How to cool down in large-scale multi-span greenhouses?
When it comes to the cooling of greenhouses, it is generally the cooling of multi-span greenhouses. Because the area of multi-span greenhouses is generally relatively large, this creates a microclimate environment inside the greenhouse, and the indoor hot air is not easy to discharge, so it needs to be cooled in time. The following are the cooling measures for multi-span greenhouses. I hope it will be useful to everyone. .
1. Internal and external shading system
This is the first cooling measure, and also the most important one. Because the sunlight is blocked first, the shading system prevents the heat from entering, which reduces the heat entering the greenhouse in time, thus reducing the temperature in the greenhouse in time. The greenhouse shading system is divided into inner shading system and outer shading system. Except for special purposes (for example, some plants are shaded and dormant), most of the purpose of the sunshade system is to cool down in summer, so the judgment of the sunshade effect is mainly to see whether it can effectively reduce the temperature.
The external shading system mainly refers to covering the outside of the greenhouse with a shading net. This method directly blocks the solar radiation outside the greenhouse, which can effectively reduce the temperature inside the greenhouse. At the same time, the external shading system should be active so as to provide enough sunlight in rainy weather. However, the external shading system needs to install the corresponding framework, wind and rain resistance system, etc., and has a certain ability to withstand external loads, and the consumables of the shading net are relatively large, so the cost of external shading is relatively high.
The inner shading system is a shading system installed inside the greenhouse and on the upper part of the crops, usually with a lighter shading net. Obviously, this kind of shading system installed indoors can't really reduce the indoor temperature, but effectively prevents the direct sunlight from hitting the crops and preventing the crops from being burned. Usually the inner shading Goshen Greenhouse original system is used together with the outer shading system.
2. Natural ventilation cooling system
The natural ventilation cooling system refers to relying on opening windows on the roof and surrounding windows to achieve the purpose of ventilation and cooling. This kind of ventilation and cooling measures have no obvious effect on cooling, and mainly play a role in ventilation. This measure is generally used on cloudy days or in spring and autumn, and it is more obvious for indoor ventilation and cooling.
The Venlo-type greenhouse has a unique skylight design, which mainly relies on opening windows on the roof of the greenhouse to use natural ventilation to cool down and let hot air escape from the top. It takes the roof ridge of each small surface as the boundary line and staggers the skylights left and right. It is controlled by the overall transmission of the rack and pinion. The length of each skylight is 2-4 meters, the width is 1.0 meters, and the ventilation window ratio is about 5%.
3. Fan water curtain cooling system
(1) Working principle
The fan water curtain forced cooling system uses the principle of water evaporation cooling to achieve the purpose of cooling. The core of the cooling system is the wet curtain that can evaporate water. The wet curtain is made of corrugated fiber paper. Due to the addition of special chemical components in the raw materials, it is corrosion-resistant and has a long service life. The specially made water transfer wet curtain can ensure that the water evenly wets the entire cooling wet curtain wall, and ensures that there is a large wet surface in contact with the flowing air, so that the air and water have sufficient time to contact and the air is approximately saturated. When the air penetrates the wet curtain medium, the water-air exchange with the surface of the wet medium converts the sensible heat of the air into the latent heat of vaporization, thereby realizing the humidification and cooling of the air.
The fan matched with the wet curtain realizes the flow of air inside and outside the greenhouse, discharges the indoor high-temperature and high-humidity gas, and supplements enough fresh air. When the temperature needs to be lowered, the fan is started to force the air in the greenhouse to be drawn out to create a negative pressure; at the same time, the water pump pumps water on the opposite wet curtain wall. When the outdoor air is sucked into the room by the negative pressure, it passes through the gap of the wet curtain at a certain speed, causing the water to evaporate and cool down. The cold air flows through the greenhouse, absorbs the indoor heat, and is discharged by the fan to achieve the purpose of cooling.
(2) System composition
The system consists of four parts: wet curtain box, circulating water system, axial flow fan and control system.
Now, according to the cooling principle of the wet curtain fan, a reduced version of the wet curtain air cooler is designed. The cooling of the wet curtain air cooler uses a circulating water pump to continuously pump out the water in the water receiving tray, and spray it evenly through the water distribution system. On the evaporative filter layer, the outdoor hot air passes through the evaporative heat exchanger (evaporative wet curtain) to exchange heat with water, and the water evaporates to achieve cooling and coolness. The clean air is sent into the room by a low-noise fan. This achieves a cooling effect.
In addition, the wet curtain fan system can also play the role of humidification and filtration. When the wet curtain is used as a humidifying medium, it is mostly used in plantations, greenhouses and other special industries that require high humidity. Because the wet curtain has the characteristics of water absorption, water resistance, fast diffusion speed and long-lasting performance, it is very suitable for adjusting indoor humidity. The wet curtain also has ventilation and corrosion resistance, and has an excellent filtering effect on dust in the air. It is an environmentally friendly material that is non-toxic, odorless, clean, humidifying, and oxygen-cooling, so it is also used as a medium for air purification and filtration.
4. Central air-conditioning cooling
This cooling method is the best cooling method with the largest investment cost and operating cost. It is generally used in ecological restaurant greenhouses, because ecological restaurant greenhouses must not only meet the needs of plant growth, but also meet the comfort of guests dining. This cooling method has a large initial investment cost and high operating costs, so the choice of cooling needs to be carefully selected and considered in detail.
