A greenhouse , glass house or greenhouse (formerly also earth house , conservation house , winter house , depending on the desired maximum temperature also warm house or cold house ) is a light-permeable construction that enables the ( frost ) protected and controlled cultivation of subtropical or tropical plants in otherwise unsuitable climates .
The covering - traditionally made of glass, now often also made of transparent plastic sheets or films - raised a hand through the greenhouse effect , the temperature in the greenhouse, but on the other hand, it also protects the plants from rain or strong winds . By regulating various factors such as B. the air temperature and the irrigation control of the climate inside the greenhouse is possible. Therefore, the necessary growing conditions for the plants cultivated in them can be optimized in greenhouses or even created in the first place, for example for year-round vegetable cultivation in the Central European climate.
The first reference to the cultivation of plants in pots, their overwintering in specially constructed buildings and the temporary cultivation under glass is provided by the ancient Roman agricultural author Lucius Junius Moderatus Columella in his work De re rustica , Volume 11, Chapter 3/52: " If it is worth the effort, larger vessels can be placed on wheels to move them out and back into the house with less effort. But also panes of glass should be covered over them so that they can be placed in the sun without danger even when it's cold on clear days. "
From the 16th century collections of orange , bitter oranges and other citrus trees were created at the European royal courts , for which the term orangery became established. In the beginning, wooden buildings were erected over the plants every winter, from around 1600 the plants were tended in plant pots and transferred to permanent buildings with pail transport trolleys (invented by André Le Nôtre in Versailles ) in winter.
In the context of European colonialism, the fashion developed to collect ornamental and useful plants perceived as exotic, especially from Asia, America and Australia. The main impetus for the development of the greenhouse came from pineapple cultivation in Europe. It was a fruit that particularly fascinated Europeans with its unusual shape, smell and taste. While the pineapple quickly spread throughout the world in the tropical zones after its discovery by Christopher Columbus , the transport of fruits to Europe was almost impossible during the time of sailing.
Shoots of pineapple plants were cultivated in the greenhouses of botanical gardens such as the Hortus Botanicus Leiden as early as the mid-17th century and were so successfully propagated that plants from the botanical garden of Leiden established the pineapple culture in South Africa. Compared with the vegetative propagation of these plants, however, it was a much greater challenge for greenhouse culture to care for a sapling so that it bore a fruit until it was ripe. This required a uniformly high temperature of the ground and the air as well as very good lighting conditions. Reliable thermometers with which one could measure the room temperature were only available around 1714, for example. In the 17th century, the Netherlands was considered the leading country in gardening culture and accordingly the first European successes in pineapple cultivation were achieved here. The decisive factor was initially the development of appropriate greenhouses. The first greenhouse in which, due to the light conditions and the achievable soil temperature, it was theoretically possible to cultivate pineapple fruits, was built in 1682 in the Hortus Botanicus Amsterdam . Three sides of the small house were glazed, the floor was heated from below by peat ovens and further pipes warmed the air of the greenhouse. Inspired by the successes in the Netherlands, the cultivation of this tropical fruit became fashionable, especially in England in the 18th and 19th centuries. The pineapple fruits, which at that time were hardly transportable and therefore rare, were produced as a status and prestige symbol of wealthy social groups, elaborately in small greenhouses (pineries) or pits covered with glass windows (pineapple pit) . Despite the high cost of building and operating such greenhouses, they were already widespread in England by 1725, and by 1770 they were part of the standard equipment of aristocratic gardens and parks. The greenhouse cultivation of pineapples was also taken up as a status symbol in other countries and thus ensured that the corresponding techniques were spread throughout Europe. Louis XV 1738 had a tropical greenhouse built for 800 pineapple plants. Here too, imitators were quickly found: lavish luxury was shown by those who, like the Duke of Bouillon, tend 4,000 plants and have several pineapples served on their table every day.
