The temperature control in greenhouse is required to maintain the set temperature suitable for crop growth, with uniform spatial distribution and gentle temporal change. The control measures include heat preservation, heating and cooling. 1.Heat preservation 2.There are three ways of heat dissipation in the greenhouse: first, heat transfer through the envelope of covering materials (wall, transparent roof, etc.); Second, air exchange and heat transfer by air leakage through the gap; The third is the heat transfer between soil and soil. These three kinds of heat transfer amount to 70% ～ 80%, 10% ～ 20% and less than 10% of the total heat transfer respectively. As a result of all kinds of heat dissipation, the heat preservation capacity of single-layer unheated greenhouse and plastic greenhouse is relatively small. Even if they are well sealed, the temperature at night is only 2-3 ℃ higher than the outside temperature. In the windy sunny night, sometimes the indoor temperature is lower than the outside temperature inversion phenomenon. The specific insulation measures are as follows: (1) Reduce ventilation (2) Multi layer covering heat preservation can be used in greenhouse or greenhouse with small arch shed, small arch shed with middle arch shed, grass curtain on both sides of large arch shed, greenhouse and large arch shed with movable heat preservation curtain and other multi-layer covering methods, which have obvious heat preservation effect. (3) Building the solar greenhouse into semi underground or appropriate will reduce the height of the room, reduce the heat dissipation area of night protection facilities, and also help to improve the indoor day and night temperature and ground temperature. (4) In the greenhouse, high ridge plastic film mulching cultivation is adopted, and more organic fertilizer and less chemical fertilizer are applied, because the decomposition process of organic fertilizer releases a lot of heat, which increases the temperature in the greenhouse, while chemical fertilizer is on the contrary. (5) In autumn, the greenhouse should be covered as early as possible to keep the heat accumulated in the soil after a summer; The cold proof ditch is set at the front and bottom of the greenhouse to reduce the transverse heat conduction loss; Try to use the water preheated in the greenhouse, not in cloudy days or at night. 2. Heating The main heating measures are: (1)coal fire heating of stove(2)Boiler water heating Generally, most of them use stove coal heating, and in recent years, boiler water heating or geothermal water heating are also used. Hot water or steam can also be converted into hot air for heating. Most of the plastic greenhouses have no heating equipment, and a few of them use hot blast stove for short-term heating, which has obvious effect on increasing production and output value. The radiation heating method of LPG through the combustion furnace also has a significant effect on the protection of greenhouse against low temperature and freezing injury. 3. Cooling The simplest way of cooling in greenhouse is ventilation, but when the temperature is too high and natural ventilation can not meet the requirements of crop growth, artificial cooling must be carried out. (1) The room temperature can be reduced by 4-6 ℃ when shading is 20% – 30%. It is very effective to hang a light screen about 40 cm away from the greenhouse roof. The lower the temperature emissivity, the better the texture of the screen. Considering the weatherability of plastic products, the general plastic shading net is made of black or dark green, and some are made of silver gray. The white non-woven insulation curtain used in Greenhouse (the light transmittance is about 70%) can also be used as shading curtain, which can reduce the temperature by 2 ~ 3 ℃. (2) The water layer can absorb about 8% of the solar radiation projected on the roof, and can cool the roof by absorbing heat with water. The room temperature can be reduced by 3 ~ 4 ℃. When using this method, the installation cost and the scale pollution on the surface of the shed should be considered. In areas with hard water quality, the water quality should be softened for reuse. (3) the spray cooling method makes the air water evaporated and cooled before sending it into the room, so as to achieve the goal of cooling. fine mist cooling method is used to spray the floating fine mist with a diameter of less than 0.05 millimeters in the indoor height, and the evaporation of fine fog can be achieved by the forced ventilation airflow to cool the whole room. the roof spray method continuously spray and moisten the entire roof, so that the cooling air below the roof will flow downward. (4)Because of the large volume of forced ventilation large solar greenhouse, forced ventilation is needed to cool down by using fan.
Article source: https://www.naturehydro.com/