Reasons for the need for ventilation in greenhouses. System options, rules for airing rooms, examples of calculating the characteristics of equipment to maintain a favorable regime in buildings. Greenhouse ventilation is a system of measures to maintain temperature, humidity and carbon dioxide replenishment to ensure the successful cultivation of crops. The task is accomplished by exchanging indoor air with outdoor air. We will talk about how to ventilate greenhouses in our article.
Features of the greenhouse ventilation system
Ventilation performs different tasks, depending on the season and the purpose of the process.
In the summer, it is necessary to humidify and cool the air. Greenhouse seedlings are very tender and can be killed by high temperatures. For example, at + 32 ° C, fruits do not set on tomatoes, and no crop can withstand + 40 ° C. Microorganisms living in the greenhouse also die.
In summer, natural ventilation is very often used, without the use of mechanisms. It may not be enough, and mold and pests will appear in the structure, and plants will start to hurt. Therefore, it is recommended to periodically ventilate the room forcibly using fans. You can do without them if the total area of door openings and vents exceeds 20% of the walls.
In winter, cold streams, harmful to seedlings, penetrate through the cracks into the structure. Therefore, in the fall, all cracks and gaps are carefully sealed, and the central road in the building is deepened. However, even at this time of the year, it is necessary to ventilate the room in order to get rid of humid air, which negatively affects the growth of plants and provokes various diseases. Also, airing allows you to get rid of fogging and condensation on the walls.
The procedure is performed if there are fans in the greenhouses, which can be used to improve the circulation of warm air from heating appliances. The process is carried out within 5-10 minutes, with the windows and doors closed.
There are several options for ventilation in the greenhouse:
- Natural, through the vents and doors. Openings are opened manually.
- Forced. It is carried out with the help of fans that supply cool air to the room or take warm air out of it.
- Automated system. Consists of various mechanisms that provide ventilation of the greenhouse without human intervention. They can be electric, hydraulic, pneumatic, bimetallic, etc.
Natural ventilation in the greenhouse
It is considered the simplest and most affordable option for ventilating a building through doors and vents. Before ventilating the greenhouse, we recommend that you familiarize yourself with the most popular cooling systems.
Ventilation through the doors
Circulation occurs due to the movement of air from a warm room to the outside and cold from the outside to the inside. If the temperature difference is small, the flow moves very slowly, which prevents drafts. A thermometer and a hygrometer are used to control the air parameters. According to their testimony, transoms are manually opened and closed, many times a day.
To automate the process, you can install special equipment that will do this work for you at any day and hour. To do this, it is necessary to purchase appropriate electromechanical actuator devices and customizable sensors. Usually they are already provided in the mechanisms. The product is triggered when the temperature reaches the set value. Also popular are hydraulic and pneumatic devices that are easy to assemble by yourself.
The simplest way to ventilate the greenhouse is through the doors located at the ends of the room. If you open them at the same time, then the air moves from one end to the other in the room, and the structure cools.
However, a rapid change in temperature is bad for plants, and they begin to hurt. To weaken the influence of a draft, a path is made in the middle of the building, along which the main air flow will pass. Crops located on the sides of the greenhouse will be less affected by draft.
It is also recommended to open openings in calm weather and only during the day. This ventilation option can be useful for seedlings, which are intended for transplanting into open ground. Landing under the open sky will be less painful.
Ventilation through the vents
If the vents are located at the ends of the structure, then ventilation through them is in many ways similar to the ventilation in the previous way, but has its own characteristics:
- Transoms are easier to install than doors. They do not require sealing as they are water does not fill the gap between the window and the frame.
- To obtain a good result, it is necessary to place the openings as high as possible. Cool air enters the structure from top to bottom, moving towards the center, without the formation of strong drafts.
- It should be remembered that the smaller the size of the vent, the greater the flow rate. The optimal total area of openings is not less than 20% of the total surface area. With such parameters, the plants are exposed to minimal temperature loads.
- Additional openings on the side walls also reduce drafts. Air enters in from different directions, mixes, but does not move in one direction.
