What is the acceptable occupant level of acceptability in subjective evaluations?

• A. 60% or more within each zone served by the system.
• B. 80% or more within each zone served by the system.
• C. 90% or more across the entire building.
• D. 100% in every zone.

Answer: (B)

In subjective evaluations for indoor environmental quality, the goal is to ensure occupants find the environment acceptable. The standard uses a zone-based target: 80% or more of the occupants in each zone served by the system must rate the environment as acceptable. This zone-specific threshold prevents a few well-performing zones from masking problem conditions in others and recognizes that comfort and air quality can vary from one area to another.

Why this makes sense: people in different zones may experience different temperatures, air velocity, odors, or fresh air delivery. Requiring 80% acceptability in every zone pushes the system design and operation toward consistently good performance across the building, rather than achieving a high average while leaving some zones underperforming. If a zone drops below 80%, adjustments to the ventilation rate, distribution, filtration, or control strategies may be needed.

The other options don’t fit because they either set a lower overall bar (60%), assume the whole building must meet a single high bar (90% across the building), or demand perfection in every zone (100% in every zone), which is impractical given natural variability in occupant perception and microclimates within spaces.