Often HVAC systems become contaminated during construction activities within a building. Newly installed HVAC systems should be clean before operated.
HVAC system inspections must be part of a building's overall indoor air quality management program.
Cleanliness-inspection scheduleHVAC systems should be routinely inspected for cleanliness by visual means. The table provides a recommended inspection schedule for major HVAC components within different building use classifications.
The inspection intervals specified in Table 1 are minimum recommendations. The need for more frequent cleanliness inspections is subject to numerous environmental, mechanical and human influences. Geographic regions with climates having higher humidity, for example, will warrant HVAC system inspections on a more frequent basis, due to the increased potential for microbial amplification.
If the inspection of the air-handling unit reveals contamination, then supply and return ductwork must be inspected at that time rather than in accordance with the intervals specified in Table 1.
System component inspectionsThe cleanliness inspection should include air-handling units and representative areas of the HVAC system components and ductwork. In HVAC systems that include multiple air-handling units, a representative sample of the units should be inspected.
The cleanliness inspection shall be conducted without negatively impacting the indoor environment through excessive disruption of settled dust, microbial amplification or other debris. In cases where contamination is suspected, and/or in sensitive environments where even small amounts of contaminant may be of concern, environmental engineering control measures should be implemented.
· The air-handling unit (AHU) cleanliness inspection should consider all components within the unit, including filters and air bypass, heat and cooling coils, condensate pans, condensate drain lines, humidification systems, acoustic insulation, fan and fan compartments, dampers, door gaskets and general unit integrity.
· The supply duct cleanliness inspection should consider a representative portion of ductwork, controls, mixing /VAV (variable-air volume) boxes, reheat coils and other internal components.
· The return duct cleanliness inspection should consider a representative portion of return system components including but not limited to return ducts, dampers, return plenums, make-up air plenums and grilles.
Microbial contaminantsThe HVAC system cleanliness inspection should include a check for microbial contamination. The inspection should evaluate the air-handling unit, humidifier and other representative system areas for microbial growth.
HVAC systems should be inspected at least twice annually when they have supplemental humidification or when they are in hot and humid climates.
When microbial sampling is performed, it shall be in accordance with ACGIH (American Conference of Governmental Industrial Hygienists) and AIHA (American Industrial Hygiene Association) industry guidelines.
Qualified personnel should perform the HVAC cleanliness inspection to determine the need for cleaning. At minimum, such personnel should have an understanding of HVAC system design, and experience in using accepted indoor-environmental-sampling practices, current industry HVAC cleaning procedures and applicable industry standards.
HVAC system cleaning shall be performed when any of the following conditions are found in the cleanliness inspection:
· HVAC systems should be operated in a clean condition. If significant accumulations of contaminants or debris are visually observed within the HVAC system, then cleaning is necessary. Likewise, if evidence of microbial growth is visually observed or confirmed by analytical methods, then cleaning is required.
If the HVAC system discharges visible particulate into the occupied space, or a significant contribution of airborne particles from the HVAC system into the indoor ambient air is confirmed, then cleaning is necessary.
See the guideline to this standard for discussion of the Aggressive Particle Profiling procedure, which may be used to confirm if nonvisible contaminants are being introduced into the indoor environment via the HVAC system.
· Heat-exchange coils, cooling coils, airflow control devices, filtration devices and air-handling equipment determined to have restrictions, blockages, or contamination deposits that may cause system performance inefficiencies, airflow degradation, or that may significantly affect the design intent of the HVAC system, shall be cleaned.
IAQ managementIndoor air quality management plans that include preventative cleaning and maintenance are recommended to minimize recurring contamination within HVAC systems. Special consideration should also be given to buildings or residences with sensitive populations such as immune-compromised individuals, and specialized environments or buildings with sensitive building contents or critical processes.
A project assessment must take place prior to commencing with cleaning work. The project assessment includes three steps:
· Building usage classification
· HVAC contamination evaluation
· Environmental impact assessment
The HVAC contamination evaluation and the environmental impact assessment must include a visual evaluation of representative sections of the HVAC components and the occupied spaces served by the HVAC system. This evaluation serves to assess conditions within the HVAC system and the physical integrity of system components and surfaces.
Information collected from the project assessment should be used to define the scope of the cleaning and restoration project, cleaning methods to be employed, the environmental engineering controls required for the workspace and any unique project requirements.
Contamination evaluationCleaning methods, project specifications, environmental engineering controls and cleanliness verification methods may vary depending on the type of contaminants found within a building and its HVAC system. Recognizing the type of contaminants present and the type of HVAC system(s) within the building are important parts of the overall project assessment.
The HVAC systems, including air-handling units and representative areas of the HVAC system components and ductwork, must be evaluated for contamination levels.
An HVAC system component is considered contaminated when evidence of significant particulate debris and/or microbial growth exists. A system is considered to have microbial contamination when the HVAC cleanliness evaluation identifies microbial growth through visual inspection and/or analytical verification.
Relative to the classification of the building, the types of contaminants present shall determine cleaning methods and environmental engineering controls required:
· The air-handling unit contamination evaluation should consider representative sections of components within the unit, including but not limited to: filters and air bypass, heat and cooling coils, condensate pans, condensate drain lines, humidification systems, acoustic insulation, fan and fan compartments, door gaskets, and general unit integrity.
· The supply duct contamination evaluation should consider representative portions of supply ductwork, mixing/VAV boxes, thermal-acoustical lining condition, reheat coils and other duct components.
The return-duct contamination evaluation should consider a representative portion of all return system components including but not limited to return ducts, dampers, return plenums, thermal-acoustic lining condition, makeup air plenums and grilles.
The activities associated with HVAC system hygiene evaluation work, system cleaning and restoration of HVAC components, have the potential to adversely influence a building's indoor environment if not properly performed. Of primary concern is the disturbance of materials and the potential for release of contaminants into occupied areas.
Engineering controls must be used to manage the workspace environment during cleaning and restoration work. Such controls also serve to keep HVAC contaminants from entering indoor spaces. An indoor environmental impact assessment must be performed to help determine appropriate environmental engineering controls for a project.
(To order a copy of NADCA's duct-cleaning manual, write to NADCA, 1515 K St. N.W., Suite 503, Washington, DC 20005; call (202) 737-2926; fax (202) 347-8847.)