- The classic placement of the vents is in the roof. Warm air rises up, and cold air sinks into the building. No drafts are formed, and the crops are not affected by temperature loads. The main advantages of this method: low energy consumption, high efficiency, no harmful effects on plants. However, it has disadvantages associated with the upper location of the vents. It is difficult to close and open them manually, so you have to use expensive mechanisms - chain drives, gear motors, etc.
In plastic greenhouses, the side walls can often be fully opened. This option is ideal for seedlings. During the day, the plants almost do not protect anything, and they are hardened from temperature extremes, and at night, after the film is lowered, the seedlings are closed from hypothermia.
Pneumatics for natural ventilation
In order not to spend money on expensive equipment, you can automate the device yourself. Consider a design that is designed for a window that opens horizontally.
To do this, you will need the following parts: a 30-liter tank, a ball chamber, a pipe or hose, with which the individual elements are connected into one system.
The work is performed in the following sequence:
- Attach a lever to the window through which force will be transmitted to open and close it. It should be adjustable to fix the frame at different angles.
- Adjust the transom so that it closes on its own.
- Place a football camera between the lever and the frame of the greenhouse and fix it in such a position that the window opens when filling with air.
- Use a hose to connect the chamber to the barrel, which should be located in the middle of the building.
- Seal all holes in the container.
Under the influence of the high temperature, the pressure in the barrel will begin to rise and air will move into the chamber. When expanding, it will move the lever and raise the transom. After cooling, the window will close the opening under its own weight.
Hydraulics for natural ventilation
For structures that open vertically, a hydraulic device can be used. It consists of two communicating vessels, one of which is located outside, the other indoors. The latter is connected to the window with a lever. When cold, the entire system must be balanced with the transom closed.
The principle of operation of the structure is as follows:
- The high temperature inside the greenhouse heats up the liquid.
- It expands, flows into the container from the outside.
- The system of two cans loses balance, so nothing prevents the window from opening.
- When the air is cooled, everything comes back.
When choosing a factory-made hydraulic structure, pay attention to the following points:
- The product is designed for a certain weight, so before buying, check with the seller if the mechanism can raise your window, and at what angle.
- The greenhouse frame often does not support heavy loads, so you need to find out if it can hold the hydraulic attachment.
- You should also determine the temperature control range on the device and compare with your requirements.
- Pay attention to the price. Good quality gadgets are not cheap, and you need as many of them as vents.
The hydraulic fixture can be made by yourself. To assemble the device, you will need: 2 glass jars for 3 and 0.8 liters, 2 lids - seaming and plastic, tubes - hard (copper) and soft (rubber or plastic), a small rail, soft wire.
Perform the following operations:
- Pour water into a three-liter jar and roll up a tin lid. Pass the copper tube through the hole and lower it down until there is a 3mm gap above the bottom.
- Secure the container above the vent.
- Pour liquid into a smaller container and close it with a plastic lid. Insert a copper tube into it and carefully seal all the cracks.
- Secure the container to the top beam of the transom with a wire and nail. Nail a block outside to act as a counterweight. He must balance the load on the window from the can of water.
- Connect the copper pipes on the containers with a soft tube.
As the temperature changes, the air will begin to expand and displace water into the lower container. The weight of the can will increase, it will push the lever and open the window.
The hydraulic system is quite reliable and does not require constant supervision. However, it works with a delay of 20-30 minutes after changing the temperature regime, which can be detrimental to seedlings.
Other devices for natural ventilation
To organize ventilation in a greenhouse of a natural type, you can also use the following devices:
- Bimetallic fixtures … The design consists of a lever and two bimetallic plates with different expansion coefficients. The principle of operation of the device is as follows: when the temperature rises, one of the plates is deformed and opens the window. When lowered, the element is aligned and the frame is pulled back. The system is very simple, but it has drawbacks: it is difficult to calculate how much the plate deforms when heated.
- Automatic vents … This is a new direction in the arrangement of ventilation in the greenhouse. The main element in the product is a cylinder with a piston, into which oil is poured. When heated, the oil expands, moves the piston and the transom fixed to it. The liquid does not compress, therefore, when expanding, the device can move a rather heavy structure. It differs from other designs in simplicity and low price.
