Greenhouse heating is one of the key conditions for the stable development of heat-loving plants in the winter. A balanced microclimate allows you to harvest 2-3 crops annually, which is impossible in the northern regions at a standard temperature without artificial heating. It remains only to decide on a suitable system for regulating microclimate parameters. As practice shows, air heating of a greenhouse is the best solution both in terms of structural and technical performance, and in terms of compatibility with the most popular crops grown indoors.
General requirements for greenhouse winter heating
Microclimatic requirements for the arrangement of greenhouses and greenhouse facilities are determined by the documentation of SP 60.13330, which combines the rules for organizing heating andventilation. In the context of considering an air heating system, this set of rules is especially relevant. So, the main requirements include the following:
- When organizing heating and ventilation systems, one should take into account the effect of equipment not only on plants, but in the complex - on soil, humidity, air circulation speed, etc.
- Heating is desirable to organize in such a way that it provides for natural heating in addition to artificial. That is, structurally, even in winter, the air heating of the greenhouse should be combined with direct sunlight.
- From the point of view of the possibilities of regulating the microbiological balance, it is desirable to combine water and air heating. This option, in particular, will provide more intensive heating of the soil.
- It is important to observe the uniformity of air heating. At a height of up to 1 m from the earth's surface, heat supply in a volume of at least 40% should be organized. 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 flows. That is, two technological processes must 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 most quickly allowsto obtain sufficient air temperature in the entire space of the room. This takes a few minutes on average, although the exact time depends on the outside temperature. On the other hand, the factor of rapid cooling after warming up is also important. With air heating of the greenhouse, an intensive drop in temperature is observed after the heating is turned off, which should also be taken into account. This is due to the fact that air has a low heat capacity - it quickly warms up the space, but also quickly loses the accumulated potential of thermal energy.
Features of air heating in a 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 must be taken into account that the effect of air masses is not just a means of temperature regulation. A kind of generated wind can both positively and negatively affect the condition of certain plant varieties. For this reason, greenhouse air heating is also considered in terms of ventilation requirements. The undoubted positive aspect of this function can be called ventilation, which in any case should be organized together with other greenhouse engineering.
Now we should return to the storage capacity 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? Fluid circulating inheating circuits, retains thermal energy longer, although it takes longer to warm up. We can also mention the higher energy costs for heating the antifreeze in the circuits, but these investments can also pay off with the high heat capacity of water, which gives off 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 in relation to the walls of the structure, but the air environment acts as a natural barrier, creating an insulating buffer in any structures with empty niches.
Options for the technical implementation of the air heating system
The fundamental choice of technology for organizing air heating will be to determine what kind of 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 discard the environmental factors that are still decisive, electrical systems will in any case benefit from optimizeddimensions, ergonomics and operational safety. Of course, there is a nuance to high energy costs, 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 such a noticeable flaw.
Calculation of greenhouse air heating
The main required unit of calculation in this case is the power of the heater. A more detailed list of initial data in industrial assessments also makes it possible to determine the optimal circulation rates and parameters for precise zone heating, but in the private sector a simple calculation by power will be sufficient. 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 the standard temperature indicators for which the system is selected:
- The required temperature regime inside the greenhouse is about +5 °C.
- Temperature conditions outside - in the range -20…-30 °C.
- Design width - 2.5 m.
- The height of the structure is 2 m.
- The length of the structure is 5 m.
- Wall material - polycarbonate or double glazing 5-7 mm thick.
These are standard and average initial parameters for which the following calculation of greenhouse air heating by power is valid - the volume of the room multiplied by 1 kW of power and divided by a factor of 2. In other words, 25 m3 1 kW / 2=12.5 kW. This is the optimal thermal power with a margin that will be sufficient wheninstallation of equipment for peak heating mode in severe frosts. Now it’s worth moving on to considering the organization of the heating system in different ways.
