Thermal comfort and its classification

Thermal comfort in buildings is the condition in which occupants are satisfied with the thermal environment (temperature, humidity, air movement and radiation) and want neither warmer nor cooler surroundings.

Classification

Thermal comfort is classified by the basis of assessment.

1. Subjective (psychological) comfort: The person's own feeling of the environment, from votes on the 7-point ASHRAE scale from -3 (cold) to +3 (hot). Example: students voting on the classroom temperature.
2. Physiological comfort: Based on the body's heat balance and on skin and core temperatures. When heat produced equals heat lost with little sweating or shivering, there is comfort. Example: a person resting at 24 °C needing no extra effort of the body.
3. Physical (environmental) comfort: Based on measurable parameters and indices such as dry-bulb temperature, effective temperature, and the comfort zone on the psychrometric chart. Example: ET of 22 to 25 °C is comfortable for sedentary work.

By season or condition

• Summer comfort: Needs cooling and ventilation; 24 to 28 °C with air movement.
• Winter comfort: Needs heating and insulation; 18 to 24 °C.

By model

• Static (heat balance) model: Fanger's PMV/PPD, assumes steady indoor conditions (air-conditioned rooms).
• Adaptive model: People adapt through clothing, windows and fans, so comfort range follows the outdoor temperature (naturally ventilated buildings, common in Nepal).

Understanding these helps the designer choose passive or active methods to meet the comfort needs of the users of the space.