Experienced gardeners know that the productivity of the plants which are grown up in the greenhouse in many respects is defined by the ventilation mode. Traditionally the manual way is applied to airing of greenhouses: for this purpose in construction arrange window leaves or the opening sections in roof. In recent years more often the systems of automatic airing where the thermodrive is used meet.
For what the thermodrive is necessary
Use of the thermodrive for ventilation of greenhouses simplifies care for plantings and allows to increase viability of plants. The main advantage of such automatic systems is that they minimize participation of the person.
That plants developed correctly, in the greenhouse the correct temperature condition has to be adjusted, inflow of fresh air is organized, the optimum moisture content is established. For regulation of microclimate of the greenhouse supply with window leaves with special closers. Usually window leaves place evenly on all area of the greenhouse, in upper part of the building as warm air has property to rise up.
Operation of the thermodrive of any type is based on automatic opening and closing of air vents at temperature change in the greenhouse. Automatic systems for ventilation differ in the physical principle which is the cornerstone of its work.
Choosing specific type of the automatic machine for ventilation, consider the sizes of the greenhouse and type of windows (window leaves, sections for airing). If the window is capable to fall under curb weight, application of the simplest designs is admissible. But if the window leaf has vertical axis, the automatic machine with the closer in the form of spring or other mechanism with counter effect is required.
Electronic thermodrive
Such system consists of fans which establish in upper part of the room and also sensors which provide temperature monitoring. The electronic thermodrive is rational, it provides precise adjustment of parameters. Power range of systems of this kind is suitable for rooms of any size. It is possible to use the electronic thermodrive in constructions of any design.
The system has also shortcoming: it entirely depends on electric energy source. To ensure trouble-free operation of the equipment, it is recommended to use accumulators or solar batteries.
The automatic machine on the basis of bimetal plate
The similar device is used so far considerably seldom. The property of metals to answer differently temperature variation is the basis for its operation principle. The design of the device includes two plates made of the metals having different coefficient of expansion. At rise of temperature the combined plate is curved in one party, at fall of temperature – in another. This feature allows to open window leaf (ventilating section in roof) and to close it in the automatic mode, without participation of the person.
The main advantage of "bimetallic" system – full autonomy. The device is extremely cheap and does not need energy source. It is very simple to mount it in the greenhouse. The term of operation is almost not limited. At the same time such system is rather inert: if air has got warm insufficiently, the window leaf will remain motionless. It is possible to use such automatic machine only on light-weight frame structures. Difficulties arise also at selection of couples of metals which capable will extend at that temperature which is necessary for specific plants.
Automatic machines on the basis of pneumatics and hydraulics
Such systems of airing differ in the principle of work: in one case working body is air, in another – liquid. It is possible to understand operation of the automatic machine of similar design on the example of hydraulics.
The device of hydraulic type consists of hollow cylinder which is filled with special liquid, and mobile rod. The rod is capable to move under the influence of force arising at expansion or compression of liquid.
At achievement of certain temperature, liquid begins to extend and pushes rod. This mechanical effort is transferred to window leaf, opening it. The system under the influence of the curb weight when the rod moves is closed. Sometimes in such systems in addition use the mechanism of counter effect; in this case the weight of window leaf does not matter.
The systems of hydraulic type are durable and very reliable. Energy source is not required to such hydraulic actuator. Mounting of system on frame requires only the screw-driver. However closing of window leaf can slow down because of inertness of system. The automatic machine is capable to trace temperature only in the place of its fastening. The hydraulic automatic machine differs in rather high price and is not profitable when using in greenhouses of the small sizes.