Using a heat gun for heating
The unit itself is an intermediate equipment between industrial and domestic devices used to generate warm air. Wind turbines, in particular, are used in dachas and construction sites not only for heating, but also to change the temperature regime when performing technological tasks. This specificity of operation is due to the possibility of directing flows, which can be useful in relation to the arrangement of the greenhouse. Placement of the 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 the reviews on air heating of this type of greenhouse show, the best result can be achieved with the point placement of several units of medium power. Moreover, the positions of some models can be arranged in a suspended version, which will allow pointwise and without obstacles to direct air flows to specific areas. However, there are significant drawbacks to heat guns. Firstly, they intensively burn oxygen, making the air drier and undesirable for plants. Secondly, at the outlet of such equipment, the flows are usually superheated regardless of the set operating mode, which imposes restrictions on the installation of housings.
Applicationelectric convector for heating
From the point of view of structural performance, the best option. These are small, easy-to-operate devices for delicate heating that practically do not require installation measures. Externally, the convector is similar to the same heat gun, but the principle of operation has significant differences. The natural convention of supplying air through the casing and spraying the streams from the inside does not dry out the air. For example, some designs involve internal moistening of the coolant, which can also be considered as an auxiliary function of micro-drop irrigation. Although it is necessary to take into account the rules for organizing irrigation as such. For a greenhouse air heating system in winter, an unbalanced humidification function is quite risky. In any case, in parallel with heating and ventilation, a full-fledged irrigation water supply 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 outdoors, then convectors are devices for indoor use. Additionally, do-it-yourself air heating of a greenhouse can be protected from external factors with the help of insulating materials. The optimal solution would be a multifunctional hydro- and heat-insulating coating, which will protect against pollution and temperature and humidity changes.
Air based heatingcar radiator
Home craftsmen should be offered a completely budgetary way to organize efficient 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 order and have a one-piece design. You can mount the 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 to physically mount the structure in a floor or pendant configuration.
The installation process itself is carried out on a prepared site, to which the heat carrier pipes must be connected. Actually, the task of the radiator will be to distribute heat flows, and the source of heating can be a domestic boiler with a pipeline branch connected to the greenhouse. In domestic conditions, it is recommended to organize air heating of a greenhouse from a car radiator with a passing movement of the coolant. For ease of flow control, you can connect a circulation pump and a return pipe with an air vent.
Characteristics of the combined greenhouse heating system
There are several concepts of combined heating. We can talk about combining several systems for heating specific plants, and about a hybrid system serving several different functional areas of the greenhouse at the same time. Both options are more likely toprovide for the heating of greenhouses by air and electrical means - this is the optimal scheme, in which both floor heating and convectors with heat guns are organically integrated. Separately, you can enter into the infrastructure and wind turbines like car radiators.
The situation is somewhat more complicated with the combined heating of green spaces. It makes sense to expand the air heating complex by means 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 onto the soil, and for this a separate zone without vegetation should be allocated. This option is ineffective, so the air heating of the room is combined with water heating. At a depth of 20-40 cm, thin polypropylene pipes are laid with a drainage layer of sand and fine gravel. They organize the circulation of the coolant with a temperature of 70–80 °C. This combination of air and water heating should improve the vegetation system of plants, which will directly affect the yield.
Conclusion
A rationally organized heating complex in a greenhouse will provide the main function of creating a favorable microclimate and at the same time will not be overly expensive. The performer faces a responsible and difficult task of combining the heating of the air environment and the soil cover. The key to success will be an initially thought-out scheme for the structural and energy support of the infrastructuregreenhouse heating. Air and electric heating methods in combination with the circulation of a water coolant will allow you to organize an optimal system for regulating the microclimate. For the convenience of its operation, it is worth including automatic controls, moisture and temperature sensors in the control complex. In addition, do not forget that the development of plants, especially indoors, largely depends on lighting, which, together with water supply and heating systems, it is desirable to calculate in a single design solution.
