Maximizing Greenhouse Efficiency: A Guide to Reducing Heat Loss

In this first edition of our newsletter this year, we'll examine the critical issue of heat loss in greenhouses and explore effective strategies for optimizing energy efficiency.

Greetings, greenhouse enthusiasts and horticulture professionals!

In this first edition of our newsletter for 2025, we'll examine the critical issue of heat loss in greenhouses and explore effective strategies for optimizing energy efficiency. As heating costs can account for more than 30% of total operating expenses in colder regions, understanding and mitigating heat loss is crucial for maintaining profitability in greenhouse crop production.

A special thanks to Thomas Thizy (greenhouse polyethylene expert) and Robert (Rob) Hanifin of RIDDER for their expert input.

Understanding Heat Loss Mechanisms

To effectively combat heat loss, it's essential to understand its primary mechanisms:

  1. Conduction Losses: Conduction is the main culprit behind heat loss in greenhouses. It occurs when warm interior air contacts the cooler greenhouse cover, transferring heat to the outside. The extent of this loss depends on the temperature differential and the insulating properties of the covering material.

  2. Convection: Losses occur when warm air escapes directly from the greenhouse through intentional ventilation or unintentional leakage. They are particularly significant during humidity-control ventilation.

  3. Leakage Losses: Infiltration losses can account for up to 20% of total heat loss. Cold air enters through openings or cracks, displacing warm air. Regular maintenance and proper sealing are crucial to minimize these losses.

  4. Radiation Losses: At night, heat stored in the greenhouse structure and plants is emitted as infrared radiation. If the greenhouse cover is not blocked, this contributes to overall heat loss.

Choosing the Right Roofing Materials

The selection of appropriate roofing materials is paramount in limiting heat loss. Let's compare some common options, ranked from least to most insulating:

  1. Single-glazed glass

  2. Single-wall polyethylene

  3. Double-walled polycarbonate (8 mm thick)

  4. Double glass

  5. Double-wall inflated polyethylene

  6. Double-wall inflated polyethylene (thermal inside layer)

  7. "Sandwich" insulating panels (e.g., Kingspan type, 3.5" thick)

The overall heat transfer coefficient (U) is a key factor in determining a material's insulating properties. A lower U-value indicates better insulation.

Inputs from Thomas Thizy, greenhouse polyethylene expert

Thomas Thizy, a greenhouse poly expert, explains that double-inflated poly significantly improves greenhouse insulation through two mechanisms: the dual poly layers act as a thermal barrier, while the air trapped between them creates an airtight insulating pad. This system, comprising a clear thermal PE external layer and an anti-drip treated internal layer, is inflated by a sensor-equipped engine to maintain optimal pressure.

Moreover, Thomas Thizy explains that thermal-treated greenhouse poly, made with EVA and mineral charges, significantly improves heat retention by blocking long infrared rays emitted by the soil at night. For example, a 6-mil thermal film retains about 65% heat compared to 40% for non-thermal, while a 7.2-mil thermal film can retain up to 75% versus 50% for non-thermal. However, exact percentages may vary based on specific formulations.

To conclude, Thomas Thizy explains that while poly thickness contributes to thermal efficiency, the optimal thermal covering for greenhouses combines three key factors: a 7.2-mil film, thermal treatment of both layers and an 8 cm air gap between them. This combination of elements provides superior insulation compared to relying solely on film thickness.

Spotlight: Single Glass vs. Double-Thermal Polyethylene

To illustrate the impact of material choice, let's compare single-glass and double-thermal polyethylene greenhouses:

  • Single glass: U ≈ 6.2 W/(m²-°C)

  • Double-thermal polyethylene: U ≈ 2.8 W/(m²-°C)

This represents a 54.8% improvement in thermal insulation for the double-layer inflated thermal polyethylene option. This significant difference explains why double polyethylene greenhouses are often preferred for greater energy efficiency, especially in colder climates (Joey Villeneuve, 2010).

Strategies to Reduce Heat Loss

  1. Installation of Thermal Screens
    Deploy thermal screens at night to create an additional barrier against heat loss. The choice of fabric quality is crucial, and many options are available.

  2. Insulating Foundations and Under-Crop Areas
    This measure reduces ground-level heat loss without affecting light levels.

  3. Use of Windbreaks
    Reducing wind speed around the greenhouse limits convection losses at the roof surface.

  4. Dehumidification
    Dehumidifiers control humidity without excessive ventilation, thus reducing heat loss. This strategy is particularly effective in semi-closed greenhouses.

  5. Smart Ventilation Management
    Optimize vent openings based on climatic conditions to balance humidity control and heat conservation.

A closer look at the thermal screen with Rob Hanifin

Exclusive expert input from Robert (Rob) Hanifin of RIDDER

Maximizing Greenhouse Efficiency: Thermal Screens Explained

Thermal screens have emerged as a critical technology for greenhouse operators seeking to reduce energy consumption and maintain optimal growing conditions. According to greenhouse climate expert Rob Hanifin, these innovative screens offer remarkable benefits for modern agricultural operations.

Energy Savings Potential: How much can we save?

Thermal screens can help reduce the energy needed to heat a greenhouse by up to 40% by effectively trapping heated air beneath them. This significant reduction in heating costs makes them an essential investment for greenhouse managers. However, the actual savings depend on multiple factors, including screen quality, installation precision, usage duration, and the specific greenhouse environment.

Winter Night Strategy

Hanifin emphasizes the critical importance of keeping screens completely closed at night, avoiding gaps that could compromise heat retention. Knitted climate screens provide an additional advantage by allowing moisture to escape, which helps manage greenhouse humidity levels.

Screen Selection Considerations

When choosing a thermal screen, growers should evaluate:

  • Energy saving properties

  • Light transmission characteristics

  • Humidity management capabilities

  • Specific crop requirements

  • Higher energy savings percentages

  • Enhanced light diffusion

  • Improved flame-retardant properties

  • More sophisticated climate management features

By implementing these expert strategies, greenhouse operators can significantly reduce operational costs while creating optimal growing environments.

The Importance of a Holistic Approach

Controlling heat loss in production greenhouses requires a comprehensive strategy. By combining judicious roofing material choices with appropriate climate management techniques, growers can significantly reduce energy costs while maintaining optimal crop conditions.

While the initial investment in insulation and climate control technologies may seem substantial, it often proves cost-effective in the long run, benefiting both the bottom line and the environment.

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Conclusion

Addressing heat loss in greenhouses becomes more critical as we face increasing pressure to optimize resource use and reduce environmental impact. Implementing the strategies outlined in this newsletter can help you create a more efficient and sustainable greenhouse operation.

Remember, every greenhouse is unique, and what works best for one may not be ideal for another. Consider consulting with greenhouse design experts or energy efficiency specialists to tailor these solutions to your specific needs.

We hope this newsletter has provided valuable insights into managing greenhouse heat loss. In our next issue, we'll explore innovative technologies in greenhouse automation.

Until then, happy growing!

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