It consists of a hollow copper sphere painted matt back to absorb radiant heat, with a temperature sensor at its centre. When it reaches a steady state (after 15 minutes or so depending on the size of the globe and the environmental conditions) the heat exchanges by convection and radiation will be in equilibrium, and the temperature recorded by the sensor will be somewhere between the air and radiant temperature. This is referred to as the globe temperature (tg) or black globe temperature and resembles the thermal conditions felt by the human body.
MRT = tg + 2.42 x air velocity in m/s (globe temperature – air temperature)
(equation ref Novalynx Corporation 2010 - this equation is dependent on the size and emissivity of the globe thermometer, and the units they show for air velocity are incorrect - cm/s, rather than the correct m/s shown above)
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