VENTILATION SYSTEMS FOR GREENHOUSES

ВЕНТИЛЯЦИОННЫЕ СИСТЕМЫ ДЛЯ ТЕПЛИЦ

Оськин Максим Витальевич

студент, Национальный Исследовательский Московский Государственный Строительный Университет,

РФ, г. Москва

Колесник Дарья Алексеевна

студент, Национальный Исследовательский Московский Государственный Строительный Университет,

РФ, г. Москва

Юдина Ирина Ивановна

научный руководитель, преподаватель, Национальный Исследовательский Московский Государственный Строительный Университет,

РФ, г. Москва

ABSTRACT

This article is devoted to the use of different types of ventilation in greenhouses. This article examines the distinctive features of various types of ventilation systems, it presents an analysis of existing ventilation systems in greenhouses with an indication of the advantages and disadvantages of each of them, it provides examples of the use of the most modern ventilation systems for greenhouses of the fourth and fifth generation, and it also gives a brief history of the development of ventilation systems in the world and in Russia.

АННОТАЦИЯ

Данная статья посвящена вопросу использования разных типов вентиляции в теплицах. В данной статье рассматриваются отличительные особенности различных типов вентиляционных систем, представлен анализ существующих систем вентиляции в теплицах с указанием достоинств и недостатков каждой из них, приводятся примеры использования наиболее современных вентиляционных систем для теплиц четвертого и пятого поколения, а также дается краткая история развития вентиляционных систем в мире и в России.

Keywords: ventilation systems, mechanical ventilation, automatic ventilation, biometallic structures, electrical structures, hydraulic structures.

Ключевые слова: вентиляционные системы, механическая вентиляция, автоматическая вентиляция, биометаллические конструкции, электрические конструкции, гидравлические конструкции.

A brief overview of the history of ventilation systems: the history of ventilation systems covers quite a huge period. The first attempt to apply steam systems to warm soil in green houses was made in 1778 in England. Later the practice was spread in Germany and France. Similar attempts in Russia were taken quite late, only in 1816, in St. Petersburg. In 1854 the first steam heating systems were introduced in Russia. Such systems were not appreciated due to the danger they posed in practical usage. The major drawback of such systems consisted in very high temperature levels of the pipes which exceeded 100 degrees Celsius. The negative effect of such systems was proved by Russian scientist G.G. Bubnovin in 1888. Later, another scientist, F.F. Erisman, claimed and proved the optimal temperature of heated surfaces should not exceed 40 degrees Celsius to be comfortable for a human being. In general, ventilation systems were poorly developed world-wide in the 18 centuries. In Russia, in particular, there existed systems of “bug blowers” and “conical sleeves” used in one-floor houses. There were systems of centralized ventilation in hospitals which included a number of ventilation holes in the ceiling and the floor of the building. Cold or warm air went through these holes from the ovens located in the basement of the building through the pipes installed inside the hospital building.

A great contribution was made in 1763 by M. Lomonosov who was carefully investigating the topic and suggested the principle of cold air ousting warm air thanks to the weight differences. In 1795 and 1799 respectively Russian scientist N.A. Lomov published two parts of his scientific research on the weight characteristics of different substances. N.A. Lomo presented a model of an air-fired unit heater which appeared to be a breakthrough in the sphere of producing heater and ventilation units of the time. These research works finally resulted in creating centralized systems of air heating and ventilation. In 1835 N. A. Amosov obtained a patent for pneumatic ovens, in other words, for air-fired unit heaters. Such systems were installed in more than a hundred buildings. The most remarkable system is the one in the Winter Palace in St. Petersburg. A further step forward took place in 1817 in France when de ’Shaban created a new type of ventilation systems known as “a single-pipe vertical type with gravity water circulation” which allowed to collect and heat water in one tank and then distribute it for different needs. A similar system found its practical application in greenhouses as well. In the course of time maintenance costs of such systems turned out to be highly unprofitable. That pushed scientists and inventors to work out the basic principles of such systems which are observed currently. In 1824 French scientists presented a ventilation principle based on reverse draught which was soon spread in Europe. The system was operated by centrifugal ventilators, which were later changed for propeller driven ones working on steam, and finally for those driven by electricity.

Ventilation in the greenhouse is a system of measures to maintain the temperature, moisture and carbon dioxide levels necessary for successful growth of agricultural crops. The major task is to ensure an efficient way of exchanging the air masses coming into the green house from the outside and those coming out of the greenhouse into the atmosphere.

Ventilation in the greenhouse is extremely important for various reasons:

1. The necessity to reduce the temperatures inside the green house

The main task of the green house is to preserve warmth and a certain level of the air heat. Meanwhile, extreme heat is highly undesirable as it produces uncomfortable conditions for crops. In particular, it sterilizes the plants inside the greenhouse.

2. The necessity to sustain a low moisture level

As a rule, non-ventilated or poorly ventilated greenhouses accumulate damp/moisture-absorbing atmosphere. All the wastes remain inside as there is no outlet for them. As a result, they deposit in the soil inside the greenhouse. This causes extreme moisture in the soil and encourages bacteria which hamper the growth of plants.

