Introduction
This document discusses the use of air curtains in industrial buildings to mitigate draughts caused by large volumes of cold air entering through open doors. It highlights the importance of a well-designed air curtain system to enhance comfort and energy efficiency.

Causes of Draught
Draughts in industrial buildings are primarily caused by:

• Building properties: Large, often non-leak-tight structures with multiple doors.
• Mechanical ventilation: Uncontrolled air inflow due to pressure differences.
• Wind effects: Wind-induced pressure differences across the building.
• Stack effect: Hot air rising and escaping, replaced by cold air at floor level.

Flow Profile and Neutral Height
The airflow through an open door is influenced by temperature and pressure differences, categorized by the neutral height:

• No net inflow: Two-sided flow with neutral height at half the door height.
• Low net inflow: Neutral height between half and three-quarters of the door height.
• Medium net inflow: Neutral height between three-quarters and full door height.
• High net inflow: Neutral height above the door height, dominated by pressure differences.

Design Rules for Air Curtains
Air curtains are designed to:

• Prevent warm air from escaping in low net inflow situations.
• Mix and heat incoming cold air in high net inflow situations.

Proper installation requires the air curtain to exceed the door width and minimize turbulence for effective performance.

Air Curtain Specifications
Air curtains are categorized by discharge jet width and velocity:

• Wide discharge jets (10 cm) with low velocity (4 m/s) provide higher heating capacity and are more energy-efficient.
• Narrow discharge jets (4 cm) with high velocity (16 m/s) have lower heating capacity.

Wide jets are preferred for sustainable energy consumption and compatibility with systems like heat pumps.

Conclusion
Effective air curtain systems are crucial for maintaining comfort and energy efficiency in industrial buildings with open doors. The choice of air curtain should be based on specific building conditions and airflow characteristics.

References
1. Cremers, B.E. (M.Sc.), ‘Computer simulations to support the development of climate separation products’. TVVL Magazine, August 2000.
2. Cremers, B.E. (M.Sc.), ‘Air Curtains: faster is not always better!’. TVVL Magazine, March 2003.