- Geothermal heating is the obvious choice for a rational owner
- Benefits of geothermal convection
- Operating principle
- Installation costs
- Preparation for construction
- We determine a suitable site
- The technical base required for the implementation of the project. Preparation for work
- Calculation of functional indicators
- Practical implementation. Mounting
- Pit and its preparation
- Duct laying and backfill
- The final stage of work
- Forced convection
- Air filtration and elimination of condensation
In this article, we will talk about, perhaps, the most optimal way to heat greenhouses and greenhouses – a geothermal heating system. You will learn about the principles of its operation, advantages, and also receive detailed instructions on how to independently set up this system at your site.
The device of greenhouses and greenhouses includes many nuances that are not inferior to each other in importance. The efficient operation of a greenhouse heating system is much more important than lighting or ventilation. Modern advances in the engineering communications industry provide an original solution for the implementation of greenhouse heating based on the laws of nature and energy from renewable sources.
Geothermal heating is the obvious choice for a rational owner
The main task of the heating system is to maintain the required temperature level in the area of growing and ripening crops. In the winter season, when the outside temperature is below permissible, the greenhouse effect is not enough, and therefore an additional heat source must be used to ensure a favorable climate. Naturally, the heating system should be not only highly efficient, but also as economical as possible..
Benefits of geothermal convection
Innovative methods of alternative energy supply are often viewed with skepticism, believing that free methods of obtaining energy cannot exist. Convection geothermal heating systems can be safely added to a number of exceptions to this rule. Despite the tangible complexity in implementation, which will be discussed below, such systems have a lot of advantages that more than compensate for all the disadvantages:
- Complete autonomy. The system does not depend on the supply of energy.
- Convection heating systems do not incur any costs during operation
- No need for maintenance, approval, periodic repair.
- Service life – from 50 years with proper arrangement.
- Maintaining the required climate throughout the year.
- Creation of a mild and balanced microclimate with automatic humidity control and uniform ventilation.
- The system is an additional source of carbon dioxide.
In order to carry out a technically competent installation in the future with a minimum investment of time, you should know the basic principles by which the geothermal convection system works. The bottom line is that deeply buried soil layers have a constant temperature of 5–7 ° С in winter and 10–12 ° С in summer. This is quite enough to ensure the base temperature, which can be increased many times due to solar radiation during the action of the greenhouse effect in winter..
In summer, the system protects plants from high temperatures by stabilizing the indoor climate with chilled air. Thus, throughout the year, the temperature is maintained in the range of 23–27 ° C, which is quite enough for growing vegetables common in mid-latitudes. It is important to note that due to air exchange, the soil plays the role of a heat accumulator: it heats up during the day and evenly gives off heat at night..
It is known that with the help of such greenhouses, perfectly functioning in the conditions of eternal glaciers, Greenland fully provides its population with exotic fruits. It is clear that in such a harsh climate, additional heating is required, but the cost of providing it is negligible.
As already mentioned, the process of building geothermal convection systems is associated with certain difficulties. First of all, with the placement of the main functional elements deep underground. The construction of structures of this kind is associated with large-scale excavation and the arrangement of underground communications, which requires a certain investment of time, effort and money. But the efficiency and economy of such a heating method for greenhouses is invaluable, and therefore they are worth all the effort expended. In addition, the cost of building materials will be low relative to the funds invested in the organization of gas or electric heating..
Preparation for construction
It is not possible to equip an already built greenhouse with geothermal heating. In any case, the effectiveness of such an improvement will be much lower than if the construction of such a system was implied at the design stage..
We determine a suitable site
As a rule, GTK-systems are used in rather large greenhouses and greenhouses focused on the year-round cultivation of vegetables or flowers. Their use is advisable with a greenhouse area of 50 sq. m, and with an increase in usable space, these systems work even more efficiently. Therefore, it is worth initially determining the size of the projected structure.
For the construction of the heating system, a site will be required, with dimensions slightly larger than the dimensions of the proposed structure, on which there are no trees and buildings: during the construction process, this site will turn into a deep foundation pit. The area of this plan should be at least a third larger than the planned area of the greenhouse, observing this dependence in linear dimensions. That is, if a greenhouse is designed with a width of 6 m and a length of 12 m, the dimensions of the plot should be 8×16 m.With overall dimensions over 14 m, the area of the pit should be increased by no more than 3.5 m: with a width and length of the greenhouse 16×20 m , accordingly, the pit should have a size of 19.5×23.5 m.
The technical base required for the implementation of the project. Preparation for work
First of all, it is necessary to ensure the possibility of placing the worked-out soil in the immediate vicinity of the greenhouse being built. In addition, if it is impractical to excavate the soil manually, you should organize the possibility of access for excavator equipment. The main consumables used in the construction of the GTK heating system are river sand, fine crushed stone, rubble bricks, plumbing pipes with a diameter of 110 mm and nodal connections for them, as well as foamed polystyrene plates. Material costs can vary greatly depending on the projected density of the system, however it is worth starting from $ 120-140 per square meter of finished greenhouse. It is worth noting that the warmer the climate in the region where the greenhouse is built, the lower the density of underground utilities should be..
Calculation of functional indicators
The main technical parameter that characterizes the operation of the heating system is the number of calories of thermal energy delivered to a certain closed volume. Detailed calculations and calculations for geothermal heating of greenhouses are available only for projects based on the operation of heat pumps. Due to the lack of regulatory frameworks for geothermal convection systems, it remains to be content with only the norms stipulated by SNiP 23-01-99 and SNiP 2.04.05-91. In these documents, we are talking about the design and implementation of general-purpose climate systems, in our case, the system of basic ratios comes to the rescue, proven by practical experience.
