A green house should be located in a place which is fairly shadow free, and where sufficient good quality water is available. A well drained area, with wind breaks on all sides free from industrial pollution will be ideal. Availability of sufficient space for further expansion of the facility in future, good motorable road, nearness to the market, electricity and communication facilities cotmecting with telephone, telex and fax etc must be considered while choosing the site.
Selection of site with congenial climatic conditions for roses to avoid energy cost for heating and cooling will be more economical. In mild climate energy requirements will be lower than at places with extreme climates. For green house operation labourers required throughout the year, hence for big green house complex availability of labourers will be another important consideration.
While constructing the greenhouses light levels and prevailing winds are to be considered critically. Plants in the green house must get adequate and uniform light, throughout the year, especially during winter. Moreover, prevailing winds should not adversely affect either the structure or the operation of the facility. Green houses could be located on hill slopes. In the Northern Hemisphere, a green house should be located on the south facing slopes for better illumination and protection from northern winds. For availability of sunlight in winter the east-west orientation of free standing greenhouses is better as compared to north-south orientation. The advantage keeps increasing as we move away from the equator.
For areas located above 40 degrees N latitude, a free standing green house should be built east to West, whereas for areas situated below 40 degrees N latitude, the ridge of the free standing green house should have a north to south orientation. But for all latitudes, the multi-span green houses should be constructed north to south to avoid the shadow of the structural components. The shadow traverse the floor during the day if the gullers are oriented in the north to south direction, and the production in the specific areas does not suffer.
If the orientation of the multi-span green house is in the east to west direction, the shadow persists in some areas, which leads to loss of production in shaded areas. While constructing the green house, care should be taken regarding the proper slope of the roof for maximum utilisation of solar radiation and also to eliminate dripping inside the greenhouse. Green house orientation should also depend on wind direction of a particular location. In a naturally ventilated green house, the ventilators should open on the lee ward side. A free standing green house should have its long axis perpendicular to the wind direction.
There are different architectural forms of green houses like quonset, modified quonset or elliptical, gothic arch, mansard roof, gable even span, gable uneven span and multi span. The types of cladding materials used are glass, plastic, polyethylene, polyvinyl, fluoride, polyester, fibre glass reinforced panels, acrylic panels and polycarbonate panels. For fabricating the structure of green houses, the most commonly used materials are wood, steel and aluminum. Due to scarcity of wood, prefabricated steel structure of galvanised steel or zinc coated pipes, or aluminium pipes, angles, channels and T-sections are preferred.
The major consideration in the design of the green house has been the design of the shape of the roof. These designs are more convenient for plastic roofs than glass cover. The design should be such that the angle of incidence of solar radiati~n is never greater than 40 degrees. The structural design of the green house must provide safety from wind and snow damage, while permitting maximum light transmission to the rose crops. The various loads should be considered to produce structurally sound and economically useful green houses.
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