AHU Coil Cleaning

Methods & Processes for AHU Coil Cleaning

The process of AHU coil cleaning can be broadly divided into steps and types as defined (for example) in the NADCA ACR 2021 standard. Below is an adapted, practical workflow tailored for Clean Air 24 Seven’s operations, integrating TR19 Air compliance and NAAD21 quality.

Pre-Cleaning Assessment & Access

• Before touching a coil, a visual and mechanical inspection is carried out: check for fin damage, corrosion, microbial film, drainage issues, and access limitations.
• If no adequate access panels exist near the coils, additional access may need to be created to comply with TR19 Air’s requirement that “access to all AHU sections is required for adequate cleaning.”
• Document the “before” condition with photographs and notes. As advised by TR19 Air, building owners or facility managers should have records and verification of cleanliness.

Dry Cleaning (Type 1)

This is the first stage, aimed at removing loose particulate without introducing moisture:

• Use HEPA-filtered vacuuming to suck loose dust and debris from coil surfaces and fin spaces.
• Employ soft or nylon coil brushes (or fin combs) to gently dislodge particles, always moving in the direction of airflow (to avoid damaging fins).
• Use low-pressure compressed air lances or “air lancing” (per TR19 internal cleanliness guidance) to push residual debris out of the coil face.
• During all dry cleaning, we isolate the coil from the duct system so that dislodged debris does not migrate further. Negative air filtration or containment may also be used.
• If post-dry cleaning inspection shows residual dirt or adhered contamination, then proceed to wet cleaning.

Wet Cleaning (Type 2)

Wet cleaning is required when deposits are adhered (greasy film, microbial biofilm, sticky particulate) and cannot be removed by dry means:

• Apply coil-safe cleaning chemical agents (ideally near-pH-neutral, non-corrosive detergents) compatible with coil materials.
• Gentle rinsing with water (often low-to-moderate pressure) or pressure-wash techniques, ensuring adequate capturing or containment of rinse water (especially for coils mounted “in-line” without integral drain pans). NADCA guidance emphasizes precautions to capture rinse water when wet cleaning duct-mounted coils without drain pans.
• Steam or hot water cleaning may be used if appropriate and safe for the coil materials.
• Clean, flush and inspect the condensate drain pan and lines; if blocked, flush them and re-check drainage flow. A clogged pan can compromise coil performance and promote microbial growth.
• Allow full drying before returning the AHU to service; on electric resistance coils, ensure they are dry before energising. NADCA ACR 2021 requires rinsing free of chemicals, thorough drying, and de-energising prior to re-energising.

Post-Cleaning Verification & Documentation

After cleaning, perform a post-inspection: visually check coil fins and surfaces, measure static pressure drop across the coil before and after cleaning to quantify improvement (as recommended by NADCA).

• For a TR19 Air–compliant service, you may carry out more stringent verification (e.g. random swab or particulate measurement) depending on risk class and client requirements.
• Produce a cleanliness report: “before / after” photos, measurement data, description of methods used, and declaration that the coil meets agreed cleanliness thresholds. This documentation supports facility managers, compliance audits, and insurance or regulatory demands.
• Advise on maintenance intervals and actions to protect cleanliness (e.g. better filtration, sealing leaks, regular inspections).

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