A Crash Course In Moisture Remediation
At Jefferson Forest High School in Forest, VA, the ultimate school kid's dream came true last spring. The building experienced a severe indoor air quality (IAQ) problem, complete with mold and fungus that prompted school officials to close it and give high school and middle school students an extra three weeks of summer vacation.
But what was a windfall for students proved a daunting challenge for school officials, as they embarked on a fast-track project to solve the problem so they could have the building ready for the start of the next school year.
The two-stage, $1.6 million project involved remediating the damage and installing a system for bringing in dehumidified fresh air. As J. Todd Owen, a principal at IMEC Engineers, the engineering firm on the project, reports, "We got the whole project done in 74 days."
IAQ Problems BeginDesigned for 800 students and built in 1973, Jefferson Forest High School lies just west of Lynchburg in Bedford County,VA. Air quality problems have existed at the school for years, according to teachers and former students. But complaints of respiratory problems, headaches, and allergy-like symptoms rose dramatically starting in November 2000, when construction began to replace the school's roof.
The school called in IMEC Engineers, an environmental and hvac engineering firm in Lynchburg, to conduct air sampling in April 2001 after a school employee filed a complaint with OSHA. They tested rooms that had received the most complaints, and in four classrooms they discovered a greenish-black fungus known as stachybotrys, known to cause a host of ailments.
As a precautionary measure, the Bedford County school superintendent closed the building for the rest of the school year on April 27, six weeks early. High school and middle school students took turns attending class in the middle school building, each occupying it for three weeks to finish their school year.
Officials believe the roof construction caused the airborne release of spores from the stachybotrys, which commonly grows on wet wallboard and other building materials. But where did the moisture come from that caused the buildup of mold and fungus? The school's ballasted (stone) flat roof had leaked since the school was built, and efforts to repair it had failed.
Leaky Roof Exposes Moisture Serious ProblemThe original roof was replaced in 1985 with another one that also leaked. "You just can't get a flat roof to seal," states Charlie Peterson, clerk of the works in safety and the environment for Bedford County Schools.
For the new roof, both old roofs and ballasting were removed to reduce the structural load and were replaced with a mechanically-fastened EPDM rubber roof. During the process, water entered the building by rain and sleet blowing in.
But the water coming through the roof was only the tip of the iceberg. Peterson recalls, "The main thing we found wrong was the air flow. There was no turnover of air. When these kids were in classrooms in April, I was finding humidity levels anywhere from the mid-70s to nearly 90%." ASHRAE recommends humidity levels blow 60% to prevent microbial growth. Temperatures were recorded in the 80s.
The existing hvac system in the core of the building consisted of a two-pipe arrangement and eight air handlers housed in mechanical rooms, with fuel oil used for heat and chillers for cooling. Rooms around the perimeter of the building had unit ventilators that also supplied hot and cold air. Owen says, "In order to cool the interior spaces, they had to go on economizer, and this didn't take into account the humidity outside. It brought in air that was cooler than it was inside, but it was moist. So the building had a high humidity."
Stringent ScheduleOther factors contributed as well. The building has three levels, with two lower levels mostly below grade. Several lower-level spaces were added and classrooms created after the school was originally constructed, and these had no ventilation.
The school board had to decide whether to repair the building, erect a new one, or use other existing facilities and set up trailers to accommodate students as necessary. Citing financial reasons and for the optimum experience of the students, they decided to repair and reoccupy the building. The kicker: It would have to be done by August 20. As Peterson recalls, "A lot of contractors and architects came out and said, 'No way. Impossible. You can't do it.' "
IMEC Engineers went to work developing a corrective action plan, identifying everything to be cleaned or replaced and designing hvac system improvements.
To facilitate matters, Bedford County carried out the project under an emergency procurement order. This meant they didn't have to get bids or go by the lowest bid but could factor in the ability of the contractor and the schedule.
