Greenhouse Glazing
(book excerpts)The greenhouse glazing, or glazing as it is referred to in the industry, represents the greatest decision in selecting the design for the greenhouse. The selection of glazing is crucial for the attainment of an optimal controlled environment, particularly relating to the solar radiation intensity and the type (diffuse/direct and partial or full spectrum of the sun) of solar energy that reaches the plants inside the greenhouse. Diffused light is better than direct light. Various glazing materials have radically different responses to environmental conditions such as solar irradiance, wind, snow, and hail and are, by composition and manufacturing parameters, quite different in physical properties. Key characteristics that should be considered in selecting glazing are the cost, its durability (how long it lasts), its weight and ease of repair or replacement, how much light is transmitted through the material, transparent versus translucent, and how much energy moves through the material. The National Greenhouse Manufacturers Association (NGMA) lists three categories of materials for glazing commercial greenhouses. Type I glazing materials are thin plastic films, which include polyethylene, ethylene vinyl acetate (EVA), ethylene tetrafluoroethylene (Tefzel), polyvinyl chloride (PVC), polyvinyl fluoride (PVF), and polyester films. Type II glazing materials are ridged plastic panels, which include fiberglass-reinforced plastic (FRP), acrylic, polycarbonate, polypropylene, and PETG (glycol-modified polyethylene terephthalate). Type III glazing materials are glass (e.g., annealed, tempered, and laminated). A description of some of the more common types of glazing materials follows.
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Topics Within This Chapter:
- Plastic Films
- Polyethylene Film
- Multi-Layered Co-Extrusion Films
- Film Polymers and Additives
- Tefzel Film
- Polyvinyl Chloride Film
- Polyester Film
- Double-Layering
- Life Span of Plastic Film
- Poly Locking System
- Rigid Plastics
- Fiberglass-Reinforced Rigid Panels
- Polycarbonate
- Acrylic
- Glass
- Advantages and Disadvantages of Glass
- Types of Glass
- Non-tempered Float Greenhouse Glass
- Tempered Glass
- Diffused Glass
- Laminated Glass
- Types of Glass
- Greenhouse Glazing Properties
- Photosynthetically Active Radiation
- Direct and Diffused Radiation
- Heat Loss
- Thermal Transmission
- Life Expectancy
- Greenhouse Thermal Model
