Relative humidity is a misleading quantity because it is a function of not only the amount of absolute moisture in the air but also the temperature (and pressure). Relative humidity is defined as 100% when the temperature is equal to the dewpoint (a measure of the absolute amount of moisture in the air). Relative humidity is the amount of moisture expressed as a percentage of the amount of moisture that would be needed for saturation of the air. Therefore, with the same amount of absolute moisture in the air the relative humidity will change with temperature. A relative humidity of 100% at 50F feels much different than 100% at 77F and reflects a much different amount of moisture in the air. A relative humidity of 100% rarely occurs around here with temperatures above 80F. The reason for this is that is very difficult to have a dewpoint over 80F. Situations such as 95F temperature and 95% relative humidity never occur.
This creates some interesting situations. For example, with a dewpoint of 77F and a temperature of 95F you have a relative humidity of 56%. This doesn't sound so bad but is actually quite miserable. If the temperature drops to 77F you then have 100% relative humidity. Therefore, with the same amount of absolute moisture in the air you can have wide variations in the value of relative humidity. Dewpoint is a better parameter to watch since it reflects the actual amount of moisture in the air. Relative humidity is, however, important if you are concerned about mold growth.
Relative humidities will generally be quite high in the mornings as the temperature will drop to the dewpoint (and dew will form). Once the temperature starts rising the relative humidity will drop even though the same amount of total moisture may be in the air.
During the summer (around here) when it is hot and humid, you can generally expect that your AC will reduce the dewpoint inside your house to something around 60F, plus or minus. Typical summer dewpoints around here are 70-78F. That difference may not sound like a lot but it makes a huge difference in how you feel. Generally, ACs will have a 20-22F drop across the coil. If the temperature inside your house is 78F then the air coming out of the vents will be around 58F. Not all of the moisture can be condensed so you will wind up with around a 60F dewpoint, plus or minus.
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Originally Posted by SFSkol
Very interesting.
From AccuWeather web site for The Villages right now;
Humidity: 94%
But, that's outside.
Could it be that since you have it set at 77 it has over time reduced the interior humidity? I've been using fans during the evening which of course sucks in the humid air. Guess I should get a hygrometer.
Humidity Averages for Florida in June - Current Results |