When it came to selecting equipment vendors, Owen says, "The main issue was the schedule. Most of this equipment takes 12 to 14 weeks to get. We had to have it in eight weeks. That right there cut out a lot of vendors." Custom equipment was out of the question.
Also, the roof wasn't structured to hold the weight of mechanical equipment, so it had to sit on grade, meaning supply ductwork had to run up and over the roof. IMEC Engineers originally wanted to incorporate energy recovery into the system but realized they would have to get return ductwork up on the roof and collect all the return and bring it back to the unit. Owen says, "When we looked at the cost and the schedule impact with the mechanical contractor, we decided we wouldn't run return ductwork and that we'd provide 100% fresh air. That meant we had to have units capable of 100% outdoor air. That cut down our list significantly."
That led Owen to conclude, "Between the schedule and that requirement, Des Champs Laboratories was the only equipment that could meet our schedule and criteria for having 100% outside air." The fact Des Champs was close by in Natural Bridge Station, VA also helped.
Des Champs manufactures its Wringer dehumidifier from its Modular Outside Air Conditioning System (MOACS) family of products as well as custom units.
A heat pipe heat exchanger forms the heart of the Wringer system the engineering firm selected. Hot, moist outdoor intake air flows through one side of the heat pipe, while cooled, dehumidified air passes through the other. The resulting heat transfer between the two airstreams precools the inlet air before it enters the dehumidification coil, thereby reducing the load on the cooling coil and the size of the refrigeration equipment required, and it reheats the supply air to a more neutral temperature.
Remediation WorkMeanwhile, restoration contractors carried out about $300,000 worth of remediation to clean and repaint the school. This included removing contaminated sheetrock, re-placing all the ceiling tile, replacing carpeting with vinyl floor tile, and removing batten insulation in ceilings. "We cleaned the school top to bottom," as Owen puts it.
While this was going on, contractors set up and operated two rental Wringers supplied by Des Champs to provide a dehumidified environment during the summer until the new equipment arrived. Each unit had a rated capacity of 10,000 cfm with a capacity to remove 230 lb of moisture/hr from 100% outdoor air.
The units arrived mounted on flatbed truck trailers, with on-board diesel-driven electric generators to power the units for their two months of operation. For easy installation, flexible ducting was used to connect the units to the building.
As the remediation and drying process came to a close, three permanent Wringers were installed outside, each capable of supplying 10,000 cfm of outdoor air. According to Owen, "We precondition all the outside air and dump it into the existing air handlers to be distributed throughout the building." Each unit has 600 MBtuh of DX cooling capacity with an integral air cooled condenser and 800 MBtuh indirect gas for winter heating.
Technicians installed humidity transducers in the building to monitor humidity, aiming for 50% space rh. The equipment was designed to dehumidify the supply air to 47 degree F dewpoint. A new Johnson Controls system controls the revamped system.
In the perimeter area of the building, outside vents on the unit ventilators were blanked off. Fresh air ductwork was installed so the space would continue to be ventilated, now with dehumidified fresh air.
Moisture: Gone!Despite the difficult circumstances, the project came off successfully. "Everything went like clockwork," Peterson says. "We were able to get the administration staff back in before school started and have everything completely done."
But the real test, of course, came in determining how well the new system solved the moisture problem. As part of a first-year protocol, the school set up an IAQ committee consisting of parents, teachers, administrators, and IMEC Engineers personnel. They meet every two weeks and conduct random sampling and microbial tests in selected spaces in the building. Owen reports, "The problem was solved, and we're proving that by taking all these additional measurements. The dewpoints in the building are actually very low." And he adds, "We're very pleased with how the building is performing from a humidity standpoint. I don't see them ever having a problem with it."
Like school districts around the country, Bedford County has studied building a new school in a few years. Located in an attractive area, the school has become overcrowded. But with its moisture problem solved, they plan to keep using the existing high school building for years to come. And as they do, students can plan on having to stay there for a full school year. ES