1. What problems should be paid attention to when designing and building an energy-saving solar greenhouse?
A good energy-saving solar greenhouse should have the following characteristics: first, good light transmission performance and high light utilization rate; Second, the temperature rises quickly and the heat preservation performance is good; Third, it is simple to operate, ventilated and dehumidified, and easy to manage; Fourth, the structure is firm, the windproof performance is good, and the service life is long; Fifth, it is easy to build and requires less investment.
In order to meet the above requirements, the following points should be paid attention to during construction:
(1), site selection of energy-saving solar greenhouse: When designing and constructing the site selection of energy-saving solar greenhouse (shed), attention should be paid to those areas with high and dry terrain, no accumulated water after rainstorm, underground water depth less than 1 m, good drainage and irrigation conditions, fertile soil, loose soil, good air permeability, deep soil layer, good fertilizer and water conservation performance, leeward and sunny, and convenient transportation.
(2) Orientation of energy-saving solar greenhouse: Practice has proved that the solar greenhouse should be built facing south and facing west (cloudy) at 3-5 degrees. It takes a long time to receive sunlight in this direction and the utilization rate of light energy is high. If the above requirements cannot be met due to terrain and other reasons, it should be adjusted to the range of 10 degrees west longitude to 5 degrees east longitude. The method is as follows: from noon 12 to noon 12: 20, 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, with a shadow of 5 degrees. The drawn straight line is the reference line in the direction of the greenhouse back wall.
(3) The size of energy-saving solar greenhouse: the length of energy-saving solar greenhouse is 50-70 meters from east to west. If the length is less than 40 meters, the size of the greenhouse will be very small, and its heat insulation performance will be reduced. In severe cold weather, indoor chilling injury or freezing injury is easy to occur. If the length exceeds 80 meters, it will take a long time to cover the grass, which is not convenient for management.
(4) Height and north-south span of energy-saving solar greenhouse: The height and north-south span of greenhouse should be determined according to local latitude. Because the height and span determine the angle of the greenhouse lighting surface (figure 1), and the angle of the lighting surface affects the incident angle of sunlight. In order to ensure the large incident angle of sunlight, the incident angle should be less than 40 degrees. Because the projection rate of sunlight is closely related to the incident angle of light. Its incidence angle is in the range of 0-40 degrees. With the increase of incident angle, the incident rate of light decreases, but the change is not obvious. When the incident angle is greater than 40 degrees, with the increase of incident angle, its transmittance decreases obviously or even sharply.
According to the figure 1, the angle of greenhouse lighting surface = 900-solar elevation angle-incident angle of sunlight (40). In a day, the solar altitude angle is the largest at noon, and it is zero at sunrise in the morning, generally at 10 in the morning, and the solar altitude angle is 6-7 degrees smaller at 2 pm than at noon. Therefore, the angle of greenhouse lighting surface should be appropriately increased by 5-6 degrees.
The altitude angle of the sun is determined by its latitude. Due to different latitudes in different regions, the solar altitude angle is also different (table 1).
Table 1 Variation of solar altitude angle at different latitudes and seasons (12 points)
northern latitude
Sun cake
Degree angle
Season 30 35 40 45 50
Beginning of spring and beginning of winter are 43.6 38.6 33.6 28.6 23.6.
Vernal equinox 59.9 54.9 49.9 44.9 39.9.
Summer solstice 84.4 79.4 74.4 69.4 64.4.
The winter solstice is 36.631.626.621.616.6.
Therefore, when building a greenhouse, the angle of its lighting surface should be determined according to the local solar altitude angle. For example, in the area around 36 degrees north latitude, when building a greenhouse, the angle of its lighting surface should be greater than 23 degrees (ι = 90-3 1.6-40+5 = 23.4).
According to the above principle, the north-south width (span) of the greenhouse built in the area of 36 degrees north latitude can be calculated by the following formula: greenhouse width = the height of the highest point of the greenhouse × CTG ι (ι is the angle of the lighting surface)+the projection length of the back slope. Its greenhouse design height is 3m, the projection length of the back slope is 1m, and the lighting angle is 23°(CTG 23° = 2.36°), so its north-south span is 8m (3× 2.36+18). If the greenhouse design height is 3.2 meters, its north-south span is 8.5 meters.
(5) Shape of front slope of energy-saving solar greenhouse: At present, the shape of front slope (lighting surface) often adopts two forms, one is vertical window type, that is, vertical window inclined type; The other is parabolic, also called semi-arch or semi-arc. Of these two forms, the latter is better because: first, it is parabolic, the lighting surface is arched, the structure is firm and the pressure resistance is strong; Secondly, the slope is convex, so it is convenient to press the film with the film pressing rope, which can eliminate the shortcomings of one vertical and one inclined greenhouse. If it is necessary to press the film with bamboo poles and tie the bamboo poles with iron wires, it will lead to many holes, poor thermal insulation performance and indoor dripping; Third, it is parabolic, with good light transmission performance and high utilization rate of sunlight, especially before 9 am, the greenhouse heats up quickly; Fourth, it is parabolic, which 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.