- Electrical devices … Such machines have high sensitivity, convenient adjustment and unlimited power. The adjustment devices are small and easy to place anywhere in the building. The device can be configured for any operation algorithm. However, the electrical system is unreliable and depends on the continuity of the system. A network outage in the summer for several hours could kill the entire crop. Therefore, it is always necessary to provide autonomous power sources in the greenhouse - batteries recharged from solar panels.
Greenhouse forced ventilation
Forced ventilation is necessary if natural ventilation cannot lower the temperature below +28 degrees. It is distinguished by the artificial movement of air masses. This method is recommended for use in large greenhouses. Standard buildings measuring 6x3 m are naturally ventilated.
Fan selection
The main element of the forced ventilation system is a fan, most often an axial "axial" fan with blades, designed for installation on flat horizontal or vertical surfaces. For the operation of the device in an autonomous mode, a thermostat is used.
The fan is selected depending on the greenhouse area and power.
When buying, pay attention to the following points:
- The speed of air movement in the room should not exceed 1.9 m / s.
- The normal rate of aeration is 50-60 times per hour. When calculating, you can use the following proportions: with a room volume of 40 m3 the fan must have a capacity of 2000 m3 in hour.
- Always buy a product with a capacity margin.
- In small buildings, you can use household appliances such as those used in toilets. They are produced in a waterproof design.
- It is advisable that the unit be equipped with a speed controller, with which you can adjust the performance depending on the temperature and humidity in the room.
Determination of fan power
When calculating ventilation in a greenhouse, it is necessary to take into account the following points:
- The degree of ventilation depends on the season and weather.
- In summer, the air in the greenhouse should be completely changed within 1 minute.
- In winter, 20-30% of fresh air is sufficient for ventilation, and the plants will not freeze.
There are many formulas for determining the fan power, which differ in accuracy and complexity. The following calculations are considered the simplest technique:
A = V * C * K, where:
A is the productivity of the apparatus (m3/ hour); V - greenhouse volume (m3); C is the rate of air exchange (hour), usually one change per minute, 60 per hour; K is the loss factor (if there is a filter on the fan), in the case of using a carbon filter, K = 1, 25, because the drop in device efficiency is 25%.
As an example, we will calculate the fan power for a greenhouse measuring 1, 2x2, 4x2, 5 m. Multiplying the values, we determine the volume V = 7.2 m3.
A = 7.2 * 60 * 1.25 = 540 m3/hour
This value determines the minimum performance of the unit. In order to have a margin for unforeseen situations, it is recommended to take the product with a capacity of 25% more.
For winter ventilation, a low power fan is required, so the selected device must be multi-speed in order to be used at any time of the year.
Rules for installing a forced ventilation system
In order for the fan to operate at its highest efficiency, it is necessary to know the rules for the placement of the product and the structure of the entire system.
The greenhouse will quickly ventilate if the following conditions are met:
- The fan should be located at the highest point in the room, to which warm hot currents rise. This can be a roof or a side wall.
- In large greenhouses, products are placed from the ends of the room. In country buildings, they are attached above the door.
- It is recommended to buy products with shutters to protect against external influences, as well as to close openings when the motors are not running.
- The room where you plan to install the fan must have a hole for air circulation. Perform it on the opposite side. In winter constructions, this can be a hand-opened window. In summer, a small opening is left, which is closed with a wet rag.
- The quality of ventilation is controlled by several sensors located in different parts of the greenhouse.
- In large buildings, the fan can be installed indoors. It mixes cold and warm air, creates laminar movement, which prevents a number of diseases in plants.
- To automatically turn on the electric motor, thermostats or humidity sensors are introduced into the system. A moisture-resistant thermostat should operate at a temperature of + 28-30 degrees.
How to make greenhouse ventilation - watch the video:
If you are growing early crops, you need to take the ventilation of the building seriously, without which most crops cannot be grown. It is not difficult to install ventilation in a greenhouse with your own hands, having studied our recommendations and spending money only on automating the process.
