How temperature affects relative humidity

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  • #1
anti_matter
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I have a fan in crawlspace that I can turn on to draw in fresh air. This could reduce the relative humidity by raising the air temperature, and lowering the moisture density. However, air temperature doesn't go up very much because the dirt and foundation wall tend to keep the air at around 55 degree (F).

Given the outside air temperature and RH, and the crawlspace air temperature and RH, how can I determine whether turning on the fan would reduce RH?

I could not find a formula to calculate RH at a second temperature given RH at one temperature.

I did find some formulas about vapor density and dew points. I just am not sure what remains constant when air travels to a cooler area. Does the water vapor density remains the same, or does dew point remain the same?
 
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  • #3
The relative humidity is defined as the partial pressure of the water vapor in the air divided by the equilibrium vapor pressure of water vapor at the air temperature (times 100 %). The partial pressure of the water vapor is equal to the total air pressure times the mole fraction of water vapor (which doesn't change in the air stream). Using these relationships, you can calculate it for yourself. T

Chet
 

What is relative humidity and how is it affected by temperature?

Relative humidity is a measure of the amount of water vapor present in the air relative to the maximum amount of water vapor that can be held at a given temperature. As temperature increases, the air's ability to hold water vapor also increases, resulting in a decrease in relative humidity. Conversely, as temperature decreases, the air's ability to hold water vapor decreases, leading to an increase in relative humidity.

Why does relative humidity decrease as temperature increases?

As mentioned earlier, as temperature increases, the air's ability to hold water vapor increases. This means that the same amount of water vapor in the air will now make up a smaller percentage of the maximum amount of water vapor that can be held at the higher temperature, resulting in a decrease in relative humidity.

How does temperature affect the amount of water vapor that the air can hold?

The amount of water vapor that the air can hold is directly proportional to temperature. This means that as temperature increases, the air's ability to hold water vapor also increases. Conversely, as temperature decreases, the air's ability to hold water vapor decreases.

What is the relationship between temperature and dew point in regards to relative humidity?

Dew point is the temperature at which the air becomes saturated with water vapor. As temperature and dew point get closer together, the air becomes more saturated and relative humidity increases. Therefore, as temperature increases and dew point remains constant, relative humidity will decrease.

How does temperature affect the comfort level of a given relative humidity?

Temperature plays a crucial role in determining the comfort level of a given relative humidity. Warmer temperatures with higher relative humidity can make a person feel hotter and more uncomfortable due to the body's decreased ability to cool down through evaporation. On the other hand, cooler temperatures with higher relative humidity can make a person feel colder and more uncomfortable due to the air feeling damp. The ideal comfort level is often achieved with a relative humidity of around 40-50% and a temperature between 68-72°F.

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