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Engineering review outlines multi-step fix for humidity at Flossmoor Hills and Western Avenue
Summary
An engineering team hired by Flossmoor School District 161 reported elevated plenum humidity, intermittent exhaust function and control limitations at Flossmoor Hills and Western Avenue and recommended a mix of low-cost repairs and larger mechanical upgrades. The board directed staff to continue targeted testing and return with bid-ready plans.
Flossmoor School District 161 on Oct. 14 heard a technical briefing from the Farnsworth Group that identified several causes of the persistent summer humidity problems at Flossmoor Hills and Western Avenue and offered a sequenced set of fixes.
The firm’s mechanical engineer, Jeff Boyer, said calibrated temperature and humidity logging, building-automation trends, room blower-door pressurization tests and test-and-balance airflow measurements show elevated plenum dew points (about 64°F) and short cycling of classroom unit ventilators that prevent effective dehumidification. Boyer said building pressure data show the buildings were sometimes at negative pressure, which draws humid outside air in through leaks and inactive exhaust points.
The report identified multiple specific, testable problems: damaged or crushed insulation on chilled-water piping saddle joints causing condensation; missing or nonfunctional restroom exhaust points and several rooftop exhaust fans with torn belts or disabled operation; outside-air dampers and RTU minimum-positions that limited makeup airflow; and unit ventilator controls that shut cooling before sufficient moisture removal.
Boyer said the team’s proposed approach combines lower-cost fixes to reduce infiltration and enable positive pressurization with longer-term mechanical solutions. The lower-cost items include sealing soffit penetrations and envelope leaks identified by the blower-door test, replacing or repairing restroom and central exhaust fans, and installing motorized dampers or backdraft dampers on restroom exhaust inlets so inactive ducts do not permit humid intake.
For mechanical systems, Farnsworth recommended programming and control changes to lengthen unit-ventilator run times and add a reheat sequence (a small reheating coil) so ventilators can run longer without overcooling classrooms. At the building level, the firm proposed increasing RTU outside-air capability to pressurize corridors and cascade positive pressure into classrooms, paired with the exhaust fans that would operate on building static pressure to flush the plenum.
District staff said the district has spent prior years on envelope and control adjustments and added warranties and that Farnsworth’s work supplements those efforts. The district confirmed the Farnsworth contract remains within the board-approved amount for now and that additional testing (including a planned whole-building pressure test) will incur further, separately proposed fees.
Board members asked for prioritization and cost estimates. Farnsworth said many of the infiltration fixes and user-controlled damper installs are relatively low-cost and should be done first; adding classroom reheat coils would be more expensive but likely the most effective single mechanical change. The firm and district staff agreed to return with bid-ready documents, cost estimates and a recommended sequence that would allow some work to be completed by spring break and larger items over the summer.
District leaders pledged to keep parents updated. Jeff Boyer said that implementing the complete suite of measures would bring results consistent with established ASHRAE dehumidification and pressurization practices; he added that, while no work can yield an absolute “guarantee,” combining the recommended strategies would materially reduce or eliminate the summer humidity conditions reported at the schools.
