What problems should be paid attention to in thermal insulation design of solar greenhouse?

(1) Because the wall has a sunlight greenhouse for producing peaches, heating equipment is generally not needed. Therefore, thermal insulation design should not only make the wall have bearing and thermal insulation functions, but also have strong bearing functions. Store a lot of heat during the day, and continuously release heat indoors at night to delay the decline of indoor temperature.

At present, there are two types of walls in solar greenhouses: one is a simple wall, and the other is a composite wall. Simple walls are made of a single soil or brick and stone; Generally, the inner and outer layers of heterogeneous composite walls are all bricks, and there is an interlayer between the two bricks with thermal insulation material in the middle. The insulation materials filled in the interlayer include dry soil, cinder and perlite. As can be seen from the table 1, the minimum temperature of solar greenhouse is higher than that of hollow sandwich wall filled with thermal insulation materials.

Table 1 Wall Insulation with Different Insulation Materials

Architectural parameters of the second generation solar greenhouse wall;

Back wall: ① Brick hollow wall. The interior wall is 12 ~ 24cm brick wall (stone can also be used), the exterior wall is 24cm brick or hollow brick wall, and the middle is 10cm perlite insulation layer, which constitutes a heterogeneous composite multifunctional wall with a thickness of 50 ~ 60cm. ② Stone-soil (grass) composite wall. The stone wall is 50 cm thick at the bottom and 40 cm thick at the top. The inner wall is vertical and the outer wall is inclined. The thickness of soil outside the wall is 30 ~ 50 cm thicker than the local maximum frozen soil layer. ③ Soil, soil (grass) composite wall. Tamp the 50-60 cm thick soil wall or grass mud pile wall, and add cultivated soil to make the composite thickness of the wall 30-50 cm thicker than the local frozen soil layer. The gables on both sides are made of earth walls or bricks, and the thickness is equivalent to 2/3 of the local maximum frozen soil layer thickness.

(2) The elevation angle of the back slope is 10 degree higher than that of the local noon sun from winter to Sunday; The covering material of the back slope is mainly heat storage and insulation material, and the seal should be tight. When straw and firewood are used as the main materials, the total thickness of cushion and covering layer reaches 2/3 ~ 4/5 of the local maximum frozen soil thickness.

(3) Front roof covering material The front roof is the main heat dissipation surface of the greenhouse. By covering the front roof, heat dissipation can be prevented and the heat preservation effect can be achieved.

At present, the external covering materials of the front roof in China are mainly grass, paper and so on. Straw mat is a traditional covering material, which is woven from reed foil and straw. Single-layer mulching with high-quality grass (covering the daylighting roof, so that no light can be seen indoors) can increase the greenhouse temperature 1 ~ 3℃. In cold areas, a paper quilt made of 4 ~ 6 layers of kraft paper is often laid under the grass. Adding a layer of paper under the straw cover not only increases the air isolation layer, but also makes up for the shortcomings of loose straw cover and improves the thermal insulation. According to the test, adding a paper quilt composed of four layers of kraft paper can increase the indoor minimum temperature by 3 ~ 5℃, and the more layers, the better the thermal insulation performance. Although the paper quilt has good thermal insulation, it has high investment, easy to get wet by rain and snow, short service life, inconvenient management and labor-consuming.

(4) The purpose of setting cold ditch is to prevent the heat from losing laterally and improve the indoor ground temperature. Cold-proof ditches are generally set outdoors with a width of 40-50 cm and a depth of 40-60 cm. Filling the ditch with dry soil, hay or other heat insulation materials can increase the indoor ground temperature by about 4℃ in the first 5 cm. The cold trench should be covered to prevent rain and snow from flowing in and reduce the cold protection effect.

(5) The gables of import and export greenhouses should be provided with an import and export (door). Generally, the import and export should be located in the Dongshan wall to prevent the northwest cold air from invading the room. Wooden doors should be set up, and then door curtains should be hung for insulation. In order to prevent cold air from pouring into the room when operators enter and leave the greenhouse, a buffer room should be set outside the Dongshan wall (door), with the door facing south, and it is best to hang a curtain in cold season.