(1) It is best to sit facing the greenhouse, north to south, and west (cloudy) 3 ~ 5. It takes a long time to receive sunlight in this direction and the utilization rate of light energy is high. The method is as follows: at11:40 ~12: 30, insert a vertical pole on the ground, select its shortest projection through observation, then make its vertical line, and then draw a straight line with the vertical line as the standard, 5 degrees to the west, and the drawn straight line is the reference line in the direction of the greenhouse back wall.
(2) Facility-scale sunlight greenhouse, which is 50 ~ 70 meters long from east to west. If the length is less than 40 meters, the area of the greenhouse will be very small and the thermal insulation performance will be reduced. In severe cold weather, indoor chilling injury or freezing injury is easy to occur (Table 8- 1). If the length exceeds 80 meters, it will take a long time to cover the grass, which is not convenient for management.
"role=" table
"role=" Table (3) The height and north-south span of greenhouse should be determined according to local latitude. The height and span determine the angle of the greenhouse lighting surface (Figure 8- 1), and the angle of the lighting surface affects the incident angle of sunlight (the angle between sunlight and the vertical line of the lighting surface). As we all know, the projection rate of sunlight is closely related to the incident angle of light. When the incident angle is in the range of 0 ~ 40, the incident rate of light has no obvious change. When the incident angle is greater than 40, the light transmittance decreases sharply with the increase of incident angle.
"role=" Figure 8- 1 shows that the angle of the greenhouse lighting surface = 90-the elevation angle of the sun (the angle between the sunlight rays and the ground plane)-the incident angle of the sunlight (40). In a day, the sun's altitude angle is the largest at noon (Table 8-2), and it is zero at sunrise in the morning and sunset in the evening. As the sun rises, the angle increases, and then gradually decreases after noon.
The angle of greenhouse lighting surface should be determined according to the local solar altitude angle. For example, in the area around 35 north latitude, the solar altitude angle from winter to noon is 365,438 0.6, so it is appropriate to reduce the solar altitude angle by 5 ~ 6 compared with that at noon when building a greenhouse. The calculation is as follows:
"role="table As can be seen from Table 8-2, the variation law between the geographical latitude and the solar altitude angle of the greenhouse location is: every latitude increase 1, the solar altitude angle decreases 1, and the lighting surface angle needs to increase 1. When building a greenhouse at 38 north latitude, the angle of the lighting surface should be increased by 3 degrees compared with that at 35, and should be greater than 26 degrees (23+3 = 26). 40 north latitude should be greater than 28, and 42 north latitude should be greater than 30.
According to the above, the height and north-south width should be determined according to the most reasonable lighting surface angle of the greenhouse, and the minimum lighting surface angle can be calculated according to the latitude of the greenhouse. Combined with the comprehensive height of the back slope and back wall of the greenhouse, the width of the greenhouse is calculated by the formula: the height of the highest point of the greenhouse ×cotα(α is the minimum angle of the lighting surface)+the projection length of the back slope. For example, in the section of 35 north latitude, if the height of the highest point in the solar greenhouse design is 3m, the projection length of the back slope is 1m, the lighting surface angle is 23, and cot23 =2.36. The calculation is as follows: 3×2.36+ 1=8. Then in the area of 35 north latitude, when the highest point of the solar greenhouse is 3 meters and the projection of the back slope is 1 meter, its north-south span should be 8 meters.
(4) The shape of the lighting surface should be a big arch circle. This form, first, the lighting surface is arched, the structure is firm, and the pressure resistance is strong; Secondly, the slope is convex, which is convenient to press the film with the film pressing rope, and the film will be pressed into a wave shape, which can increase the lighting area by more than 20%, and has good light transmission performance and high utilization rate of sunlight, especially before 9 o'clock, the greenhouse will heat up quickly; Third, the film on the lighting surface is pressed tightly, which has less fan movement when it is windy, good windproof performance and good heat preservation effect; Fourth, it is convenient to pull the straw curtain, and there is less snow in the lighting area when it snows, which is convenient to clean the snow in the lighting area; Fifthly, after covering the grass curtain at night, there is a big gap between the film and the grass curtain, forming a triangular belt of closed air, which can significantly improve the thermal insulation performance of the greenhouse.