The miniature greenhouse developed by Nathaniel Ward in the 1830s made it possible for the so-called plant hunters who wanted to import plants that were perceived as exotic from Africa, America and Asia to transport sensitive plants to Europe. In order to preserve these tropical plants under European climatic conditions, a further development of the orangeries was necessary. As early as the end of the 18th century, greenhouses were built as glass-wood constructions, but only occasionally with the first glazed gable roofs, e.g. B. the "Iron House" in Stuttgart-Hohenheim (RF Mr. Fischer, 1789 or 1791). Another type of building are the lean-to greenhouses , in which a sloping glass roof “leaned” against a massive wall shielding from the north.
The industrialization opened new possibilities for the use of iron and glass as building materials. At the beginning of the 19th century in England, George Steward Mackenzie and John Loudon experimented with curvilinear houses , greenhouses with semicircular arched iron-glass roofs in order to use as much sunlight as possible evenly. In 1812 Mackenzie designed a quarter-sphere-hothouse for growing peaches and vines, which consisted of a glass quarter-sphere in front of a brick wall. Louden built various test greenhouses in Bayswather near London in 1818 in order to experimentally find the most favorable construction form for optimal solar radiation. In 1817 he published the Remarks on the Construction of Hothouses and in 1818 the Sketches Of Curvilinear Houses , which were received throughout Europe and significantly influenced the further development of glass house construction.
An early example of an iron and glass greenhouse outside of Great Britain is the Serres, built by Charles Rohault de Fleury in 1834–36 in Paris' Jardin des Plantes . In England, Joseph Paxton built 1836–1841 The Great Conservatory (Large Plant House ) in Chatsworth House Park , which was the model for the Palm House in Kew Gardens, built in 1841–1849 . In 1850, also in Chatsworth, Paxton built a tropical water lily house with a heated basin, the Victoria Regia greenhouse . A highlight of the iron-glass-wood construction was the Crystal Palace exhibition building by Paxton , built in 1851 .
The earliest known hot water central heating system was built by Marten Trifvald for a greenhouse in Newcastle in 1716. However, it was not until around the 1830s that steam heating became more widespread in greenhouses and replaced older individual stoves.
These glass houses, also known as “plant museums”, which staged the collected exhibits under the sign of nature control and exoticism, spread in the second half of the 19th century in the metropolises of Europe and North America, especially in botanical gardens and in urban parks as commercial ones Entertainment venues. For example, the Schönbrunn Palm House was opened in Vienna in 1882 . In Berlin, the large tropical house in the botanical garden was built from 1905 to 1907 . An outstanding example of 19th century greenhouse architecture are the Serre du Congo and Grote Wintertuin in the park of Laken Castle in the north of Brussels.
The construction, heating and management of large tropical houses constantly required enormous costs. It was only when rich manufacturers and merchants were able to emulate the luxurious lifestyle of the nobility that glasshouses also emerged as places of bourgeois-private representation, in which festivals were celebrated and the tropical flora was the subject of upscale conversation. Since the use of cooling technology and the acceleration of overseas logistics, more and more tropical fruits came to Europe and took away the exotic charm of the glass houses. Public palm houses were still maintained and rebuilt in botanical gardens, but as private representative buildings they have hardly been built since the end of the 19th century. Historical glasshouses as part of villa architecture also rarely survived changes of ownership, corrosion damage, storms and vacancies.
The first greenhouse in the shape of a geodesic dome was the Climatron, completed in 1960, in the Missouri Botanical Gardens in St. Louis. A well-known example of this type of construction are the greenhouses of the Eden Project , which opened in 2001 and are currently the largest greenhouses in the world. At the end of the 1980s, attempts were made to create a self-sufficient ecosystem in the greenhouse of the Biosphere 2 project .
Structure and components of a greenhouse
The basic components of a greenhouse are:
- The foundation , with thermal insulation against ground frost (see also perimeter insulation )
- The supporting structure of the greenhouse resting on the foundation made of masonry , wood or, as is usual in commercial horticulture , of a metal structure made of steel and / or aluminum .
