The fan wet curtain cooling system is a cooling method that is currently applied and popularized in the flower greenhouse production greenhouse, with remarkable effect and suitable for crop growth. So how to install the fan wet curtain system reasonably in the construction of the flower greenhouse to give full play to its effect. Does flower growth play a role in promoting it?

System principle

First of all, let’s understand the working principle of the down fan: when the outdoor hot air is sucked through the wet curtain filled with water, the water on the wet curtain absorbs heat and evaporates, thereby reducing the temperature of the air entering the greenhouse. Usually, the wet curtain wall consisting of the wet pad, the water distribution system of the wet pad, the water pump and the water tank is built continuously along one wall of the greenhouse, while the fans are concentrated on the other gable of the greenhouse. The wet curtain must be kept moist to ensure the completion of the evaporative cooling process. According to the size and area of ​​the greenhouse, a suitable fan can be installed on the wall opposite the wet curtain to make the air flow smoothly through the greenhouse.

The effect of evaporative cooling is related to the dryness of the air, that is, the difference between the wet bulb temperature and the dry bulb temperature of the air. The difference between the dry and wet bulb temperature of the air varies not only with geographic location and season, but also within the greenhouse. While the dry bulb temperature in a greenhouse can vary by as much as 14°C, the wet bulb temperature varies by only about 1/3 of the dry bulb humidity. As a result, the evaporation system is still able to cool down during the midday hours in high-humidity areas, which is also required for greenhouse production.

selection principle

The selection principle of the wet pad size is that the wet pad system should achieve the desired effect. Usually 10 cm thick or 15 cm thick fibrous wet curtains are often used in flower production greenhouses. A 10 cm thick fibrous pad running at 76 m/min air velocity through the pad. A 15 cm thick paper pad requires an air velocity of 122 m/min.

The thickness of the wet curtain to choose should not only consider the geographical location and climatic conditions of the location, but also the distance between the wet curtain and the fan in the greenhouse and the sensitivity of flower crops to temperature. If the distance between the fan and the wet curtain is larger (generally more than 32 meters), it is recommended to use a 15 cm thick wet curtain; if the cultivated flowers are more sensitive to the greenhouse temperature and have poor tolerance to high temperature, it is recommended to use a 15 cm thick wet curtain. Wet curtain. Conversely, if the distance between the wet curtain and the fan in the greenhouse is small or the flowers are less sensitive to temperature, a 10 cm thick wet curtain can be used. From an economic point of view, the price of a 10 cm thick wet curtain is lower than that of a 15 cm thick wet curtain, which is only 2/3 of its price. In addition, the larger the size of the air inlet of the wet curtain, the better. Because the size of the air inlet is too small, the static pressure will increase, which will greatly reduce the efficiency of the fan and increase the power consumption.

Methods of estimating cooling equipment for traditional multi-span greenhouses:

1. Necessary ventilation volume of greenhouse = length of greenhouse × width × 8cfm (Note: cfm is the unit of air flow, that is, cubic feet per minute). The ventilation volume per unit floor area should be adjusted according to the altitude and light intensity.

2. Estimate the required wet curtain area. If a 10 cm thick wet curtain is used, the wet curtain area = the necessary ventilation volume of the greenhouse / wind speed 250. If a 15 cm thick wet curtain is used, the wet curtain area = the necessary ventilation volume of the greenhouse / wind speed 400. Divide the calculated wet pad area by the length of the ventilation wall covered by the wet pad to obtain the wet pad height. In humid areas, the fan air volume and wet curtain size should be increased by 20%. According to the principle that the hot air is up and the cold air is down, the fan wet curtain should be installed above the greenhouse, and the same is true for the greenhouses built in the early days.

However, in recent years, there has been a downward trend in the installation of fan wet curtains in potted greenhouses. Now in the process of greenhouse construction, generally 1/3 of the fan height is installed below the seedbed, 2/3 above the seedbed surface, and the wet curtain is installed 30 cm above the ground. This installation is mainly based on planting on the bed surface. Designed for the temperature actually felt by the crop. Because although the temperature at the top of the greenhouse is very high, the leaves of the plants cannot feel it, so it does not matter. There is no need to spend unnecessary energy consumption to reduce the temperature of the areas that the plants cannot touch. At the same time, the fan is installed under the seedbed, which is conducive to the growth of plant roots.