(5) Wall structure The wall is the most important part of the greenhouse, which can not only support the closed greenhouse and play the role of heat preservation, but also store heat during the day, release heat at night and stabilize the temperature of the greenhouse at night. Wall can be divided into solid wall and hollow wall, and hollow wall can be divided into thermal insulation filling material and non-thermal insulation filling material. From the point of view of thermal insulation effect, as long as it is tightly closed, the thermal insulation effect of hollow wall is better than that of solid wall, and the wall filled with thermal insulation material is better than that without material. But the function of the wall is not only to keep warm, but also to store heat at high temperature and release heat at low temperature to stabilize the room temperature. If the greenhouse encounters continuous cold weather, the indoor night temperature of the hollow wall will be significantly lower than that of the greenhouse built with solid wall of the same thickness, because it has less heat storage and less heat release. Therefore, instead of building a hollow wall, it is better to build a solid wall with appropriate thickness, with cooling holes inside and insulation layer outside the wall, which has the best comprehensive insulation effect.
In the concrete construction, it is best to use soil mixed with wheat straw to build an earth wall, and then use iron pipes to make holes in the oblique upper part of the wall, every 40 cm 1 row, every 40 cm 1 row. Or brick wall, with holes of 12cm inside, and a solid clay wall with a thickness of about 100cm outside the wall. Holes with a diameter of 5-6cm are evenly distributed on the inner wall of the wall (Figure 8-2), and the holes penetrate into the wall 80- 100cm.
"role="figure" The advantages of this kind of wall are less bricks, less investment, firm wall, weatherproof and long service life. The wall is covered with soil, which is the second only heat storage material to water. It can accumulate and store more heat during the day and release more heat at night, which is beneficial to increase the night temperature in the facility. The inner wall of the wall is full of holes. When the temperature is high during the day, hot air can enter the interior of the wall through holes, heating the wall, raising the temperature and accumulating heat. At night, when the wall cools down, more heat can be released into the room through the cooling holes and air convection, thus stabilizing and improving the indoor temperature.
Practice has proved that in general, the temperature difference between two greenhouses with different walls can reach about 2℃ at night, and it can reach about 3℃ in case of cold weather lasting 2 ~ 3 days.
(6) Adding insulation layer As mentioned above, most of the heat stored in the greenhouse wall is dissipated to the outside. In order to reduce the heat loss and improve the indoor temperature at night and in continuous cold days, after the wall is completed, it is necessary to add an insulation layer to the wall to prevent the heat from spreading outward. Methods: The back wall and gables were tightly wrapped with ordinary agricultural film or the old film replaced in the greenhouse. Then fill the gap between the wall and the film with broken grass, and the thickness of broken grass is about 20 cm. Then use soil to bury the upper and lower edges of the film in the back slope and ground soil of the greenhouse, and tie 1 ~ 2 iron wire to reinforce the film.
After the insulation layer is added to the outside of the wall, the heat of the wall will no longer be emitted. When it is cold at night, the heat stored in the wall is only released indoors, which can significantly increase the indoor night temperature, which is 3 ~ 5℃ higher than that of the greenhouse without insulation layer. It has a good effect on stabilizing indoor night temperature in severe cold period. In this way, the thermal insulation effect of a greenhouse with a wall thickness of about 100 cm is equivalent to or even higher than that of a greenhouse with a wall thickness of 5 meters.
