September 28, 2021
Greenhouse Ventilation system - ventilation cooling
In most areas, it is hot in summer, and the outdoor temperature is above 30℃. Due to the greenhouse effect, the internal temperature of the greenhouse can easily exceed 40℃. Therefore, cooling means must be taken to ensure normal production in the greenhouse.
At present, the commonly used cooling methods in the greenhouse are ventilation cooling, shading cooling, wet curtain fan cooling, micro fog long temperature, roof spray cooling, roof spray white, and so on. Ventilation cooling can be divided into natural ventilation cooling and forced ventilation cooling, shading cooling can be divided into internal shading cooling and external shading cooling. In the design and use of a greenhouse, ventilation, and cooling are always inseparable.
In general, greenhouse ventilation has three main purposes:
1, eliminate the waste heat in the greenhouse, and reduce the temperature;
2, eliminate the excess moisture, and reduce humidity:
3, adjust the indoor air gas composition, eliminate harmful gases, and improve the content of C02 in the air.
For summer, the main purpose of ventilation is to reduce the indoor temperature, requiring adequate ventilation; And for winter, the main purpose of ventilation is to adjust the composition of indoor air, in order to heat preservation and energy saving, rely on cold air permeability ventilation, maintain the lowest ventilation volume can meet the ventilation requirements.
1, Natural ventilation is generally set window at the top or side wall of the greenhouse, relies on hot press or wind pressure in ventilation, and can be adjusted by adjusting the size of the window ventilation rate, main factors determine the size of the natural ventilation rate generally have: indoor and outdoor temperature difference and height of greenhouse vents, vent area, vents orifice resistance, and outdoor wind speed and direction, etc. Indoor and outdoor temperature difference, outdoor wind speed, and direction are generally uncontrollable factors, therefore, the evaluation of greenhouse natural ventilation performance mainly depends on the height difference and ventilation area of the vent.
It is to use side wall ventilation, use roof ventilation, or use roof and side wall joint ventilation, according to greenhouse size, type, and local specific climate environment to decide. Under normal circumstances, the ventilation volume of roof and side wall joint ventilation is the largest. But for the total width of the greenhouse is less than 30 meters of the greenhouse, the side wall ventilation occupies a large proportion of the whole greenhouse ventilation. For a large area of the townhouse greenhouse, the general roof vent area and large dry side wall vent area, so the roof ventilation is generally dominant.
The setting of the vent should conform to the law of airflow. The roof vent, should be located outside the highest roof as far as possible to form a large height difference. The ventilation of the dry side wall should be located as low as possible, and the side window should be perpendicular to the dominant wind direction of the season from late spring to Mid Autumn Festival.
An important indicator of natural ventilation performance is the percentage of the actual vent area to the floor area of the greenhouse. The higher the ratio, the better the ventilation performance. Therefore, the general greenhouse window opening Angle should be as large as possible to increase the actual air intake area.
Natural ventilation is affected by the outside climate, and the cooling effect is unstable. Generally, the indoor temperature is 5-10 ℃ higher than the outdoor temperature.
The advantage of forced ventilation is that the ventilation volume of the greenhouse is little affected by the outside climate.
2, currently commonly used ventilation equipment accessories roll film ventilation for plastic carrier room. The main accessories for film winding devices can be divided into manual types and electric types.
For side wall ventilation, ①19 or ①22 steel pipe is generally used as the coiling film shaft, and the shaft and the film are fixed together with a film card. The film-type device is installed at one end of the greenhouse, and the vertical guide rail of the film coiling device is made with ①19 or ①22 steel pipe, and the film coiling device and the film coiling shaft are connected with the shaft joint. It should be noted that the electric film winding device also needs to adjust the stroke switch.
The method of roof ventilation is similar to that of side wall ventilation, except that the manual film winding device needs to be lengthened with a crank, and the electric film winding device needs to be added with a telescopic sleeve. The maximum coil length and the maximum coil length should be known when selecting the film winding device.
Side window winding film or roof winding film, ventilation window types are various, but according to the transmission, type can be divided into rack and pinion drive system, punching rack and pinion drive system, crank link window system, VENLO type greenhouse push rod window system, etc.