Understanding AHU & FCU Classification in HVAC Systems



The unsung heroes of the intricate world of HVAC (Heating, Ventilation, and Air Conditioning) are Air Handling Units (AHU) and Fan Coil Units (FCU). These dynamic elements constitute the foundation of every temperature control system, yet many people are unaware of or misunderstand the many classifications and uses for them. We peel back the layers of AHU and FCU categorization in this thorough investigation, offering vital insights for engineers, technicians, and students eager to learn the craft of HVAC systems.

A Deep Dive into AHU Classification

AHUs are the powerhouse of ventilation, capable of moderating air temperatures, humidity, and distribution. Within the AHU realm, there are various classifications that dictate their function and usage.

Types Based on Configuration

  • Single-Zone: Designed to condition a single area with air at a constant temperature and humidity, these are commonly found in small to medium-sized buildings with uniform climate needs.
  • Multi-Zone: With the capacity to serve several areas independently, these AHUs are ideal for structures with diverse climate zone requirements like mixed-use buildings.
  • Variable Air Volume (VAV): A more sophisticated system that adjusts the air flow and temperature based on real-time demand, providing significant energy savings in larger facilities.

Types Based on Operation

  • Constant Air Volume (CAV): The most widely used and straightforward AHU function. It is appropriate for situations where variable air volumes are not needed since it provides a constant air volume at a constant temperature.
  • changing Air Volume (VAV) Systems dynamically modify the air volume supply to maintain a constant temperature and air quality, making them ideal for spaces with changing occupancy.
  • Dual Duct: By using two ducts—one for warm air and one for cool air—these systems expand on the adaptability of VAV. Although they offer precise climate control, their intricate design results in worse energy efficiency.