The degree of muscular activity is one of the most important ways in which the body regulates its temperature. Atmospheric influences on our sensation of thermal conditions depend on the interaction of heat, moisture, and air. Air - as air temperature rises, its volume increases and its capacity to hold moisture increases. As air temperature decreases so its volume decreases and its capacity to hold moisture decreases. More commonly, we talk about the humidity ratio or relative humidity of the air.
Vertical effects are especially problematic in buildings.
Mean radiant temperature may be higher or lower than the air temperature in a room. The operative temperature is usually made using a globe thermometer placed at trunk level. With a far-inside globe, equilibrium time is 6 minutes, and using a thermocouple instead of a mercury thermometer the time is 10 minutes. In equilibrium the net heat exchange is zero. The faster the air moves over the globe thermometer the closer tg approaches ta.