- The light permeable covering consisting of glass , plastic films (for example PVC or PE , partly also in multi-ply or coated versions for better durability and light transmittance) or plastic plates (for example of plexiglass ( PMMA ), polycarbonate , glass fiber reinforced polyester (GUP) or PVC).
Plastic sheets are often used because of their better insulating effect in the form of twin-wall sheets (double-walled sheets - also known as SDP for short - or triple-walled sheets - also called S3P for short).
- The cultivation areas for the plants to be grown. A distinction is made between different bed forms , tables or hanging (hanging structures).
The Bodenbeet has connection to the "grown" bottom, when Grundbeet , however, the culture substrate carrying layer is separated from the natural ground by a barrier layer of concrete or foil. In the case of a trough bed , the culture substrate is placed in troughs made mostly of concrete, so the substrate layer does not have any connection to the grown soil in these either. The culture on tables is used for potted plants; the tables or tabletops are either fixed or designed to be movable (for better space utilization by eliminating path areas). With hanging devices in the form of hangers for individual pots, channels, etc., the usable area can be increased by using space above the beds or tables, but the disadvantage of hanging crops is the obstruction of light on deeper cultivated areas and the more complicated cultivation.
- Devices for ventilation for the purpose of influencing the oxygen and carbon dioxide content of the greenhouse air and for temperature control .
Many greenhouses / glasshouses are also equipped with:
- Systems for irrigation or sprinkling
- Devices for shading or darkening , e.g. B. by means of, if necessary, compactly collapsible shading fabric .
- Electrical or electronic control technology ( greenhouse computer ) for climate control and irrigation automation
- So-called energy screens as additional insulation against heat loss, e.g. B. made of UV-stabilized bubble wrap
- Insect nets
- Lighting systems for artificial lighting of the cultures
- CO 2 fertilization systems for carbon dioxide fertilization
- Combined heat and power plants ( combined heat and power )
- Ventilation systems to bring about an exchange of air or to generate artificial wind. Wind load leads to more stable stems that are less likely to kink.
A distinction is made between the greenhouses depending on the interior temperature
- Cold houses for temperatures below 12 ° C,
- Temperature-controlled houses for temperatures from 12 to 18 ° C,
- Hothouses (greenhouses, engl. Hothouse ) for temperatures above 18 ° C.
When exposed to sunlight , there is a rapid and greater increase in the internal temperature in the greenhouse compared to the air and soil temperature outside the greenhouse. The reason for this is a kind of heat build-up : the energy of the solar radiation first heats the soil , the plants and parts of the greenhouse. The air heated by the heated interior is only slightly cooled from the outside when the glass surfaces are closed due to the low air exchange. The poor permeability of the glass for thermal radiation ( infrared ) plays only a minor role in the build-up of heat.
This effect, first referred to by Joseph Fourier as the greenhouse effect (French: effet de serre ), is also used in residential houses ( winter gardens ) and roof surfaces (e.g. studios ), but also on a large scale in orangeries and castles. Meanwhile, the expression of the German partially greenhouse effect used the difference to the functioning on a different principle atmospheric greenhouse effect to make it clear.
On a normal sunny day, the internal temperature can rise to 35 ° C and more, which is harmful to plants. Therefore, one has to greenhouses can also reveal what usually with roof or floor wall ventilation takes place, also known as "ridge and sidewall ventilation flaps".
Effect of selective transparency
Ordinary window glass is transparent to visible light and short-wave infrared as it is emitted by the sun. It is more impermeable to long-wave infrared (the range of thermal radiation at greenhouse temperatures). This means that incident heat radiation from the greenhouse is reflected or absorbed or transmitted by the glass ( transmission ). Absorbed heat is passed on in the glass by conduction , the glass then cools down by radiation or heat dissipation to the surrounding air (in which the heat is transported by convection of the heated air molecules or in the form of evaporation heat convecting water vapor; see greenhouse heating ).
