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Building Health Sciences - Healthy buildings, healthy people, healthy business

Root Cause Investigation

In a low profile, highly-secure facility, BHS performed a root cause investigation into the existing conditions, activities, multiple HVAC systems and circumstances which may have contributed to fungal growth in the sound-lined return air ductwork systems and overall undesirable indoor environmental and air quality. This request preceded execution of a building-wide duct cleaning and sound-liner replacement with flexible elastomeric insulation applied internally to the existing sheet metal ductwork. These were conceived and designed to solve all comfort issues and concerns in this complaint building.

The location was a single story, twenty year old, building served by 45 gas-fired, self-contained roof top units (RTU), ranging from two-to-twenty ton capacity. These units provided heating and cooling seasonally for the comfort of the building occupants. The building, formerly a dedicated computer center with raised access floor, was also served by 25 Computer Room Air Conditioning (CRAC) units from five-to-ten ton capacity. These provided cooling only, year round, through under floor plenum distribution offset heat generated by localized, heavy concentrations of electronic equipment.


The RTUs, after twenty years of operation and exposure to the weather, were at the end of their useful life and in the expected condition. Externally, these units exhibited substantial rust on various side panels, roof panels, disconnect and exposed gas piping. The entire return air ductwork system for each RTU was completely sound-lined, from each return air grille back to the RTU. Based on visual inspections of all units, there was degradation, de-lamination, flaking and general deterioration of the sound liner. In some cases, this impeded return airflow and contributed to the accumulation of dust and contaminant deposits in the ductwork. There was no liner on the interior of supply ductwork.

The CRAC units were floor mounted on stands with a down-flow configuration. They provided un-ducted supply air to the plenum space created by the raised access floor system and distributed it through perforated floor panels. Return air was pulled from the occupied portion of the space directly into the open return on top of the CRAC units.

Over time, the building had undergone multiple uses and occupancy re-configurations. No consideration had been given to the HVAC systems’ lay-out as a component of the floor plan or demising wall installation, or to the resultant impact on occupants’ comfort or discomfort in the work environment. Other potential contributing factors or environmental contaminants had simply been overlooked.

The original investigative focus into the condition of the ductwork was necessarily expanded by BHS’ team to evaluate other contributing factors within the building. These included contaminant source control, housekeeping, air filtration, HVAC operations and maintenance protocols, building pressurization zones and competing static pressures, IEAQ lack of awareness, the age of the building and its carpet, ceiling tiles and office systems furniture. The source of dust and contaminants, in this building, was predominantly internally-generated for the reasons and conditions outlined above.

Lessons Learned

The scheduled remediation would have been ineffective and proven even more costly than anticipated, if performed in isolation. In order to manage this set of existing contributory conditions, the key to BHS’ assessment was development of an efficient, cost effective building operations scheme integrated with successful implementation of an IEAQ Awareness Program for occupants. As a result of this effort, building performance was enhanced, contributing factors were reduced or eliminated and occupant discomfort was significantly reduced through improvement of the overall indoor environment: all at a reasonable cost.

Document: Competing Systems