Lesson 2 – Thermal Comfort Is Not Just Temperature
Lesson Objective
Understand why thermal comfort depends on more than air temperature, and why focusing only on the thermostat leads to repeated complaints.
The Temperature Trap
Many HVAC decisions are based on a single number: room temperature. While temperature is important, it is only one part of thermal comfort. People feel comfortable—or uncomfortable—based on how their bodies exchange heat with the surrounding environment.
The Missing Comfort Factors
Even when air temperature is correct, comfort can be lost due to other factors such as air movement, radiant heat from surrounding surfaces, humidity effects on perception, and direct contact with cold or warm surfaces. These factors explain why two spaces at the same temperature can feel completely different.
Example 1 – Cold Feeling Near the Façade
An office space is maintained at 24°C. Occupants sitting near the glass façade complain of feeling cold, while interior occupants are comfortable. The air temperature is correct, but the cold surface temperature of the glass lowers the mean radiant temperature around the occupants, making them feel uncomfortable.
Air Movement and Draft
Air movement can improve comfort in warm conditions, but it can also create discomfort if poorly controlled. High local air velocities cause drafts, especially when occupants are seated for long periods. Low air movement, on the other hand, can make spaces feel stuffy even at acceptable temperatures.
Example 2 – “The Air Is Hitting Me”
In an open office, several desks are located directly under supply diffusers. Temperature measurements show acceptable values, but occupants complain of constant cold air blowing on their necks and hands. The issue is air distribution, not cooling capacity.
Humidity and Comfort Perception
Humidity has a limited effect on thermal comfort within normal ranges, but it strongly affects how people perceive air quality and freshness. Very low humidity causes dry eyes and throat irritation, while high humidity creates a feeling of heaviness and discomfort, even if temperature is controlled.
Example 3 – Dry Office Complaints
During summer operation, occupants complain of dry eyes and headaches. Temperature remains stable. The real issue is excessive dehumidification caused by low supply air temperatures and high airflow rates, not a temperature problem.
Why Engineers Miss These Issues
Thermal comfort factors like radiant temperature and air speed are harder to visualize and measure than air temperature. As a result, they are often ignored during design and troubleshooting, even though they strongly influence occupant comfort.
Key Insight
Thermal comfort is a balance between air temperature, air movement, radiant effects, and humidity. Ignoring any one of these can lead to discomfort, even when the HVAC system appears to be operating correctly.
Key Takeaway
If occupants are uncomfortable, do not adjust the thermostat first.
First, identify which comfort factor is actually causing the problem.
Reflection
In your projects, how often are comfort complaints solved by changing temperature—
and how often do they return shortly after?