People's level of Thermal Comfort or discomfort is a measure of the effort required to sustain a balance (Homeostasis) between the human body's Metabolic production of heat and moisture and the surrounding conditions. If a loss of thermal balance results in overheating, Hyperthermia results; extreme cooling can result in Hypothermia.

Thermal Comfort is affected by a number of interrelated factors:

• The amount / effectiveness of Clothing

• Air Temperature

• Radiation to or from surroundings (including the sun)

• Relative Humidity (RH) of the air

• Air Movement

Environmental Temperature (te):

As a measure of thermal comfort or dis-comfort, simple ('Dry-Bulb') air temperature is inadequate, but to incorporate a measure of Relative Humidity (RH) is too complex for manual computation. However, the primary modes of heat transfer to and from surroundings are Convection and Radiation. So, a measure for the sensation of thermal (dis)comfort (adequate except in situations of very high humidity), to be used in calculations of thermal performance of buildings is given by environmental temperature. 

Radiant Temperature

Applies equally in the case of Radiation to the human body from hot bodies and surfaces - from the sun, from a fire, from stoves or heaters, and from hot building surfaces (such as unshaded and uninsulated walls land roofs and unshaded windows in hot weather), and of radiation from the human body to cold building surfaces (such as uninsulated walls and roofs/ceilings and uncurtained windows during cold weather, especially during winter nights, when horizontal surfaces lose heat to the Night Sky).

Comfort and Discomfort

These are partly subjective matters: they depend on cultural and personal factors - custom, Acclimatisation, age, state of health, specific experience, and expectations. In general, people tend to be able to stand higher temperatures in summer during the day than at night, and lower temperatures in winter during the night, when they can use warm bedclothes, than during the day.