(6) Angle and projection length of the back slope of the energy-saving solar greenhouse: The back slope of the solar greenhouse can significantly improve the thermal insulation effect of the greenhouse. It can also improve the height of the greenhouse, increase the angle of the lighting surface, facilitate the injection of sunlight, and facilitate the placement and uncovering of heat preservation covers (straw mats, paper quilts, etc.). ) on the illuminated 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 northern part of the greenhouse, which worsens the lighting conditions in the back part of the greenhouse, leading to the poor growth and development of crops in the back part of the greenhouse, and the yield and quality of products are obviously not as good as those in the front part. Weighing the advantages and disadvantages, in order to facilitate the placement and uncovering of thermal insulation covering, a back slope should be set. However, the width of the back slope should not be too wide, and its projection length should be kept around 1 m to minimize the occlusion. If conditions permit, it is best to build a semi-mobile type on the back slope, with the upper part transparent, and provide insulation and covering facilities at night to improve the insulation effect of the greenhouse; Dismantle the insulation facilities during the day and increase the incidence of scattered light to improve the lighting conditions behind the greenhouse; The lower part is a permanent slope, which has good thermal insulation performance and is beneficial to the placement and uncovering of thermal insulation and thermal insulation covering.
The elevation angle of the back slope should be reasonable, and it should be kept above 38 degrees in the area around 36 degrees north latitude, so that the sunlight can directly hit the inner wall of the back slope in the coldest season (winter to two months before and after), which is conducive to raising the temperature of the greenhouse and improving the lighting conditions at the back of the greenhouse.
(7) Transparent covering material for lighting surface of energy-saving solar greenhouse: multifunctional composite film with light transmission, no dripping, dust prevention, good thermal insulation performance, high tensile strength and long service life is adopted. Better ones are polyethylene long-life drip-free film, three-layer extrusion composite film, polyethylene drip-free light conversion film, ethylene-vinyl acetate three-layer drip-free heat preservation anti-aging film and PVC drip-free film.
2. How should the wall of the greenhouse be constructed, so that the heat preservation effect will be better?
Greenhouse wall is the most important part of greenhouse. It can not only support the closed greenhouse, but also play the role of heat preservation, and has the functions of storing heat during the day, releasing heat at night and stabilizing 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. However, 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 rapid heat release.
Practice has proved that in general, the temperature difference between two greenhouses with different walls can be about 2 degrees at night, and if it is cold for 2-3 days, the temperature difference can reach about 3 degrees. Based on the above situation, it is best to build a brick-clad composite cavity solid wall, which is covered with insulation layer for better insulation effect.
3. What is a brick-clad composite cavity solid wall? What are the benefits of it? How should it be built?
"Brick-wrapped composite cavity solid wall" refers to a wall composed of bricks and soil. The inner wall and the outer wall of the wall are single-layer bricks and cement mortar, each with a thickness of 12cm. There is an earth wall with a thickness of 1 layer of 76- 120cm between the double-layer single brick walls, and the inner single brick walls are evenly distributed with a layer of thickness.
The wall constructed in this way has the advantages of less bricks, less investment, firm wall, no fear of wind and rain and long service life. The inner layer of this wall is sandwiched with solid soil, which has a large heat capacity and is a heat storage material second only 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 in the daytime, hot air can enter the interior of the wall through the holes, so that the temperature of the wall rises rapidly, the internal temperature of the wall is increased, and the heat storage of the wall is increased. Cooling the wall at night can release more heat and stabilize and improve the indoor temperature. Practice has proved that under the same conditions, the night temperature of greenhouse with cave walls is 3-5℃ higher than that of other greenhouses.
The concrete operation of building this wall is as follows: firstly, build a foundation with stones mixed with cement mortar, which should be more than 20 cm above the ground and about 120 cm wide, and then build a brick bucket wall with cement mortar on the foundation, with a thickness of about 1 m (the thickness of the area around 45 degrees north latitude can reach 150 cm) and a bucket wall thickness of/kloc. The width of the bucket is about 76 cm and the height of the bucket is the same as the height of the wall. Every two buckets are separated by a brick wall with a thickness of 12 cm. The inner wall of the wall must be built into a hole shape, and a row of square holes (6 cm ×6 cm) should be built every five layers of bricks (about 30 cm high). That is, when laying bricks on the fifth floor, each brick should leave a space of 6 cm, and then the second brick should be laid, so that every two bricks are separated by 6 cm (Figure 3).
After the wall is completed, its inner wall is hole-shaped, and the distance between the hole and the center of the hole is 30 cm. Empty barrels in the wall must be filled with soil, and the filling should be carried out in layers after the cement of the wall is solidified, that is, once every 100 cm high cable wall, and then step by step. After the wall is built and completely solidified, use locust sticks with a diameter of 5-6 cm and a length of 80 cm to cut the front end into a sharp shape and construct on the inner wall along a square hole with a depth of 40-60 cm. All holes can be drilled deep.
