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Saturday, July 22nd, 2006

Considerations About Humidity

Categories: [ Science ]

PVS Relative humidity is the ratio of the current amount of water (vapor) in the air over the maximum amount of water the air can hold (when the air is saturated with water vapor). The latter value depends on the temperature of the air: the warmer the air, the more water it can hold. The graph on the left shows this value, called the saturation vapor pressure, and has ben drawn based on the Goff-Gratch equation

The temperature to which a given volume of air must be cooled down in order for the water it contains to reach the saturation vapor pressure is called dew point. When the dew point is below 15 °C, the atmosphere is comfortable. Between 15 °C and 20 °C it is uncomfortable, and above it is considered as oppressive. Moreover, a sane living atmosphere should have a relative humidity comprise between 30 and 50%. From this we can infer that limit comfortable conditions are e.g., 26 °C at 50% humidity, 30 °C at 40% humidity or 35 °C at 30% humidity.

Also, dry air feels cooler at room temperature. When relative humidity is ideal, temperatures in buildings can be lowered without causing discomfort to people in them.

Finally, when the relative humidity is low, one is more prone to electrostatic discharge, which is prevented in humid conditions because the surface layer of moisture on many objects conducts electric charges harmlessly to earth and prevents electrostatic charges to accumulate on the human body.

Humidex and Wet Bulb Globe Temperature Wet Bulg Globe Temperature

Formulas about dew point

[ Posted on July 22nd, 2006 at 19:55 | no comment | ]