About Greenhouses

 

Greenhouses are structures covered with translucent materials such as glass, plastic, fiberglass, which can be controlled or regulated in order to provide suitable conditions for the growth of plants. Energy losses in greenhouses are directly proportional to the combination of convection, radiation and infiltration. Energy loss through the surface coating of a greenhouse is determined by the following equation;

Energy Losses = Convection + Radiation + Infiltration

 

Greenhouse cultivation with plastic greenhouse covers enables the transformation of seemingly inefficient lands into modern agricultural fields. Different polyethylene materials such as Poly Vinyl Chloride (PVC), Poly Carbonate (PC) and Low Density Polyethylene (LDPE) are widely used in the coating of greenhouse structures.

However, most plastic polymer films are prone to photodegradation when exposed to UV radiation (290-400 nm) or visible radiation (400-700 nm). With the use of agricultural chemicals, deterioration is a bigger problem in hot regions. Durability in plastic greenhouse covers is one of the issues that most concern and worry end users. The production of covers resistant to greenhouse operations is the battlefield of companies in this sector, and phytosanitary products such as sulfur and chlorine have become their greatest enemy. Among these products, burning sulfur is particularly aggressive, and the current method of application has a huge impact on the degradation of the polyethylene greenhouse cover.

 

 

Greenhouse Covering Materials

 

The covering material used in a greenhouse affects the productivity and performance of the greenhouse. Coating materials affect the level and quality of light available to the crop. Diffused light is better than direct light. Fluorescent and pigmented films can increase the good red light ratio. Dust attracted by plastic films reduces the transmission of radiation. It has been observed that water droplets inside the coatings reduce light transmission by 8% and also block thermal radiation.

All of the greenhouse covers reduce the light to some extent. As the covers get dirty and aged, less light enters the greenhouse. Condensation (water droplets) on the coating material also reduces light. Light colored materials such as white weed cover in the greenhouse increase the light the crop can receive. Basic features to consider when choosing a coating material; cost, durability, weight and ease of repair or replacement, how much light is transmitted through the material, and how much energy passes through the material.

The diffused materials are designed to diffuse incoming light and provide better light conditions for crops - for example, a cloudy white plastic film diffuses light better than a clear plastic film.

 

Glass:

It has been the traditional greenhouse covering material for a long time. Its beneficial properties include:

• high transmission in the bandwidth of photosynthetically active radiation

• good heat retention at night

• low UV light transmission

• durability

• low maintenance costs.

 

Plastic coating:

There are essentially three materials in this category; polycarbonate, acrylic (polymethyl methacrylate) and glass fiber ones. Plastic-coated greenhouses are more durable than greenhouses made of plastic films and have very good heat retention and low UV light transmission.

 

Plastic Greenhouse covers:

They are used as the most common and lowest cost greenhouse covering material. Available film types are polyethylene (polyethylene), EVA (ethyl vinyl acetate) and PVC (poly vinyl chloride). With continuous improvements in plastics, these coating materials offer numerous flexibility and performance options. The coatings can have a variety of additives used to impart beneficial properties to plastic films. For example, films can be used to exclude ultraviolet (UV) light for chemical-free pest control or to reflect long-wave infrared (IR) radiation to improve heat retention at night. As a result, some plastic coating materials are colored or colored.

Additives to plastic;

• durability

• capacity to reduce heat loss

• droplet reduction capacity

• transmission of certain wavelengths

• They are used for purposes such as the capacity to reduce the amount of dust adhering to the film.

Types of Additives:

1. UV (290-400 nm) absorbers and stabilizers increase durability, reduce potential damage to biological systems in the greenhouse and control some plant pathogens

2. Infrared (700-2500 nm) absorbers reduce long wave radiation and minimize heat loss

3. Long wave radiation (2500-40000 nm) absorbers reduce heat loss from materials and objects (including plants) inside the greenhouse

4. Light diffusers scatter the light entering the greenhouse, reducing the risk of burning plants and improving the amount of light available to the lower parts of the plant.

5. Surfactants reduce the surface tension of water, dissipate condensation

6. Antistatic agents reduce the tendency of dust to accumulate on plastic films.

In addition,

1. Color pigments can improve plant growth by varying the ratio of selected wavelength ranges.

2. Fluorescence can be used to increase the red light emission

3. Shiny surfaces can repel insects

The multi-layer film making process enables superior composite films to be made by combining thin layers of materials with different properties.
Properties such as durability, creep (deformation over time) and long wave radiation absorption can be improved.

 

Maintenance:

A poorly maintained coating material can lose a lot of energy and increase production costs significantly.

Glass coverings should be kept clean and broken glass should be replaced. Plastic coverings need to be changed routinely. The performance of plastic coatings decreases over time. Old coatings reduce light transmission, which can restrict efficiency. The lifetime of plastic films depends on the properties of the plastic purchased. All plastic covering materials must be replaced before they begin to deteriorate visibly; for example, discoloration is an early indicator of wear.