Greenhouse cooling in summer
Temperature is one of the most basic and most important environmental conditions for crops. The level of temperature directly affects the normal growth and development of crops. Most regions in China belong to the continental monsoon climate, and the annual temperature difference is relatively large. At present, researches on greenhouse warming, heating and energy saving in winter are more in-depth and easy to solve. The real problem lies in the problem of cooling in summer. Such climatic conditions are unfavorable to the growth of crops in greenhouses. Due to the strong solar radiation and greenhouse effect in summer, the temperature in the greenhouse has reached above 40°C. The growth of the crops has stopped and the crops have wilted and died. Therefore, solving the problem of greenhouse temperature cooling in summer is the key to ensure the normal growth of crops. Natural ventilation, mechanical ventilation, mechanical refrigeration, evaporative cooling, internal shading nets, external shading nets, and curtain fan cooling are commonly used for cooling. Mechanical refrigeration is the use of freezers. Usually the greenhouse area is large, the required cooling load is high, and the mechanical refrigeration equipment and operating costs are high and the use is extremely uneconomical. Evaporative cooling is the use of sensible heat in the air to evaporate water to achieve a cooling measure to reduce air humidity. However, it will increase the humidity of the air and it will not be effective under high humidity conditions. Internal shading nets generally use ULS14-18 series dipping aluminum synthetic fiber slatted nets. The shading rate is 20% to 50%. The sunlight entering the greenhouse is reflected by the internal net. When the roof covers the material, some sunlight is trapped indoors due to reflection. , Resulting in heat accumulation, so that the indoor temperature increases, so the cooling effect of the internal shade net alone is not very satisfactory. With the addition of external shading nets and integrated use of various shades within the shading nets, the cooling effect is significant. External shading nets are generally made of dipping aluminum synthetic fiber slats, Tianfu nets, etc. The former shading rate can meet the shading requirements, but it is light, easy to crack, poor in wind resistance and expensive. The latter has a shading rate of 50% to 80%, high strength, resistance to typhoon level 15, resistance to aging, and a service life of more than 10 years. Because of the addition of external shading nets, heat radiation can be directly reduced during the hot summer months to avoid the greenhouse effect. This combination of internal and external shading nets has a significant cooling effect. From a practical point of view, in the past few years, Fuyang City, Henan Province, introduced 2 hectares of Dutch greenhouses for flower production. However, due to the greenhouse effect, the indoor temperature in summer reached more than 40 °C, and the production of flowers was seriously affected. In the summer of 1999, after the external sunshade net was designed by the College of Water Conservancy and Civil Engineering of China Agricultural University, the room temperature did not exceed 32°C and the flowers in the greenhouse grew well. The Beijing Laitai Flower Market, at the beginning of the design of the greenhouse, uses cooling skylights, roof spray, roof spray paint, and central air-conditioning. However, in fact, from July to August, the average indoor temperature is up to 10°C to 15°C higher than that of the outdoor without the central air conditioning. Even in the warm spring season, on certain sunny days, the indoor greenhouse can reach 35°C, which is 10°C higher than the outside. When the central air conditioner is turned on, since the sunroof must be closed, the entire market is closed and cannot be ventilated, and due to the planting of flowers for sale in the greenhouse, the indoor humidity is high, people feel hot and uncomfortable, and due to the entry of a lot of indoor heat radiation, according to statistics, When the outdoor temperature is 36°C, the indoor temperature can reach about 40°C. The staff sweats and can't work. The customer also expects the heat to stop. The business is extremely light and the operating costs are high. In the summer of 1999, after Beijing Sanjisheng Agricultural Engineering Technology Co., Ltd. used the patent technology of Sanyi Greenhouse to add an external sunshade net, the normal outdoor temperature was 35°C to 37°C, and sometimes the extreme temperature reached 40°C. Only about 32 °C, average cooling 5 °C to 8 °C. According to Laitai staff and stall owners, the cooling effect is generally very good. The optimum growth temperature for some crops should not exceed 30°C, for example, the suitable temperature for the growth of Phalaenopsis is from 25°C to 27°C. Obviously, the use of external shading net cooling results is not enough, which requires the increase of wet curtain fan cooling system for comprehensive cooling, open the fan for forced ventilation, at the same time, the water from the wet curtain above the water pipe, wet curtain When the outdoor hot air passes through the wet curtain, it is in full contact with the wet curtain. The moisture evaporates and absorbs the heat in the air to cool the hot air, thereby achieving the purpose of cooling. Last summer, Beijing Sanzhisheng Agricultural Engineering Technology Co., Ltd. tracked the overall temperature reduction of the greenhouses constructed in the Sangao Agricultural Demonstration Zone in Shunyi. Every afternoon, at 2 o'clock in the afternoon, the average outdoor temperature is about 34°C. The indoor temperature is usually It is cool and pleasant from 25°C to 26°C. It has been well received by leaders and colleagues from all over the country and affirmed by relevant experts. In short, according to the climatic environment of different regions, the comprehensive use of different cooling measures in the summer to ensure that the indoor temperature is appropriate is an important issue for the development of the greenhouse industry.