Question

Relative humidity isn't everything. Why is it that outdoor air of 80 Fo at 55% humidity will feel more “muggy” than a 50 Fo cave at 75% humidity? What other parameter is a better measure of the actual amount of moisture in the air, and how do we define it? Then give two examples of when keeping close track of moisture in the air is important.

Answer 1

1) The reason that the outdoor air of 80 degrees F at 55% humidity will feel more “muggy” than a 50 degrees F cave at 75% humidity is the higher dew point.

Dew point, parameter other than relative humidity is a better measure of the actual amount of moisture in the air.

The dew point is the temperature at which the air needs to be cooled at constant pressure, to achieve 100% relative humidity.

At dew point the air cannot hold anymore water (becomes saturated) in the gas form. Then water vapor have to come out of the atmosphere in the liquid form such as fog or precipitation.

Dew point is directly proportional to the moisture level. The higher the dew point, the more the amount of moisture is in the air. This affects how much comfortable or muggy we feel.

2) Keeping close track of moisture in the air is important because :

- Water vapour is an important atmospheric greenhouse gas as without water vapour we would be 31 °C colder.

- Tracking of moisture helps in achieving correct environmental conditions and minimize the energy cost.

- Tracking of moisture is used to prevent condensation, corrosion, mold, warping or other spoilage - highly relevant for foods, pharmaceuticals, chemicals, fuels, wood, paper etc.