Indices of Thermal Comfort

INDICES OF THERMAL COMFORT

Measurement of thermal comfort level are complex and many indices have been proposed over the years. They are: 

Air temperature

• Initially the air temperature as measured from a dry bulb thermometer was taken as the indicator of thermal comfort.

• But it was found to be a unsatisfactory measure as comfort levels depend on other factors too.

Air temperature and humidity

• Later air temperature and humidity levels were considered to convey the thermal comfort levels.

• This was also unsatisfactory.

Cooling power

• This takes into consideration the following factors

• Air temperature

• Humidity

• Air movements

• A device called Kata thermometer devised by Hill is used atasquan to measure cooling power.

• A dry Kata reading of 6 or above and a wet Kata above 20 indicates thermal comfort.

Effective temperature

• The different factors determining thermal comfort 89889aib, IS temperature, humidity and air movements are combined together into a single index - Effective temperature.

• Effective temperature is the temperature in an environment with 100% humidity and no air movements which will induce the same level of rajons thermal comfort as in the present situation.

• For example, if the effective temperature is said to be od beau 30°C, it means that the thermal comfort is equivalent 9oneisto one in an environment with temperature 30°C, 100% bas eldstromos humidity and no air movements.

• But as effective temperature does it not take into consideration, the effect or radiant heat energy.

Corrected effective temperature

• The effective temperature is adjusted by considering the loss or gain of heat by radiation to arrive at a corrected effective temperature (CET).

• Thus CET is determined by 4 factors.

• air temperature

• humidity

• air movements

• radiant heat

• Corrected effective temperature is measured using a combination of

• globe thermometer - to measure air temperature adjusted for radiant heat

• wet bulb thermometer - to measure humidity

• air speed measurement