3. The necessity to maintain the optimal levels of carbon dioxide and oxygen

Dense plantations inside the greenhouse decrease the carbon dioxide level which, in its turn, slows down the process of photosynthesis which is of crucial importance for plant life in general. The correct ventilation system prevents the plants inside the greenhouse from shortage of carbon dioxide and ensures sufficient oxygen supply which is essential for the development of the root system of plants and stimulates access of the root system to nutrients.

4. The necessity to ensure correct air circulation

Correct air circulation in the greenhouse encourages equal temperature, moisture, carbon dioxide and oxygen distribution inside. This way all the plants in the greenhouse are nourished equally. Ventilation generates a type of wind which strengthens the stems of the plants and encourages pollination.

There exist several types of ventilation systems for greenhouses. At present there are two major types:

• mechanical ventilation (natural air exchange);
• automatically -controlled ventilation (artificial air exchange), which can be subdivided into bio-metal, electrical, hydraulic.

• Natural air exchange.

Mechanical ventilation (which is performed manually) means airing the space with the help of a system of doors, panes and windows. The method is pretty simple and quite affordable. It is generally known as natural ventilation. It means a system of doors and windows of different sizes. These are installed in the walls of the greenhouse and are opened and closed when necessary.

The main principle of air exchange claims that air ventilation directly depends on the size of the window or pane. So, the smaller the window, the more windows are needed in the greenhouse. The second principal claims that the inflowing air mass should be equal to the air mass flowing out. This means an equal number of windows that, however, should be located at a different height. Windows for the incoming air should be installed at a lower level, closer to the ground surface, while the windows for the air masses that come out are to be located at a higher level, the roof is the best position for them. When an equal number of windows is open there is a natural air exchange due to the temperature differences. Heated warm air goes up and out. Cool fresh air flows in through the lower windows.

The systems of such type possess a number of advantages. Firstly, this is simplicity of installation and practical application. Secondly, absolute independence of power generators.

Still, mechanical systems are characterized by a number of disadvantages. Firstly, systems of such type are applicable only in constructions of small sizes. Secondly, such ventilation systems require constant monitoring of the microclimate inside the greenhouse which necessitates constant presence and control of the owner which makes such systems extremely time-consuming.

Artificial (forced) air exchange.

Natural air exchange is a good solution in greenhouses of a small size. It turns out to be troublesome in green houses of bigger sizes as it requires constant maintenance of the necessary micro-climate. Installing systems of artificial air exchange seems to be a good solution to the problem. Systems of artificial ventilation are more efficient and save a lot of time and effort. Such systems become absolutely necessary when natural ventilation cannot sustain the temperature level above zero.

Electric systems of ventilation are organized by installing a number of suitable fans or ventilators which are powered by electricity. The system has a number of advantages. Firstly, airing the green house is rather cheap. Secondly, it’s possible to install the required number of ventilators and ensure quality airing on the whole territory of the green house. Besides, such systems ensure proper control of the micro-climate in the green house as ventilators are equipped with a system of modes which allow to vary the temperature and the volume of air masses coming in and out. Finally, temperature detectors installed in the system can automatically control the operating period of the system turning it on and off when necessary. However, the system has one crucial drawback. This is absolute dependence on electrical power. If the source of power is cut off, there is a huge problem, especially in warm seasons when the temperature inside the closed space of the greenhouse can reach critical levels within a couple of hours.

A hydraulic system of ventilation can become a perfect alternative. It means a system of anchor ties driven by hydraulic power. The operation principle of the system goes as follows. Two tanks with liquid are placed inside and outside the greenhouse. The one located inside functions as a temperature detector. When heated, the liquid expands and moves along the system of flexes, pushes the lever on the transom and opens it. The system has some drawbacks. Firstly, the liquid inside the tanks changes its properties when heated or cooled. As a result, it may fail to close the windows of the green house in case of unexpected sharp frosts. In addition, it relies on inert processes. In case of low temperatures, it takes the system a lot of time to close the windows. This can affect plants that cannot resist chills and cold air. Secondly, this system lacks small panes, which is inconvenient for growing some species. Still, there are certain advantages. The system is simple in servicing and cheap for installation. In addition, it’s long-lasting. Finally, there is no need to constantly monitor and control the ventilation process.

Bio-metal ventilation systems are based on the same principle as hydraulic ones. The operation of the system relies on the properties of metals. Two different metals are applied in the system. They are characterized by different properties of expansion when heated. As a rule, steel and brass are used in the system and function as temperature detectors. When heated, the metal expands and opens the transom. When cooled, the metal squeezes and closes the transom. All in all, the system is very reliable and long-lasting as there are no sources of power or details that can break. This is an indisputable benefit of the system. However, there are some shortcomings. The system can be installed only on small windows. Besides, it’s extremely difficult to achieve accuracy in setting the required temperature.

