Greenhouse or Greenhouse refers to a limited space that can control the suitable environmental conditions for plant growth from different regions during different seasons of one year. According to this definition, including greenhouse performance, providing the necessary environmental conditions is a specific product requirement.
Each plant needs special conditions in terms of light intensity, daily temperature, night temperature, relative humidity of air and soil moisture in order to have optimal growth. In order to produce and commercially grow high-quality plants and all year round, optimal environmental conditions should be controlled by damage factors such as wind, devastating storms, cold and frost, etc. We are through a building called greenhouse which is considered as a controlled environment and due to the increasing market needs, both in terms of production of flowers and ornamental plants and in terms of vegetables and off-season, this method of production has become one of the most profitable agricultural sectors today, which of course demands a lot of initial investment. Due to the great investment in this field, lack of proper management in greenhouse construction, selection of location, type of greenhouse and its coverage will lead to lack of proper productivity of capital and facilities.
A greenhouse orGreen house refers to a limited space that can control the suitable environmental conditions for plant growth from different regions during different seasons of one year. According to this definition, including greenhouse performance, providing the necessary environmental conditions is a specific product requirement. Greenhouses are divided into fixed and moving types depending on what type of building materials are used in them. Fixed greenhouses are greenhouses in which the building materials used are of stable and durable materials. So they should be used for many years.
Greenhouse Construction Site:
One of the first decisions to be made is for the greenhouse to be built as a separate unit, in contact with existing buildings or as part of new buildings. Interconnected greenhouses typically have lower construction and heating costs and easier access, but plants get less light. Interconnected greenhouses must be built facing the south. An independent greenhouse can be built in a place farther away from existing buildings.Plants in such a greenhouse receive sunlight from all directions. These greenhouses are very expensive in terms of construction and thermal system and require tremendous costs for water and electricity lines. A greenhouse can be built in any size but the smallest greenhouse that can be considered is about 200 square feet (18.4 square meters). Smaller greenhouses are very expensive in terms of construction and performance. The issues that should be considered for greenhouse construction are:
● Access to transportation routes that are minimized by constructing as much as possible closer to the main roads of this problem. The type of fuel consumed in the greenhouse, in areas where natural gas is available, can be used to reduce the costs to a large amount in the production of cold season.
● Access to water resources with good quality and quantity.
Environmental impacts, where it constantly has inclement weather, heavy rains, shade caused by being located on the northern slopes of high mountains or skyrocketing trees, is not suitable for greenhouse construction. Light intensity is one of the determinants.
The type of product that is placed in the production schedule. Considering that the trends are towards the specific production of products and the production agenda is determined after the initial study of the domestic and foreign market, before construction, they must first determine what product is produced and then decide to construct a greenhouse in the region and the appropriate climate of the product. *Considering the laws regarding the land of urban areas and the construction and operation of greenhouses and....
The construction site should be as flat as possible because in case of roughness and steepness, creating a large greenhouse will be accompanied by many problems and costs for leveling.
Direction of greenhouses:
The greenhouse skeleton creates shadows and varies according to the angle of radiation of these shadows, it is important to pay attention to this, especially in winter production, because few changes in the percentage of light reached to plants can play an important role in the quantity and quality of production. The position of the greenhouse should be such that it receives the highest amount of light. The first choice for the position of the greenhouse is in the form of a south or southeast view. All-day light provides the best conditions for the plant. The construction site should be as flat as possible because in case of roughness and steepness, creating a large greenhouse will be accompanied by many problems and costs for leveling.
Direction of greenhouses:
The greenhouse skeleton creates shadows and varies according to the angle of radiation of these shadows, it is important to pay attention to this, especially in winter production, because few changes in the percentage of light reached to plants can play an important role in the quantity and quality of production. The position of the greenhouse should be such that it receives the highest amount of light. The first choice for the position of the greenhouse is in the form of a south or southeast view. All-day light provides the best conditions for the plant.
