7.7.1 Introduction

Air curtains are local ventilation devices that are used in industrial buildings to re­duce leakage of airflow through apertures in building enclosures and process equipment. Their operation is based on the damping effect of air jets that are sup­plied into the area of the open aperture. The advantages of air curtains include

• Improvement of working conditions near open apertures

• Reduction of heat (cold) consumption and electrical energy for heating (cooling) of buildings and process equipment

• Reduction of heat loss in the building by using overheated air from an upper zone of the room

• Reduced loss of usable working area near gates due to the ingress of outdoor air into the building

Traditional air curtains, which utilize only indoor air heated in the curtain heaters, are not always economical (due to considerable thermal energy con­sumption). Reduction of heat consumption is achieved by curtains that utilize unheated indoor or outdoor air, and also combined air curtains, which heat 3only part of the supplied air. Air curtains that use unheated air conserve 30­70% of thermal energy.