Planning and Design of Greenhouse

Greenhouses play a crucial role in modern agriculture by providing a controlled environment that enhances crop production irrespective of external climatic conditions. They protect plants from adverse weather, pests, and diseases, while also allowing farmers to optimize yield and quality. Effective planning and design of a greenhouse require a thorough understanding of site selection, structural design, and appropriate covering materials.

1. Purpose and Importance of Greenhouse:

• Controlled Growing Environment: Greenhouses are designed to create and maintain an optimal growing environment, resulting in enhanced production and maximum yield.
• Extended Growing Seasons: By regulating temperature, humidity, and light, greenhouses allow year-round cultivation, extending the growing season of crops.
• Protection from Adverse Weather: They protect crops from extreme temperatures, heavy rainfall, hail, snow, and strong winds.
• Pest and Disease Control: The enclosed structure minimizes the exposure of crops to pests and diseases, reducing the need for chemical pesticides.
• Efficient Resource Utilization: Greenhouses use resources like water, fertilizers, and energy more efficiently due to the controlled environment.
• High-Value Crops: They enable the cultivation of high-value and sensitive crops, such as flowers, vegetables, and exotic plants, in regions where open-field farming is not feasible.

2. Site Selection and Orientation:

Proper site selection and orientation are critical to maximizing the efficiency and productivity of a greenhouse.

Location and Climatic Conditions:

• Wind, Snow, and Crop Loads: The greenhouse must be designed to withstand local wind speeds, snow loads, and crop weights. The structure should be location-specific to ensure durability and safety.
• Solar Radiation: The site should receive maximum sunlight, especially during winter. In the Northern Hemisphere, greenhouses should be oriented east-west for maximum light exposure.
• Temperature and Humidity: The location should support the temperature and humidity requirements of the crops to be grown.

Terrain and Soil Conditions:

• Level Ground: A level site reduces the cost of grading and ensures uniform irrigation and drainage.
• Soil Quality: Although the soil inside the greenhouse can be modified, the external soil should support the foundation and drainage requirements.

Drainage and Water Supply:

• Drainage System: The site must have good drainage to prevent waterlogging and soil erosion.
• Water Availability: An adequate and reliable water supply is essential for irrigation and maintaining humidity levels inside the greenhouse.

Windbreaks and Protection:

• Natural Windbreaks: Selecting a site with natural windbreaks such as hills or trees can protect the greenhouse from strong winds.
• Distance from Trees: In snow-prone regions, trees should be at least 30.5 m away to prevent snow drifts. To avoid shading, trees on the east, south, or west should be at least 2.5 times their height away from the structure.

Accessibility and Infrastructure:

• Proximity to Markets: The greenhouse should be close to markets for ease of transport and reduced logistics costs.
• Utilities and Facilities: Availability of electricity, water supply, and road access are crucial for the operation and maintenance of the greenhouse.

3. Structural Design:

The structural design of a greenhouse plays a vital role in ensuring its stability, durability, and efficiency in maintaining a controlled environment.

Basic Requirements:

• Protection from Weather: The structure must protect crops from harsh weather conditions like high and low temperatures, snow, hail, rain, and wind.
• Maximum Light Intensity: The design should allow maximum natural light to penetrate the greenhouse for photosynthesis.
• Ventilation and Cooling: Proper ventilation and cooling mechanisms are necessary to regulate temperature and humidity.
• Heating and Insulation: During cold weather, the structure must retain heat or have provisions for heating to maintain suitable growing conditions.

Types of Greenhouse Structures:

1. Straight Side Wall with Arched Roof: Most common shape for general-purpose greenhouses. Provides good headroom and space utilization.
2. Gable Roof Greenhouse: Suitable for areas with heavy snow as the sloped roof prevents snow accumulation. Allows better air circulation.
3. Arch Roof and Hoop Style: Economical and easy to construct. Made of galvanized iron pipes, suitable for low-growing crops like lettuce. Ideal for temporary and seasonal use.
4. Gothic Arch Frame: Combines the benefits of an arched roof with additional side wall height. Suitable for taller crops without compromising structural strength.

Load Considerations in Structural Design:

• Dead Load: The weight of the structural elements such as frames, glazing materials, and fixtures.
• Live Load: The weight of equipment, crops, and personnel inside the greenhouse.
• Wind Load: The structure should be designed to resist wind speeds up to 130 km/h.
• Snow Load: In snow-prone areas, the roof must be designed to bear the snow load without collapsing.
• Seismic Load: In earthquake-prone regions, the design should include seismic resistance features.

Structural Materials:

• Galvanized Iron and Steel Pipes: Provide strength and durability. Commonly used for hoop and arch-type structures.
• Aluminum Frames: Lightweight, corrosion-resistant, and durable.
• Wood: Economical and easy to work with but prone to decay and pest attacks.

4. Covering Materials:

The choice of covering material affects light transmission, temperature regulation, durability, and cost.

Factors to Consider:

• Light Transmission: Should allow maximum visible light for photosynthesis while filtering harmful UV rays.
• Temperature Regulation: Should retain heat during the night and reflect excessive heat during the day.
• Durability and Stability: Resistant to impact, weathering, and thermal changes.
• Cost and Lifespan: Should provide a balance between cost and durability.

Types of Covering Materials:

Ideal Properties:

• High Light Transmission: For effective photosynthesis.
• UV Absorption and Fluorescence: Converts UV light into visible light useful for plants.
• IR Reflection and Absorption: Controls internal temperature by managing infrared radiation.
• Cost-Effective: Should be economical and easy to replace.
• Long Lifespan: Preferably between 10 to 20 years for cost efficiency.

5. Design Considerations for Efficient Greenhouses:

1. Climate Control Systems: Include heating, cooling, ventilation, and humidity control for consistent internal climate.
2. Automation and Technology Integration: Use of sensors, automated irrigation, and climate control systems for enhanced efficiency.
3. Energy Efficiency: Utilizing solar energy, thermal screens, and energy-efficient fans.
4. Water Management: Efficient irrigation systems like drip or misting systems to conserve water.
5. Pest and Disease Management: Incorporating pest-proof nets and strategic ventilation to minimize disease outbreaks.