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Old 07-14-2022, 06:42 PM   #1
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Help for the air conditioner

Hey guys just thought I would post this to all the rver's in high humidity areas like Texas ...hope it helps ....Will dehumidifier help air conditioner?

Using a whole-home dehumidifier with your air conditioner improves energy-efficiency in your RV and keeps you feeling comfortable all summer long. So yes, a dehumidifier does help your air conditioner.Jul 25, 2019
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Old 07-14-2022, 06:58 PM   #2
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Not sure I totally agree with your statement. An air conditioner dehumidifies as well as cools the air space it conditions. In the process of cooling, it takes warm air out of the living space and rejects it to an outside area. A dehumidifier does just that, dehumidifies, there is no sensed cooling but during the process of dehumidifying , it adds heat to the space it occupies. So it may help reduce moisture, but it will increase the heat load on the air conditioner.
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Old 07-14-2022, 07:52 PM   #3
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In high humidity areas a dehumidifier does help.

When ambient humidity is 85+ percent you can often have the AC set low, like 68-70 degrees and you end up with 68 degrees and a sticky 65% humidity inside, cold and sticky.

Personal experiance in the gulf coast region, if I run a dehumidifier along with the AC, the house is perfectly comfortable at 76-77 degrees. Without it I choose to either be at a desired temp but sticky, or cold and slightly sticky.

Some higher end ($$$$) ACs will slow down to dehumidfy more and cool less, but I've never seen one in an RV.
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Old 07-15-2022, 07:26 AM   #4
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Well I'm going by personal experience I live in a 31 ft motorhome on the gulf coast where the humidity gets up to 80 percent and higher and I have two rooftop a)c with foil insulation in all windows outside temp 100 degrees inside would only get to around 80 degrees so I had read that a small humidifier would help with a/c to lower temp inside and it worked my inside temp went down to around 76 @ 100 degrees outside temp
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Old 07-15-2022, 09:06 AM   #5
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Originally Posted by Pelledan View Post
Not sure I totally agree with your statement. An air conditioner dehumidifies as well as cools the air space it conditions. In the process of cooling, it takes warm air out of the living space and rejects it to an outside area. A dehumidifier does just that, dehumidifies, there is no sensed cooling but during the process of dehumidifying , it adds heat to the space it occupies. So it may help reduce moisture, but it will increase the heat load on the air conditioner.

Dan
Air conditioners recirculate the inside air.

They do not reject warm air. If they did, that would create a negetive pressure and warm moist air would be drawn in from cracks and seams.

Dash AC will draw outside air but that keeps the dirty the outside air from creeping in from other sources.
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Old 07-15-2022, 10:20 AM   #6
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Quote:
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Air conditioners recirculate the inside air.

They do not reject warm air. If they did, that would create a negetive pressure and warm moist air would be drawn in from cracks and seams.

Dash AC will draw outside air but that keeps the dirty the outside air from creeping in from other sources.
The warm air that the A/C unit rejects is the air across the condenser. It would be proper to say that the A/C unit rejects the HEAT outside via the condenser.

The point of the heat on the dehumidifier is that it is nothing more than a small A/C unit in a box inside the RV. It takes the room air and cools it and removes the moisture. The air coming off the evaporator is near the dew point of the evaporator. This air is then blown across the condenser to heat the air and move it away from the dew point which will lower the relative humidity. The point is that the dehumidifier will remove some moisture, but it will also add an additional heat load to the room.

The definition of the air conditioning process is that it removes heat from one area where you do not want the heat and rejects it to an area where the heat is not objectionable.

For a dehumidifier, the added heat is from the heat of compression. The total heat rejected by the condenser is the sum of the evaporator load plus the heat of compression. On the A/C unit, the heat is rejected outside, and on the dehumidifier is rejected inside the RV.

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Old 07-15-2022, 03:49 PM   #7
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Quote:
Originally Posted by twinboat View Post
Air conditioners recirculate the inside air.

They do not reject warm air. If they did, that would create a negetive pressure and warm moist air would be drawn in from cracks and seams.

