how is humidity removed?

[dtx]

reading posts about properly sized systems remove humidity from the air when the system is running....however, do some of the systems (Carrier Infinity) also remove humidity by just running the fan?

is humidity removed by just having air flow or does somehow the coil work when the compressor is off? ie- does just running a ceiling fan effectively remove humidity out of a room?

[Panama]

To remove humidity from the air the fan must blow the air across a coil that is colder than the dew point of the air. This causes the water in the air to condense on the coil. The water then drains off the coil and out through the drain line. The air coming out the supply vents will then be drier than the air that entered the air conditioner coil.

If you simply run the fan without turning on the air conditioner the air will absorb any water left on the coil and thus increase the humidity.

[iamrichard]

To remove humidity you either have to use something (a desicant) to absorb the moisture or you have to have the coil cooler than the dewpoint and preferably above freezing conditions (32 degrees F.).

Humidity is nothing more than water vapor. The most common method for removing humidity in residential systems is removal with the air conditioning unit. Since the coil normally operates below the dewpoint it causes the water vapor to change state to a liquid where it falls into a pan and then down the condensation drain.

With less humidity in the air people feel cooler.

Richard
http://highperformancehvac.com

[RoBoTeq]

Just another way of stating what has already been stated; to remove humidity you must first condense it into a liquid and then either drain it away or absorb it into a disicant that will release it out of the conditioned area.

A fan alone will not remove humidity. Some system controls do turn on the cooling system when the thermostat is not calling for cooling. I am not one to want my customers to loose control of the temperature they have set their thermostats to.

[amickracing]

To add to what they have said, Trane, American Standard, Infinity systems (and I'm sure other's aswell) have made inprovements for removing humidity.

They'll slow the fan speed down when the call for cooling 1st starts. Doing this allows more time for the air to go across the coil, lowering both the temp of the coil and air and removing more moisture. It won't run like that very long, maybe a few minutes or so then it will ramp up closer to full speed and go about cooling the air a bit farther with out worrying so much about humidty (since a lot of it was taken out in the 1st few minutes).

Aint' technology great?

[RoBoTeq]

Originally posted by amickracing
To add to what they have said, Trane, American Standard, Infinity systems (and I'm sure other's aswell) have made inprovements for removing humidity.

They'll slow the fan speed down when the call for cooling 1st starts. Doing this allows more time for the air to go across the coil, lowering both the temp of the coil and air and removing more moisture. It won't run like that very long, maybe a few minutes or so then it will ramp up closer to full speed and go about cooling the air a bit farther with out worrying so much about humidty (since a lot of it was taken out in the 1st few minutes).

Aint' technology great?

Unless you are using an aftermarket control, a variable speed blower is required for this feature. I believe all brands have a variation of this feature for their variable speed blower units.

Also, the fan can be reduced for more then a few minutes with variable speed blowers. Systems will operate quite well for long times at lower blower speeds. The problem has always been that when the blower speed was reduced with a psc motor, the excessive moisture on the coil creates so much static pressure that the blower reduces its cfm capacity more and more until the coil gets cold enough to freeze up.

With variable speed motors, the more static that is created by excessive condensate on the coil, the more the VS motor ramps up to compensate in order to maintain enough air across that coil to keep it from freezing up.

Yes; technology is great.

[re2ell]

dtx,

all those who have replied say it well. if you would like to simulate for yourself what goes on when an a/c system is de-humidifying, try this.

fill a glass about 3/4 full of tap water and place on the counter. the exterior surface will remain dry. place ice in the water and in about 2 - 3 minutes you will see condensation forming on the outside of the glass.

you will witness exactly what happens in the process of air conditioning.

by adding the ice, you are lowering the surface temperature of the glass to drop below the dewpoint temperature of the air, and presto!, humidity in the air is condensing.

(this works best outdoors, out of an air conditioned area)

[nina]

RoBoTeq wrote:
> the fan can be reduced for more then a few minutes with variable speed blowers. Systems will operate quite well for long times at lower blower speeds.

very true. I've reprogrammed my Trane XL19i to run unconditionally for 30 minutes using the smaller 1.5 ton compressor, thus giving it more than just a few minutes at low speed to remove moisture. After that, it shuts off the small compressor and prepares for the 'big one' and temps drop quickly. keeps house in S.Florida nicely at 45-48% RH

[RoBoTeq]

Originally posted by nina
RoBoTeq wrote:
> the fan can be reduced for more then a few minutes with variable speed blowers. Systems will operate quite well for long times at lower blower speeds.

very true. I've reprogrammed my Trane XL19i to run unconditionally for 30 minutes using the smaller 1.5 ton compressor, thus giving it more than just a few minutes at low speed to remove moisture. After that, it shuts off the small compressor and prepares for the 'big one' and temps drop quickly. keeps house in S.Florida nicely at 45-48% RH

Sounds like a nice way to set up a two stage system in your neck of the woods.

[MadeinUSA]

The third way the humidity is removed from a system is being thrown back on the condenser coil by means of a water ring on the condenser fan blade like on window units where it evaporates and helps to control the head pressure.

[tmoss]

Nina,
How did you reprogram your xl19? Do you mean you went with a specific stat that provides such ability?

[NormChris]

Originally posted by MadeinUSA
The third way the humidity is removed from a system is being thrown back on the condenser coil by means of a water ring on the condenser fan blade like on window units where it evaporates and helps to control the head pressure.

That is not another method of moisture removal, that is a method of moisture disposal.

[MadeinUSA]

Originally posted by NormChris

Originally posted by MadeinUSA
The third way the humidity is removed from a system is being thrown back on the condenser coil by means of a water ring on the condenser fan blade like on window units where it evaporates and helps to control the head pressure.

That is not another method of moisture removal, that is a method of moisture disposal.

I said removed "from the system", not removed from the air. I just thought being how this thread was in the public section, people might want to know "all" of the ways the water is "disposed" from the system or "removed" from the system.