4. Can the previously built earth-wall greenhouse be transformed into a brick-covered hole wall? How to transform?
The method is as follows: firstly, the exterior of the earth wall is bricked with cement mortar and covered with 1 single brick wall, and then the interior of the wall is covered with 1 single brick wall with holes. After the wall is solidified, an iron pipe with a diameter of 5-6 cm is used to build an earth wall with a depth of 40-60 cm from the hole in the wall. After the transformation, the wall is solid and firm, and the temperature in the greenhouse can be increased by about 3 degrees at night.
5. How to cover the insulation layer outside the greenhouse wall? What is the effect of adding insulation layer?
The method of adding insulation layer outside the greenhouse wall is: replacing the old film with ordinary agricultural film or greenhouse, cutting and processing into a long film with a film width of about 3 meters and a film length = greenhouse length+gable length. After that, the two ends of the film were heated with an iron and bonded into a seam tube of about 65,438+00 cm. Insert 3-meter-long bamboo into each seam pipe, pull it open and tighten it to cover the back wall and the second half of the gable. Phyllostachys pubescens at both ends, the lower head of which is buried in the soil, is more than 30 cm deep, and the upper head is fastened and fixed on the outer edge of the gable with iron wire, and the bottom edge of the membrane is buried in the soil outside the wall. Then fill the gap between the wall and the film with broken grass with a thickness of about 30 cm, and then bury the upper edge of the film on the back slope of the greenhouse with soil.
After this treatment, there is a good insulation layer outside the greenhouse wall, and the heat of the wall is no longer radiated. When it is cold at night, the heat of the wall is only released indoors, which can significantly increase the night temperature in the greenhouse, which is 3-5 degrees higher than that in the greenhouse without insulation layer. The effect of stabilizing greenhouse temperature at night in severe cold period is very obvious.
6. What are the advantages of setting cold ditches in greenhouses? How to set the cold ditch?
In the past, the method of building a greenhouse was to dig a cold-proof ditch outside the greenhouse in front of the light surface, fill the ditch with grass and cover it with film. It is found in practice that the cold-proof ditch set in this way, after pulling the grass curtain, the operator walks back and forth, and it is not long before it is trampled and loses its thermal insulation effect. Cold-proof ditches should be set on the edge of the greenhouse, and not only on the south edge, but also on the four sides of the greenhouse. The south edge of one of the greenhouses should be changed into a cold ditch to store water and store heat. The method is: dig an east-west ditch with a depth of 50 cm and a width of 40 cm in the front, and to the south of the ditch, close to the outer edge of the greenhouse, vertically bury a row of foam plastic plates with a depth of 50 cm and a thickness of 2-3 cm. If there is no plastic board, you can replace it with broken hay wrapped in old film. 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 two layers of old films. After that, plastic film pipes (double-sided plastic barrels, about 50 cm thick and 80 cm wide) with the same length as the greenhouse were laid in the ditch. After laying, wrap the opening at one end of the plastic pipe with string and raise it above the ground, then fill the opening at the other end with well water, and then wrap it with string and raise it to prevent the opening from leaking outwards.
On the other three sides, dig a narrow ditch with a depth of 40 cm and a width of 20 cm, and fill it with broken grass. Grass should be filled and practical, and there is no need to cover it with plastic film.
The advantages are: firstly, 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; Secondly, completely prevent the transfer of soil heat to the outside and increase the soil temperature; Thirdly, the broken grass in the ditch will be decomposed and fermented by soil microorganisms after absorbing water, which can not only release heat, raise indoor temperature, but also release carbon dioxide, provide raw materials for photosynthesis of leaves, and significantly improve indoor crop 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 disadvantages of low temperature at night and high temperature at day along the greenhouse. Well water in the pipeline can also be used to irrigate indoor crops, which solves the problems of low temperature of irrigation water and low ground temperature after watering in winter.
7. How to set the ventilation openings in the greenhouse?
There should be two air vents in the greenhouse, 1 at the top of the greenhouse and 1 at the front of the greenhouse, with the height of 1.2- 1.5 meters, and the air vents should be provided with insect-proof nets. Vents (top vent and front vent) are arranged in this way for easy management. During ventilation, outdoor cold air enters the room from the height of 1.2- 1.5 m, and is quickly heated by the hot air rising from the front of the room, thus avoiding the phenomenon that cold air directly blows crops. Moreover, air convection will be formed between the front air outlet and the top air outlet, which will promote indoor air circulation, facilitate the rapid discharge of hot air from the top air outlet, not only make the indoor temperature uniform, but also effectively reduce the indoor temperature and prevent pests and birds from passing through the air outlet.
At present, many greenhouses only have top vents, but no front vents, and most of the vents are not equipped with insect nets, which will bring a lot of inconvenience to management. First, when ventilated, pests and birds are easy to invade from the vents and endanger crops; Second, once there is high temperature in the room, it is difficult to cool down only by ventilation at the top vent. Even if the ventilation window in the back wall is opened, it is difficult to reduce the temperature in the front of the greenhouse, so we have to pull open the bottom film and open the bottom opening for ventilation. In this way, outdoor cold air directly blows on indoor crops, which often causes the temperature in front of the house to plummet, causing crop leaves to lose water and dry up, bringing undue losses.
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