A greenhouse (also called a glasshouse or hothouse) is a building where plants are cultivated.
A greenhouse is a structure with a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building. Air warmed by the heat from hot interior surfaces is retained in the building by the roof and wall. These structures range in size from small sheds to very large buildings.
Greenhouses can be divided into glass greenhouses and plastic greenhouses. Plastics mostly used are PEfilm and multiwall sheet in PC or PMMA.
Commercial glass greenhouses are often high tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment like screening installations, heating, cooling, lighting and may be automatically controlled by a computer.
The glass used for a greenhouse works as a selective transmission medium for different spectral frequencies, and its effect is to trap energy within the greenhouse, which heats both the plants and the ground inside it. This warms the air near the ground, and this air is prevented from rising and flowing away. This can be demonstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. This principle is the basis of the autovent automatic cooling system. Greenhouses thus work by trapping electromagnetic radiation and preventing convection. A miniature greenhouse is known as a cold frame.
Greenhouses are often used for growing flowers, vegetables, fruits, and tobacco plants. Bumblebees are the pollinators of choice for most greenhouse pollination, although other types of bees have been used, as well as artificial pollination.This helps the plants to produce more plants for future plantations.
Besides tobacco, many vegetables and flowers are grown in greenhouses in late winter and early spring, and then transplanted outside as the weather warms. Started plants are usually available for gardeners in farmers' markets at transplanting time.
The closed environment of a greenhouse has its own unique requirements, compared with outdoor production. Pests and diseases, and extremes of heat and humidity, have to be controlled, and irrigation is necessary to provide water. Significant inputs of heat and light may be required, particularly with winter production of warm-weather vegetables. Special greenhouse varieties of certain crops, like tomatoes, are generally used for commercial production.
Greenhouses are increasingly important in the food supply of high latitude countries. One of the largest greenhouse complexes in the world is in Almeria, Spain where Greenhouses cover almost 50,000 acres (200 kmē) and where almost 5% of Spain's salad vegetables are grown.
Greenhouses protect crops from too much heat or cold, shield plants from dust storms and blizzards, and help to keep out pests. Light and temperature control allows greenhouses to turn inarable land into arable land. Greenhouses can feed starving nations where crops can't survive in the harsh deserts and Arctic wastes. Hydroponics can be used in greenhouses as well to make the most use of the interior space.
Biologist John Todd invented a greenhouse that turns sewage into water, through the natural processes of bacteria, plants, and animals.
The idea of growing plants in environmentally controlled areas has existed since Roman times. The Roman emperor Tiberius ate a cucumber-like vegetable daily. The Roman gardeners used artificial methods (similar to the greenhouse system) of growing to have it available for his table every day of the year. Cucumbers were planted in wheeled carts which were put in the sun daily, then taken inside to keep them warm at night. The cucumbers were stored under frames or in cucumber houses glazed with either oiled cloth known as "specularia" or with sheets of mica, according to the description by Pliny the Elder.
The first modern greenhouses were built in Italy in the thirteenth century to house the exotic plants that explorers brought back from the tropics. They were originally called giardini botanici (botanical gardens). The concept of greenhouses soon spread to the Netherlands and then England, along with the plants. Some of these early attempts required enormous amounts of work to close up at night or to winterize. There were serious problems with providing adequate and balanced heat in these early greenhouses.
Jules Charles, a French botanist, is often credited with building the first practical modern greenhouse in Leiden, Holland to grow medicinal tropical plants.
Originally on the estates of the rich, with the growth of the science of botany greenhouses spread to the universities. The French called their first greenhouses orangeries, since they were used to protect orange trees from freezing. As pineapples became popular pineries, or pineapple pits, were built. Experimentation with the design of greenhouses continued during the Seventeenth Century in Europe as technology produced better glass and construction techniques improved. The greenhouse at the Palace of Versailles was an example of their size and elaborateness; it was more than 500 feet long, 42 feet wide, and 45 feet high.
In the nineteenth Century the largest greenhouses were built. The conservatory at Kew Gardens in England is a prime example of the Victorian greenhouse. Although intended for both horticultural and non-horticultural exhibition these included London's Crystal Palace, the New York Crystal Palace and Munich’s Glaspalast. Joseph Paxton, who had experimented with glass and iron in the creation of large greenhouses as the head gardener at Chatsworth, in Derbyshire, working for the Duke of Devonshire, designed and built the first, London's Crystal Palace. A major architectural achievement in monumental greenhouse building were the Royal Greenhouses of Laeken (1874-1895) for King Leopold II of Belgium.
In Japan, the first greenhouse was built in 1880 by Samuel Cocking, a British merchant who exported herbs.
In the Twentieth Century the geodesic dome was added to the many types of greenhouses.
Solar greenhouse (technical)
A solar greenhouse works by letting in solar radiation and trapping the energy from that radiation to increase and maintain the internal temperature above that of the temperature outside - see greenhouse effect for details.
The most basic aspects of greenhouse design are: first, to thermodynamically isolate the system to stop convection and conduction from equalizing the temperature with the ambient temperature; and second, to provide a covering with a controlled difference between the transparency in the solar radiation band (280 nm to 2500 nm wavelengths) and the terrestrial thermal radiation band (5000 nm to 35000 nm), for the purpose of either raising or lowering the temperature inside the greenhouse. A greenhouse covering which is more transparent to the solar radiation band and less transparent to the thermal radiation band will result in a temperature higher than the surrounding environment, and a greenhouse covering which is more reflective of solar radiation and more transparent to thermal radiation will lower the temperature relative to the surrounding environment.
For the traditional case of a warming greenhouse, such as with a glass covering, a covering material is chosen which will absorb some of the outgoing IR and radiate a portion of it back into the greenhouse environment to reduce radiative energy loss to the sky from the amount that the ambient environment experiences. The use of insulation and more infrared-absorbent glazing enhances the effect by reducing heat loss by conduction and IR radiation.
The soil mass at the base of the greenhouse acts to absorb a portion of the available heat during the solar period of the day for later use as a night time radiant heat source. Installations of subterranean air circulation tubing can be designed to enhance the soil mass heat absorption potential.
With proper subterranean design, underground air circulation tubing can absorb most of the daytime solar gain directly into this soil mass to provide air cooling, prevent overheating and serve as an additional heat source at night. Also the addition of heat storage materials with high heat capacity, such as containers of water or bins of sand and rock absorb heat energy during the day to help prevent greenhouse overheating, and release that energy to maintain the internal temperature during cooling periods, such as during the night.
The modern development of new plastic surfaces and glazings for greenhouses has permitted construction of greenhouses which selectively control the transmittance of both incoming solar radiation wavelengths and outgoing thermal IR wavelengths.
The new materials also provide insulation to reduce conductive loss through the glazing in order to better control the growing environment. The research starts with the blocking of convective heat loss as a given in an isolated system and works toward improving IR absorption and insulation to further reduce radiative and conductive energy loss.
Gardeners sometimes use a "greenhouse-in-a-greenhouse" technique, in which they lay additional IR absorbent plastic sheeting inside a greenhouse in order to provide additional warmth in an isolated area to plants or water pipes.
Another practical application of the greenhouse effect is in the creation of solar cookers. The analysis here compares the thermodynamic properties of several solar cooker designs.
Greenhouses are sometimes outfitted with integrated irrigation systems, and/or heat sink-systems which can respectively irrigate the plants or help to store energy from the sun and redistribute it at night (when the greenhouses starts to cool down).