Relative Humidity

Relative humidity is a term used to describe the amount of water vapor that exists in a gaseous mixture of air and water vapor.

The relative humidity of an air-water mixture is defined as the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at a prescribed temperature.

Relative humidity is normally expressed as a percentage and is calculated by using the following equation:^[1]

Humans are very sensitive to humidity, as the skin relies on the air to get rid of moisture. The process of sweating is your body's attempt to keep cool and maintain its current temperature. If the air is at 100-percent relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high. If the relative humidity is low, we can feel much cooler than the actual temperature because our sweat evaporates easily, cooling ­us off. For example, if the air temperature is 75 degrees Fahrenheit (24 degrees Celsius) and the relative humidity is zero percent, the air temperature feels like 69 degrees Fahrenheit (21 C) to our bodies. If the air temperature is 75 degrees Fahrenheit (24 C) and the relative humidity is 100 percent, we feel like it's 80 degrees (27 C) out.

People tend to feel most comfortable at a relative humidity of about 45 percent.Humidifiers and dehumidifiers help to keep indoor humidity at a comfortable level.

Buildings

When controlling the climate in buildings using HVAC systems the key is to control the relative humidity in a comfortable range - low enough to be comfortable but high enough to avoid problems associated with very dry air.

When the temperature is high and the relative humidity is low, evaporation of water is rapid; soil dries, wet clothes hung on a line or rack dry quickly, and perspiration readily evaporates from the skin. Wooden furniture can shrink causing the paint that covers these surfaces to fracture.

When the temperature is high and the relative humidity is high, evaporation of water is slow. When relative humidity approaches 100 percent, condensation can occur on surfaces, leading to problems with mold, corrosion, decay, and other moisture-related deterioration.

Certain production and technical processes and treatments in factories, laboratories, hospitals and other facilities require specific relative humidity levels to be maintained using humidifiers, dehumidifiers and associated control systems.

What is the ideal humidity for electronics?

The `ideal' humidity would be very low, simply because humidity lends itself to corrosion of the circuit boards and connectors. When humidity reaches a higher level, items such as rusting of any of the steel components, corrosion of the circuit boards and connections tend to deteriorate.

So unless you're in a sealed chamber where humidity can be controlled, you might want to consider things like room dehumidifiers or even central air conditioning in the summer to help control the humidity levels. In the winter months, humidity tens to be less in the colder climates and that's part of the reason that humidifiers are installed on furnace systems among other things. Humidity control is more for `creature comfort' than anything else.

But this leads to another problem, which is static electricity when the humidity is too low.That too, can be bad for circuit boards because a static discharge can reach potentials of several thousand volts.

According to CompTIA A+, a safe humidity is between 50 and 80 percent.

Read more: http://wiki.answers.com/Q/What_is_the_ideal_humidity_for_electronics#ixzz1E0kmT3DA


references:
1. wikipedia
2. http://science.howstuffworks.com/dictionary/meteorological-terms/question651.htm
3. http://wiki.answers.com/Q/What_is_the_ideal_humidity_for_electronics