Currently, hydraulic ventilation systems are considered to be the most optimal ones in terms of price, maintenance and utility correspondence. However, further research is conducted in the sphere. A group of physicists and chemists from Switzerland, headed by professors from the University of Zurich Raffaele Mezzenga and Ehud Landau, has recently worked out an unusual way of preventing water from crystallization. Water preserves its liquid properties even at extreme temperatures below zero. This method, known as “Glass water”, can become a real breakthrough in the construction industry in general and in ventilation systems in particular.

Here are some examples of practical usage of modern ventilation systems in greenhouses.

In the modern world ventilation systems of VENLO type appear to be the most widely-spread ones. These are systems of the fourth generation which make it possible to put into practice the most advanced technologies in crop growing. The systems of this type are characterized by a number of advantages. Firstly, this is a very high level of automation. Secondly, they possess good hermetic properties. Thirdly, such systems present a combination of ventilation technologies with those of protoculture. Such a combination makes it possible to double the amount of crops grown per a square meter. However, even these modern and high-tech systems have a number of drawbacks.

1. The major one is the inability of green houses with such systems of ventilation to sustain an optimal microclimate in certain seasons, in spring particularly. These systems cannot get rid of excessive humidity inside the greenhouse. Greenhouses of this generation are known as “half-closed” as they combine both automatic ventilation systems and panes (which are normally parts of mechanical systems). In the spring period the greenhouse is overheated which necessitates using panes which are opened and closed as needed. This, in its turn, causes excessive use of heat energy and a heat shock to plants because of the cold air. Panes cannot but be opened as the plants inside the greenhouse start experiencing “the greenhouse effect”. Meanwhile, opening the panes in the greenhouse leads to plant damage and increases warming expenses. Greenhouses with the ventilation systems of the fourth generation are not capable of sustaining the necessary microclimate bin the summer period.

Currently, the title of the most modern greenhouses is ranked to the “half-closed” greenhouses of the fifth generation which apply ventilation technologies like UltraClima (the Netherlands, КUBO (Russia) and SuprimAir (Latvia).In Russia the efficiency of the greenhouses using this type of ventilation is proved by practical application. The first greenhouse of this type was constructed by company FITO in partnership with company “Greenhouse Technologies” in the city of Dankov in the Lypetsk region, Russia.

2. The greenhouse with such type of ventilation sustains an ideal microclimate in any season.

The system of ventilation includes very few panes the number of which is 90% smaller than that in the greenhouses of the fourth generation. Their main purpose is to remove excessive pressure and heat. The ventilation system constantly removes the air from the greenhouse and prevents the plants from the heat shock. The greenhouse is able to cool itself in the summer period. The greenhouse is equipped with a system of panels located in the perimeter of the construction. The panels are supplied with water which evaporates and removes some part of heat energy. This way the greenhouse is supplied with cool air which ensures artificial air circulation and provides an active microclimate.

3. The greenhouse with such type of ventilation reduces heating expenses.

Greenhouses with such ventilation systems can use recycled heat energy. In the greenhouses of the fourth generation the air from the heating pipes goes up and is removed by the ventilators. Then it is again supplied for heating through the plastic tubes. This way the heat energy returns from the roof to the basement of the construction. The removed air is warmed up by the system of calorifiers.

4. The greenhouse with such type of ventilation sustains the optimal level of carbon dioxide.

It appears extremely difficult to sustain the optimal level of carbon dioxide in the period when pane opening is necessary. In such conditions the parameters of carbon dioxide tend to reach the level outside the greenhouse. The “half-closed” system of the ventilation in the greenhouse of the fifth generation (which means a combination of natural and artificial air circulation) allows to sustain the optimal concentration of carbon dioxide.

5. The greenhouse with such type of ventilation is protected against invasion of crop pests.

Greenhouses of the fifth generation are characterized by excessive pressure inside. When the mechanical elements of the ventilation system (panes and the entrance gate) are open, crop pests are prevented from getting inside thanks to the excessive pressure.

6. The greenhouse with such type of ventilation prevents air blanketing.

Air blanketing inside the greenhouse is prevented thanks to the system of film tubes located under each plant bed. The tubes serve to supply the air with the set parameters and help to provide an active microclimate. To achieve the same effect, the greenhouses of the fourth generation required register heating which caused excessive usage of heat energy.

7. The greenhouse with such type of ventilation saves heat energy and reduces the shadow factor thanks to a small number of mechanical elements (panes).

In conclusion, the brief analysis of the existing systems of ventilation in greenhouses, presented in the article, makes it possible to conclude the following. Nowadays the principles of “green” building are attached a great importance to in the construction industry. Proper ventilation systems appear to be an indispensable part of “green” building. The principles of “green” building are widely applied in the construction of greenhouses, in ventilation systems in particular. The ventilation systems which are currently used in greenhouses have their advantages and drawbacks. The existing systems of ventilation for green houses are able to satisfy different needs of the user. Scientists and inventors keep investigating the problem in search of better “green” solutions and possible innovation in the spheres. Nowadays most greenhouses are equipped with ventilation systems of the fifth generation which make it possible to considerably reduce consumption of heat energy, ensure non-stop air circulation of proper quality and significantly increase the amount of crops grown per a square meter.

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