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Factors affecting human comfort

Short answer

Thermal comfort is the condition when the body's heat loss equals its metabolic production without sweating or shivering. Factors: air temperature, humidity, velocity, mean radiant temperature, activity, clothing, air quality. Design conditions: summer 24–27 °C, 45–60% RH; winter 20–23 °C, 30–50% RH, with air velocity 0.1–0.25 m/s.

Write short notes on thermal comfort. State the factors that affect human comfort and the typical comfort conditions used for design.

Thermal comfort is the state of mind in which a person feels satisfied with the thermal environment, i.e. neither too warm nor too cold. The body rejects its metabolic heat (about 100 W at rest) by convection, radiation, evaporation and respiration; comfort exists when this heat loss equals heat production without sweating or shivering.

Factors affecting comfort

  1. Dry bulb temperature of the air.
  2. Relative humidity: high RH reduces evaporation of sweat; very low RH dries the skin and throat.
  3. Air velocity: moving air increases the heat loss by convection and evaporation (draughts if above about 0.25 m/s).
  4. Mean radiant temperature of walls, windows and ceilings.
  5. Activity level (metabolic rate) and clothing.
  6. Air purity: freedom from dust, odour and CO₂; adequate fresh air.
  7. Age, sex and acclimatisation of the occupants.

Effective temperature

Effective temperature (ET) is the index of the combined effect of DBT, humidity and air motion. It equals the temperature of still, saturated air that gives the same feeling of warmth or cold as the actual condition.

Typical design conditions

SeasonDBTRH
Summer24 to 27 °C45 to 60 %
Winter20 to 23 °C30 to 50 %

Air velocity of 0.1 to 0.25 m/s in the occupied zone and about 0.3 to 0.5 m³/min of fresh air per person or more as per code are used for design.

✓ Answer checked by Claude Opus 5.5 (high effort)

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