Our skin has hundreds of thousands of sweat pores, they have sensors that sense surrounding temperature. If it is so hot it spills sweat thus cooling body. This is perfect example for cooling by evapouration, you might have observed in India we use clay containers in summer wrapped by wet cloth to cool water. Our sweat exactly does the same. If the sweat pore sensors sense too cold surrounding temperature the tissues themselves shrink to prevent heat loss, just like we wrap up when so cold. Shivering when so cold is something we did not learn, it is automatically fed in our brain we do it by impulse. Shivering creates heat in body when muscles are rubbed against each other. Allah has embedded thermal system in us which consists of skin (Surface), sweat pores (sensors), blood (coolant), brain (in built memory space)