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

Decommissioning for Sustainable, Idle Building Operation

Increased commercial tenant vacancies caused by the prevailing economic hardships have led to tough decisions for sustainable and efficient building operation. A similar situation is also being faced by owners of high rise condominiums, who are challenged with protecting building assets while facing operating shortfalls, declining sales, unfinished construction, and foreclosed dwellings. Having learned how such decisions impacted building performance and associated costs in more robust economic times, we describe below an actual situation Building Health Sciences (BHS) encountered.

BHS was engaged to perform a condition assessment of the Mechanical Equipment Rooms (MERs) at a two-year-old, thirteen-story, commercial office building. Tenants occupied the first, second, tenth, eleventh, and thirteenth floors. The MERs on each floor housed a single Air Handling Unit (AHU) utilizing the entire room as a mixing plenum for return air and outside air – a common design practice. Each MER contained, at a minimum, base building chilled water risers, chilled water run outs, vertical condensate risers and associated AHU coil connection piping. All chilled water risers, base building and tenant, had future connections stubbed out and valved off. All other building mechanical equipment was located in the mechanical penthouse.

The unoccupied floors' HVAC systems had been "turned off" for cost savings approximately eighteen months prior. With partial occupancy, the building engineer had been instructed to "turn off" each of the two HVAC systems on the eight unoccupied floors to save utility costs. The two AHUs on each floor were shut down; not throttled back. When an opportunity to lease the unoccupied space for a major, multi-floor tenant arose, the developer expressed concerns to BHS about reported water damage and apparent mold growth, as well as the potential effect on the indoor air quality of the tenant space, through the respective AHUs' ductwork.


BHS observed saturated pipe insulation, evidence of water and associated water damage on gypsum wallboard and ceilings, as well as mold amplification on air filters and air handling units' casings in the unconditioned mechanical rooms. Additionally, un-insulated pipes, riser clamps, pipe supports and hangers were heavily rusted. Several root cause hypotheses which could account for the mold in the mechanical rooms on the unoccupied floors were considered. Visual inspections of the MERs on the occupied floors revealed none of the adverse conditions seen in the MERs on the unoccupied floors.

With regard to the source of the moisture resulting in condensation generation, opinions varied. The primary source appeared to be the introduction of unconditioned, humid air into the building through the outside fresh air supply to each MER. This continuous moisture source led to mold growth on various surfaces since the AHUs were off on the unoccupied floors and the humid air was confined to the MER. BHS' investigation focused on how the moisture behaved within the dead air space of the MER plenum and how temperature differentials created by "idle" equipment led to the mold growth on the chilled water pipe's insulation, condensate drain pipe's insulation, mechanical room's walls, and the air handler units.

There was no single condition which caused the mold growth, but rather a variety of factors, including some, if not all, of the following:

  • Faulty installation workmanship on the pipe insulation during base building construction which allowed the humid, non-conditioned, outside air to penetrate through the insulation seams or gaps directly onto the cold surfaces of the chilled water piping. This was supported by the pattern of mold amplification at insulation joints on the chilled water piping;
  • Degradation of pipe insulation value diminished by water soakage allowed the chilled water temperature to be transmitted to the surface of the insulation. The cooler insulation surface temperature came into contact with the humid ambient air. The outer surface temperature of the insulation jacket fell below the dew point for ambient conditions, causing condensation on the surface and mold amplification;
  • Potential slow condensation leaks at insulation butt joints, plastic elbows or exposed valve components in the chilled water pipe system such that condensation traveled along the interior piping until a gap or opening in the insulation allowed it to leak to the outside jacket of the insulation.
  • Mold amplification through progressive thermal transfer and cooling effect onto the filters from the active chilled water risers circulating through the AHUs' coils with no fan operation or controls.
  • Human error such that excessive, humid, outside air was introduced to non-conditioned, "idled," mechanical rooms. The outside air dampers were opened under normal building automation sequencing and had not been overridden to isolate the "idled" MERs from the building outside air delivery system.

Each of the above scenarios had different effects on the mold growth in the MERs and on the gypsum liner of the outside air shafts. Contamination of the AHUs' supply ductwork at each level and the outside air shaft presented a potential source from which contaminants spread to the rest of the building.

With tenant construction underway, the HVAC systems on previously-unoccupied floors needed to be made operational quickly. A health-based remediation plan was designed by BHS to prioritize and sequence the activities which needed to take place so that the unoccupied floors' HVAC systems could be remediated and placed into immediate operation without risk to the health of the prospective tenants.

Lessons Learned

Ultimately, calculations revealed that the anticipated energy savings realized over eighteen months were insignificant when compared to the costs of an environmental assessment, remediation planning and the costs incurred in remediating the existing conditions. Building owners and facilities managers or anyone charged with the responsibility for building performance must consider both the impact of cost-driven decisions, as well as properly-designed protocols for sustainable, idle building operation, in order to avoid downstream adverse occupant health consequences.