Dash AC will draw outside air but that keeps the dirty the outside air from creeping in from other sources.

Quibbling, I think. Reject isn't a good choice of terms but the a/c does transfer heat to the outside via the condensor.
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Old 07-15-2022, 04:04 PM   #8
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TXiceman, the heat is ejected not rejected on all cooling systems. I realize it was a typo.

I thank the OP for the post. Being closer to dirt. I now cannot stand humidity. My house has 12Ē thick walls. It takes allot of extended heat outside to raise or cold to lower the temperature inside. The killer for me is the humidity in the summer. A window AC unit does reduce the humidity in the summer.

I hope I am never down on the gulf with those high heat & humidity issues in my camper. I would buy a dehumidifier because of this post if I was. The camper AC I have would not have a problem with the small amount of heat generated by the dehumidifier. But my comfort level would be much better. Heck a dehumidifier would be like one more person in the camper heat wise I would think.
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Old 07-15-2022, 05:39 PM   #9
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FWIW, in the experimentation of trying to invent a de-humidifier, the value of the chilled air byproduct was realized, and Mr. Carrier became famous.
ref: https://www.answers.com/Q/Who_invented_the_dehumidifier


The only way to have a dehumidifier without chilled air is to use a desiccant-type dehumidifier.
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Old 07-15-2022, 06:18 PM   #10
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Originally Posted by Gary2220 View Post
Well I'm going by personal experience I live in a 31 ft motorhome on the gulf coast where the humidity gets up to 80 percent and higher and I have two rooftop a)c with foil insulation in all windows outside temp 100 degrees inside would only get to around 80 degrees so I had read that a small humidifier would help with a/c to lower temp inside and it worked my inside temp went down to around 76 @ 100 degrees outside temp
A dehumidifier cannot make the temperature lower in a space. It will always make it warmer because it releases heat. It would violate laws of physics and win you a Nobel Prize if you could demonstrate it.
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Old 07-15-2022, 07:37 PM   #11
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It takes more BTU's to remove moisture from the air then it does to cool the air. If the air is dryer, it is easier to cool. So the amount of heat added by the dehumidifier is easily removed by the A/C unit.
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Old 07-15-2022, 08:41 PM   #12
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It takes more BTU's to remove moisture from the air then it does to cool the air. If the air is dryer, it is easier to cool. So the amount of heat added by the dehumidifier is easily removed by the A/C unit.
No. Not even a little bit right. Moisture in the air does not change how well the air conditioner removes heat. You have misunderstood the idea that itís easier to make a room feel cool when the humidity is low, but there is no difference in BTU needed to make a temperature change.

If the magical effect of removing moisture did make things easier for the air conditioner, it still would have no benefit because the amount of heat generated by the dehumidifier would be more than the energy saved by the magical cooling effect since a dehumidifier is just an air conditioner where the evaporator and condenser coil are in the same air, so either way the moisture is removed by the same mechanism.
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Old 07-15-2022, 09:44 PM   #13
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It is ashamed that people do not understand psychometrics and the cooling and heating processes. I spent a career working with this as well as applied heat transfer and thermodynamics.

The load on the air conditioner for cooling consists of sensible cooling and latent cooling loads. The sensible part of the load is the smaller of the load normally which is only lowering the dry bulb temperature in the space and no moisture removal. The latent cooling load is the removal of the moisture from the air which is usually the larger load on the unit. The amount of moisture removal can be affected by how low you operate the evaporator temperature which is the coil dew point. The lower the coil temperature, the more moisture is removed and the harder the compressor has to work.

Running a mechanical dehumidifier in the space will reduce the moisture in the space (latent load) and reduce the relative humidity, but now you are adding to the sensible load on the A/C system. So, in essence, you gain nothing and are probably at a net loss.

Often in the cooler months when it is damp, we will run the A/C system and operate a small electric space heater to put a little reheat into the room which will give the A/C system enough load to have it run and thereby reduce the humidity in the room without the need of a separate dehumidifier. And we never have to empty the water collected by our space heater.

And with that I am finished with this thread. Good luck down the road and enjoy your travels folks.

Ken
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