Airflow in the greenhouse:
Air circulation in the greenhouse is essential. When a plant is exposed to fresh air flowing outside the greenhouse, fresh air is provided near the leaves and the plant can back oxygen and use fresh carbon dioxide. Airflow also helps to keep relative humidity low and temperature control in the greenhouse. Commercial greenhouses depend on all the requirements mentioned above and even more. In a commercial greenhouse, the main goal is profitability, in order to achieve this goal, the greenhouse must be efficient in terms of providing favorable environmental conditions. The light and temperature of the greenhouse must be strictly controlled. Computers have been widely used for such controls recently. Also, the presence of toxic gases and dust in the greenhouse may be a serious problem. These gases include carbon monoxide, nitrous oxide and nitrogen dioxide, which may be emitted by thermal devices.
Control of greenhouse environmental conditions:
Chemical activities performed in photosynthesis process of plants are directly affected by environmental conditions. Photosynthesis depends on factors such as temperature, light intensity and the presence of water and food. Plant respiration is different from environmental temperature. The recommended temperature range for most greenhouse plants leading to the highest photosynthetic efficiency is between 50 and 85 degrees Fahrenheit. Therefore, no matter what the greenhouse is used for, its environment should be controlled, which is essential for the health of greenhouse plants.
Temperature in greenhouses:
Setting temperatures in greenhouses is the primary condition for the growth and development of many plants. Plants need different temperatures. Some plants require higher temperatures, such as tropical plants. Others grow well at temperatures below 20 degrees Celsius, such as plants that are isolated from cold regions such as primrose, which can be seen in the forests of the north. But how temperatures are regulated in greenhouses depends on the heat system. Types of heaters or gas systems and ... can be used. Thermal systems must be able to distribute temperature uniformly and have no environmental impact. Recommended daily and night temperatures for several common greenhouse products, overnight temperature product (F) daily temperature (F) tomato 66-60 80-70 lettuce 55 78-70 cucumber 65 80 peppers 62 80-70 chrysanthemum 63-62 80-75 geranium flower 60-55 75-700
Optical requirement of plants:
Not all plants need light at the same size.
Plants are divided into three groups in terms of optical requirement.
Long Day Plants: Long Day Plants need light for between 10 and 14 hours to flower, such as seasonal summer plants such as ahar, atlases, cute and monkeys.Short day plants need less than 12 hours to flower. In contrast to long day plants, such as chrysanthemums.Plants indifferent to day length NDP: Neutral Day Plants are very suitable for home maintenance. Like henna flowers or begonias that are not allergic to day length and have flowers all year round.
Irrigation of greenhouses:
Moisture supply is one of the most important parameters for plant growth and development. After recognizing the moisture requirements of plants, we replace them in our own greenhouses, i.e. not all plants are kept in the one type of greenhouse. At large and specialized levels, each greenhouse is considered for a product or a number of similar products with the same requirements.
A variety of irrigation methods are briefly as follows.
A) Surface irrigation (gravity): Surface irrigation systems have low efficiency and water loss is high. At the same time, it washes salts, increases weed growth and causes a variety of fungal, parasitic and decay diseases. These systems are implemented in the form of curtie and tape irrigation.
B) Pressurized irrigation:
1- Sprinkler irrigation: The purpose of sprinkler irrigation is to distribute water uniformly to all plants and reduce ambient temperature and increase moisture. Water use efficiency is 75 percent. The initial cost is a lot of disadvantages of this system.
2- Drip irrigation: In this method, water, chemical fertilizers and other materials required by the plant are provided solublely by emitters installed on the side pipes. The water use efficiency is 90% and since emitters are located next to the plant plant or stem, the possibility of weed growth and development disappears.
Carbon gas in greenhouses:
The application of Co2 is almost equivalent to the use of food. In Iran, where plants are in good light condition, the efficiency of the crop can be increased by increasing co2 consumption. Co2 is essential for photosynthesis. This chemical reaction leads to the production of a green product. Co2 is a very important factor in this reaction. For many years, sources of carbon dioxide enrichment in greenhouses have been discovered to increase plant growth and production. Carbon dioxide is one of the most essential components of photosynthesis. Photosynthesis is a chemical process that uses sunlight energy to convert carbon dioxide and water into sugary substances in green plants, then these sugars are used during plant respiration to grow it.
