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Is it colder in damp air?

  1. It feels colder when the air is damp. Is this true?

     

     

  2. But what actually causes the feeling of cold?

     

     

  3. But it definitely feels colder when in water than in air. How is that?

     

     

  4. Summer is more comfortable when the air is dry than when it is humid. Yes or no?

     

   Written by: LEE Boon-ying


  1. It feels colder when the air is damp. Is this true?

    The feeling of cold depends on many factors --- for instance, the wind, humidity, whether the person is standing in the sun or shade, whether he/she is exercising, the clothing worn, and whether his/her skin is damp.

    Let's first look at how heat is taken away from the body. To simplify the argument, let's assume that the body is dry, exposed, motionless, in still air and in the shade. The question now becomes: whether dry air or damp air takes away heat from the body faster, i.e. whose thermal conductivity ('conductivity' from hereon) is higher.

    Many people think that the conductivity is higher for moist air than for dry air. However, this is not true. Below is a curve obtained from experiments:-

    figure 1

     

    The diagram above shows that the conductivity of water vapour is actually much less than that of dry air. So, if humidity (i.e. water vapour) has any effect on the conductivity of air, it would make it less conductive, not more.

    So the simple answer is no.

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  2. But what actually causes the feeling of cold?

    Moving air, i.e. wind, which carries heat away from the body. People sometimes call it the 'wind chill' effect. It feels much colder in a windy day than when it is calm.

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  3. But it definitely feels colder when in water than in air. How is that?

    In answering this question, we can no longer refer to Figure 1 above, which refers to water vapour, not water. The conductivity of water is about 25 times that of air, i.e. water conducts heat 25 times faster than air. You may feel chilly standing naked in still air at 10 degrees Celsius, but it would be much harder to jump into a pool at 10 degrees water temperature.

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  4. Summer is more comfortable when the air is dry than when it is humid. Yes or no?

    Yes. When the air is dry, the moisture on your skin evaporates faster. This cools the body more. It would be even better if there is a breeze, which would speed up evaporation and make it more comfortable.

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Reference: 'Weatherwise', T. Schlatter, p.42-43, July/August 2002

Last revision date: <19 Dec 2012>