By Bob Krell, President, IAQ Technologies, Inc.
Few building owners or facility managers would argue whether HVAC (heating, ventilating, and air conditioning) systems are important factors in a building’s indoor environment. After all, it seems only logical that the systems relied upon to condition and transport air through a facility would play a key role in the quality of the air in an 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 HVAC in particular, take a back seat in the spending line.
HVAC Hygiene is a Key Component to IAQ
An important component in a successful IAQ strategy is regular hygiene maintenance of any facility’s HVAC systems. Left un-serviced over time, these systems may become filled with debris and subsequent amplified microbial growth. When poorly maintained, internally insulated components such as fibrous thermal/acoustic lining and ductboard can begin to break down and shed fibers into the air stream. These conditions may be compounded by the fact that regular inspections for cleanliness and performance of air handling systems (AHS) fans, coils, airflow control devices, and ductwork are rarely performed. Of course, the lack of such a maintenance strategy is short-sighted, since it is these HVAC systems that are relied upon to remove a building’s foul air and replace it with clean, conditioned air. Facility renovations may serve to complicate matters by altering airflow patterns, changing area usages, and introducing many contaminants. Without a deliberate program in place to monitor the performance and maintenance of the HVAC systems, it is difficult to provide acceptable indoor air quality at a facility.
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 IAQ, and may even be the problem source. The common deficiencies include air handling units (AHUs) that collect and hold water, inadequate filtration, improper sizing for cooling and dehumidification (which can lead to excessive moisture downstream in the supply air side of the system), insufficient airflow to occupant breathing zones, and poor maintenance access design for duct systems. In many cases, a facility’s HVAC system suffers from several (or all) of these problems, resulting in compromised indoor air quality and increased mechanical operating costs.
Problems are not limited to inadequate designs—in fact, poor installation of components is also a major source of potential IAQ trouble. For example, even a properly designed condensate drain system will malfunction and hold water if the pan is not 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 IAQ problems in areas served by that HVAC 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 internal insulation with excessive moisture and subsequent microbial growth from duct leakage, or one of the earlier mentioned problem sources, and the liner breakdown will accelerate.
Poor AHS design and installation can lead to excessive contamination and create potentially serious indoor environmental problems for a facility. This is especially true when combined with a lack of regular HVAC hygiene maintenance. Since systems are rarely designed to facilitate inspections and cleaning, such proactive remedial action becomes more cost prohibitive, and as a result (unfortunately) may not be performed.
Internal system contamination can adversely affect IAQ in several ways. Dust and debris are constantly entering an HVAC system through its outside air intakes, return air grills, and any air 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 contaminants; the remainders migrate through the AHU and the downstream (supply) side of the HVAC system. The buildup of gross debris in the ductwork and on system components such as coils, turning vanes, and dampers can impede air flow.
These restrictions may limit the system’s ability to provide the necessary air changes in the facility and ultimately degrade IAQ in the building. Dirty systems experience higher static pressure drops across system components, as well as decreased thermal transfer from coils, which can also lead to increased facility operating costs. Debris can also make it difficult or even impossible to properly balance an HVAC system.
A sound approach to managing IAQ risks must include a thorough inspection, and cleaning (if necessary) of a facility’s HVAC systems by qualified professionals on a regular basis. Verifying that the HVAC systems are clean is also important prior to air balancing, as delivery rates can be greatly affected by contamination buildups.
This is especially true in bathroom and shower exhaust systems. It is often misconceived that since exhaust systems vent directly outside, they have little effect on a facility’s indoor air quality. However, these exhaust systems may play a critical role in pressure relationships, and ultimately, in supply air delivery rates to occupied areas. Inadequate exhaust ventilation, of course, may also lead to unpleasant odors and indoor air pollution.
Getting Your Ducts in a Row
It is important to have a clear understanding of the procedural game-plan and the attainable goals before contracting for HVAC cleaning services. Hospitals and other facilities with susceptible occupant populations or sensitive operations warrant special care with regards to containment controls. Without such clear-cut objectives in place prior to commencing a cleaning project, the outcome may fall well short of the client’s expectations at a minimum, or even create threats to the health and well-being of the building’s occupants.
HVAC system cleaning alone may (at times) be a symptomatic treatment, rather than an actual cure to an existing IAQ problem. For successful remediation, it is essential to address the source of the IAQ 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.
Once the IAQ problem source is identified and 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:
- The Building Population – The demographic’s susceptibility to potential indoor environmental pollutants, odors, noise, etc.
- The Facility & Its Activities – Building use (office, patient care, laboratories, classrooms, residences, etc.), hours of occupancy, custodial/maintenance practices, renovations, and building age.
- The AHS Contamination – The nature of the contamination (microbial contamination, general nuisance dust, construction debris, hazardous materials, etc.), the degree of contamination within the system, and the necessary indoor environmental controls/containment measures for safely implementing the project.
- HVAC System Design & Accessibility – AHS configuration (rooftop units, mechanical rooms, ceiling plenums, underground duct systems, ductwork covered plaster/gypsum board, non-removable ceiling components, etc.), types of components (internally-lined ductwork or ductboard, flex duct, transite pipe, control devices, reheat coils, diffusers, etc.).
Properly managed AHS cleaning projects, in conjunction with corrective measures to any IAQ problem sources, provide a more comprehensive approach to improving indoor environmental quality. To maximize project results and minimize hassles it is essential for the aforementioned consideration points to be thoroughly discussed and understood by the cleaning contractor, the client, and any other third-party consultants or contractors, prior to commencement.
For additional information and videos about air duct cleaning & HVAC hygiene, check out the cover story in the March 2015 issue of Healthy Indoors Magazine: http://hi.healthyindoors.com/i/475354-hi-march-2015/37, and visit the National Air Duct Cleaners Association (NADCA) website at: https://nadca.com/
Bob Krell is president of IAQ Technologies, Inc., a Syracuse, NY-based indoor environmental firm offering consulting, mitigation and training services. He has been a nationally recognized indoor environmental consultant and trainer in the IAQ industry for over 27 years, having designed and managed successful indoor environmental projects for residential, commercial, educational, and healthcare facilities throughout the U.S. and abroad, and has conducted hundreds of investigations since 1990. He can be contacted at bkrell@IAQ.net. Connect with him at https://www.linkedin.com/in/bobkrell/ and https://twitter.com/IAQMAN