This document discusses factors that affect thermal comfort for humans. Thermal comfort is defined as satisfaction with one's thermal environment and is influenced by both physical and physiological factors. Key physical factors discussed include air temperature, relative humidity, air movement, and surface temperatures. The recommended air temperature range for thermal comfort is 19-28°C. Both low and high relative humidity can cause discomfort, and moderate air movement from fans can improve comfort in warm conditions.

1. THERMAL
COMFORT

2. THERMAL COMFORT
• That condition of mind which expresses
satisfaction with the thermal environment.
• Those characteristics of environment which effects
a person heat lose.
• In terms of bodily sensation thermal comfort is a
sensation of hot, warm, slightly warmer, neutral,
slightly cooler, cool and cold.
• It’s the condition when someone is not feeling
too hot or too cold.

4. SIGNIFICANCEOF THERMAL
COMFORT
⚫ Satisfaction with the thermal environment is
important for its own sake and because it
influences productivity and health.
⚫ Office workers who are satisfied with their thermal
environment are more productive.
⚫ Thermal discomfort has also been known to lead to
sick building syndrome symptoms.

5. ⚫ Although a single static temperature can be
comfortable, thermal delight,is usually caused by
varying thermal sensations.
⚫ The human thermal environment is not straight
forward and cannot be expressed in degrees. Nor
can it be satisfactorily defined by
acceptable temperature ranges. It is a personal
experience dependent on a great number of criteria
and can be different from one person to another
within the same space.
SIGNIFICANCE OF THERMAL
COMFORT

6. ⚫ Adaptive models of thermal comfort allow
flexibility in designing naturally ventilated
buildings that have more varying indoor
conditions. Such buildings may save energy and
have the potential to create more satisfied
occupants.
⚫ The combination of high temperature and high
relative humidity serves to reduce thermal comfort
and indoor air quality.
SIGNIFICANCE OF THERMAL
COMFORT

7. FACTORS AFFECTING THE
THERMAL COMFORT
The consciousness for comfort of human beings
depends on conditions for the thermal balance
between the body and the environment. It is
determined by the following factors:
Physical factors:
⚫ Air temperature,
⚫ Temperature of the surrounding surfaces,
⚫ Relative humidity,
⚫ Air movement in the vicinity of the body,
⚫ Air quality
⚫ Noise level

8. Physiologic factors:
⚫ Weight and body height,
⚫ Metabolism or heat production of the body
⚫ Clothing
⚫ Well being generally and sickness, such as the
common cold or flu which affect our ability to
maintain body temperature

9. AIR TEMPERATURE
A temperature is a comparative
objective measure of hot and cold.
Air temperature is the temperature of
the air surrounding the body. It is
usually given in degrees Celsius
(°C).The temperature in a building is
based on the outside temperature
and sun loading plus whatever
heating or cooling is added by the
HVAC or other heating and cooling
sources. Room occupants also add
heat to the room since the normal
body temperature is

10. ⚫ The temperature of the air that a person is in
contact with, measured by the dry bulb temperature
(DBT)
⚫ The recommended temperature range to optimize
indoor thermal comfort for most people is 19°C to
28°C*. This temperature range is appropriate for
the sedentary or near sedentary physical activity
levels that are typical of general office work. This
recommendation assumes that people dress
appropriately to the external seasonal demands.
⚫ The temperature in a building is based on the
outside temperature and sun loading plus whatever
heating or cooling is added by the HVAC or other
heating and cooling sources. Room occupants also
add heat to the room since the normal body
temperature is much higher than the room

11. Warm weather
⚫ Wear clothing appropriate to the external climate.
⚫ Drink cool water frequently, even if you are not
thirsty.
⚫ Try to increase air movement to allow evaporation
of sweat by opening windows and doors where
practical and with the use of personal or ceiling
fans.
⚫ Use blinds, curtains and solar film to decrease
radiant heat from the outside environment.
⚫ Negotiate with local management for staff and
students to take breaks in cooler and/or less humid
areas or transfer some work to cooler and/or less
humid areas.
⚫ Negotiate to alter working hours so that work can
be done in the cooler parts of the day such as early
morning.

12. Cold weather
⚫ Wear sufficient clothing with high thermal
properties (eg wool, polar fleece).
⚫ Use a throw rug.
⚫ Move around and engage in active tasks as
physical activity generates bodily warmth.
⚫ Shelter from external winds.
⚫ Drink warm fluids.
⚫ Use approved room heaters in un-heated
or non air-conditioned areas.

13. TEMPERATURE OF THE
SURROUNDING SURFACES
RADIANT TEMPERATURE
⚫ Thermal radiation is the heat that radiates from a
warm object. Radiant heat may be present if there are
heat sources in an environment.
⚫ Radiant temperature has a greater influence than air
temperature on how we lose or gain heat to the
environment.
⚫ Examples of radiant heat sources include: the sun; fire;
electric fires; ovens; kiln walls; cookers; dryers; hot
surfaces and machinery, molten metals etc.

15. RELATIVE HUMIDITY
Humidity
⚫ Air will generally include moisture in the form of water
vapour. Absolute humidity is the mass of water vapour
in a volume of air divided by the mass of dry air.
⚫ Humidity can be measured using a hygrometer.
⚫ If water is heated and it evaporates to the surrounding
environment, the resulting amount of water in the air will
provide humidity
⚫ Relative humidity is the ratio between the actual amount
of water vapour in the air and the maximum amount of
water vapour that the air can hold at that air temperature
⚫ RH = (actual water vapour density / saturation water
vapour density) x 100

16. ⚫ Humidity influences thermal comfort. The higher the relative
humidity, the less heat a person is able to lose heat through
the evaporation of moisture on the skin, and so the hotter
they will feel.
⚫ Conversely, air that is too dry can cause problems such as
dry eyes, nose, ears and throat. Typically, a relative
humidity of 40 to 60% is appropriate in many buildings.
⚫ Humidity also affects the performance of buildings, causing
slip hazards, damage to equipment and the corrosion and
decay of the building fabric as well as poor performance of
insulation.
⚫ High humidity environments have a lot of vapour in the air,
which prevents the evaporation of sweat from the skin. In
hot environments, humidity is important because less
sweat evaporates when humidity is high (80%+)

17. AIR MOVEMENT
⚫ Air speed is defined as the rate of air movement at a
point, without regard to direction
⚫ The heat balance of human beings is also influenced
by air movements or the air velocity in its immediate
surroundings.
⚫ Higher air velocities lead to higher heat transfer at
areas of exposed skin and to local cooling of the skin,
which is sensed as uncomfortable.
⚫ At normal room temperatures (20 to 22 °C), acceptable
air velocities of 0.1 to 0.2 m/s are given.
⚫ Apart from the mean air velocity, also the frequency
and amplitude of the velocity variations influence the
comfort.

18. ⚫ At the same constant mean air velocity, airflows
with high level of turbulence are sensed
uncomfortable.
⚫ In contrast, at high ambient air temperatures and
humidity, high air velocities lead to better thermal
comfort (ceiling or table fans in summer
conditions).