Greenhouse Technology
Greenhouses are structures that collect solar energy, usually to provide a climate-controlled environment in which plants can be grown. Greenhouses allow for plants that are not in season to be cultivated indoors where a controlled environment can mean a higher survival rate. There are several principles, techniques and components that make greenhouse technology work. Does this Spark an idea?
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History
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The first greenhouses were build in the first century A.D. by the Romans and known as Specularia. While Roman greenhouses were built from transparent minerals and rocks (such as mica), the invention of glass made greenhouses much more practical. A massive glass greenhouse was built at Versailles for the French royalty to enjoy oranges year-round. Greenhouses flourished during the Victorian era as wealthy British gardeners grew fruit and flowers. Today greenhouses are common among garden hobbyists and an essential tool for the flower, fruit and vegetable industries.
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Construction Methods
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The technology behind a modern greenhouse begins when it is initially planned and designed. Choosing a site that receives adequate sun exposure is essential. The slope of a greenhouse roof can be anywhere from 20 to 60 degrees and is generally angled to provide maximum exposure to the sun during the season when heat and light are most needed for the plants. The angle of the roof and the orientation of the greenhouse will depend on the latitude of the greenhouse (its distance from the equator) and the climate of the region.
Glazing
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The materials available for greenhouse construction have continued to evolve over time. New materials and manufacturing methods allow for several types of glazing to be used, both for letting sunlight enter the greenhouse and to retain the appropriate amount of heat inside. Because plants grow more evenly under diffused sunlight, glazing that breaks up the spectrum of sunlight while allowing the full range of radiation to pass through is ideal. This includes glass with a rough surface, fiberglass panels and double-layered plastic glazing (polyethylene).
Heat and Ventilation
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Because different materials absorb and release heat energy at different rates, the materials placed inside a greenhouse will determine how quickly the heat that enters through the glazing will remain inside the greenhouse. Concrete, rocks and water all retain heat for long periods of time and can be used to keep a greenhouse warm overnight.
Ventilators are fitted to most greenhouses to provide artificial movement of air and keep fresh air moving toward the plants so that their respiration cycle can occur normally. Use automated ventilators to ensure that there is always adequate air movement, or construct a greenhouse to receive natural ventilation when its doors are opened.
Other Technologies
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In some cases, additional technologies may be needed to keep the desired conditions inside a greenhouse. Horticulture lamps can be employed when there is not enough sunlight. When heat retention is the issue, materials that store heat through a phase change can be used. Chemical compounds such as sodium thiosulfate pentahydrate and calcium chloride hexahydrate can be placed inside the greenhouse where they will melt during the day, absorbing heat from the sun. At night, these materials will turn back into solids and release their stored heat into the air inside the greenhouse.
References
Resources
- Photo Credit "Nunobiki Herb Garden, Mount Rokko, Kobe, Japan" is Copyrighted by Flickr user: yeowatzup (Kok Leng Yeo) under the Creative Commons Attribution license.
