What is Thermal comfort ?

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The building provides shelter and protection from external weather conditions and, living environment for the occupants. Since the occupants spend more than 80% of their time in either house or office, therefore, evaluation of indoor thermal environment is essential. Previous studies of thermal comfort have revealed that buildings built with climatic considerations provide an acceptable thermal environment for building occupants. 

Urbanization, civilization and high expectation of occupants have increased the demand of thermal environment within a narrow comfort bandwidth in all types of buildings. The methods and different approaches used for the assessment of indoor thermal environment, comfort practices and findings of previous studies are some of the important aspects to understand the thermal comfort in buildings. 

As per ASHRAE 55-2010, thermal comfort is that condition of mind, which expresses satisfaction with the thermal environment, and it is assessed by subjective evaluation. Similarly, thermal comfort is also defined by ISO 7730 (2005). 

Acceptable range of operative temperature and humidity conditions
(Source: ASHRAE 55-2010)

Mainly, two approaches are commonly being used in contemporary thermal comfort research: heat balance approach and adaptive comfort approach. Literature reveals that Professor Ole Fanger in 1972 developed the first heat balance model for thermal comfort, and still it is widely used for defining thermal environmental conditions. This approach defined method to evaluate indoor thermal environment conditions from the built spaces maintained under uniform and steady thermal environment.

PO Fanger defined thermal comfort index called PMV (Predicted Mean Vote) and PPD (Percentage Predicted Dissatisfied) which is a function of four thermal environment variables, namely 
1. Room air temperature, 
2. Mean radiant temperature, 
3. Relative humidity, 
4. Air velocity 

and two personal factors such as 

5. Activity level 
6. Clothing insulation.

Percentage Predicted Dissatisfied (PPD) as a function of Predicted Mean Vote (PMV)
(Source: Fanger P.O.  1972. Thermal comfort, analysis and applications in environmental engineering. McGraw-Hill, New York.)

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