How Does An AHU Improve Indoor Air Quality?

How Does An AHU Improve Indoor Air Quality?

1. Filtration of Airborne Contaminants

AHUs are equipped with multi-stage air filters that remove harmful particles and pollutants from both incoming fresh air and recirculated indoor air. This includes:

Dust, pollen, and pet dander (common allergens).

Mold spores and bacteria (which thrive in moist environments).

Particulate matter (PM2.5, PM10) from outdoor pollution or indoor sources (e.g., cooking, smoking).

Volatile Organic Compounds (VOCs) in some advanced systems (using activated carbon filters).

Filters vary in efficiency (e.g., MERV ratings for particle capture), and AHUs are designed to accommodate higher-grade filters (e.g., HEPA filters in hospitals) to meet strict IAQ standards.

2. Introduction of Fresh Outdoor Air

Stale indoor air can accumulate carbon dioxide (CO₂), odors, and harmful gases (e.g., from cleaning products or appliances). AHUs address this by:

Using mixing chambers to blend a controlled volume of fresh outdoor air with recirculated indoor air.

Adjusting the ratio of fresh to recirculated air (via dampers) based on occupancy or CO₂ levels (monitored by sensors).

This ensures a steady supply of oxygen, dilutes pollutants, and prevents the buildup of stale air—critical for spaces with high occupancy (e.g., offices, schools, airports).

3. Humidity Regulation

Excess humidity promotes mold growth and dust mite infestations, while low humidity causes dry skin, irritated eyes, and respiratory discomfort. AHUs actively control humidity through:

Dehumidifiers: Cooling coils that condense moisture from air (removing excess humidity in humid climates).

Humidifiers: Steam injectors or evaporative pads that add moisture to dry air (common in cold, dry regions).

By maintaining optimal humidity levels (typically 30–60%), AHUs reduce the risk of mold, improve comfort, and preserve building materials (e.g., wood, paint) that can warp or degrade with extreme moisture.

4. Temperature Control

Consistent temperature is key to comfort, but fluctuations can also impact IAQ (e.g., condensation from cold surfaces promotes mold). AHUs regulate temperature by:

Passing air over heating coils (using hot water from a boiler or electric heaters) to warm air in cold conditions.

Passing air over cooling coils (using chilled water from a chiller) to cool air in hot conditions.

This ensures uniform temperature distribution across large spaces, preventing hot/cold spots that could compromise IAQ.

5. Air Circulation & Ventilation

Stagnant air allows pollutants to settle and accumulate. AHUs use powerful fans to:

Circulate conditioned air through ductwork to all areas of a building, ensuring even distribution.

Remove stale air via return ducts, which is then either recirculated (after filtration) or exhausted outdoors.

Proper airflow prevents pockets of poor air quality, such as in corner offices or basements, and ensures that treated air reaches every zone.

6. Integration with IAQ Monitoring Systems

Modern AHUs often connect to Building Management Systems (BMS), which use sensors to monitor IAQ metrics (CO₂ levels, humidity, particle counts). The BMS automatically adjusts AHU operations—for example:

Increasing fresh air intake if CO₂ levels rise (indicating high occupancy).

Boosting filtration or humidity control if mold spores are detected.

This real-time adjustment ensures IAQ remains consistent even as conditions change.