What is Green Building?

A greenhouse (also called a glasshouse) is a building where plants are grown. These structures range in size from small sheds to very large build-ings. A miniature greenhouse is known as a cold frame.

A greenhouse is a structure with different types of covering materi-als, such as a glass or plastic roof and fre-quently glass or plastic walls; it heats up be-cause incoming visible solar radiation (for which the glass is trans-parent) from the sun is absorbed by plants, soil, and other things inside the building. Air warmed by the heat from hot in-terior surfaces is re-tained in the building by the roof and wall.

In addition, the warmed structures and plants inside the green-house re-radiate some of their thermal energy in the infra-red, to which glass is partly opaque, so some of this energy is also trapped inside the glasshouse.

However, this lat-ter process is a minor player compared with the former (convective) process. Thus, the pri-mary heating mechanism of a greenhouse is con-vection. This can be dem-onstrated by opening a small window near the roof of a greenhouse: the temperature drops considerably. This princi-ple is the basis of the autovent automatic cooling system.

Thus, the glass used for a greenhouse works as a barrier to air flow, and its effect is to trap energy within the green-house. The air that is warmed near the ground is prevented from rising indefinitely and flowing away.

Although there is some heat loss due to thermal conduction through the glass and other building ma-terials, there is a net increase in energy (and therefore tem-perature) inside the greenhouse.

Greenhouses can be di-vided into glass green-houses and plastic greenhouses. Plastics mostly used are PEfilm and multiwall sheet in PC or PMMA. Commer-cial glass green-houses are often high tech production facili-ties for vegetables or flowers. The glass greenhouses are filled with equipment like screening installa-tions, heating, cooling, lighting and may be automatically con-trolled by a computer

Greenhouses protect crops from too much heat or cold, shield plants from dust storms and blizzards, and help to keep out pests. Light and tem-perature control al-lows greenhouses to turn inarable land into arable land, there by improving food produc-tion in marginal envi-ronments.

Because greenhouses allow certain crops to be grown throughout the year, greenhouses are increasingly impor-tant in the food supply of high latitude coun-tries. One of the larg-est greenhouse com-plexes in the world is in Almeria, Spain, where greenhouses cover al-most 50,000 acres (200 km2). Sometimes called the sea of plastics.

Greenhouses are often used for growing flow-ers, vegetables, fruits, and tobacco plants. Bumblebees are the pol-linators of choice for most greenhouse polli-nation, although other types of bees have been used, as well as artifi-cial pollination. Hydro-ponics can be used in greenhouses as well to make the most use of the interior space.

Besides tobacco, many vegetables and flowers are grown in greenhouses in late winter and early spring, and then trans-planted outside as the weather warms.

Started plants are usu-ally available for gar-deners in farmers' mar-kets at transplanting time.

Special greenhouse va-rieties of certain crops such as tomatoes are generally used for commercial production.

The closed environment of a greenhouse has its own unique requirements, compared with outdoor production. Pests and dis-eases, and extremes of heat and humidity, have to be controlled, and irriga-tion is necessary to pro-vide water. Significant in-puts of heat and light may be required, particularly with winter production of warm-weather vegetables.

HistoryThe idea of growing plants in environmentally con-trolled areas has existed since Roman times. The Ro-man emperor Tiberius ate a cucumber-like vegetable daily. The Roman garden-ers used artificial meth-ods (similar to the green-house 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 selenite (a.k.a. lapis specu-laris), according to the description by Pliny the Elder.

The first modern green-houses were built in It-aly in the 13th century to house the exotic plants that explorers brought back from the tropics. They were origi-nally called giardini botanici (botanical gar-dens).

The concept of green-houses 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.

Today the Netherlands has many of the larg-est greenhouses in the world, some of them so vast that they are able to produce mil-lions of vegetables every year.

The French botanist Charles Lucien Bona-parte is often credited with building the first practical modern green-house in Leiden, Hol-land to grow medicinal tropical plants

Originally on the estates of the rich, with the growth of the science of botany, greenhouses spread to the universi-ties. The French called their first greenhouses orangeries, since they were used to protect or-ange trees from freez-ing. As pineapples became popular pineries, or pine-apple pits, were built. Ex-perimentation with the design of greenhouses continued during the Seventeenth Century in Europe as technology produced better glass and construction tech-niques improved.

The

Netherlands The Netherlands has some of the largest greenhouses in the world. Such is the scale of food produc-tion in the country that in 2000, green-houses occupied 10,526 hectares, or 0.25% of the total land area of the Neth-erlands.

Greenhouses began to be built in the Westland area of the Netherlands in the mid-nineteenth cen-tury. The addition of sand to bogs and clay soil created fertile soil for agriculture, and around 1850, grapes were grown in the first greenhouses, simple glass constructions with one of the sides consist-ing of solid wall.

By the early 20th cen-tury, greenhouses began to be constructed of nothing but glass, and they began to be heated. This also allowed for the production of fruits and vegetables that did not ordinarily grow in the area. Today, the Westland and the area around Aals-meer have the highest concentration of green-house agriculture in the world. The Westland pro-duces mostly vegetables, besides plants and flow-ers; Aalsmeer is noted mainly for the production of flowers and potted plants.

Since 2000, technical innovations include the "closed green-house", a completely closed system allow-ing the grower com-plete control over the growing process while using less en-ergy. Floating green-houses are used in wa-tery ar-eas of the country.

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