GREENHOUSES AND ITS STRUCTURE

 

A greenhouse is a building with transparent glass or plastic roof and walls. •The roof and sides (walls) allow light to penetrate.

• Greenhouse =Glasshouse when roof and walls are glass covered.
• Hothouse is a heated greenhouse for plants that require an even, relatively warm temperature

AND SO, The environment in a greenhouse is usually warmer than the outside. • It heats up because incoming solar radiation from the sun warms plants, soil, and other things inside the building faster than heat can escape the structure.
•This effect has been related to the natural process that warms the Earth’s surface. When the Sun’s energy reaches the atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by gases.

• The Greenhouse effect: Inside a Greenhouse

• All types of transparent cover cause “greenhouse effect” • All radiation entering from the sun passes through the transparent covers. • Radiation from inside the enclosed structure escapes at lower rate (long wave radiation, less shortwave)

THE GREENHOUSE EFFECT:

• Consequences of the phenomenon:
• (i) Net trapping of energy
• (ii)This energy builds up and within minutes of full sunshine the interior is so hot that it will kill plants

(iii)Thus Greenhouses must be equipped to remove heat

• In all greenhouses the equipment consist of flow-through systems where outside air is pulled through so as to push hot air out (CO2 , water vapor, etc., travel with this air stream)

GREENHOUSE INSTALLATION

They may be installed with:

• – Permanent heating system
• –light supply systems
• – Carbon dioxide supply system
• – Misting/fogging systems
• –Dehumidifiers –Soilless plant culture facility
• COMPONENTS OF GREENHOUSES
• A frame

Is the main structural component.Provides both structural strength (support and reinforcement) and insulation;

 It may consist of columns, beams, straps, etc. that support the covering (cladding) material(s) and devices / accessories that are installed, including trellises for plants.

Properties of frame materials used in greenhouses

• They should be light and strong; • Economical and easy care materials; • Susceptible of being extended; • Occupy the surface optimally: minimum shading and maximum freedom of internal movement; • Be adaptable and modifiable to cover materials The most widely used frame materials: • Wood, • Galvanized steel, • Iron, • Aluminium,

The most widely used frame materials: • Resin • PVC. • Concrete. • galvanized wire or profiles of steel & aluminum

roofcommon materials used

• • Porous fabric sheets (Polyester Polypropylene or cotton)
• – Used as shading nets.
• • Plastics – Plastic Films (Flexible plastic films including polyethylene, polyester and polyvinyl chloride)
• – Rigid plastics

(Polyvinyl chloride, fibre glass – reinforced plastic, acrylic and polycarbonate rigid panels)

• • Glass – originally the only material used.

wall +- accessories like -Artificial media – Irrigation/Fertigation system –Heating system – Aeration system – Light system – CO2 generator – Means for plant pollination

Importance of Greenhouses Advantages

• • Protects plants against adverse weather conditions (cold, rain)
• • Protects plants against insects
• • Increases water use efficiency
• • Ensure clean working environment
• • Increase crop productivity as result of improved environment
• LIMITATIONS
• • Very expensive
• • Suitable for high value crops
• • Affect flower pollination
• •Needs high management and labour skills
• • Too hot during summer season or in lowland tropics Green houses are used to protect and conserve tropical plants in temperate climate = Plant conservation greenhouses.

• Greenhouse serve as exotic botanical gardens.