Solar greenhouse lighting design

Solar greenhouses rely on the heat of the sun to obtain heat, and nighttime heat mainly depends on the solar radiant heat accumulated during the day. However, in the north of the Great Wall, in the event of severe winds and heavy snowfall, the outdoor temperature may reach minus ten Celsius. When it reaches tens of degrees, indoor heating is needed. Therefore, the construction methods and temperature increase measures of solar greenhouses in different regions are not the same, and they should be built according to the local conditions. First, the principle of solar greenhouse construction The construction of solar greenhouses on a practical basis, should focus on the following points: 1 good light and heat storage and insulation properties; 2 size and size of the appropriate size; 3 have sufficient strength, can resist wind, Loads resulting from snowfall, etc.; 4 Reasonable adjustment of environmental conditions such as temperature, light, water and gas; 5 Construction materials as far as possible from local sources, focusing on practical results, and reducing investment costs. Second, the solar greenhouse construction points The sun is a huge hot sphere, it maintains a stable high temperature for a long time, it has a great deal of energy. The main wavelength range of solar radiation is between 0.15 and 4 microns, accounting for about 99% of the total solar radiation energy. In the solar radiation reaching the ground, it can be divided into ultraviolet (wavelength less than 0.38 micron radiation), visible (wavelength 0.38 ~ 0.76 micron radiation) and infrared (wavelength greater than 0.76 micron radiation). According to the nature of solar radiation, when building a solar greenhouse, we should consider the following points. (a) The orientation of the greenhouse and the orientation of the solar greenhouses are generally extended east-west and north-facing. The location of the sun at noon local time should prevail. In practice, however, some people claim that the south-facing position is eastward, so that in the morning, the grasshoppers can be lifted early to allow the light to shine as early as possible. Because the temperature in the greenhouse is lowest before the sun comes out in the morning, this kind of eastward sitting can be Increase the temperature in the greenhouse as soon as possible. Some people also claim that the southwesterness is to the west. This has the advantage of extending the sunshine hours in the afternoon and favoring heat storage. Regardless of the method used, the bias should not exceed 10 degrees. (II) Plastic film and lighting Most of the solar greenhouses in China currently use plastic films as the transparent covering material for the roof of the skylight. The thickness is generally between 0.08 and 0.12 mm. The drip-free film can reduce the reflection and absorption of water droplets into latent heat and increase the light transmittance. Compared to other films, dripless membranes generally increase the temperature in the greenhouse by 2°C to 4°C. (3) After the angle of the front roof and the sunlight transmitted onto the roof of the film, most of the light penetrates the room, but some of the light is absorbed and reflected by the film. The absorption of the film is fixed, and the transmission and reflection are inversely related. Of course, our goal is to maximize the rate of transmission, so that we should do everything possible to reduce the reflectivity. In practice, it is known that the ratio of light transmittance is proportional to the angle of incidence between the light and the film (Fig. 4.1). The smaller the incident angle, the higher the light transmittance; otherwise, the lower the light transmittance. The angle of incidence here is the angle between the person's light and the normal. However, the size of the human angle of view has a certain relationship with the height of the sun and the slope of the solar greenhouse (Figure 4-2). However, the height of the sun changes every moment, and the slope of the greenhouse's lighting surface cannot change with the height of the sun. Therefore, what is before us is the determination of the lighting slope of the greenhouse, and the slope of the lighting surface in different regions should be different. In principle, the annual positive temperature level shall prevail. At this time, the temperature in the greenhouse can be maximized when the temperature is the lowest. Of course, the best one is 0, but the maximum should not exceed 40. Third, the design of the visual greenhouse and material selection (a) the overall size of the solar greenhouse 1. Span refers to the width from the south side of the greenhouse to the inner wall of the northern wall. The span is generally between 6 and 7 meters. This span, together with a certain ridge height, can ensure that the front roof has a more reasonable lighting angle and more convenient operating conditions, and it can also ensure that the leeches have ample living space. 