1. Selection of greenhouse materials
The selection of greenhouse frames should take into account the service life of the greenhouse body, the anti-rust and anti-corrosion properties of the frames, and the light requirements of the plants in the greenhouse. When the plants have high requirements for lighting conditions, white spray-coated frames should be selected. The outer surface of the white spray-coated frames is beautiful and neat, and the rectangular tube has a large reflective surface. At the same time, the application of highly reflective spray-coated paint effectively reduces the heat absorption rate. In hot weather on sunny days in summer, the surface temperature of the spray-coated frames is 1/3 lower than that of ordinary steel structure greenhouses. The selection of curtains should also consider the light requirements of plants. In greenhouses with efficient production, it is appropriate to use highly reflective curtains to create a good lighting environment for the plants.
2. Natural ventilation
Set up air vents with sufficient area so that the designed ventilation volume of the ventilation system can meet the maximum necessary ventilation volume. Natural ventilation is the most important and economical way to cool down the greenhouse. The top window ventilation design must have leeward windows and windward windows, because the wind direction changes throughout the year, and the windward windows have a good cooling and dehumidification effect. When the greenhouse needs to be cooled slightly, the leeward skylight can be opened. In addition, in summer, the combination of leeward windows and windward windows can be used for cooling through natural ventilation, avoiding the increase of later operating costs due to the premature opening of the wet curtain fan.
3. Reduce the shaded surface
The greenhouse unit area in the Netherlands is large, and the truss is installed only in the gutter direction. The trusses of most greenhouses in my country are installed in both the gutter and the bay direction. Based on the structural calculation, this installation method of the Netherlands can be used as a reference to save costs while reducing the shaded surface of the truss.
When installing the curtain system, the shaded surface after the curtain is retracted should be considered. It is recommended to use the cable curtain installation method. Although this installation method has extremely strict requirements on the installation process, it can save costs and reduce the shaded area compared with the rack and pinion curtain system installation method.
4. Consider the energy-saving effect of different installation forms of the curtain
Triangular installation of the curtain: When the area of the greenhouse is large, the temperature in the greenhouse is uneven, resulting in a large temperature difference between the plants. A combination of internal insulation curtain and triangular curtain can be used to establish multiple small areas to make the temperature of each small area more balanced.
Opposite installation of the curtain: When the curtain is fully extended, the air does not circulate. When the internal shading and internal insulation are installed on the opposite side, the air circulation can be increased. However, it is necessary to ensure that the spacing between the curtains is small after they are retracted, otherwise the shade surface will be increased.
5. Reasonable positioning of the inter-column heating pipes
Different positions of the inter-plant heating pipes have different effects on fruit ripening. When the heating pipe is placed at the position of the first ear of fruit, it will accelerate the fruit color change and advance the harvest period, which is suitable for tomatoes with a long harvest period. When the pipe is placed in the middle (equivalent to the position of the third and fourth ears of fruit), the fruit can swell, but due to insufficient root nutrition, it cannot supply the nutrients needed by the plant, resulting in a shortened harvest period. Therefore, the greenhouses currently used for growing tomatoes all use double-layer heating pipes. Before designing, you must communicate well with the planting technicians, clarify their planting needs, and reasonably determine the location of the heating pipes.
6. Balance of temperature and humidity
The high-pressure spray system, which is widely used in the Netherlands, can achieve precise control of air humidity and temperature, and can better control the water absorption of crop leaves. The temperature of an unshaded greenhouse can be reduced by 5°C, and the temperature of a shaded greenhouse can be reduced by 7°C. The high-pressure spray system can provide instant humidification, minimize bacterial growth, and avoid damage to crops and flowers.
The spray system can operate at an extremely high pressure of about 10 MPa, producing fine droplets of about 10 μm. The fine water droplets cool the air, and the cold air moves down to the plant level and is then replaced by the rising hot air. The biggest advantage of these extremely small droplets is that they evaporate quickly and will not fall on the leaves of the plants, thus achieving the best cooling effect. Compared with other systems, it can also reduce water consumption. If some plants do not need humidification while cooling, a spray cooling system can be installed on the outside of the top of the greenhouse, which can generally reduce the temperature by 1 to 2°C.
7. Consider the problem of light pollution
In order to avoid light pollution affecting the lives of people around, side-rolling systems can be installed around. The side-rolling system has three functions: it can insulate in summer, prevent heat from entering the greenhouse, and play a cooling role; it can keep warm in winter, prevent heat loss in the greenhouse; and avoid light pollution.
8. Consider the comfort of workers at work
Consider the comfort of workers at work, create a good working environment for them, stimulate their enthusiasm for work, and improve their work efficiency. For example, the height of the cultivation trough is generally 70 to 80 cm from the ground, so workers do not need to bend over and it is easy to operate; only install white sunshade nets above the greenhouse aisle to avoid direct sunlight and reduce the temperature of the aisle, which not only creates a comfortable working environment for workers, but also does not affect the light requirements of plants on both sides of the aisle.
