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What is not "automatically" is "manually". Opening the greenhouse doors, we ourselves - and the temperature sensor (or analyzer - if there is a thermometer), and the drive ...
The gardener is the most sensitive and trouble-free "mechanism". "Disadvantages" - non-stationarity, the desire to work in multitasking mode in combination with a limited number of hands.
Greenhouse ventilation machine
In greenhouses and greenhouses to shift the duty to maintain the microclimate in the norm on the automation:
- to save the energy of the gardener, who has other concerns, in addition to supplying the greenhouse with the necessary volume of outside air;
- for the opportunity to leave the garden plot (for a city dweller):
- keep several greenhouses and keep up with everything (for the farmer).
When discussing the ventilation of the greenhouse, they talk about the vents, because where there is a temperature difference at the same level, forced ventilation should not be required.
However, there is one more microclimate parameter, more inertial - humidity... A fan will help to cope with its redundancy at normal temperature in the greenhouse.
The second reason to use it is - greenhouse design features: lack of vents, their failure or poor location. Since there is definitely a door to the greenhouse, it is opened slightly, and the fan mixes the internal air, and it cools down (or does not heat up) in all zones of the volume equally.
Turning on the fan in the absence of the gardener will be able to thermal relay.
Features of recirculation systems fan + thermal relay
- Convenient to operate.
- They can have a lot of power.
- Modifiable (you can complicate the system by including additional elements in the circuit).
To the disadvantages refers to the so-called volatility. A backup power supply is required in case of a power outage.
By the way, the same problem (with the same solution) for aquarists: there is no current - oxygen and light in fish too.
To create "traction" openings in the roof are often arranged at two levels: above the floor (if the plants are on the shelves - slightly above the shelves) and close to the ridge (or the zenith of the arch).
But the retention of microclimate parameters within acceptable limits is ensured by the timely start and stop of ventilation, as well as its intensity (that is, the width of the opening of the flaps).
Let's consider what types of vending machines there are for greenhouses.
- Elements that have in their design, the physical characteristics of which, when heated from the ambient air, change so significantly that they are able to perform significant mechanical work.
- Responsive to readings of temperature sensors.
By type of drive
The mechanism converts the force of fluid pressure into mechanical work. Do it yourself - a visual aid in physics for the student.
The simplest and, at the same time, man-made version of the execution - rocker, at the ends of which one container with liquid is fixed, connected by a hose. The law of conservation of energy works inside the system "tank-1 - hose - tank-2". The pressure in the system tends to be the same throughout its entire volume.
The process starts pressure difference inside tanks... Since one end of the rocker arm is in the greenhouse, the other is outside, they heat up differently. The working medium shifts to the colder side, that is, to the outer cylinder; the outer end of the rocker, under its weight, lowers and pulls the leaf of the window.
In the "double-glazed" era, two ends of the rope descended from the school windows into the classroom. If you pull on one, you open it, and for the second, you close it. Instead of hydraulics, the muscles of the hands of the class attendant worked.
On sale hydraulic mechanism with one cylinder (aluminum or steel). The machine is located entirely inside the greenhouse. In the cylinder: oil, piston, rod, seals. In the simplest modification, the free end of the rod rests against the transom and is fastened to it.
The liquid expands, pushes the piston, the rod pushes the door outward. With the return stroke of the piston, the transom rod will pull towards itself (more slowly, but will pull). Additional elements (levers, springs) are sometimes arranged between the stem and the window.
Unprotected from direct sunlight the oil cylinder will heat up from them, and not from the air in the greenhouse.
The peculiarity of this particular design
External mechanical pressure on the vent can damage such a hydraulic drive. Therefore, in addition to the sunscreen, the system is supplemented with latches for the maximum position of the door: cables, ropes or tapes. They contact only with the frame and transom.
Hydraulic automatic greenhouse ventilators vary:
- the weight of the canvas being opened;
- piston stroke (and the angle of change in the position of the blade);
- the material of the cylinder and the presence of reinforcement couplings;
- dimensions, cross-sectional shape and material of the stem, as well as levers.
We choose the response threshold ourselves, with a special nut, in the range suggested by the manufacturer.
Oil acts as a hydraulic fluid; when working with it, it is necessary to comply with safety regulations.
- Simplicity of design.
- Great power.
- Productive tandem forms only with horizontal vents.
- Insensitivity (any liquid cools much longer than it heats up; with a sharp cold snap, the air in the greenhouse may have time to cool down).
- There are restrictions on the maximum operating temperature.
Greenhouse ventilation machine Belarusian production will start opening the door no heavier than 7 kg at a temperature selected by the owner in the range of 15–25 ° С. Finish work in 30-degree internal heat.
Identical domestic machine differs in the possibility of partial detachment from the sash without dismantling, which allows you to open the window wide manually.
Producer of the Republic of Bashkortostan declares a maximum stem force of 100 kg for one of its thermal actuators and 125 for the other.
When choosing do not ignore the maximum allowable temperature an environment in which the manufacturer guarantees the performance and integrity of the device. (The reputation of the guarantor is also important, so that the declared figure can be considered real).
Electric for natural air exchange (motorized drive)
Gardeners make such designs on their own, using actuators from satellite dishes, a geared motor from a car heating stove, etc.
Are they on sale as well?
For example, a domestic "Linear Drive" (12V / 3A) with a motor-reducer and "Radial" (transmission - rack-pinion) in just 5 seconds promises to open the door by 140 °, work complete with a control unit (220V / 4A). One unit is required for 4 linear or 2 radial actuators.
Good a large opening angle of the ventilation opening.
Minus - dependence on the notorious power outages - volatility.
- Completely autonomous.
- Inexpensive and simple.
- Small power (amplify it by sequential arrangement of several pushers).
Sensing element - a plate of two metals (for example, brass-steel). She's a pusher.
The plate changes shape in response to changes in room temperature. Being connected to the door, it pushes it or pulls it towards itself (like the loose end of a bimetallic tape in a thermometer moves the arrow along the dial).
The essence in the fact that both metals, heating the same, change their linear dimensions in different ways. (Brass will increase 1.4 times stronger than steel, and copper - 1.3 times). The bimetallic plate is bent towards the metal layer with a high coefficient of thermal linear expansion.
The same effect underlies the work of the elements that automatically close the electrical circuit.
When self-made you can take a composite material (usually steel), or you can connect two plates mechanically - with rivets, or bolts. Two different materials are also combined: for example, an iron galvanized plate not thicker than 1 mm is fastened to plexiglass up to a centimeter thick.
The larger the greenhouse, the more self-opening vents are needed to control the temperature. It is good if the total area of the ventilation openings is a quarter of the greenhouse roof surface.
Successful location frequency automatic greenhouse vents - 1 to 2–3 meters in length.
The elongated shape requires additional - longitudinal - flow. It will be created by two vents at the ends, one opposite the other.
Effective natural air exchange will allow you to maintain optimal temperature and humidity values inside the greenhouse in any weather.
Greenhouse vents openers that respond to fluctuations in environmental parameters are readily used by gardeners, since the variety of offers on the market and the availability of self-production reciprocate.
And here are videos about the design of an automatic greenhouse ventilation system, the mechanism for opening the vents in the greenhouse from the temperature (pusher, automatic opener, other devices and their device).