2. Height refers to the height of the roof to the ground. When the height is high, the lighting effect of the front roof can be directly increased, which is beneficial to the light transmission during the day and increases the space for heat capacity. However, the height is too large and the heat dissipation is faster at night, which is not conducive to heat preservation. In practice, it is concluded that a span of 6 meters in a solar greenhouse is suitable for a height of 2.6 to 2.7 meters; a span of 7 meters in a solar greenhouse, with a height of 3 to 3.1 meters is appropriate. 3. Front and rear roof angles The front roof angle refers to the angle between the plastic film roof and the ground plane. The angle of the front roof has a direct relationship with the light reception, generally should be between 23 and 28, but the specific angle should be based on the height of the sun. The angle of the back roof is generally determined by the height of the back wall. The larger the angle, the more favorable it is to absorb and store thermal energy, but it is not conducive to night heat preservation. Therefore, it is generally advisable to receive direct sunlight at noon between the beginning of the winter and the beginning of the next year. 4. The wall thickness of the wall and back roof is generally between 0.8 and 1.5 meters. Different regions are different, the more northerly, the lower the outdoor temperature, the thicker the wall should be. The thickness of the back roof is generally 40 to 70 cm. 5. Cold-proof ditch is to dig l trenches on the outside of the front foot of solar greenhouses, filled with heat-insulating materials such as hay, horse dung, or finely crushed straw. The ditch is 40-60 cm deep and 30-50 cm wide. It is best to cover the old film around the cold ditch. The ditch must be covered with grass mud to prevent rain from seeping through the ditch. 6. Vents are mainly used to regulate the indoor temperature and humidity. Usually 3 film butt joints are used. The first interface is 1 to 1.5 meters away from the ridge, and the top sheet presses 20 to 30 centimeters; the second interface is 1 to 1.2 meters from the ground, and the bottom sheet presses the top sheet. The film at the interface is added with a pull cord. It can also be heat sealed or sewn on the edge of the film to increase the pull strength. 7. Sunlight greenhouses with large import/export areas should be set up at one end of the operation room and be opened on the gables to serve as a population. Of course, the smaller the population, the better. It is advisable to facilitate access. The operation room can be used for operations and cold air can be prevented from entering the greenhouse directly. For a greenhouse without work space, install the door at the entrance and exit, and pay close attention to it at all times to prevent cold air intrusion. 8. Greenhouse length The length of the greenhouse should be determined according to the scale of the cultivation, but one greenhouse is too short (below 20 meters), the shaded area of ​​the gable covers a larger proportion of the total area of ​​the greenhouse, so it will not be a greenhouse effect; the greenhouse is too long (60 Above meters, operation and management are inconvenient. The general greenhouse length is between 30 and 60 meters. (2) Selection of Sunlight Greenhouse Frames, Walls, Back Roofs, and Lighting Insulation Covering Materials The design and construction of solar greenhouses should be based on the principle of local materials, practical results, and reduced investment. 1 . Skeleton materials Skeleton materials can be divided into bamboo and wood skeletons, reinforced concrete prefabricated parts and bamboo arch rods mixed skeletons and steel or steel tube skeletons. Under normal circumstances, there are many skeletons with mixed properties, ie, columns, concretes, rubs, etc. are mainly made of reinforced concrete prefabricated parts. Bamboo pieces are used in the north-south direction with an interval of 20-40 cm, and 8th-iron wire is used for the east-west direction. The distance between the wire and the ridge should be closer. The wire is fixed on the ground anchor outside the gable. 2 . Wall materials Wall materials are generally available for earth walls, brick walls, and hollow bricks. The role of the wall is to reduce the loss of indoor temperature and the invasion of outdoor cold air. 3 . The general requirements for the rear roof material are light, warm and strict, and have a certain thickness. The function of the rear roof material is that thermal energy can be stored when the temperature is high during the day, and when the temperature in the room is lowered at night, the stored heat energy is released again to maintain the balance of the indoor temperature. After the roofing material, corn stalks are generally used as house foils, and then the grass mud is applied twice. 4 . Insulation material insulation materials are generally grasshoppers, paper quilts, quilts and non-woven fabrics.

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