(7) Angle and projection length of the back slope of solar greenhouse; The solar greenhouse has a back slope, which can significantly improve the thermal insulation effect of the greenhouse; You can also appropriately increase the height of the greenhouse and increase the angle of the lighting surface, which is conducive to the injection of sunlight; It is also convenient to place and uncover the thermal insulation cover (straw cover, paper quilt, etc.). ) lighting surface. In order to ensure the indoor temperature of greenhouse in severe cold period, it is necessary to set up a back slope. The back slope can block the incidence of scattered light in the air in the north of the greenhouse, which worsens the lighting conditions in the back of the greenhouse, resulting in the poor growth and development of hot (sweet) peppers in the back of the greenhouse, and the yield and quality of products are obviously not as good as those in the front. Weighing the advantages and disadvantages, in order to facilitate the placement and uncovering of the thermal insulation cover, an upward slope should be set, but the width of the upward slope should not be too wide, and its projection length should be kept at about 1 m to minimize shading. Conditional, the back slope should be semi-movable, the upper part should be transparent, and thermal insulation facilities should be provided at night to improve the thermal insulation effect of greenhouse. During the day, the thermal insulation facilities should be dismantled and the incidence of scattered light should be increased to improve the lighting conditions at the back of the greenhouse. The lower part should be a permanent slope with good thermal insulation performance, which is conducive to thermal insulation, placement and uncovering of thermal insulation covers. Furthermore, the elevation angle of the back slope should be reasonable, and it should be kept above 38 in the area around 36 north latitude, so that in the coldest season (from winter to two months before and after), sunlight can directly hit the inner wall of the back slope, which is beneficial to raising the indoor temperature and improving the lighting conditions behind the greenhouse.
(8) Set up cold trench. Cold trenches should be set at the four sides of the room. One of the south edges should be changed into a cold-proof ditch for storing water and storing heat, that is, an east-west ditch with a depth of 40 cm and a width of 30-40 cm should be dug in the front, and a row of foam plastic plates with a thickness of 2 cm should be buried in the south edge of the ditch near the outer edge of the greenhouse, or broken hay wrapped with old films should be used instead. The bottom of the ditch was covered with a layer of broken grass, and then the bottom and side of the ditch were covered with old films. After that, a plastic film tube with a diameter of about 50 cm (double-sided plastic bucket with a width of 90 cm) was laid in the ditch, and the length was the same as that of the greenhouse. One end of the plastic pipe is closed to make it higher than the ground, the other end is filled with well water, and then the opening is padded and closed.
On the other three sides, dig a narrow ditch with a width of 20 cm and a depth of 30 cm, and fill the ditch with broken grass, which should be solid and practical. The broken hay filled in the ditch can absorb the water vapor in the air in the facility, reduce the air humidity and help prevent diseases; The second is to completely prevent soil heat conduction and improve indoor soil temperature; Thirdly, the broken grass in the ditch is decomposed and fermented by soil microorganisms after absorbing water, which can not only release heat, improve indoor temperature, but also release carbon dioxide, provide raw materials for photosynthesis of leaves, and significantly improve indoor hot (sweet) pepper yield. The front foam board can prevent heat from being transferred to the outside of the greenhouse, and the heat preservation effect is good; The well water in the plastic pipe absorbs heat and stores heat during the day, and releases heat at night to stabilize the room temperature, which changes the disadvantage that the temperature in the front of the greenhouse is low at night and high at day. Well water in the pipeline can also be used to irrigate indoor hot (sweet) peppers, which solves the problems of low irrigation water temperature in winter and low ground temperature after irrigation.
(9) The transparent covering material of the lighting surface should be a multifunctional composite film, which is light-transmitting, non-dripping, dustproof, good in heat insulation, strong in tensile strength and long in service life. The better ones are polyethylene long-life drip-free film, three-layer extrusion composite film, polyethylene drip-free light conversion film and ethylene-vinyl acetate three-layer drip-free heat preservation and anti-aging film.
(10) Installation of Vents At present, most greenhouse vents only have 1 vents, which are not at the top of the greenhouse. This ventilation is not smooth, and it is difficult to cool down at high temperature. Only by opening the bottom of the greenhouse to ventilate, cold air can directly blow the seedlings, causing cold damage.
It is best to set 2 ~ 3 ventilation channels. When three ventilation channels are set, 1 channel is at the top of the back slope, with a width of 20 ~ 30 cm. Road 1 is at the highest point of the daylighting surface on the front slope (before the grass curtain rolls), with a width of 80 ~100 cm; The road 1 is in front of the lighting surface 120 ~ 140 cm high and about 10 cm wide. Set 2 channels, and only keep the last two. This arrangement facilitates ventilation, such as adjusting the temperature. There is no need to open the bottom of the greenhouse at high temperature, and there will be no phenomenon that cold air directly blows the seedlings. The rear slope tuyere is beneficial to ventilation and dehumidification at night.