To ensure the efficient operation of the system, the following rule should be followed: the density of the placement of air ducts under the ground should be at least 2.7 m per square meter of the usable greenhouse area. A decrease in this indicator will make the operation of the system less efficient, and a denser placement of underground utilities will give an advantage in a more stable climate with a smaller amplitude of temperature fluctuations..
Practical implementation. Mounting
The process of building such a heating system can take from two weeks to one month, depending on the degree of participation and the size of the facility being built. If it is problematic to carry out excavation work only on your own, then the independent construction of a communications network will not cause difficulties.
Pit and its preparation
The pit should have a depth proportional to the level of soil freezing in winter. The system is guaranteed to work at a depth of 3–3.2 m, but this figure can be much lower when it comes to southern regions affected by continental air currents. The fertile soil layer is removed to a depth of 25–30 cm and is preserved, while clay and soil interspersed with it can be partially removed. The pit should have a rectangular or trapezoidal shape; there is no need to fasten the walls. The pit slopes at a depth of more than 0.7 m are insulated with expanded polystyrene plates. The bottom of the pit is first covered with a layer of fine crushed stone by 10-15 cm, and then – with sand up to 30 cm and lightly compacted. With the help of stretched threads, the internal contours of the walls of the future greenhouse and its longitudinal axis are marked.
1 – fertile soil; 2 – clay; 3 – sand (250-300 mm); 4 – crushed stone or gravel; 5 – PPS plates
Duct laying and backfill
Sewer PVC pipes with a diameter of 110 mm are fixed on the prepared bed using cold-rolled wire 6 mm thick. Laying is carried out along a predetermined contour of the laying, providing the necessary density of the underground duct. It is best to use “snake” pipe-laying, breaking the pipeline into sections up to 1.5–2 m wide. Pipes should be laid at a distance of 30–50 cm from the pit walls. Each section of the duct must have a tee connection in the center with three sockets, the central branch from which is brought to the surface strictly along the longitudinal axis of the planned structure with a possible deviation of up to 0.5 m to the west.
1 – tee D 110 mm with three sockets; 2 – double-sided 90 ° elbow; 3 – lateral branch; 4 – central branch
The lateral branches of each segment are also brought to the surface, but at a distance of 20-25 cm from the walls of the future greenhouse and together with the central branches they are tightly muffled with polyethylene membranes or plastic plugs. It is better to fix vertical sections of the duct with powder at the base. When the duct system is fully assembled, the pit is backfilled to the upper boundary of the heat-insulating layer, that is, up to 0.7 m from the ground surface. In this case, it is necessary to control the strictly vertical position of the branches reaching the surface.
The final stage of work
After filling the pit to the required level, the area located outside the perimeter of the greenhouse is covered with expanded polystyrene and covered with black earth to ground level. Inside the future greenhouse, a pit 90 cm deep should be formed, and its walls should be secured using panel formwork and insulated from the outside with PPS plates. The deepening under the greenhouse is filled with the amount of chernozem necessary for growing crops so that the surface of the earth is 35–40 cm below the plane of the adjacent land plot. After the greenhouse has been built, it is necessary to extend the central branches of the duct so that the ends of the pipes are at a distance of 30–35 cm from the roof level. Side branches remain at the same level, or can be cut to 10-15 cm from the soil level.
A conventional ventilation fungus can be used as the termination of the outlets coming out to the surface: the system in most cases works well without forced air exchange. If you want to increase performance and avoid strong temperature changes, you can use homemade exhaust fans and filtering units. The device for forced air exchange includes the function of coarse air filtration and can be made independently using a simple and effective scheme..
1 – fan; 2 – mesh; 3 – sealant
As the base of such a device, a case is used – a connecting or an expansion joint for sewer pipes. An electric exhaust fan is inserted into the middle of the case (note the direction of the generated flow) and secured with silicone sealant with careful sealing of the gaps. Electric fans used in forced ventilation systems are expensive, and therefore either devices removed from inexpensive ventilation grilles or case coolers for office equipment are quite suitable. The latter, it is worth noting, have an operating supply voltage of 12 V, and must work in constant on mode, while other fans can be switched using a daily or periodic time relay: a short time switch for 15 minutes per hour is sufficient. The finished device is installed on the side branches and closed on top with a ventilation fungus.
Air filtration and elimination of condensation
Filters are not required per se. It is enough to use two layers of a mosquito net with a mesh size of 0.2–0.4 mm to avoid insects (butterflies, ants, spiders) from entering the system. It is better to pull the net on a homemade hoop and glue it into a case with a fan.
Due to the temperature difference between the air and the ground, a large amount of condensate can collect in the pipeline. To avoid this, you can drill holes with a diameter of 5 mm in the amount of 10-15 pieces per running meter of pipe before laying the pipes. Naturally, when laying, the pipe should be oriented with the holes straight down. If such an improvement is carried out, the water from the duct will go into the loose layer of the bed, and the air humidity in the greenhouse can be evenly regulated by adding a small amount of water (3-5 liters) to each segment of the duct.
Greenhouse heating systems based on geothermal air convection are the most economical means of providing a stable and warm climate favorable for the cultivation and maturation of crops. It does not require any maintenance, except for periodic cleaning of mosquito filters, and recommends itself as a completely autonomous climate control equipment.