Greenhouse heating is one of the key conditions for the stable development of thermophilic plants in the winter. A balanced microclimate allows you to collect 2-3 crops annually, which is impossible in the northern regions at standard temperature without artificial heating. It remains only to determine the appropriate system for regulating microclimate parameters. As practice shows, air heating of the greenhouse is the optimal solution both in terms of structural and technical performance, and in terms of compatibility with the most popular crops that are grown in closed conditions.
General requirements for winter heating in a greenhouse
Microclimatic requirements for the arrangement of greenhouse and greenhouse farms are determined by the documentation of SP 60.13330, which combines the rules for organizing heating and ventilation. In the context of considering an air heating system, this set of rules is particularly relevant. So, the main requirements include the following:
- When organizing heating and ventilation systems, it is necessary to take into account the influence of equipment not only on plants, but in the complex - on soil, humidity, air flow velocity, etc.
- It is desirable to organize heating in such a way that it provides for natural heating in addition to artificial. That is, structurally, even in winter, air heating of the greenhouse should be combined with direct sunlight.
- From the point of view of regulating the microbiological balance, it is desirable to combine water and air heating. This option, in particular, will allow for more intensive soil heating.
- It is important to maintain uniform heating of the air. At a height of up to 1 m from the earth's surface, heat supply should be organized in a volume of not less than 40%. A decrease in this coefficient is allowed in technological areas and places with plants, which, in principle, are not demanding for heating.
What is an air heating system?
This type of heating system works on the principle of circulation of heated air currents. That is, two technological processes should be implemented - heating and air movement. Why does this system justify itself as a means of regulating the greenhouse microclimate? According to experts, this method of heating is the fastest way to get a sufficient air temperature in the entire space of the room. This takes an average of several minutes, although the exact time depends on the outside temperature. On the other hand, the factor of quick cooling after heating is also important. During air heating of the greenhouse, an intense drop in temperature is observed after turning off the heating, which should also be taken into account. This is due to the fact that the air has a small heat capacity - it quickly warms up the space, but also quickly loses the accumulated potential of thermal energy.
Features of air heating in the greenhouse
As you can see, air heating systems have their pros and cons. In this case, it is worth considering in more detail the operational features of this method of heating the greenhouse. First of all, it should be borne in mind that exposure to air masses is not just a means of temperature regulation. A kind of generated wind can both positively and negatively affect the state of certain plant varieties. For this reason, air heating of the greenhouse is also considered in terms of ventilation requirements. An absolute positive aspect of this function can be called ventilation, which in any case should be organized together with other engineering of the greenhouse.
Now it’s worth returning to the accumulative abilities of air. From this position it is appropriate to compare which choice would be better for heating modern industrial greenhouses - an air or water system? The liquid circulating in the heating circuits retains thermal energy longer, although it requires more time for heating. We can mention the higher energy costs for heating antifreeze in the circuits, but even these investments can pay off with the high heat capacity of the water, which gives its heat to pipes and radiators. That is, the advantages of liquid heating are obvious, but do not rush to conclusions. The fact is that air has a significant plus of a heat insulator, which is especially pronounced in greenhouses made of cellular polycarbonate. Water-heated circuits practically do not affect the insulation function with respect to the walls of the structure, but the air environment acts as a natural barrier, creating an insulation buffer in any structures with empty niches.
Options for the technical implementation of the air heating system
The fundamental choice of air heating technology will be to determine which equipment will form the basis of the system. If we talk about specialized units, then these include heat guns (wind generators), electric heaters and convectors. It must be emphasized right away that all effective methods of air heating a greenhouse to one degree or another involve the consumption of other energy resources. Generator systems can also run on liquid fuel, but it is best to give preference to electric motors. Even if we ignore environmental factors, which are nevertheless decisive, electrical systems will benefit in any case due to optimized sizes, ergonomics and safety during operation. Of course, there is a nuance of high energy consumption, since electricity is still considered the most expensive means of supporting the function of heating equipment. But just in the case of air heat generators, this is not so noticeable flaw.
Calculation of air heating greenhouses
The main unit of calculation in this case is the heater power. A more detailed list of initial data in industrial assessments also allows you to determine the optimal indicators of the circulation speed and parameters for accurate zone heating, but in the private sector a simple calculation of power will suffice. To begin with, it is worth deciding on the initial data relevant for determining the thermal power of the equipment. First of all, we are talking about normative indicators of the temperature under which the system is selected:
- The required temperature inside the greenhouse is about +5 ° C.
- The temperature regime outside is in the range of -20 ...- 30 ° C.
- The width of the structure is 2.5 m.
- Construction height - 2 m.
- The length of the structure is 5 m.
- The material for making the walls is polycarbonate or double glazing with a thickness of 5-7 mm.
