Ontario’s hot and humid summers pose challenges for livestock and poultry, making effective barn cooling essential to prevent heat stress and production losses. The two primary cooling methods are air-based and water-based systems, with tunnel ventilation being the most common air-based approach. This document outlines the principles, design, and management of tunnel ventilation, with and without evaporative cooling, to optimize barn environments.
Tunnel Ventilation: How It Works
Tunnel ventilation operates by drawing fresh air through inlets on one end of the barn and exhausting it through fans on the opposite end. This creates a high-speed airflow, mimicking a wind tunnel effect that cools animals through convection. Airspeeds of 1.0–2.5 m/s (200–500 ft/min) are typical, with newer systems designed for even higher speeds for improved cooling efficiency.
Research shows that at 2 m/s (400 ft/min), the wind chill effect lowers the effective temperature by approximately 3.7°C, leading to improved animal growth rates. However, tunnel ventilation is not recommended for young or sensitive animals, as excessive airflow can be stressful at lower ambient temperatures.
Enhancing Tunnel Ventilation with Evaporative Cooling
When temperatures exceed 40°C, additional cooling is required. Evaporative cooling pads are increasingly used in Ontario barns to lower incoming air temperatures. These pads work by pulling air through a water-saturated medium, which removes heat through evaporation while increasing humidity.
Properly designed evaporative cooling systems can achieve 55–75% efficiency, provided air velocity through the pads remains within recommended limits. However, excessive humidity (above 80%) can be detrimental, particularly for poultry, as it hinders their ability to release heat through panting.
Key Design Considerations
Fan Capacity & Placement: The number of fans needed depends on barn dimensions and target airspeed. Large, energy-efficient fans (typically 1,200 mm/48 inches in diameter) are standard. Recent advancements in variable-frequency drive (VFD) technology allow for greater energy savings and precise airflow control.
Air Intake Sizing & Location: Properly sized inlets ensure adequate airflow distribution. Ideally, air inlets should be located on the end wall to prevent dead air zones. Service rooms and external wind patterns can also impact airflow efficiency, requiring strategic placement of obstructions and deflectors.
Control Strategies: Tunnel ventilation operates in multiple stages, adjusting fan speeds based on barn temperature. VFD fans offer gradual speed adjustments, improving energy efficiency and reducing sudden temperature fluctuations.
Potential Challenges & Solutions
- Dead Air Zones: Avoid placing air inlets on sidewalls, as this disrupts airflow direction.
- Obstructed Airflow: Service rooms should be placed near exhaust fans rather than at air inlets.
- External Wind Interference: Deflectors at inlets help maintain uniform air distribution.
- Humidity Control: Monitor relative humidity to prevent excessive moisture buildup that could stress animals.
Conclusion
Tunnel ventilation remains the most effective air-based cooling method for Ontario barns, with evaporative cooling becoming an increasingly necessary supplement in extreme heat. Proper system design, fan placement, and control strategies can significantly enhance animal comfort and productivity while improving energy efficiency. By integrating these technologies effectively, livestock operations can mitigate heat stress and maintain optimal production levels throughout Ontario’s hot summers.
