OT - Dehumifier and Air Conditioner

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Submitted by briansd1 on May 31, 2011 - 2:14pm

Anyone lived in a humid climate before?

Being from San Diego, I hate the humidity in Philly where I have my second home.

What do you think of getting a dehumifier in addition to running the central air conditioner?

Would I save energy? Would my comfort level increase?

I'm thinking about getting a dehumidifier on each of the 3 floors. I can get some drains installed so that the dehumifiers drain directly into the sewer system. That way I don't have to constantly drain the water.

http://bensbargains.nextag.com/dehumidif...

Submitted by Hatfield on May 31, 2011 - 2:23pm.

I don't think you'd see any additional benefit at all because dehumidifiers and air conditioners use the same underlying principle: cold air cannot hold as much moisture as warm air. Air conditioners and dehumidifiers both use a refrigerant to cool the air, forcing it to precipitate moisture out. Since your house air conditioner is already doing that, the dehumidifiers would be superfluous.

Both processes generate net heat. The main difference between the two is that the air conditioner vents the heat (and the moisture) to the outside, whereas the dehumidifier just dumps the heat into the room and collects the water into a bucket.

Submitted by briansd1 on May 31, 2011 - 2:54pm.

Hatfield, thanks for the answer. I was aware of the technology.

The AC is temperature controlled. Once the indoor temp reaches say 70F, the AC will turn off, so the drying will stop.

The thing is that I want drier air, but not necessarily cooler temp.

Some dehumifiers have a hose attachment so you can have the water drain directly into the sewer and not the bucket.

As a San Diegan, I'm used to drier air.

Submitted by UCGal on May 31, 2011 - 3:05pm.

My sister used one, in addition to an AC, when she lived in Okinawa. On a visit to see her I remember having to drain the reservoir at least once a day. I wasn't paying the utilities... I was just a freeloading sister taking advantage of a free place to stay, overseas. I know she felt the AC didn't remove enough humidity... and Okinawa was even more humid than Philly. Having the drain lines definitely sounds like a good plan to avoid it overflowing.

I also lived in Philly. As a native San Diegan, I feel your pain on the humidity thing. The cliche is correct - it IS the humidity more than the heat that makes you miserable. I was able to get by with AC... but then again, I lived in a leaky, 1900 era, uninsulated house... so the AC only cycled off when I turned it off. I didn't have it on during the day when I was working, so I'd always get home to a hot/humid house... but in 30 minutes I had the house cool enough - even with window units.

Your place is newer construction, right? So I assume you have central air. Are there settings to have it use less power... It may be that your AC unit is oversized for the space - and that's why it's cycling off so much.

Submitted by briansd1 on May 31, 2011 - 3:37pm.

UCGal wrote:

Your place is newer construction, right? So I assume you have central air. Are there settings to have it use less power... It may be that your AC unit is oversized for the space - and that's why it's cycling off so much.

The house is brand new. It's extremely well insulated. In the winter, when freezing outside, it will be 60F inside the house, without heat, just from the lights, applicances and people living inside.

The central AC cycling on and off is not excessive, IMHO -- about the same as my AC here in San Diego.

I think that I'm spoiled. I don't like humid air at all. I'm willing to pay a little more to have a dry house.

Submitted by XBoxBoy on May 31, 2011 - 7:35pm.

I vote to get at least one dehumidifier. I grew up just outside of DC. My bedroom was in the basement, and running the AC helped, but turning on my dehumidifier was far more important for comfort. And yes, definitely get one that drains into a drain so you don't have to empty the pan.

XBoxBoy

Submitted by RichardJamesEsquire on May 31, 2011 - 9:07pm.

"The central AC cycling on and off is not excessive, IMHO -- about the same as my AC here in San Diego."

Yes it is excessive, otherwise you wouldn't be complaining about the humidity.
A good residential unit will run the fan at a lower speed for a longer duration when dehumidification is needed. Variable speed fans and 2 stages of cooling capacity have made dehumidifying residential applications really easy. Your unit either isn't set up correctly, or it's a plain jane old school single stage single speed unit doing 80% sensible heat and 20% latent heat just like it was designed to do. Sized correctly you can see what happens with a higher latent and lower sensible heat load. Oversized in San Diego has no consequence. Throw in humidity and game over.
Get it set up right, get some control over the fan speed, or get a unit to suit the application.

I should add not only will you be comfortable with a 2 stage unit you energy usage should go down as well. The local utility may have a rebate or incentive. Not sure if the fed has a write off this year, they did last.

Submitted by MANmom on June 1, 2011 - 8:51am.

I have lived in Virginia, we had both, only the dehumidifier was in the basement. Mold grows quickly in a damp area, you will need at least a humidifier in the basement or lower floor in the summer so the house doesn't smell like a mold farm...

Submitted by briansd1 on June 1, 2011 - 10:14am.