These are standard and average initial parameters for which the following calculation of air heating of a greenhouse by power is applicable - the volume of a room multiplied by 1 kW of power and divided by a factor of 2. In other words, 25 m 3 * 1 kW / 2 = 12.5 kW. This is the optimal thermal power with a margin, which will be sufficient when the equipment is installed at the peak heating mode in severe frosts. Now it’s worth moving on to considering the organization of the heating system in different ways.
The use of a heat gun for heating
The unit itself is an intermediate equipment between industrial and domestic devices used to generate warm air. Wind generators, in particular, are used at dachas and construction sites not only for heating, but also in order to change the temperature regime when performing technological tasks. This specifics of operation is due to the possibility of flow direction, which can be useful in relation to the arrangement of the greenhouse. Placing a heat gun does not require special technical operations - the main thing is to prepare a reliable and even base on which the supporting structure of the equipment will be fixed. As reviews of air heating of this type of greenhouse show, the best result can be achieved with the point placement of several medium-power units. Moreover, the positions of some models can be arranged in a suspended version, which will allow to direct air flows to specific areas in a precise and unobstructed manner. However, there are significant disadvantages of heat guns. Firstly, they intensively burn oxygen, making the air drier and undesirable for plants. Secondly, at the output part of such equipment, the flows are usually overheated regardless of the established operating mode, which imposes restrictions on the installation of cases.
The use of an electric convector for heating
From the point of view of structural performance, the best option. These are small, easy to operate and practically do not require installation measures devices for delicate heating. Externally, the convector is similar to the same heat gun, but the principle of operation has significant differences. Natural convention with air supply through the casing and spraying flows from the inside does not dry out the air. For example, some designs suggest internal humidification of the coolant, which can also be considered as an auxiliary function of microdrop irrigation. Although it is necessary to take into account the rules of watering as such. For the winter heating system of the greenhouse, an unbalanced humidification function is risky enough. In any case, in parallel with heating and ventilation, a full-fledged water supply irrigation network with a jet break of at least 50 mm should be provided.
When organizing heating by means of an electric convector, it is important to ensure reliable insulation of the equipment. If the heat gun is initially designed for harsh operating conditions, even in the open air, then convectors are devices for indoor use. In addition, it is possible to protect the air heating of the greenhouse with your own hands from external factors by using insulating materials. The optimal solution will be a multifunctional hydro- and heat-insulating coating, which will protect against pollution and temperature and humidity differences.
Car radiator-based air heating
Home masters should offer a completely budgetary way to organize effective heating without specialized equipment. Unless you take into account the old radiator, which is present in any car. Of course, it must be in working condition and have a solid structure. You can install air heating of the greenhouse with your own hands from a car radiator using a computer unit, electrical wiring from a VAZ and plumbing pipes. Fasteners should also be prepared for the physical installation of the structure in a floor or suspended configuration.
The installation process itself is carried out on the prepared site, to which the coolant pipes should be brought. Actually, the task of the radiator will be to distribute heat fluxes, and the heating source may be a home boiler with a pipeline branch connected to the greenhouse. In domestic conditions, it is recommended to organize air heating of the greenhouse from a car radiator with the accompanying movement of the coolant. For the convenience of flow control, you can connect a circulation pump and a return pipe with an air vent.
Features of the combined greenhouse heating system
There are several concepts of combined heating. It could be a combination of several systems for heating plants specifically, and a hybrid system serving several different functional zones of the greenhouse at one time. Both options are more likely to provide for the heating of greenhouses by air and electric means - this is the optimal scheme in which both floor heating and convectors with heat guns are organically integrated. Separately, wind turbines like automobile radiators can also be introduced into the infrastructure.
The situation is somewhat more complicated with the combined heating of green spaces. Expanding the air heating complex makes sense at the expense of soil heating with a direct effect on the root system. How is air heating of the earth implemented in a greenhouse? The only way is to direct the warm currents to the soil, and for this a separate zone without vegetation should be allocated. This option is ineffective, therefore, air heating is combined with water heating. Thin polypropylene pipes with a drainage layer of sand and small gravel are laid at a depth of 20-40 cm. They organize the circulation of the coolant with a temperature of 70–80 ° . Such a combination of air and water heating should improve the plant vegetation system, which will directly affect the yield.
Conclusion
A rationally organized heating complex in the greenhouse will provide the main function of creating a favorable microclimate and at the same time it will not be excessively costly. The contractor is faced with a responsible and difficult task of combining heating of the air and soil cover. The key to success will be an initially thought out scheme of structural and energy support of the heating infrastructure of the greenhouse. Air and electric heating methods in combination with the circulation of water coolant will allow you to organize the optimal climate control system. For the convenience of its operation, it is worthwhile to include in the control complex automatic controls, moisture and temperature sensors. In addition, do not forget that the development of plants, especially in enclosed spaces, is largely dependent on lighting, which, together with the water supply and heating system, is desirable to be calculated in a single design solution.