One of the most important issues in the construction of a greenhouse is paying attention to greenhouse drainage. In areas with hard textured lands with impenetrable surface layers, by placing vented clay pipes of substructurds or in other innovative ways, they are considering necessary measures to improve drainage.
In windy areas, a row of trees or a natural barrier such as a hill is used to reduce wind damage. The minimum distance of trees from the greenhouse in the east and west should be about 2.5 times the height of the trees. This distance in the southern part is more than one height of trees.
Types of greenhouse coatings
Before 1950, there were only glass greenhouses, today it is the costliest type of greenhouse. Because fuel consumption in these greenhouses is high, they require solid skeletons. Depending on the width of the greenhouse, different skeletons can be used to build it. At a width of less than 6 meters, the wooden skeleton can be used without the need for middle columns. For greenhouses with a width of up to 12 meters, the tubular skeleton can be used without the need for vertical middle columns, but they must be attached to the window frame for strength.
B) Plastic coatings:
Plastic coatings can be made of polyester, polyvinyl chloride (P.V.C) polyvinyl fluoride (P.V.F). One of the advantages of these coatings is the lack of need for heavy skeletons and a drop in the cost of heating up to about 40% compared to one-layer glass greenhouses. Today, plastic greenhouses account for a high percentage of greenhouses in the world. But it is not very popular in Eastern Europe. The flaws in plastic coatings are low durability because the sun's ultraviolet rays cause fragility and darkness of plastic. Most plastic coatings are polyethylene, usually mixed into a differentiator against UV (ultraviolet radiation), in which case their lifespan can be extended to about 3 years. Another disadvantage of these coatings is that in winter, if the greenhouse air is colder and by hitting the wet air inside the greenhouse, the water vapor droplets on them are formed, which by joining together, and by dripping droplets on the surface of the leaves, they increase the moisture content of the leaves and cause fungal diseases, and on the other hand, by falling droplets on the bottom of the greenhouses, increase the moisture of the soil bed and reduce the amount of moisture. Oxygen is soiled. This can lead to a decrease in nutrient uptake and a decrease in plant growth. The solution to this problem is the use of spraying detergent solution in water that sprays on the inner surface of the coating, which of course these materials are cleared very soon. This is to prevent the droplets from growing. Today, in advanced countries, polyethylene and other coatings combine plastics into infrared light preservatives (IR), which reduce greenhouse temperature losses by 15 to 25 percent at night. PVF is also a new plastic coating that lasts up to ten years and its reaction to light and its price is roughly equivalent to glass.Plastic double coatings also play an effective role in reducing the cost of fuel by up to one-third. It is easier to do double layer coatings in niche skeletons with fewer columns. The distance between the lower two layers is not less than or greater than 1.25-10 cm. Semi-cylindrical greenhouses are suitable for bilayer coatings. The amount of plastic stretching is very important. When installed on a cold day, it should be pulled tightly and dragged less on a hot day with cold weather not to contract and tear. Today, most new greenhouses in the United States are made either permanently or temporarily with plastic coatings.
c) Polycarbonate coatings.
One of the advantages of polycarbonate coating instead of glass is the lower cost and lighter weight. Also, its high resistance to plastics has led to its increasing demand as a coating in greenhouse industry. Polycarbonate coating is often intended to cover the front, rear and semicircles of the relevant or the sides and roof of the greenhouse in case of customer's demand. Polycarbonate sheets are a good alternative to glass and save energy. In summer, heat is prevented from entering and in winter they prevent the exit and wasting of heat inside.
Polycarbonate sheets are resistant to inorganic acids, oils and solutions of neutral salts, aliphatic hydrocarbons and alcohols at room temperature. The chemical resistance of these sheets against many detergent sealants and adhesives in the market has been determined according to the results of several experiments.
Impact and scratch resistance
The impact strength of polycarbonate sheets is 250 times the same thickness as glass. A variety of polycarbonate sheets show a close resistance to scratches and scratches under very harsh test conditions.
