Human thermal environments
The sun, at a temperature of around 5500°C, provides heat to the earth at the top of the atmosphere at a rate of around 1370W m−2 (the Solar Constant-the exact value depending upon the orbit of the earth around the sun). Human existence, along with that of other organisms, depends upon that energy. On the earth, the energy is transferred from place to place and from one form to another hence creating a wide range of environments. The challenge for every person is to successfully interact with his or her local environment. The human body responds to environmental variables in a dynamic interaction that can lead to death if the response is inappropriate, or if energy levels are beyond survivable limits, and it determines the strain on the body as it uses its resources to maintain an optimum state. In the case of the thermal environment this will determine whether a person is too hot, too cold or in thermal comfort.