In 1909, RW Wood compared the warming of two pitch-black cardboard boxes in sunlight. One cardboard box was covered with window glass, the other with rock salt . A thermometer measured the air temperature. In contrast to glass, rock salt also allows long-wave infrared radiation to pass through. There was a temperature difference of one degree Celsius with a maximum temperature of about 55 ° C. Wood concluded that the suppression of heat dissipation by blocking the radiation of heat through the glass exists, but plays a subordinate role, and that most of the warming in a glass house is due to the suppression of heat dissipation by convection. The warming of the greenhouse is mainly based on the fact that the incident solar radiation heats the room and the heat dissipation is prevented by air exchange with the outside air.
The radiation balance depends on the difference to the fourth power of the temperatures. The greater the temperature difference, the more important the radiation component becomes. By choosing the glazing, you can take advantage of this fact in a targeted manner, for example through an IR-absorbing sandwich structure of the glass.
Even solar panels use the effect. Here the selective transparency of the glass can be supplemented by the selective absorption of the collector in order to reduce its heat emission. In the case of vacuum collectors , convection between the glass and the collector is also largely prevented.
Polytunnels are often used in commercial vegetable growing . A tunnel-shaped framework is built from metal tubes bent into a semicircle and connecting rods and covered with foil. The film is simply secured on the ground (against wind drift) that around a meter of it is covered with earth. Sometimes "piping film" with reinforced edges is used, which enable it to be fixed to the scaffolding poles. Advantages of a foil tunnel are the low costs and the quick construction and dismantling. The disadvantage is that ventilation at the highest point only takes place on the front sides and they quickly overheat. Foil tunnels are therefore more likely to be used for plants that remain small (for example lettuce, strawberries, kohlrabi, aromatic herbs). For ventilation in early summer, the side wall foils are also rolled up or removed entirely.
Floor covers made of transparent film, perforated fleece (to let in rain) or black film (to capture more heat from the sun) are even simpler than polytunnels. These are often unrolled hundreds of meters long on fields and weighed down on the ground by stones, soil or 2 sheets of film each by used tires against the effects of the wind. With this method an early harvest is achieved (new potatoes give higher financial yields than potatoes at a time when "all at the same time" are harvested).
Newer types, so-called convertible greenhouses, can largely push their roof area together. This allows the indoor temperature to be controlled so that it almost corresponds to the outdoor temperature. This leads to a significant quality improvement in cold cultures and during the summer months .
For commercial vegetable growing , plastic films are often used today, which sometimes cover large areas and entire valley floors. In El Ejido there are more greenhouses covered with plastic sheeting than anywhere else in Europe.
State-of-the-art technology is often used initially in research greenhouses. In the PhyTec plant experimentation facility at Forschungszentrum Jülich , for example, glasses from the solar industry are used, which have maximum transparency and mechanical stability.
For the Pillnitz camellia in the park of Pillnitz Castle , a 13.2 meter high, hinged greenhouse that could be moved on rails was built in 1982. It protects the tree from October to May. The rest of the time, the greenhouse is moved to the side and the tree is in the open.
The Seawater Greenhouse , which was developed in the 1990s for arid regions and whose water requirements are covered by seawater that is desalinated in the greenhouse itself , is completely new . It uses the water for cooling at the same time and generates drinking water at the same time.
In a different direction closed greenhouses, such as the "Watergy" project (a box word out, water '[dt. Water ] and energy' [dt. Energy ]). The idea of a closed system is simple and was already used in the Wardschen bottle (also Wardsche Kiste): If the system is closed, no water vapor can escape and so water can be saved; there are also other advantages (see below).
Water vapor is created by watering and breathing the plant. This is collected in a central, high cooling tower and the relative humidity is increased via cooling , so that the steam condenses and the (distilled) water can be collected. The water can now be used again for irrigation or as drinking water, which means that the system can also be used to treat gray water .
The water vapor is condensed with the help of cold water via a heat exchanger. This heated water can be stored so that it can be used again later to heat the greenhouse. There are two variants in this regard: Either you need it overnight or during cold seasons. The former is relatively easy to implement using water tanks, while the latter option requires storage up to 200 meters deep (in the ground). In this way, extreme temperatures can be smoothed out, which is essential for some crops - and if you want to grow them all year round. This type of "heating" also makes sense from an economic and ecological point of view, in contrast to conventional heating systems that are operated with electricity.