Resistance to stretching and bending (flexibility)
Tensile strength of polycarbonate sheets more than 70 N/mm2 (N/mm²) is the physical yield of these sheets, the bending strength of these sheets is about 2500 N/mm2 (N/mm²) which is considered as a desirable resistance.
Thermal insulation and energy saving
Polycarbonate sheets absorb sunlight and consequently reduce the cost of air conditioning in the heat season, this feature also saves fuel consumption in winter and due to better insulation properties than glass, it is possible to save 30 liters of liquid fuel per square meter annually.
Self-extinguishing and ignition
Polycarbonate sheets do not catch fire, do not flare up and slowly melt at high temperatures, preventing the fire from spreading and extinguishing spontaneously.
UV resistance and other atmospheric conditions
This product has a very high resistance to UV radiation due to its ultraviolet coating and its color does not change due to sunlight and maintains its transparency for a long time.
Polycarbonate sheet has disadvantages like any man-made sheet. Despite all the mentioned advantages of polycarbonate sheets, one of its most obvious disadvantages can be the overheating of the underlying space of these sheets, especially in the hot months of the year. At the time of the fire, although it does not flare up, it is smoke. In addition to the similar transparency of glass, it is not possible to avoid the rustling problem of the surface of the sheet, which itself causes the surface of the sheet to become tarnished and the visibility damaged. With many properties in this product, its expensive price is inevitable, because the price of raw material, especially its anti-UV coating, is one of the most remarkable cultivars in this regard.
Platforms and substrates:
The platform is part of the greenhouse space, a place for pots or plant cultivation in substrates above the ground, as the name suggests, platforms are always placed at a level above the greenhouse floor. This action, while preventing the spread of plant-borne and pathogenic agents, helps to better ventilate and warm the bed earlier. The choice of the shape of the platforms and their ingredients depends on the type of plant, greenhouse and the taste of the manufacturer. In general, the characteristics of a good platform are: a_ have good drainage. (b) The width is such that the workers have easy access to the platform center. C_ Installed to absorb maximum light. Working with rigs to put pots allows workers to do their job without bending, while the rigs are better used to cultivate plants 30-15 cm deep and have good drainage. The height of the platforms from the ground level should be such that the measures should be possible with the worker's dominance of the product, which depends on the type of product. Platforms can be made of aluminum, Iranian, wooden timber or concrete materials. Aluminum has a long life, but it is expensive and wood is inexpensive, but it has a short life and the probability of decay is high and pathogens also penetrate it. How the platforms are located should be installed so that the maximum greenhouse space should be used for plant breeding. The number and width of the corridors depends on how they are used and the type of product. The height of the cultivation platforms is 80-90 cm. The width of the platforms adjacent to the walls is about 90 cm and the width of the middle platforms accessible on both sides should be at most 180 cm. The cultivation platforms of pot plants should not be walled and the floors of the platforms should be as vented as possible. Perforated wooden boards with tight thoracics are suitable for building the floors of platforms. In the new method, moving platforms are used to effectively use the maximum greenhouse space. This system increases production space up to more than 90% of greenhouse area. The corridors are occupied by moving platforms, which open the corridor from one side and close on the other.
Platforms and ground beds of cut flowers:
Cut flowers are cultivated in greenhouse conditions in both land and platform beds. Plants such as chrysanthemums and monkeys can be cultivated on platforms. But these platforms should be placed near the ground so that the removal of buds, foliage and harvesting is possible, and cloves are also grown on short platforms due to susceptibility to bacterial wilting disease. Disinfecting the soil of platforms is easier and more successful than ground beds. The ground beds should be such that they separate the soil around the roots from other parts. Concrete is suitable for ground beds.
Supplies in greenhouses:
The equipment and equipment required by the greenhouse can be heating, cooling, dehumidifier or fugro power system and intelligent control and automation. Noted.
Types of heating systems:
a) Central heating system or radiator system.
(Due to the high initial cost of this heating system, it is used for greenhouses above 4000 square meters.)
In this system, water vapor or hot water is used.
b) Heating heating heating system or hot air furnace.
In this system, the heat generated by the burner is transmitted to the surroundings of the furnace through the wall of the stainless steel heater and is driven to the greenhouse environment by one or more blower fans.
c) Jet heating heating system heater.
