1. Introduction to AHU
AHU (Air Handling Unit), also known as an air conditioning box or air handler, is a key component in HVAC systems. It primarily works by circulating indoor or outdoor air through internal heat exchange coils while filtering impurities, thereby regulating temperature, humidity, and air quality.
AHUs can operate in two modes:
- Recirculation mode: Processes only indoor air.
- Fresh air mode: Draws in outdoor air for ventilation and conditioning.
2. Main Components of an AHU
AHUs are modular and can be customized based on specific application needs. The configuration may vary among manufacturers, but generally, an AHU consists of the following key sections:
2.1 Fresh Air Section
- Function: Introduces outdoor air and removes large airborne particles.
- Components: Fresh air damper with an actuator, linked to the fan operation.
- Optional: Temperature sensors placed in shaded outdoor areas to assist in return air temperature compensation.
2.2 Filtration Section
- Function: Filters impurities from fresh and return air to maintain air quality.
- Types of Filters:
- Primary (Coarse) filter: Removes large dust particles.
- Medium filter: Captures smaller pollutants.
- High-efficiency filters (optional for cleanroom applications).
- Additional Feature: Differential pressure sensors installed before and after filters to detect clogging and trigger maintenance alerts.
2.3 Return Air Section
- Function: Mixes fresh and return air for energy efficiency.
- Components:
- Return air damper with actuator for regulating airflow.
- Exhaust air damper—acts in opposition to the return air damper.
- Humidity and temperature sensors to monitor indoor conditions and adjust cooling, heating, or humidification accordingly.
2.4 Cooling Coil Section
- Function: Cools the air and removes humidity.
- Components:
- Cooling coil with a three-way control valve to regulate chilled water flow.
- Frost protection switch—linked to fans and dampers to prevent coil freezing.
- Working Mechanism:
- The valve modulates based on return air temperature and humidity.
- Excess chilled water is bypassed to prevent excessive pressure buildup.
2.5 Heating Section
- Function: Provides heating in winter or reheats air after overcooling during dehumidification.
- Types:
- Hot water heating coils (used in two-pipe systems, where the same coil is used for cooling and heating).
- Electric heating elements (for additional heating when required).
2.6 Humidification Section
- Function: Adds moisture to prevent dryness in winter or to meet specific industrial requirements.
- Types of Humidifiers:
- Evaporative (wet membrane) humidifier.
- Steam humidifier (for precise control).
2.7 Fan Section (Supply Air Section)
- Function: Distributes conditioned air into the indoor space.
- Components:
- Fan motor and blower assembly.
- Air outlet damper with an actuator (optional).
- Control: The fan operation is linked with dampers to optimize airflow and energy efficiency.
3. Summary of AHU Components and Functions
| AHU Section | Function | Key Components |
|---|---|---|
| Fresh Air Section | Introduces and pre-filters outdoor air | Fresh air damper, actuator, outdoor temp sensor |
| Filtration Section | Removes dust and pollutants | Primary, medium, and high-efficiency filters, pressure sensors |
| Return Air Section | Mixes fresh and return air for energy efficiency | Return & exhaust dampers, temperature & humidity sensors |
| Cooling Coil Section | Lowers temperature and removes humidity | Cooling coil, three-way valve, frost protection switch |
| Heating Section | Provides heating when needed | Hot water coils, electric heating elements |
| Humidification Section | Adds moisture to maintain humidity levels | Wet membrane or steam humidifier |
| Fan Section | Distributes conditioned air to indoor spaces | Fan motor, blower, outlet damper |
By understanding the key components and functions of an AHU, HVAC systems can be optimized for energy efficiency, comfort, and air quality. 🚀
AHU (Air Handling Unit) Components and Functions