The temperature of the normal human body is 98.6 degrees Fahrenheit. Our body is like an engine, which generates power and heat by consuming fuel. The food that we eat contains lots of calories and when we consume it, it gets converted partially into energy, and partially into heat. Further, when we perform some physical work, additional heat is produced as the previously stored energy gets used up.
For the body to remain comfortable, the total amount of heat generated inside the body should be released to the surroundings, this is called body comfort. The body comfort is achieved at certain values of temperature, relative humidity and flow rate of air inside the room. Though the body itself needs a certain amount of heat to maintain its temperature, it usually produces more heat than it requires. This is the reason the person tends to feel uncomfortable.
The body gives up its heat by three natural processes, namely convection, radiation and evaporation. The heat given up by convection and radiation process depends on the temperature of the surroundings, and heat given up by evaporation process depends on the humidity of air. If the surrounding temperature is excessively lower than body temperature, which happens during the winter months, the body loses an extra amount of heat and it feels uncomfortable. When the surrounding temperature is excessively high, which occurs during the summers, the body absorbs heat from the surroundings, thus additional heat is generated inside the body that causes highly uncomfortable conditions for the body. The body always loses heat by evaporation, the less is the humidity of air, and more is the loss of heat.
Factors affecting Body Comfort
After a lot of research, ASHVE (American Society of Heating and Ventilating Engineers) found that the body tends to give up most of the excess heat within certain range of temperature, relative humidity and proper flow rate of air inside the room. Due to this, the body feels comfortable and works highly efficiently at these conditions. These conditions are called comfort conditions or comfort zone. Here are the comfort conditions:
1) Surrounding temperature: It has been found by ASHVE that the body feels comfortable at a temperature of around 27.7 degree Celsius during summers and around 22 degree Celsius during winters.
2) Relative humidity of air: Relative humidity is the content of the dew or moisture in the air. If the dew is too low the body becomes very dry, and if it is very high the body becomes wet as the moisture given up by the body will not get evaporated. ASHVE found that the human body feels comfortable within the relative humidity value of 35 to 65%.
3) Velocity of air in the surroundings or inside the room: The velocity of air inside a room should be high enough for the person to feel comfortable and at the same time it should be within limits to avoid excessive noise from an air conditioning unit.
HVAC designers perform lots of calculations to find out various sources of heat inside the room. Then they suggest the size of the air-conditioning unit which will be able to remove the excessive heat inside the room so as to maintain comfort conditions.