Healthy Indoors Magazine
Issue link: https://hi.healthyindoors.com/i/1179928
18 | October 2019 The various system components like coils and air control devices also dictate specific cleaning methods. Different duct types call for different cleaning techniques. More aggressive methods can easily damage fibrous glass ducts, coil fins and gaskets, so that always must be taken into account. Many HVAC systems use a combination of some (or all) of these duct types, which may require the need for multiple cleaning techniques on a given project. A second consideration is the nature of the contamination in the system. Is it simply a benign form of common nuisance dust from the building, or something of greater concern such as contamination from microbiological or regulated hazardous ma- terials like asbestos or lead? In the case of regulated materials, the HVAC cleaning procedures must defer to procedures spec- ified by appropriate regulatory agency that governs its handling. Another very important factor is the type of building where the HVAC system in question is located. There are significant differences in how you should handle cleaning a single-story ranch house versus a hospital operating room. While engi- neering controls are important for all projects, they become increasingly more critical in acute care environments. Some facilities necessitate the use of portable containment enclo- sures, HEPA air scrubbers for ambient air, and ongoing moni- toring to ensure that the HVAC cleaning work doesn't adverse- ly affect the indoor environment. Some indoor environmental engineering controls are needed on any job, and ensuring the proper measures are taken is paramount to achieving success with a project. Af- bility of cross-contamination from vacuum exhaust. Large commercial ducts sized sufficiently for technicians to en- ter also have commonly been cleaned by contact vacu- uming with brush attachments connected to smaller HE- PA-equipped shop-vac style vacuums. This technique can yield excellent results when access is available. As a rule, the size and capacity of the vacuum collection device dictates the amount of ductwork that can be effective- ly cleaned from each set up point. More powerful collection equipment can potentially clean longer duct runs, but that fac- tor alone does not always mean such equipment does a better job. HVAC systems can often be zoned-off for cleaning work to allow the effective use of smaller collection devices. Cleaning efficacy is more dependent on the effectiveness of the agitation method and the thoroughness of the techni- cians performing the actual work, than the actual size of the vacuum collection unit. So, it's not necessarily how big it is, but how you use it (yeah, I went there...). Not All Ducts Are Created the Same If the systems aren't cleaned by just sucking them out with a vacuum, how does the process work? First, you need to realize that there are several "flavors" of air ducts. There's bare sheet metal, sheet metal with fiberglass thermal/acoustic liner, fiberglass composite ductboard, spiral flex duct, and building interstitial spaces (suspended ceiling plenums, wall cavities, spaces between floor joists, etc.) pre- tending to be ductwork. The latter can be the most problem- atic for maintenance and cleaning, due to difficult access and the sheer volume of some of these spaces. Internally lined and ductboard systems have the added pleasure of potential deterioration and fiber release, in addition to the propensity for holding moisture and debris in their porous matrix. Yes, Virginia, fibrous internal air duct products DO break down and end up blowing out in the air stream causing issues!