How much does an air conditioner dehumidify?

Question

Providing an air conditioner is powerful enough to cool a room well and is rated at, say 3 litres an hour of water extraction, how would the relative humidity of the room be affected? If the relative humidity, was %80 before the AC was turned on, what, roughly, would the relative humidity be a few hours after use? I know many factors are involved, not least being the make and model of the AC but I am looking for a very vague idea. Could a reduction of %40 humidity be achieved, or is %5 more likely?

Answer 1

There really isn't enough information given to perform a calculation.
Getting the Right Size is Essential to Getting the Most from Your New Equipment

The following is taken from the EPA "Energy star" site. (Link given below)
Some contractors will use rules of thumb to size your air conditioner, but rules of thumb can overestimate the size needed. A good contractor will use a design load calculation to size a central air conditioner to your home. The contractor will need to check the following six factors.

How well your house is insulated
How well air leaks are sealed
How well your ducts are sealed and insulated
The size, type and number of windows and the direction they face
Shading provided by overhangs and landscaping
The size, layout, and orientation of your house
(End of Energy Star site quote)

Some more info on humidity, if there is absolutely no addition of water vapor into the room (Or make up of 80% RELATIVE humidity air, or sweating of people, vapor in people's breath, or steam from cooking) but there was heat input into the room through the walls, etc, that would allow the AC to continue to operate you would expect that eventually the dew point of the air in the room would drop to the dew point of the temperature of the cooling coil, which would be very dry air indeed.

To give you an idea of what is missing, you have not indicated what temperature the room is at. 80% RELATIVE humidity at 72 degrees F is far more water than 80% RELATIVE humidity at 0 degrees F .

The term Relative is important because % relative humidity is measured against the total handling capacity of the air at the given temperature. If the air can hold a maximum of 5% water vapor at a given temperature, than 5% water vapor is 100% relative humidity, at that temperature. 4% water would therefore be 80% relative humidity, and 2% water vapor would be 20% relative humidity.

If humidity control is important in your climate, choice of AC is pretty important. If you get an AC that is too big it will only run part of the time and will therefore be extracting that moisture put into the atmosphere by humans and the outdoors part of the time. People with AC's that are way too large discover that they have cool, damp rooms.

http://www.energystar.gov/index.cfm?fuseaction=sizing.showIntro
If you are trying to figure out how to size a central a/c unit the link above can provide guidance, but contractors in the area can also help.

If you are looking at sizing a room AC without going to the expense of hiring a contractor to help would involve, talking to people in the area who use room AC's in rooms similar to the one where you need AC, or talking to the Home Depot people should give you a relative feeling for what is the right size AC to buy for optimum Temperature and Humidity control for your section of the country.

The Energy Star site also gives some direction for Room AC's that would also be helpful.
http://www.energystar.gov/index.cfm?c=roomac.pr_properly_sized

Answer 2

This Site Might Help You.

RE:
How much does an air conditioner dehumidify?
Providing an air conditioner is powerful enough to cool a room well and is rated at, say 3 litres an hour of water extraction, how would the relative humidity of the room be affected? If the relative humidity, was %80 before the AC was turned on, what, roughly, would the relative humidity be a few...

Answer 3

I would presume the relative humidity difference would be directly proportional to the relative temperature difference outside. If you achieved a 10% temp difference expect a 10% humidity difference. The air conditioner only removes water as a consequence of cooler air being unable to hold the same amount of water as warm air. Hence the two factors are directly related.
Hope this helps

Answer 4

That's a design question. It can be designed to make the air almost arbitrarily dry. Units like this are used to help dry out a house (like mine) after the wind blew away the roof during a heavy rainstorm. You could do some research and figure out how much water is contained by the air in the room you are considering at 80% RH, then figure out how long it would take this AC to remove it at 3 liters per hour. As the reference shows, 40-60% RH is the customary target.

Answer 5

it dosent. it is not a de humidifier. an air conditioner does not cool the air, it removes the heat from the air and transfers it to the outside