Air Handler Unit Anatomy

It is crucially important to understand the basic air handler unit anatomy of a chilled water HVAC system. This knowledge successfully steers the cleaning and maintenance for each section of the AHU. It also provides visibility to its respective impact on system performance, indoor air quality, and energy efficiency. ASHRAE Standard 62.1 Section 8 gives detailed information on the regular inspection and cleaning of these components. However, guidelines may vary depending on the manufacturer and design of the AHU in question.

Air Handler Unit Anatomy

Below you will find a brief description of the main sections of the air handler unit anatomy based on the typical direction of airflow through the system. Also noted are common concerns and recommendations for maintenance.

  1. Intake Section:

The intake section of the AHU is responsible for drawing in outdoor air or recirculating indoor air. It typically consists of grilles, dampers, and filters. Regular cleaning and maintenance of filters are crucial to maintain good indoor air quality by removing particulate matter, dust, and allergens. Clogged or dirty filters can lead to reduced airflow, increased energy consumption, and decreased system performance. Regular filter replacement or cleaning is essential to prevent pressure drop across the filters and ensure efficient operation of the AHU.

  1. Mixing Chamber:

The mixing chamber blends the outside and return air to achieve the desired air temperature and humidity levels. It may contain dampers, actuators, and sensors. Regular inspection and cleaning of dampers and actuators are necessary to ensure their proper functioning, as any malfunction can disrupt the air distribution and temperature control. Moreover, cleaning the mixing chamber itself helps to prevent the accumulation of dirt, debris, or microbial growth, which can adversely affect indoor air quality and system performance.

  1. Cooling and Heating Coils:

The cooling and heating coils are responsible for heat transfer and conditioning the air. These coils are typically made of finned tubes and can accumulate dirt, dust, and microbial growth over time, reducing their efficiency. Regular cleaning and maintenance of these coils are essential to ensure proper heat transfer, optimize energy efficiency, and prevent the risk of contamination in the air stream. Cleaning methods may vary based on coil type and manufacturer recommendations.

  1. Drain Pan and Condensate Drainage System:

The drain pan collects condensate generated by the cooling coils and directs it to the condensate drainage system. Regular cleaning of the drain pan, and proper maintenance of the drainage system are crucial to prevent microbial growth, clogs, or blockages. Accumulated moisture and microbial growth in the drain pan can lead to mold and bacteria dispersion, affecting indoor air quality. Additionally, clogged, or obstructed drain lines can cause water leakage, leading to equipment damage and potential indoor air quality issues.

  1. Supply Air Plenum and Ductwork:

The supply air plenum and ductwork distribute the conditioned air to various areas within the building. These components can accumulate dirt, dust, and biological contaminants over time. Regular cleaning and maintenance of the supply air plenum and ductwork are necessary to prevent the buildup of contaminants and ensure the delivery of clean, high-quality air to occupied spaces. Clean ductwork also helps to maintain system performance and energy efficiency by reducing pressure losses and minimizing airflow restrictions.

ASHRAE 62.1 Section 8

ASHRAE Standard 62.1, titled “Ventilation for Acceptable Indoor Air Quality,” provides guidelines for the design, construction, and operation of HVAC systems to achieve acceptable indoor air quality. Section 8 of this standard focuses on maintenance and operations based on air handler unit anatomy. While it does not specifically address air handler unit cleaning, it emphasizes the importance of proper maintenance, including filter maintenance, inspection, and cleaning, to ensure adequate ventilation effectiveness and system performance. Regular cleaning of AHU components is often a part of a comprehensive maintenance program that aligns with the intent of ASHRAE 62.1 to maintain good indoor air quality.

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