lower the temperature in areas that the plants cannot reach. Additionally, installing the fans below the seedling beds is beneficial for the growth of plant roots.