---
title: "Factors affecting human comfort"
subject: "Applied Thermodynamics"
chapter: 4
key: "semester_3/applied_thermodynamics:human-comfort-factors"
source: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/human-comfort-factors
site: BCT Engineering
---

# Factors affecting human comfort

Applied Thermodynamics · Chapter 4: Air-Conditioning

- Asked in: year not given, 4 marks
- Video: [factor affecting human thermal comfort](https://www.youtube.com/watch?v=c1iiIU2azSg) — BEST MECHANICAL ENGINEERING
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/applied_thermodynamics/human-comfort-factors
- Whole chapter: https://www.bctengineer.com/md/semester_3/applied_thermodynamics/chapter-4

## Question

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

## 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.

## Answer

**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
| Season | DBT | RH |
|---|---|---|
| Summer | 24 to 27 °C | 45 to 60 % |
| Winter | 20 to 23 °C | 30 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.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Thermal comfort exists when:
   A. Heat loss from the body equals heat production without sweating or shivering
   B. The body stops producing heat
   C. Air is saturated
   D. DBT is exactly 20 °C
   Answer: A. Comfort is a balance between metabolic heat production and heat rejection, with no shivering or sweating. (Key point: Meaning of thermal comfort)

2. Which is NOT a main factor affecting comfort?
   A. Mean radiant temperature
   B. Air velocity
   C. Atmospheric pressure at sea level in kPa measured by the barometer reading of the room
   D. Relative humidity and clothing
   Answer: C. The factors are DBT, RH, air velocity, mean radiant temperature, activity, clothing, air purity and occupant traits. Barometric reading is not one. (Key point: Factors affecting comfort)

3. Effective temperature is the temperature of:
   A. Still, saturated air giving the same sensation of warmth as the actual condition
   B. Dry air at 50% RH
   C. Moving air at 100 °C
   D. The mean radiant surfaces
   Answer: A. ET combines DBT, humidity and air motion into one index relative to still, saturated air. (Key point: Effective temperature)

4. Typical summer comfort design conditions are:
   A. 20-23 °C, 30-50% RH
   B. 24-27 °C, 45-60% RH
   C. 30-35 °C, 80-90% RH
   D. 15-18 °C, 10-20% RH
   Answer: B. Summer design is 24 to 27 °C and 45 to 60% RH; winter is 20 to 23 °C and 30 to 50% RH. (Key point: Design conditions)

## Related in other subjects

- [Human thermal comfort and thermal balance](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ahuman-thermal-comfort-balance) — Building Technology, chapter 1, asked 4×
- [Thermal comfort and its factors](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Athermal-comfort-factors) — Building Technology, chapter 1, asked 2×
- [Factors affecting thermal performance](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Athermal-perf-factors) — Building Technology, chapter 1
- [Thermal comfort and its classification](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Athermal-comfort-classification) — Building Technology, chapter 1