Automation of ventilation and organization of drip irrigation in a greenhouse

There are a number of designs for direct-acting regulators that use air as the working fluid. In the design shown in Figure 55, the transom opens due to the lifting of a flexible reservoir (an inner tube), which is connected to a sealed vessel secured in the upper part of the greenhouse.

The flexible vessel is placed in a barrel of water; as the air expands, it increases in volume and floats, opening the transom.

A regulator in which the transom opens due to the moment created by the redistribution of water between two containers during air expansion differs slightly in design. The operating principle of the regulator is clear from the figure.

Although regulators with air as the working fluid are simple in design, they require large-volume operating elements due to the low heat capacity of air and are therefore rather bulky.

They can be made more compact if low-boiling liquids, such as Freon, are used instead of air. However, the operation of such regulators is complicated by Freon leakage.

Having ensured the plant protection from frost and overheating, it is also necessary to consider supplying them with water. This issue is especially relevant for greenhouses located at a significant distance from their owners' place of residence.

When addressing irrigation, it is necessary to have:

• A water source;
• A system for delivering it to the plants.

If the site has a water supply network, a borehole, or a well with an installed pump, the first issue is already solved. In the absence of such sources, it is necessary to install a special water container and periodically fill it.

Recommended parameters for the container installation:

It is advisable to have a container even in the first case to stabilize the pressure in the system and to warm the irrigation water. If there is a water supply inlet, a float valve from a flush tank can be installed in the barrel to maintain a constant water level. If a larger reserve of irrigation water is required, two or more barrels are connected in parallel.

As an irrigation system, it is convenient to use a drip system (homemade or factory-made). Drip irrigation components called "Vodomer" for individual greenhouses are available in stores. A drip system can also be made by oneself.

A polyethylene hose or pipe with a diameter of 15–20 mm, laid along the center of the bed, is used as a sprinkler. Water is supplied to the plants via micro-tubes — lengths of polyvinyl chloride insulation from electrical wires with an internal diameter of 0.9–1.0 mm and a length of 50–60 cm. One end of the insulation length is secured in a hole pierced in the pipe with an awl, and the other end is led to the plant. This end of the tube can be secured on a special stand so that the water outlet is raised 2–3 cm above the soil and is 5–6 cm away from the plant.

The temperature of the water used for irrigation of plants in the greenhouse should always be higher than the soil temperature.

Those who heat water in a boiler with firewood should keep in mind that the water temperature at the top of the boiler is always slightly higher than at the bottom. Therefore, the water should be stirred with a slat before irrigation.

If a hose is used for irrigation, a valve, similar to a samovar tap, is installed at a distance of 10–15 cm from its end. With such a tap, one can regulate the flow rate of water and shut it off when moving the hose. A water diffuser, like those used in shower heads, is attached to the end of the hose.

The hose can be used for irrigation both inside and outside the greenhouse by feeding it through the door or by removing one of the removable frames.

The hose is also convenient to use when watering from a watering can:

• A piece of hose about 1 m long is put onto the spout of the watering can.
• The frame is removed from the greenhouse wall, the watering can is placed on the bottom frame beam, and the end of the hose is brought to the line of planted crops.
• The watering can is tilted and the hose is led along this line; the flow rate of the water is regulated by the tilt of the watering can. The force should be such that the soil is not washed away and the root system is not exposed.

If the design of the greenhouse is such that the frames are easily removable, it is more convenient to water from a watering can while standing outside the greenhouse.

Irrigation control can be easily managed by using soil moisture sensors. Several principles of moisture measurement can be used. One of them is based on the change in the bulk density of the soil upon moistening. The moisture regulator contains a moisture sensor in the form of a water-filled chamber 1, and a siphon 3 connected to it, which is suspended on a spring-loaded lever 5. One end of the lever is equipped with a valve 19, which closes the drain pipes 17 and 18 of the hydraulic cylinder 10.

An increase in soil moisture leads to an increase in its mass, deflection of the membrane in chamber 2, and the overflow of a portion of the water into siphon 3. The increase in the mass of the siphon leads to the closing of pipe 17, the movement of piston 11 to the upper position, and the closing of the gate valve. An adjusting screw 8 is used to set the soil moisture control limits.

An electronic moisture controller can be used. One such circuit diagram is shown in Figure 58. The moisture sensor here consists of two carbon rods from a 3336L battery with a depolarizer (only the zinc casing needs to be removed from the elements). The rods should be embedded into the soil at a distance of 20 cm.

At reduced moisture, the system parameters are as follows:

Automation of irrigation allows for maintaining optimal soil moisture in a greenhouse without constant human presence. By setting up an automatic control system, water can be supplied strictly according to a schedule and in accordance with the current needs of the plants. This requires a simple control board and a reliable actuator valve.

• Diameter of the SVM solenoid valve — 20–25 mm
• Capacity of the main barrel — 200–250 l
• Volume of the start-up container — 2–3 l
• Volume of the working container — 8–10 l

To assemble the control board, MP16B, MP25, MP42 transistors or their equivalents are used, as well as an output relay of the RES-10 type. The circuit is adjusted using two elements. Variable resistor R1 is responsible for the controller's trigger threshold, while variable resistor R2 sets the initial soil moisture.

The water supply to the system is coordinated by an electromagnetic valve, a motorized gate valve, or an SVM-type solenoid valve. If necessary, the shut-off unit can be assembled independently. A homemade valve is made from a standard toilet flush valve, connecting it via a stainless steel wire linkage to an actuator electromagnet.

Setting up irrigation cycles and calculating water reserves

Automatic irrigation operates on a cyclic principle based on the weight difference of the filling vessels. The water flow rate is regulated by a dispenser, which allows for setting the required frequency. The operation of the entire system is divided into several successive stages.

1. Water from the main barrel flows through the dispenser into the start-up container, which is held in its initial position by a weight and linkage.
2. When the start-up container fills, its equilibrium is disturbed, and it tips over. Support bars at this moment shift the center of gravity for reliable drainage.
3. Water overflows into the working container.
4. As soon as the working container is full, the siphon triggers and water supply to the greenhouse begins.

By adjusting water flow through the dispenser, different modes can be programmed. For example, if the dispenser is set to a flow rate of 2 l/h with a main barrel volume of 250 l and a working container of 10 l, irrigation will last for 125 hours (5 days). In this case, the breaks between irrigations will be 5 hours, and the irrigation cycle itself will take 10–12 minutes. During this time, 9–10 l of water will enter a 10–12 m² greenhouse, meaning each plant will receive 0.3–0.4 l.

For mature plants, the average water consumption is 5 l/m² per day. Based on this rate, the required volume of water for a five-day period of autonomous operation is calculated. The necessary parameters for standard greenhouses are given in the table.