This type of heating system is similar to the hot air furnace system, except that the heaters do not have a chimney and the heating energy generated by a fan device is blown directly into the greenhouse environment.
This type of heating system is not recommended due to dissipation and low combustion quality in the long term and high production of pollutant gases such as carbon dioxide and carbon monoxide.
d) Radiant heating system:
Benefits of radiant heating:
The data in this section are based on the experiences and reports of manufacturers, consumers as well as various universities and research institutes. Many of these results have been approved by relevant government agencies as well as consumers in recent years following the implementation of numerous projects in various industries in Iran. Undoubtedly, familiarity of managers and industry owners as well as the general public with radiant heating systems and radiant heating characteristics will provide the basis for further development and expansion of radiant heating technology and benefiting industries and different parts of our country from the benefits of radiant heating.
Industrial halls and radiant heating:
In the previous section, the characteristics of radiant heating systems in comparison with hot air systems were studied in terms of energy savings. In the following, other characteristics of radiant systems will be investigated in comparison with hot air heating systems.
● Removal of central motorhome:
The space occupied by the equipment and facilities of hot air heating systems (including engine rooms, network of pipes and hot air transmission channels, etc.) is far more than radiant heating systems. The dimensions of radiant heating systems equipment are generally smaller and on the other hand, by installing it in the ceiling or on the wall, the useful and usable space inside the hall will not be occupied (the likelihood of theft also decreases). Obviously, the use of this system will have a significant impact on reducing the cost required for allocating the space needed for the mentioned facilities. In addition, the removal of the engine room and its equipment will speed up the heating facilities of the hall.
On the other hand, as mentioned in the previous section, by eliminating the central engine room, the thermal losses inside the engine room, which includes about 5% of the total thermal losses, along with the losses of the intermediate fluid transmission route to the hall (about 15 to 20% of the total thermal losses) are eliminated.
●Simplicity of steering and maintenance:
Although radiant heating systems use more advanced technology than hot air heating systems, however, their structure is less complex. For this reason, its maintenance compared to the hot air heating system, which includes large and complex steam and water facilities, air duct network, pipes, etc. It is much simpler and therefore will cost less.
The building of radiant heating systems has much less components than hot air heating systems and the only moving part in them is the sucker fan, so the performance of these systems is also associated with less exhaustion, which increases the lifespan of the device, on the other hand, in case of failure of part of the radiant heating system, repair or replacement of parts related to that part is also associated with lower cost. It's done. The relative simplicity of the structure of radiant heating systems significantly reduces the cost of installing and commissioning them and minimizes the time required for this purpose.
●Maintaining environmental health:
Central heating systems, due to the necessity of using the network of hot air transmission channels or fan-powered connectors such as heater units, always cause the displacement of fine particulate matter in the air and the growth and dispersion of microscopic organisms in the indoor space, while in radiant heating such problems will not be caused. In addition, the production and distribution of heat required in this method is done with the lowest amount of noise production and also the problem of hot air flow rate of distribution valves, which is inevitable in central heating systems, is eliminated. Thus, radiant heating systems provide healthier air than other heating systems. This leads to an increase in the work productivity of industrial and commercial units employees. Even regardless of energy efficiency, providing healthy heating and maintaining air quality in accordance with the standards required by certain industries such as pharmaceuticals, food industry, paint workshops, poultry farms, etc. It shows the existential necessity of appropriate radiant heating systems.
Reduce side problems
In radiant heating systems, there are no common problems associated with peripheral installations of central heating systems such as water hardness, freezing of pipes, leakage of pipes and canals, insulation, etc., and in this regard, there is no damage to the radiant heating system (such as bursting pipes and all kinds of leaks).
Reduce environmental impact
Radiant heating systems have fewer negative effects on the environment for three main reasons: 1. Lower fuel consumption per unit area under heating 2. Higher combustion efficiency than other systems leading to reduction of NOx and CO pollution.... it is. 3. Discharge of air and combustion products with lower temperatures in the earth's atmosphere, which will have less impact on the increase of global entropy.