HVAC Design – Factors Affecting Body Comfort Conditions Such As Climate, Activity & Air Velocity

The human body feels comfortable within certain range of temperature, relative humidity and velocity of air inside the room, these are called comfort conditions or comfort zone. The values of the parameters within comfort zone depend upon a number of factors. These are:

1) Climatic and seasonal variations throughout the year: It has been found that people living in the colder climates, like people in US, and Europe feel comfortable at the temperatures lower than the people living in the warmer climates like India, Sri Lanka, etc. However, comfort conditions will also vary as per the seasons, thus the comfort temperature rises during the summers.

2) Clothing worn by the person: The heat loss by the body by way of convection, radiation and evaporation greatly depend upon the clothing worn by the person. If the person wears light clothing, they prefer lower surrounding temperature. This is the reason why people in US prefer higher temperature than the people living in UK.

3) Age and sex: By nature, the rate of metabolism is lower in women than in men, hence women feel comfortable at  temperature higher (1 degree Celsius) than men. Similarly, children require higher temperature than adults. This is the reason why the temperature inside maternity halls is maintained at 2-3 degrees higher than that used by adults.

4) Activity of the person: The person performing physical work in a factory will need temperatures lower than those required by the person sitting inside a cinema hall. The HVAC design of dancing halls is usually very tricky as the area near and around the stage has to be maintained at a temperature less than the audience sitting area.

5) Duration of stay: The person working in an office stays there continuously for 8 hours or more, while the person going to a bank or an ATM center will remain there hardly 10-15 minutes. It has been found that the shorter the duration a person stays in a room, the temperature a person feels comfortable at gets closer to the external temperature. This means that if the atmospheric temperature is high then the person will feel comfortable at the higher temperatures. But as they stay longer, they will feel comfortable at the lower temperature.

6) Velocity of air: The velocity of the air inside the room should be high enough so that there is no suffocation and there is sort of a natural flow of air. It should not be so high that the air-conditioning units will start making disturbing noise.