The closed system also has the advantage that less CO 2 can escape, which is required by the plants for photosynthesis . With an increased CO 2 concentration, which can be up to three times as high as in open systems, a significantly higher yield can be achieved. CO 2 can be "imported" into the greenhouse, for example via pipelines from CO 2 -emitting industries (carbon dioxide is a component of natural natural gas and is separated when the gas is processed) or from exhaust gases from the heating system. It can also be obtained directly in the greenhouse, for example through composting (with simultaneous use of the heat of rotting).
The closed system also makes it unlikely that diseases or pests can enter.
The small greenhouse is not about mass production, but about the love for plants and the opportunity to extend the gardening year. A small greenhouse allows different types of use depending on the air conditioning via heating, ventilation, and shading:
- the extended or year-round cultivation of vegetables and herbs in your own garden
- own young plant cultivation
- Wintering of potted plants, fruit trees in pots
- Forcing (chives, cut flowers, winter salad)
- Growing wine or kiwi fruit even in less suitable climates
- Accommodation for collections of plants that are sensitive to the cold or need warmth: for example cacti, bromeliads, bonsai, ferns, palms, orchids.
There is a large range of small greenhouses for the hobby gardener. They differ e.g. B. in terms of size, construction, roofing material, technical equipment (temperature control systems, irrigation systems).
Depending on the type of use and the resulting heat demand, heating may be necessary in the winter months. In order to save heating costs and also for environmental reasons, when buying a greenhouse to be heated, attention should be paid to thermal insulation through appropriate construction and covering materials. On the other hand, the summer months are often very hot - sufficient ventilation and shading can be accordingly important. In addition, it should be noted that not every covering material or every film allows UV light to pass through.
Greenhouses are occasionally also built in the form of so-called "domes" (" Platonic solids " or other polyhedra constructed from triangles ). Both large houses (for example Eden Project or Biosphere 2 ) and small greenhouses in the home garden.
The advantage of these structures is that they can be erected with a minimum of load-bearing materials, including "thin" wood, because of their spherical shape, they make best use of solar energy (the wandering sun) and are very wind-stable.
The disadvantage of these buildings is that shading and heat-insulating energy screens are difficult to produce. If this were absolutely necessary due to the climate, then a barrel-shaped construction (similar to a polytunnel but also made up of triangles) should be given preference.
Until the 1970s, Europeans were used to buying seasonal vegetables and using classic winter vegetables like cabbage and potatoes for the winter . Through preservation and later through freezers , the menu remained varied even in winter and spring. Then, however, first Dutch and later southern European companies grew fruit and vegetables in increasingly extensive greenhouse complexes and were able to guarantee a year-round supply of the most important types of fruit and vegetables until the end of the 1980s. The price of the goods is of course higher outside of the respective season. By using beneficial insects as standard, the population of harmful insects and mites can usually be kept below the damage threshold for insecticide use (which is gentle on beneficial insects). In addition, today's greenhouse systems with standing wall heights of 4 m have an optimal climate, so that there is less infestation with fungi.
The success of the greenhouse cultures has also led to the expansion of such plants in the German-speaking region. In Austria, for example, the center of vegetable cultivation for peppers and tomatoes is in southern Seewinkel .
Greenhouses are also used in the cultivation of ornamental plants. Here, with the help of forcing, ornamental plants are brought forward so that they can be offered in bloom at the beginning of the season. Cold-sensitive plants, on the other hand, are grown longer in the greenhouse.
The soilless production (French. Hors sol , outside the bottom), also soilless culture substrate culture, hydroponics or hydroponics or hydroponics called, is a method of cultivation without the use of soil or earth-like substrates . The crops, mostly vegetables and strawberries, are planted in a soil-free material such as rock wool or coconut fiber , with a precisely defined nutrient and water supply in a greenhouse or in a hall that can also be heated. This type of production is economically efficient, but, depending on the conditions, requires a large amount of energy.
