Few building owners or facility managers would argue that HVAC systems are important
factors in a building\'s indoor environment. After all, it only seems logical that the systems
relied upon to condition and transport air throughout a facility would play a key role in the
quality of the air in occupied building space. As such, one would expect that in these times
of rampant litigation and media frenzies, due consideration would be given to the design,
installation, and maintenance of these air handling systems. Unfortunately, in the real
world, budget cuts and limited financial resources in general often dictate that indoor air
quality, and ventilation system in particular, take a back seat in the spending line. One of
the most important components in a successful indoor air quality strategy is regular hygiene
maintenance of any facility\'s heating, ventilating and air conditioning (HVAC) systems. Left
unserviced over time, HVAC systems may become filled with debris and subsequent amplified
microbiological growth. Internally insulated system components such as fibrous acoustic
lining and ductboard can begin to breakdown and shed fibers into the air stream.
Until recently regular inspections for cleanliness and performance of air handling systems
(AHS) fans, coils, airflow control devices, and ductwork were rarely performed. Such a
limited maintenance strategy is short-sighted since it is these HVAC systems that are relied
upon to remove the building\'s foul air and replace it with clean, conditioned air for a safe,
comfortable indoor environment. Plant renovations may serve to complicate matters by altering
airflow patterns, changing area usage, and introducing many contaminants. Without a
deliberate program in place to monitor the performance and maintenance of the HVAC air
handling systems, it is difficult to provide acceptable indoor air quality at a facility.
Internal system contamination can adversely affect indoor air quality in several ways. Dust
and debris are constantly entering an HVAC system through the outside air intakes, return air
grills, and any leaks on the negative pressure side of the system. At best, filtration in the
air handling unit (AHU) can only remove a portion of the potential contaminants. The
remainder migrates through the downstream side of the HVAC system. The build-up of debris in
HVAC ductwork and on system components such as coils, turning vanes, and dampers can impede
These restrictions may limit the HVAC system\'s ability to provide necessary air changes in
the facility, and ultimately degrade indoor air quality in the building. Obstacles To Indoor
Major stumbling-blocks in maintaining HVAC system hygiene are their design and installation.
The unfortunate fact is that most air handling systems are not designed with indoor air
quality in mind. As a result, HVAC systems often operate in ways that adversely affect indoor
air quality, and may even be the problem\'s source.
The common deficiencies include AHUs that collect and hold water, inadequate filtration,
improper sizing for cooling/dehumidification (which can lead to excessive moisture in the
supply air side of the system), and general poor airflow and maintenance access design for
duct systems. In many cases, a facility\'s HVAC system suffer from several (or all) of these
problems, resulting in compromised indoor air quality and increased mechanical operating
Problems are not limited to inadequate designs, in fact poor installation of components is
also a major source of trouble. For example, even a properly designed condensate drain system
will malfunction and hold water if the pan isn\'t correctly pitched when the unit is
installed. In such cases, the standing water becomes a potent breeding ground for fungi and
bacteria which can create serious indoor air quality problems in areas served by that system.
Another common problem is poor quality installation of internal fibrous AHS linings, which
can lead to insulation breakdown and fiber shed into the supply air stream. Combine poor
workmanship of the internal insulation with excessive moisture and subsequent fungal growth
from duct leakage or one of the earlier mentioned sources, and the liner breakdown will
A sound approach to managing indoor air quality risks must include a thorough inspection and
cleaning (if necessary) of the air handling systems by qualified professionals on a regular
HVAC system cleaning alone may be a symptomatic treatment, rather than an actual cure to an
existing indoor air quality problem. For successful remediation, it is essential to address
the source of the indoor air quality problem that is causing the contamination in the AHS.
Otherwise, even the most thorough HVAC cleaning procedures will only provide short-term
benefits to a building\'s indoor air quality. Key Maintenance Considerations
Once the indoor air quality problem source is corrected, HVAC hygiene measures can be
implemented more effectively. There are at least several key considerations to be made when
designing an AHS cleaning project at any facility. They include:
Building Population - Their demographics, susceptibility to potential indoor environmental
pollutants, etc. Facility & Its Activities - Building use (office, patient care,
laboratories, classrooms, operating rooms), hours of occupancy, custodial/maintenance
practices, renovations, and building age. AHS Contamination - The nature of the contamination
(i.e. mold, dust, construction debris, hazardous materials), the degree of contamination
within the facility\'s AHS, and the necessary containment measures for safely implementing the
project. HVAC System Design & Accessibility - AHS configurations (roof packages, mechanical
rooms, ceiling plenums, underground duct systems, ductwork covered by plaster or non-
removable ceiling components, etc.), types of components (such as VAV boxes, internally-lined
metal ductwork, ductboard, flex ducts, transit pipe, and reheat coils).
To maximize project results and minimize hassles, it is essential for these points to be
thoroughly discussed and understood by the cleaning contractor, the client, and any other
third-party consultants involved, prior to commencement. Hazardous Materials
Many older facilities have materials such as asbestos insulation in duct chases and areas
above finished ceilings. Such contaminants could pose serious safety hazards to cleaning
technicians, occupants, and facility staff, and present potential liability pitfalls, if not
properly handled. Visible moisture and animal debris in the AHS are also clear warning signs
which indicate the need for action.
In the case of animal debris remediation, extreme care with limited technician exposure and
containment is essential, as they may present an immediate health threat. Service personnel
should safely discard protective clothing and immediately scrub-down face and hands with
antibacterial cleaner after leaving the work area. Any equipment which was in contact with
the contaminated area should be thoroughly cleaned and sanitized prior to reuse. Planning For
How can a building manager ensure the best quality work for their dollar spent? It all starts
with creating good bid specifications, especially in competitive bidding situations. This is
your only way to get competitive bids on an "apples-to-apples" scope of work. Determine how
the remediation work will be verified for acceptance, and include that with bid
specifications. You should gain a clear understanding of what remediation methods will be
employed and exactly how the work will be done. OSHA Confined Space regulations may have a
direct impact on what procedures should be used on a given project.
Above all, building occupant exposure to contaminants being removed from the HVAC systems and
any chemical products must be controlled. Applicable containment procedures should be
determined and followed for any HVAC cleaning/remediation project.
Many projects may warrant a building manager\'s use of outside consultants to assist the
facility\'s engineering staff in verifying the need for cleaning, specification development,
contractor selection, and even project quality monitoring. When looking for a consultant,
choose one who has specific experience and expertise in HVAC systems hygiene remediation.
Ideally, a qualified consultant should have visual inspection and imaging equipment to
monitor pre/post conditions in the HVAC systems.
In summary, it is vital for there to be a clear understanding between you and the service
contractor as to the project\'s goals, specific considerations, and method of verification and
acceptance for an HVAC hygiene remediation, prior to bid acceptance and project commencement.
Hygiene remediation projects at facilities pose many potential problems for a service
contractor, which must be addressed to ensure a satisfactory end result. This is no job for
amateurs. The building manager should look for service providers with specific experience,
bring in qualified consultants when necessary, ask a lot of questions, and above all,
scrutinize the answers.
Bob Krell is first vice-president of the National Air Duct Cleaners Association (NADCA) and
is president of IAQ Technologies, Inc., a Syracuse, N.Y.-based firm providing consulting,
remediation and training throughout the U.S.