Comfort  A condition of the mind that expresses        

                                        satisfaction with the thermal environment


We routinely use the word Comfort with little to no perception of the underlying complexity of the human physiology involved. It's understandable since Dave Lennox, Lewis Carrier and James Trane are so convincing that all you need to assure exceptional comfort is one of their new and improved heating and cooling machines. But the truth is, comfort is not found in a mechanical box. Its a "condition of the mind" with the brain calling the shots. Perhaps this misconception explains why over 60% of American homeowners are not satisfied with the comfort of their homes.   


The human body is an exothermic chemical reactor, converting food and nutrients into energy for work. The process is called metabolism and a byproduct is excess heat. An average resting person generates about the same amount of heat as a 100 watt light bulb.  













The Physiology of Comfort


A Balancing Act

To protect our organs and maintain cell chemistry, our bodies must operate around 98.6F, +/- 1°F.  Deviations of more than 2°F can lead to serious consequences. Thankfully, our bodies were created with their own internal cooling system AND it's totally automatic.


The body's thermostat is located in a region of the brain called the hypothalamus. It sits right behind yours eyes, just above the brain stem. It is about the size of an almond. One of its functions is the control of body temperature. 


Although the hypothalmus senses temperature itself, it also receives input from some 166,000 temperature sensors located just beneath the surface of our skin. These sensors are called thermoreceptors and they come in two varieties - hot and cold.













Cold receptors sense cold and are found in greater density than heat receptors. They start to perceive cold sensations when the surface of the skin drops below 95°F. Hot receptors start to perceive hot sensations when the surface of the skin rises above 86°F


The highest concentration of thermoreceptors can be found in the face and ears. This is why your nose and ears always get colder faster than the rest of your body on a cold winter day.


The hypothalmus uses input from these thermoreceptors to determine the appropriate response.

Infrared image of thermal plume from human body

When the body's core temperature drops,  vasoconstriction occurs. The blood vessels constrict and move deeper into skin tissue. This preserves body heat by reducing heat loss through the skin. If necessary, involuntary shivering occurs, generating internal heat. Goose bumps appear which stand body hair erect, increasing its insulation value.


When the body's core temperature rises, blood vessels dialate and move closer to the skin's surface.  Blood flow near the skin's surface naturally cools the body. Next, prespiration appears and breathing increases, providing  additional cooling.  The process is called vasodilation.

Thermoregulation - The human balancing act.  

Textbook Reference - Physiological Regulation and Homeostasis, pp. 785-786