Hatfield wrote:
dehumidifiers and air conditioners use the same underlying principle: cold air cannot hold as much moisture as warm air.

I was thinking about this earlier.

Is there a maximum amount of moisture that a certain temperature air can hold? If so, then I'm thinking that the AC would evacuate the moisture at a faster rate when the air is warmer.

Then after a lower temperature is reached, less moisture can be extrated.

What are the physics of air and moisture? Interesting question.

RichardJamesEsquire wrote:
"The central AC cycling on and off is not excessive, IMHO -- about the same as my AC here in San Diego."

Yes it is excessive, otherwise you wouldn't be complaining about the humidity.
A good residential unit will run the fan at a lower speed for a longer duration when dehumidification is needed. Variable speed fans and 2 stages of cooling capacity have made dehumidifying residential applications really easy. Your unit either isn't set up correctly, or it's a plain jane old school single stage single speed unit doing 80% sensible heat and 20% latent heat just like it was designed to do.

Thanks for the suggestion. I've never had a two stage unit where the fan speed is variable.

I'll check with the builder of the house.

Right now, I think that the AC is working fine. It's not that I'm complaining as much as, being from San Diego, I have a lower tolerance for humid air.

I'll see if there are settings that can be adjusted.

Submitted by sdrealtor on June 1, 2011 - 10:14am.

I just got back from NYC. It was 94 and humid on Monday. I feel your pain. Having grown up in Philly I know it all too well. Dont even think about visiting in from July 10th to July 31st unless you want to experience the worst of it.

Submitted by briansd1 on June 1, 2011 - 10:18am.

MANmom wrote:
I have lived in Virginia, we had both, only the dehumidifier was in the basement. Mold grows quickly in a damp area, you will need at least a humidifier in the basement or lower floor in the summer so the house doesn't smell like a mold farm...

My favorite area of the house is the finished basement. It's warm in the winter and cool in the summer.

The washer/dryer is in the basement. I ordered a dehumidifier and I'll mount it on the wall with the condensate hose directly into the sewer drain. We'll see how it works.

Submitted by KSMountain on June 1, 2011 - 10:21am.

briansd1 wrote:

What are the physics of air and moisture? Interesting question.

http://en.wikipedia.org/wiki/Dew_point

Submitted by RichardJamesEsquire on June 2, 2011 - 12:12am.

Yes dew point is the maximum, when the air is saturated and moisture starts falling out of it. Psychrometrics is the science. Enthalpy is the total heat content of the air. When someone says "but it's a dry heat" it's absolutely true. More humid air has more heat content than less humid air of the same dry bulb temperature. Your air conditioner is removing about 80% sensible heat and 20% latent heat (moisture removal).It's bringing the dry bulb temperature down quickly, the enthalpy is going down, but it's not removing enough moisture (latent heat). The warmer the air, the more moisture it can hold. Relative humidity (how much moisture the air can hold at a given temperature by percentage) may actually be going up as the temperature is going down. This is why I say your unit doesn't fit the application. You need one that will remove more latent heat. This is done by moving less air across the coil while at the same time reducing the capacity of the unit. It lowers the dry bulb temperature slower giving more time to remove latent heat. From what I've read (cause I have no practical experience having only worked in dry climates), pretty much everyone living in humidity who goes to a variable speed 2 stage unit will never go back.

Submitted by disimilar1 on June 2, 2011 - 11:28pm.

I would never live again without my dehumidifier. I cannot comment about the science between an a/c and a dehumidifier. My lungs seem to know the difference though.

Submitted by LuckyInOC on June 4, 2011 - 2:22pm.

RJE has it right...

AC units in humid climates need thicker coils to remove the latent (moisture) from the air. Restaurants, auditoriums, churches and such with high occupancies have similar problem even here in dry So. Cal.

Here is a simple psychrometric chart to understand dry bulb, wet bulb, and relative humidity.
http://en.wikipedia.org/wiki/File:Psychr...

You should check with an AC professional to see if it is possible to put a dehumidifier in the return air for your AC. This could reduce the latent load on your existing AC unit with less expense.

The best solution would be verify the capacity of your existing AC unit (condenser [outside] and evaporator [inside]) meets both the temperature and humidity requirements you want. Most designs are only for nominal environmental peaks, not extremes.

Secondary systems are sometimes a cost effective way to handle extremes without impacting the performance on nominal peak usage.

I'm very...
Lucky In OC

Submitted by briansd1 on June 6, 2011 - 1:07pm.

Thanks for the response, lucky in OC.

I did some more reading:
http://en.wikipedia.org/wiki/Thermal_com...

I got the plumber to come out and setup a drain for me on the main floor where the living room is.

I will set the dehumidifier to automatically run to remove the humidity when I'm not home.

Then I'll use the AC when home. I'm leaving the AC on at 78 when not home. That's what my friend in Florida does.

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