Greenhouse Structures and Design
Greenhouse Site Selection
Careful planning before construction is essential in developing a successful, profitable greenhouse production system. Before starting, it is important to have an idea of the type of plants you want to raise and sell and a decision as to whether you wish to be retail or wholesale. Sometimes, one or two factors are so important that the choice of site is obvious, but more commonly, each site has good and bad attributes. If desired, make a list of potential greenhouse sites and compare them using a decision matrix. The following major factors should be investigated before greenhouse plans go beyond paper.
Microclimate
The primary limiting factor to greenhouse crop production is low light intensity during the winter. Areas with frequent fog, inclement weather, or shadows cast by trees or tall mountains are poor for greenhouse crops.
Water Availability and Quality
One of the most frequently overlooked requirements in the establishment of a greenhouse is the quantity and quality of the water. A sufficient quantity of high-quality water is extremely important to produce greenhouse crops. The need for frequent irrigation requires careful planning and management to ensure that operations have sufficient water to maintain adequate supplies for crop production.
Topography
The topography of the site affects where a growing structure is built. Topography refers to the shape of the land, e.g., hilly, steep, rocky, flat. The surface of the ground of the greenhouse should be level.
Windbreaks
Outside the greenhouse, a windbreak can reduce the infiltration of cold air and the convection of heat away from the greenhouse. Wind speed greatly affects infiltration rates; 15 miles per hour (mph) winds can double heat loss in a greenhouse.
Room for Expansion
A parcel of land larger than the grower’s immediate needs should be acquired. The ultimate size of the range should be predicted. The area should then be added to this predicted figure to accommodate service buildings, storage, access drives, and a parking lot
Availability of Labor
Present and future labor needs should be assessed and should be in accord with the labor supply in the area. Procurement of a labor supply has been a perennial problem in the horticulture industry.
Infrastructures
Proximity to transport networks (e.g., roads, railway), access to communication systems (e.g., telephone, internet), sewer services, and availability of energy (e.g., gas, electricity) must all be considered.
Market Accessibility
Locating near the market is very important for retail growers who rely on customers getting to the greenhouse. The market potential should be explored before building. The competition should be scouted out and surveys conducted (if possible) as to the greenhouse market demands of the local area.
Legal Considerations
Site selection involves various legal considerations. Permits, licenses, and zoning regulations govern where a greenhouse may be built and often even dictate what type of building materials may be used. If water from the site drains into ecological, protected areas, the land may be subject to various state and federal regulations. Some states require the owner to obtain certification to purchase restricted-use pesticides. In addition, the greenhouse owner must also be aware of relevant mandates from the Occupational Safety and Health Administration (OSHA) that ensure employee safety.
Greenhouse Orientation
Quite possibly, the largest design consideration when planning a winter or year-round greenhouse is determining the orientation and angle of glazing for the structure. In general, growers optimizing for winter growing should orient their freestanding greenhouse in an east-west orientation, meaning that the longer, glazed side of the greenhouse should face south, with the shorter ends facing east and west. This orientation allows low-angle light from the winter sun to enter from the side, where it will not be blocked by the ribs of the frame. In the orientation of multi-bay greenhouses, structural components come into play.
Angle of Incidence
The pitch of a roof means the degree of slant or the angle of divergence from the horizontal. The glass of the roof not only allows the light and heat rays to pass through it, but it also acts to some extent as a mirror, thus reflecting a part of the rays. The amount of light lost by reflection is proportional to the angle of incidence. The angle of a material, relative to light, is often called the angle of incidence and plays a role in light transmission.
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