The optimum effective temperature for human comfort is

✅ Explanation:
Effective temperature 
It is the temperature of saturated air at which a person or human being would feel the same level of comfort as in the actual environment.
It includes comfort temperature, velocity, and purity.
Factors affecting the effective temperature
Climatic and seasonal differences
People living in a warmer region feel comfort at higher effective temperature than the people living in a colder region.
In summer the effective temperature is 21.6 ° C and in the case of winter, the optimum effective temperature is 20 °C.
Age and Gender
Children and old age persons need 2-3 °C higher effective temperature in comparison to adults. Same the case is with the women.

Kind of activity
If a person is involved in the foundry shop, dancing or jogging, etc needs a lower effective temperature in comparison to the person in the rest.
Density of occupants
Highly densely occupied needs a lower effective temperature in comparison to the less densely occupied.
Kye point-
ASHRAE (American Society of Heating Refrigeration and  Air conditioning Engineers), conducted a survey on different kinds of people subjected to a wide range of environmental temperature conditions, humidity purity, and air velocity and developed the above comfort chart. 
If the value of relative humidity is above 60%, then the tendency of sticky sensation develops and if the value of relative humidity is less than 50%, then the skin surface is too dry. So the relative humidity for comfort air conditioning is 60%.