Plastic film has been used in agricultural production for decades. The principle is that plastic greenhouses and glass are almost "transparent" to solar radiation, and most of the solar radiation can enter. But for ground long-wave radiation, plastic greenhouses and glass are not "transparent", and long-wave radiation is rarely transmitted. In this way, the greenhouse allows the external solar energy to continuously enter the room, while the indoor heat is rarely dissipated, thus playing the role of heat preservation and heating, so that we can also eat fresh vegetables produced by farmers and friends in the cold season.
The ventilation and cooling methods commonly used in agricultural production greenhouses include natural ventilation cooling and mechanical forced air cooling.
1. Principles and methods of natural ventilation and cooling in greenhouses
The principle of natural ventilation and cooling in greenhouses is to use the principle of hot air rising and cold air sinking. Many greenhouses generally open vents on the top or both sides of the greenhouse, allowing the hot air inside the greenhouse to be discharged to the outside, and then the cold air from the outside enters the room. This method is more effective in the cooling of greenhouses in spring and autumn. But in hot summer, when the outdoor temperature is about 38 degrees, this effect is not very effective.
2. The principle of forced air cooling by fan water curtain
The water curtain is a special paper honeycomb structure material, and its working principle is the natural physical phenomenon of "water evaporation absorbs heat". That is, water flows from top to bottom under the action of gravity to form a water film on the corrugated fiber surface of the wet curtain. When the fast-flowing air passes through the wet curtain, the water in the water film will absorb the heat in the air and evaporate and take away a large amount of water. The heat reduces the temperature of the air passing through the wet curtain to achieve the purpose of cooling. The principle of this mechanical ventilation cooling is to install the fan and the water curtain on the opposite surface, and draw the air through the push-pull fan to make the air inside the greenhouse form negative pressure. , The air outside the greenhouse is cooled by the water curtain and then enters the greenhouse indoors, so as to achieve the effect of ventilation and cooling.