New Technique Solves IAQ Mystery In Office Building
Fogarty is a modern-day IAQ sleuth. Instead of a magnifying glass, he uses a P-Trak™ Ultrafine Particle Counter to solve difficult IAQ problems. Manufactured by TSI Incorporated (St. Paul, MN), this instrument counts ultrafine particles or UFPs (those less than 0.1 micrometer in diameter) to track indoor pollutants to their source. Once a source is identified, building management can control or eliminate the source and stop related IAQ complaints.
"The ability to quickly track UFPs to their source is the key to this new technology," stated Fogarty. "Problems that used to take months to solve now have their sources identified in hours and are usually solved within a few days, if not immediately."
With this new instrument and technique, Fogarty has conducted over 2,000 IAQ surveys in office buildings, hospitals, schools, and other commercial facilities. The following case describes just one of his successful investigations.
The MysteryThe story starts at an eight-floor office building in a downtown business district. The general air quality near the building was impaired by heavy motor vehicle traffic and harbor activity.
The building itself was not unusual. Used exclusively for offices, it was built in the 1970s. Its two duplicate hvac systems, mounted on the east and west sides of the building, used 60 dust-spot percent filters to remove outside contaminants. Its boiler system ran constantly year round to maintain proper air and water temperatures for its occupants.
Occupants throughout the building routinely complained to building management about poor IAQ. Their symptoms included headaches, eye irritation, sore throat, and fatigue. These widespread and persistent complaints were primarily general in nature and could not be correlated to particular locations, time of day, or specific events. Management was also aware of anecdotal claims of more serious illnesses. Although never specifically related to air quality, these claims heightened occupant concern.
Building management made many attempts to address the complaints. The most comprehensive efforts related to air quality evaluations based on ASHRAE Standard 62, "Ventilation for Acceptable Indoor Air Quality." These evaluations failed to reveal any deficiencies based on the standard. "The resulting reports were interpreted by some occupants as a message from management saying, 'You're not sick. It's your imagination,'" said Fogarty.
The InvestigationWhen all conventional approaches were exhausted, building management asked Fogarty to conduct an investigation using the P-Trak Ultrafine Particle Counter. He started out by measuring UFP concentrations in outside air and at various locations throughout the building.
The UFP concentrations in outside air, measured at ground level and upwind of the building, averaged 5,230 (all measurements in particles per cubic centimeter). With 60%- efficient filters in the rooftop air-handling unit, Fogarty expected an indoor reading of 2,000 to 3,000. "When I saw average indoor readings of 16,200, I knew something really was wrong. It wasn't the occupants' imaginations," said Fogarty. The highest indoor reading - 22,600 - was tracked to a supply air diffuser.
Additional investigation by Fogarty demonstrated that UFP readings within the building were consistently higher than those at ground level outside the building. Most significantly, he tracked the highest outdoor reading - 40,000 - to the outside air intake located near the roof.
These findings focused Fogarty's investigation on the roof, specifically just above the outside air intakes. Readings of 40,000 between the exhaust stack and the air intake suggested that the exhaust from the building's own boiler was being pulled down to roof level by downdrafts caused by a nearby 12-story building. This exhaust air was then drawn back into the building's hvac system. Fogarty tested his hypothesis by having the boiler turned off and then on. As he expected, UFP levels fluctuated with boiler use.
"The real-time data from the P-Trak was extremely helpful to both building management and occupant representatives. Once everyone understood the problem, we were able to move quickly to a solution," added Fogarty.
The SolutionOnce the boiler exhaust was identified as the likely source of the IAQ complaints, the issue now became identifying a proper course of action. Two alternatives quickly came to the fore: improve the filter efficiency to control this re-entrained boiler exhaust or raise the stack to blow the exhaust outside the building envelope. The occupants favored replacing the filters because the solution was straightforward and had a high likelihood of success. However, the high cost of this alternative was a concern to building management.
The premise of the second alternative - raising the stack - was also clear. However, determining the new stack height was not an easy task, because formulae to predict stack and building effects are not accurate in the complex environment of downtown areas. Employing this alternative would mean "trial and error" stack modifications and would require the occupants' willingness to wait for the result of the trials. The occupants were willing to wait, once they had building management's commitment to quickly evaluate the modifications and rapidly proceed with further improvements as necessary.
With this agreement in hand, management raised the original exhaust stack beyond its original 6-foot height. A section was added to the stack to make it 13 ft tall. Fogarty was then asked the crucial question: "Did the remediation work?" Again, the P-Trak gave him the answer. By measuring the UFP concentrations around the roof and the outside air intake, he showed that, while these concentrations had decreased by 75%, an unacceptable amount of UFPs still entered the building.
Since the goal was eliminating this re-entrainment, building management ran the stack horizontally 25 ft toward the intakes, increased the stack height to 25 ft, and placed an exit cone at the top of the stack. After this second improvement, Fogarty's P-Trak measurements showed that the particle concentrations at the air intakes were the same as those upwind of the stack.
Follow-up measurements with the P-Trak now showed a substantial reduction in UFP concentrations within the building. The reduction was accompanied by a dramatic decrease in complaints and a "thank you" from the occupants for the successful effort by management to improve air quality.
"Building management was fully satisfied that the complaints were finally explained and the source was efficiently eliminated," concluded Fogarty. The total cost of the initial investigation by Fogarty, the repairs and the follow-up investigation was less than $10,000, compared to a potential $50,000 capital cost for new fans to handle higher- efficiency filters.
With both owners and occupants satisfied that the mystery was solved, IAQ sleuth Fogarty had closed one more case.ES