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Ventilation – forbedret indeklima på skole

A severe indoor air quality problem at Jefferson Forest High School in Forest, VA, USA gave students a few extra weeks of summer vacation – a bonus for the students, but an unexpected problem for school officials. Due to the high levels of mold and fungus, the school was immediately closed and officials were forced to embark on a fasttrack project to renovate and repair the building before the new school year. The project involved remediating the damage and installing a ventilation system for bringing in dehumidified, fresh air.

When the IAQ Problems Began

The school was built in 1973 and designed for a capacity of only 800 students. According to teachers and former students, air quality problems had been a concern for years. Reports of respiratory problems, headaches and allergy-like symptoms rose dramatically 20 years later when construction occurred to replace the school’s roof. That Spring, the school called in IMEC Engineers, an environmental and HVAC engineering firm in Lynchburg, to conduct air sampling of four classrooms where a greenish black fungus was discovered. Following the results of the air test, the superintendent closed the building for the rest of that school year, six weeks early in order to quickly address the mold issue. Officials believe the roof construction caused the airborne release of spores from the Stachybotrys mold, which commonly grows on wet wallboard and other building materials.

“The main thing we found wrong was the air flow,” said Charlie Peterson, clerk of the works in safety and the environment for Bedford County Schools. “There was no turnover of air. When the kids were in classrooms in the Spring, I was finding humidity levels anywhere from the mid-70s to nearly 90%.”

ASHRAE recommends humidity levels to be below 60% to prevent microbial growth.

After much deliberation, school officials decided to repair and reoccupy the building in less than four months.

“A lot of contractors and architects came out and said, ‘No way. Impossible. You can’t do it,’” Peterson said.

In addition to the time constrains, prospective dedicated outside air systems (DOAS) needed to provide 100% outside air and be pad mounted because the roof was not structured to hold the weight of mechanical equipment.

“Between the schedule and those requirements, Munters was the only equipment that could meet our schedule and criteria,” Owen said.

During repairs and renovations, Munters' rental dehumidification units were brought in to provide short-term moisture and comfort control. Energy recovery units were installed to treat 100% outside air, while saving on operating costs and preventing moisture-related problems.

Problems Solved

Three energy recovery units were installed outside, each capable of supplying 10,000 cfm of outdoor air aiming for 50% space RH and 47°F (8°C) dew point. A heat pipe heat exchanger forms the heart of the systems. 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.

“We precondition all the outside air and dump it into the existing air handlers to be distributed throughout the building,” Owen said.

Each unit has 600 MBtuh of DX cooling capacity with an integral air cooled condenser and 800 MBtuh indirect gas for winter heating.

“Everything went like clockwork,” Peterson says. “We were able to get the administration staff back in before school started and have everything completely done.”

As part of a first-year protocol, random samples and microbial tests were taken every two weeks throughout the building to ensure the mold issues were remedied.

“The problem was solved,” Owen said. “The dew points in the building are actually very low. 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.”

Hurtige fakta

  • Air conditions using 100% outdoor air, compared to conventional AC units that use minimum outdoor air with mostly recirculation air
  • Provides superior IAQ
  • Uses significantly less energy to air condition than conventional systems
  • Reduces peak electrical demand
  • Provides winter heat recovery
  • Qualifies for utility rebates and/or LEED credits

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