Grade 11 D
Table of Contents
Free Hand Sketches
Two Point Perspective
A greenhouse (also called a glasshouse) is a building in which plants are grown. These structures range in size from small sheds to industrial-sized buildings. A miniature greenhouse is known as a cold frame. A greenhouse is a structural building with different types of covering materials, such as a glass or plastic roof and frequently glass or plastic walls; it heats up because incoming visible solar radiation (for which the glass is transparent) from the sun is absorbed by 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. In addition, the warmed structures and plants inside the greenhouse re-radiate some of their thermal energy in the infrared spectrum, to which glass is partly opaque, so some of this energy is also trapped inside the glasshouse. However, this latter process is a minor player compared with the former (convective) process. Thus, the primary heating mechanism of a greenhouse is convection. 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. Thus, the glass used for a greenhouse works as a barrier to air flow, and its effect is to trap energy within the greenhouse. The air that is warmed near the ground is prevented from rising indefinitely and flowing away. Although heat loss due to thermal conduction through the glass and other building materials occurs, net energy (and therefore temperature) increases inside the greenhouse.
Greenhouses can be divided into glass greenhouses and plastic greenhouses. Plastics mostly used are polyethylene film and multiwall sheets of polycarbonate material, or PMMA acrylic glass. Commercial glass greenhouses are often high-tech production facilities for vegetables or flowers. The glass greenhouses are filled with equipment such as screening installations, heating, cooling and lighting, and may be automatically controlled by a computer. For temperature control purposes, three types of greenhouses exist: a hot greenhouse, a warm greenhouse, a cool greenhouse.
A hot greenhouse's inside temperature is maintained at a minimum of sixty five degrees. You can at some future date increase the temperature, but a hot greenhouse is intended for growing tropical and exotic plants. If you live in a very cold region, you will need to install heating and lighting equipment to satisfy the requirements of tropical and exotic plant species.
The temperature inside a warm greenhouse, on the other hand, is at about fifty-five degrees F. At this temperature, a larger variety of plants can be grown, perhaps as many as you would in your outdoor garden. You may still need to resort to the use of additional heat and light during the winter months.
A cool greenhouse (frost-free greenhouse) is maintained at a temperature ranging from forty to forty five degrees F. This temperature is ideal for growing seedlings or any plants that do not need warmer temperatures to survive. A cool greenhouse is perfect for starting your plants and vegetables in anticipation of the summer months. Generally, the use of heat or lights isn't required for a cool greenhouse.
As for structure, there are generally three types: lean-to, detached, ridge and furrow or gutter connected.
The lean-to type of greenhouse is rarely used for commercial purposes because of size restrictions, but is the most popular among hobbyists.
Detached greenhouses - as the name suggests - are independent and are stand alone structures. However, they may still be attached to a work area or else provide access to another greenhouse...
Bibliography: * Cunningham, Anne S. (2000). Crystal palaces : garden conservatories of the United States. Princeton Architectural Press, New York, ISBN 1-56898-242-9
* Lemmon, Kenneth (1963). The covered garden. Dufour, Philadelphia
* Muijzenberg, Erwin W B van den (1980) A history of greenhouses. Institute for Agricultural Engineering, Wageningen, Netherlands;
* Vleeschouwer, Olivier de (2001). Greenhouses and conservatories. Flammarion, Paris, ISBN 2-08-010585-X
* Woods, May (1988). Glass houses: history of greenhouses, orangeries and conservatories. Aurum Press, London, ISBN 0-906053-85-4
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