Building problems can cause degraded air quality in all phases of a building's lifecycle: design, operation, and maintenance. The purpose of this article is to examine common design characteristics that may be problematic to the achievement of acceptable IAQ and that are generally easily identified and are usually avoidable.

Sizing Symptoms

A not-so-uncommon problem is an oversized air conditioning system. The oversized system could be due to a design error or seasonally reduced occupancy/thermal loads such as often occurs in schools in summertime. The oversized system causes rapid response to high temperatures. However, because of oversizing, hot, humid air brought into the system is not adequately dehumidified, producing increased relative humidity (rh) in the space. Sustained rh above 60% increases the likelihood of microbiological growth on environmental surfaces. The air-handling system can serve as a distribution conduit for microbes throughout the zone.

Insulation

One of the most common forms is unfaced fiberglass insulation, which is glued and/or pinned to ductwork. When such insulation becomes saturated, this duct lining becomes an amplification site for microbial contamination.

In addition, this fiberglass can be easily eroded because of high-velocity air contact with the surface of the insulation. This erosion can result in the dissemination of fiberglass throughout the zone where occupants can either inhale the fiberglass or, quite commonly, appear to experience dermal irritancy from contact with settled fiberglass. There is concern, and considerable debate, about the carcinogenic potential for inhaled fiberglass. Until the debate is settled, it is a prudent measure to minimize avoidable exposures.

Lastly, fiberglass-lined ductwork is extremely difficult to fully clean. HEPA vacuums will not adequately remove all spores throughout the full depth of the insulation and diligent vacuuming of the surfaces may actually tear or abrade the surface, thus creating an airborne fiberglass exposure problem. Thus, from an IAQ perspective, exterior lining is preferable to interior lining.

No Access, No Replacement

The result can be that filters may go years without being changed and are extremely loaded, and other components in the system may fail and become unhygienic. Many of these systems receive no periodic maintenance until the system fails completely. The lack of hygiene in these systems may contribute to IAQ problems.

Poor Air Distribution

A common problem in many commercial office buildings is the inability to precisely control heating and cooling in individual offices or occupied spaces.

This problem can be caused by a design that only permits regulation of relatively large zones containing many offices with differing thermal loads and exposures. Under these conditions, it is quite common to have several, if not the majority, of office occupants complaining of thermal discomfort. More zoning would allow for better control of thermal conditions. Another common variant of this problem is controls that are broken, miscalibrated, or misprogrammed. All of these conditions can exacerbate existing temperature control problems.

Building ventilation standards and codes for buildings constructed during the 1970s and much of the 1980s included provisions for what is now generally viewed as underventilation. During much of this era, building codes specified an outside air minimum of 5 cu ft/min/person, which often results in complaints of stuffy, dry air and a perception of objectionable odors. Subsequent revisions to ASHRAE standards and building codes have increased outside air quantities to 15 to 20 cu ft/min/person. In many instances, the only solution to this problem is to upgrade the existing ventilation system.

Smells And Grilles

Rooftop air-handling units that have poor resistance to weather and animal fouling can result in problems. We have observed rain and snow infiltrating both the air handlers and ductwork. Such moisture intrusion is highly undesirable because microbial contamination is likely to result. In addition, we have often observed bird feces, feathers, rodent feces, and nesting materials in and around these air handlers. Contamination from bird feces carries a potential for histoplasmosis and coccidiosis, two potentially deadly diseases.

From an IAQ perspective, engineers should specify equipment and exterior ductwork that has high resistance to moisture intrusion and animal fouling. Alternately, some type of weatherproof enclosure could be constructed around the units to prevent fouling by animals and the intrusion of moisture.

Building inspections frequently uncover placement of supply and return or exhaust grilles in close proximity to each other. Such a condition may result in "short circuiting" of building supply air. ASHRAE 62 ventilation rates assume a well-mixed condition. Without adequate separation between supply and return air, stratification could occur and, a significant fraction of outdoor air may be drawn into the return airstream and not adequately mix with room air. This condition, if not corrected, may necessitate an increase in the outdoor air fraction to compensate for the reduction in mixing.

Humidification Dilemmas

Malfunctioning humidifiers can wet internal insulation and ductwork, be contaminated with microorganisms, or cause particulate generation due to evaporation of water sprays. If a design professional decides to specify a humidification system, it should preferably utilize steam according to ASHRAE 62, but care should be exercised to avoid contamination from water treatment chemicals.

Filters: Worth The Effort

Higher efficiency filters in excess of MERV 11 and up to HEPA filters at MERV 17 efficiency are desirable in instances where human health is a major concern. While such filters are expensive and initial design must accommodate pressure drops caused by high-efficiency filters, such filters need only be replaced every one to two years. A prefiltering system is usually installed to capture the greatest particulate load prior to impingement on the HEPA filters. The prefilters may be changed more frequently, thus allowing the high-efficiency filters a longer lifecycle.

Legionella Primer

However, this disease is highly preventable with an effective biocide/treatment program. Cooling tower treatment protocols are crucial in preventing growth of Legionella. Most protocols are designed to provide continuous maintenance levels of biocide and periodic "shock doses" to ensure that strains resistant to chronic treatment are overcome by huge doses of a different type of biocide.

Such treatment strategies are quite effective, if appropriately monitored. Currently there is no recommendation to periodically test treatment towers for Legionella pneumophila or the biocide concentrations. Building operators should be aware that tests for total cooling tower bacteria are not generally capable of detecting the presence of Legionella pneumophila. Specialized media must be used to detect the presence of this organism and testing for the biocide concentration is generally performed through pesticide testing laboratories.

While periodic testing programs can be expensive, an outbreak of Legionnaire's disease can be devastating to large-building owners and operators. The author was involved in a major Legionnaire's outbreak in a midsized hospital, and subsequently the hospital was found to be substantially free of any negligence.

Nevertheless, the negative public relations and the cost of defending itself in a lawsuit had a severe crippling effect on the hospital. Legionella is an entirely preventable disease, which, with appropriate care and attention, should never occur.

The Second Time Around

Buildings should ideally be slightly positively pressurized by design, but installation of these devices can quickly change building pressurization from positive to strongly negative. When buildings become negatively pressurized, outside air is then pulled into the building from every building penetration, including doors, windows, cracks, etc. Because such air is not forced through the hvac system, it is neither properly conditioned, nor have any of the outside contaminant burdens been filtered. Such problems are easily preventable if design professionals consider the impact of such process changes.

Conclusion

It further seems that, while not required by local building codes, design professionals without extensive experience related to IAQ issues would be well served by collaborating with firms having greater experience with these issues. After construction of a building, semiannual air testing and inspections are highly advised in most buildings. ES