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Council approves humidification controls with higher humidity allowance for some climate zones
Summary
Building Code Council approved a revised humidification control proposal that keeps adiabatic humidification as the preferred method, allows steam with enthalpy recovery, and raises the upper relative-humidity threshold for certain climate zones after a floor debate about health and efficiency.
The Building Code Council on March 21 approved a revised humidification and dehumidification proposal that adopts new equipment and control guidance while setting different humidity thresholds by climate zone.
The council’s action approves the proposal as modified to allow up to 67 percent of some existing fossil/electric systems to remain in limited circumstances and — crucially for humidification — sets higher permissible indoor relative-humidity limits for warmer climate zones. Proponents and opponents argued over whether limiting humidification above a 30 percent relative-humidity threshold would harm indoor health outcomes and whether energy-recovery requirements would preserve efficiency.
The approved language folds previously separate system and controls sections into a single, consolidated code section. It calls for adiabatic (direct evaporative) humidification except where enthalpy (energy) recovery is used; in the latter case steam humidification is permitted subject to maximum humidity thresholds. The council adopted a compromise assigning a 50 percent threshold in some warm climate zones and a 30 percent threshold in cooler zones, with a final table of scoping and exceptions captured in the adopted text.
Supporters said the rewrite simplified the code and preserved engineer choice while keeping a performance focus. “We came to a great place,” said Eric Bedell, the proponent, noting the combined section reduced duplication and clarified controls requirements. Several mechanical engineers and manufacturers raised technical concerns about the practicalities and maintenance needs of adiabatic systems; the council’s language keeps existing commissioning, water-treatment, and maintenance expectations in place.
Opponents warned the proposal still imposed equipment constraints and could be difficult for projects with existing mechanical infrastructure. Dwayne Johnlin and others argued the changes would effectively require higher-efficiency systems while restricting some equipment choices for projects under tight budgets.
The council voted to approve the modified humidification proposal. The roll call showed the motion carried; the final tally reported by the council was 10 yes, 5 no and 1 abstention on the final form presented at the meeting.
