Root Cause Investigation

Diagnosing Competing HVAC Systems and IAQ Failures

Overview

In a low profile, highly secure government facility, BHS performed a root cause investigation into the existing conditions, building 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.

Facility Profile

  • Single-story, 20-year-old building
  • Former data center with raised access flooring converted to office workspace
  • Served by 45 rooftop gas-fired HVAC units (RTUs), 2–20 tons each serving the traditional workspace
  • Supplemented by 25 CRAC units (Computer Room Air Conditioner), 5–10 tons each served the high-density electronics zones
  • The RTUs and CRAC units operate simultaneously in the workspace

Key Findings

RTUs:

  • Units had significant rust and weather damage
  • Return ducts were fully lined with degraded sound-absorbing insulation
  • Insulation exhibited delamination, flaking, and airflow restriction
  • Supply ductwork was unlined

CRAC Systems:

  • Dumped un-ducted supply air to the common underfloor plenum
  • Pulled return air directly from the occupied space conditioned by RTUs
  • Configured for data cooling, not aligned with new workspace layout

Building Use Conflicts:

  • Space reconfigurations ignored original HVAC layout restrictions
  • No air flow design adjustments for reconfigured workspace and prior use as a data center
  • Conflicting HVAC systems created static pressure differentials and pressurization issues which competed for controllable comfort control.

Expanded Investigation

BHS broadened its root cause analysis to include:

  • HVAC operations & maintenance
  • Housekeeping practices
  • Filter quality and replacement frequency
  • Pressurization zoning and imbalance
  • Old carpeting, ceiling tiles, and dusty modular furniture
  • Predominant contaminant sources were internally generated

Lessons Learned

Executing duct cleaning alone would have been ineffective and wasteful. Instead, BHS developed a cost-efficient operations strategy. As a result of this effort, building performance was enhanced, contributing factors were eliminated and occupant discomfort was significantly reduced through improvement of the overall indoor environment: all at a reasonable cost.