Temperature Control in Multi-span Greenhouses

Temperature control in double-layer multi-span film greenhouses is a systematic project that typically requires a combined strategy of “external defense, middle ventilation, and internal cooling” to ensure a dynamic balance of temperature, light, water, and air. The same combined strategy is equally indispensable in a Venlo Glass Greenhouse, where the glass envelope intensifies summer heat accumulation and demands even more precise ventilation management.

First, the coordinated use of external and internal shading nets forms the foundational defense. The external shading system can block most solar radiation outside the greenhouse, providing the most significant cooling effect and effectively preventing crops from direct intense light and sunburn. In practice, adjustments must be made flexibly according to the season and weather. For example, during the high-temperature summer period, fruiting vegetables can be covered with a shading net with approximately 60% shading rate from 10:00 AM to 4:00 PM on sunny days; leafy vegetables can be covered all day, but the net should be removed before harvest to enhance their color. Additionally, a ventilation gap of 10-30 cm must be maintained between the shading net and the film to form an air channel. The nets should be firmly fixed with durable greenhouse aluminium accessories such as clamp rails and profiles so that they remain stable under strong winds. Continuous all-day coverage should be strictly avoided to prevent a high-temperature, low-light environment that would impair normal photosynthesis.

Second, increasing the ventilation area is the key method for exhausting heat. Multi-span greenhouses should fully utilize top roof vents and side vents to form a “crosswind,” achieving natural convection of hot air. In an Aluminum gutter venlo glass greenhouse, the roof vent windows are typically hinged along the aluminum gutters; they must open synchronously and smoothly so that hot air escapes through the highest points while rainwater drains cleanly away from the crop zone. Regarding operational standards, on sunny days, all ventilation openings must be opened promptly when the internal temperature exceeds 30°C. In rainy weather, short-term ventilation should be conducted around noon when the temperature is relatively high to exhaust moisture. Furthermore, insect-proof nets with a mesh size of 40-60 must be installed at the ventilation openings to effectively block pest intrusion while cooling, thereby reducing pesticide use.

Finally, when natural ventilation cannot meet cooling demands, active cooling equipment must be introduced. The most commonly used is the “wet pad-fan” (evaporative cooling pad and fan) forced ventilation system, which utilizes the principle of evaporative cooling to rapidly drop the internal temperature by 5-10°C. For high-value-added crops, high-pressure micro-sprinklers or fogging systems can be used in conjunction, applying intermittent sprays during the high-temperature period from 11:00 AM to 3:00 PM. This utilizes water vapor evaporation to carry away heat and increase air humidity. Additionally, circulating well water through pipes for cooling is an innovative, energy-saving, and eco-friendly method. When comprehensively applying these devices, special attention must be paid to avoiding excessive cooling that leads to high-humidity environments, which can trigger disease outbreaks.

Temperature control in multi-span greenhouses is by no means the application of a single technology, but rather the scientific integration of shading, ventilation, and spraying. With the development of agricultural IoT technology, future temperature control will increasingly rely on real-time sensor monitoring and the precise execution of automated control systems. Only by playing this “combination punch” tailored to local conditions can we ensure healthy crop growth while extending the service life of the facilities, truly realizing the economic and ecological value of modern greenhouse agriculture.