Lesson 6 – Noise, Air Distribution, and the Comfort You Can’t Measure
Lesson Objective
Understand why occupants may feel uncomfortable even when temperature, humidity, and air quality are acceptable, and how noise and air distribution silently destroy comfort.
Comfort Is Also Psychological
Thermal comfort is not purely physical. Noise, drafts, and uneven air movement create stress and fatigue, even if occupants cannot clearly explain what is wrong. When people say “the space feels uncomfortable,” they often mean something they cannot easily measure or describe.
Noise as a Comfort Killer
HVAC noise is one of the fastest ways to turn a technically correct system into a failed one. Continuous background noise, sudden airflow sounds, or vibration transmitted through structure all affect how occupants perceive the space.
Example 1 – “The System Is Too Loud”
An office meets temperature and humidity targets perfectly. However, occupants complain of headaches and difficulty concentrating. Measurements show acceptable noise levels on paper, but diffuser hiss and fan noise are constant. From the occupant’s perspective, comfort is lost.
Air Distribution vs Air Quantity
Supplying enough air does not guarantee good comfort. How air enters the space matters more than how much air is delivered. Poor diffuser selection, bad placement, or incorrect throw patterns create drafts, stagnant zones, or short-circuiting.
Example 2 – Draft Without Cooling
A space feels cold even though temperature readings are normal. Occupants sit directly under diffusers with high local air velocity. The discomfort comes from draft, not overcooling. Reducing airflow locally solves the issue without changing the setpoint.
Minimum Airflow and Stagnation
At very low airflow rates, especially in VAV systems, air circulation becomes insufficient. Spaces may feel stuffy and uncomfortable even when temperature is correct. Low air motion reduces contaminant dilution and increases the perception of poor air quality.
Example 3 – Low Load, Low Comfort
During mild weather, a VAV system reduces airflow to minimum levels. Temperature remains stable, but occupants complain the space feels “dead” and uncomfortable. Increasing minimum airflow improves comfort without changing temperature.
Return Air and Short-Circuiting
Poor return air placement can short-circuit supply air, preventing proper mixing in the occupied zone. Fresh air leaves the space before it benefits occupants, leading to comfort and IAQ complaints despite correct airflow calculations.
Example 4 – Fresh Air That Never Reaches People
A meeting room meets ventilation requirements, but occupants complain of stuffiness. Investigation shows that supply air flows directly to the return grille above the ceiling. The issue is air distribution effectiveness, not airflow quantity.
Why These Problems Are Missed
Noise and air distribution issues are often discovered only after occupancy. They are hard to predict using simple calculations and are rarely visible in drawings. Once the building is occupied, fixes become expensive and disruptive.
Key Insight
Comfort can be lost even when all measurable design targets are met. Noise, drafts, and air distribution quality strongly influence how occupants experience a space.
Key Takeaway
If occupants say “everything seems fine, but it still feels uncomfortable,”
look at noise and air distribution before changing temperature or humidity.
Final Reflection
Think about a project where complaints never fully stopped.
Was the problem measurable—or was it something the design never truly addressed?