One advantage of hors-sol production is that it is independent of weather, climate and soil. This makes this type of production particularly popular for sensitive plants like tomatoes. It is even indispensable for mushrooms, as they have very narrow cultivation limits.
Soil-free production for organic products is not permitted in most EU countries , although there are exceptions for (organic) mushrooms, young plants, ornamental plants and potted herbs. In Sweden, Finland and Denmark, however, the EU organic regulation is interpreted in such a way that hors-sol production with natural substrates is permitted. Even in Canada and the USA, whose organic standards have been recognized as equivalent by the EU, organic plants do not have to grow in the soil. (Last updated 2012)
Plants and their fruits grown in nutrient solution are often said to be tasteless or the difference in quality and taste between natural and hors-sol cultivation is controversial. It is important to note the variety, which has often been optimized for maximum yield at the expense of taste, and the origin of the product. In exporting countries, due to the shelf life, the harvest must be carried out earlier, which also has an effect on the taste. However, it cannot be ruled out that some substances that a plant produces (in small quantities) and that are relevant for humans have not yet been discovered and are missing in the product in a soil-free cultivation method. Plants also form aromatic substances to protect themselves from microbial and herbivorous pests and predators (see also feeding defense ); the reduction in contamination of such pests by hydroponics can also be the cause of aroma deficiency.
Vertical greenhouses or vertical columns are also suitable for Hors-sol . One of the largest hydroponics farms in the world is the size of a soccer field, 10,000 heads of lettuce are harvested there on shelves up to 18 floors high, the trend is towards 30,000 heads of lettuce per day. Due to the mass culture and rather only one type of vegetable per company, the work (especially the distribution) can be designed more rationally and the space can be used better, vegetables can also be grown in large quantities in the city, which reduces transport costs and CO 2 - Reduces emissions from traffic.
In organic farming there are - depending on the association - various restrictions with regard to heating the greenhouses. At Bio Suisse, for example, the heating temperature for vegetable crops is set to max. 10 degrees, and from 2020 - with a transition period for existing businesses until 2039 - only renewable energies are permitted. In the course of the energy transition , individual food retailers have also declared their intention that the suppliers' greenhouses should be heated with 100 percent renewable energies in the future. For example, Migros announced a change by 2025.
Greenhouses are also heated directly with heating cannons, in which the exhaust gases are led directly into the greenhouse space. With the help of pore burners or other catalytic burners, the combustion temperature of a flame can be reduced to below 1200 ° C, which means that fewer nitrogen oxides are formed in the flue gas.
If heating is planned, the base of the greenhouse must also be thermally insulated in the floor: either on the outside (as " perimeter insulation ") or under the inner wall with root-resistant, non-porous panels (for example made of polystyrene or polyurethane ) or generally with a glass foam floor filler ( foam glass Granulate ). Otherwise the base is a thermal bridge . A greenhouse absorbs warming sunlight for around 1/3 of 24 hours and cools down around 2/3 of the time , thermal curtains , thermal screens or covers also reduce heat losses.
Up to 35% of the heat loss of a greenhouse is lost when ventilating the latent heat stored in the water vapor ( evaporation heat ), so heat recovery using dehumidifiers or water curtains (see also fog condensation ) leads to significant heating cost savings.
The waste heat from a bio-stacker made of stacked wood chips in the greenhouse can also be used for heating. As with a hotbed (see also cold frame ), the heat of rotting creates the necessary heat from the ground and air temperature. In the case of the biomeiler, the heat generated is used either via built-in water-filled pipe coils or by watering and collecting the heated seepage water or by layering it like a hill bed .
- Mini greenhouse , harvest factor , winter garden , flat glass , earth greenhouse / Walipini
- Radiation balance , passive house , leaning house
- List of palm houses
- Greenhouse gas
- Greenhouse effect
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