Posted by
axptguy38
15 yrs ago
I've been trying to figure out which is more efficient.
- A stand-alone dehumidifier.
- A split air conditioner running in the "dry" mode.
As I understand it, the "dry" mode on an air conditioner is the same thing as a dehumidifier. Any idea which uses less power per liter of water removed from the air?
Thx.
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momi
15 yrs ago
according to an article i read in the newspaper, a standalone dehumidifier costs less. I remember it says air conditioner running in the dry mode costs more than cool mode -- but i forgot why this is so...
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Good to know thanks. I guess it makes sense that a purpose built unit does it better than one with the function as a secondary one.
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One point to factor in, is that the dehumidifier will create some heat inside the room, whereas a split system air conditioner will not, because the motor is outside.
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My husband thinks the split-type aircon is more efficient for dehumidifying an area (although I'm inclined to disagree).
When it was really humid just recently, our dehumidifyer just wasn't able to do the job - it was on continuously and it was still 70% humidity. But as soon as we use the split-type aircon, it was a rapid way of drying out the rooms.
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Both the split Ac and the dehumidifier has compressor which basically cools the humid air under pressure and temperature to extract the water and send the dry air back to the room. One could compare the energy consumption looking at the electricity usage in the units manual or online at the manufacturers website.
On the flip side of the argument for the split unit during summer, the split unit not only help to take the water out but also cool the room - being a standard output of the dehumidifying cycle.
Possibly running your fan and dehumidifier would be fairly high from the environmental point.
I will check with my E&M Engineers friends, I am curious too....
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I think perhaps we need to separate the question into two parts:
- Does a "normal" sized split air conditioner have more or less dehumidifying capacity than a "normal" stand-alone dehumidifier?
- Assuming equal capacity, which uses more power?
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follow up question: if i used my split-type, do i need to select the 'dry' function to dehumidify or does the 'cool' function automatically also 'dry'?
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I find the A/C does a much better job however, after I last had water dripping back through the unit down the inside wall, the A/C mechanic man advised me not to use it for this purpose. I find it did also cool the room a lot better, the portable DH takes the moisture out of the room but seems to heat it also...
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In "cool" mode, the air conditioner both cools and dries the air. Drying is a natural by-product of the cooling process. As air passes over the coil, it is cooled. Since this decreases the moisture retention capability of the air, excess moisture will condense out and drip out of the unit through the water exhaust (plus be expelled with the exhaust air on the outdoor side of the unit). This is the same process that leads to an ice cold glass of beer being covered in condensation on a hot summer night.
The "dry" mode of an air conditioner works, as fliedlice says, just like a dehumidifier. The intake air is cooled to condense water out Then the (now dry) air is sent over the hot side of the coil to heat it back to the same temperature as the intake air. That last part is the difference between "dry" and "cool" modes.
"One could compare the energy consumption looking at the electricity usage in the units manual or online at the manufacturers website."
I thought of that. Unfortunately all I find are max consumption figures. There's no separation of dry mode vs. cool mode. So all I can compare is a/c running full blast vs. dehumidifier. That's apples and oranges.
"I last had water dripping back through the unit down the inside wall,"
What about the exhaust hose? If you don't have one, the water will seep into wherever it can get through gravity and surface tension.
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axptguy's last explaination is almost 100% correct - however most split type A/Cs do not re-heat the cooled/dry air as the hot coils are in the outside unit. the "dry" function is merely a "normal" operation on a reduced cooling power setting - it will still cool the air by a certain amount.
A high performance dehumidifier like the Sharp DW-R268A has a rated power input of 360W. Your average split type aircon has 2,000 to 10,000W.
so you can run the dehumidifier for 6h and use the same amount of energy as anything between 12min and 1h of aircon operation, depending on the particular system.
However, the aircon with it's high volume throughput will reduce the humidity in the room in just a few minutes, whereas the dehumidifier needs some time.
So - the my suggestion is: if you need to dry out a room quickly, use the aircon, to maintain the humidity at that lower level use the dehumidifier.
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Totally agree Flyboy, which is think was my husband's point - although he had no facts to back it up. We could leave the dehumidifier running all day long to reduce the humidity - thereby using more energy in the longrun, or just run the aircon for a short burst.
Of course, if it's a small room, I think the dehumidifier is best because it will shut off automatically once the right humidity is reached.
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"So - the my suggestion is: if you need to dry out a room quickly, use the aircon, to maintain the humidity at that lower level use the dehumidifier."
Sounds like a good rule of thumb. Also thanks for correcting my error.
Follow-up questions then. What does the temperature setting on the air conditioner do when set to "dry"? Would this be equivalent to a humidity threshold on the dehumidifyer?
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cd
15 yrs ago
We always use the stand alone dehumidifiers and have to empty them once a day. On bad days our bedroom windows (patio doors) are soaking and drip water. the dehumidifer clears it in half a day. The other week we tried the a/c on dry mode, and after several hours it hadn't made a difference. Same when trying to dry clothes, dries much faster next to the dehumidifer than having the a/c on dry.
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Cd - maybe your a/c is not that good on dry mode?
When drying clothes, I usually use the dehumidifier because we can direct the vent towards the clothes. But our appliance couldn't cope with the recent humid weather so we had no choice but to use our split-air con on dry mode.
Our aircon doesn't allow us to input a humidity percentage, so I have no idea what the percentage is preset at. We also can't input a temperature setting. We can only choose the dry mode and that's it!
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The answer is a very simple one
Dehumidifiers are not efficient and need to be on for long periods to reduce the humidity to an acceptable level.
Dehumidifers do not have a cooling function but the room 'feels' cooler because of the lower humidity. the effiency of many models available in HK is very low. The best are Japanese models made in Japan NOT China
They will never work as well as an air con and although the air con costs more to run per hour it is not necessary to run the air con for long periods to achieve an acceptable result thus the air con running cost is probably less.
Any air con dries the air and it is not necessary to have reverse cycle or 'dry' mode.
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axptguy - the temp setting in dry mode is (with most of the cheaper "cooling only" A/C's) just that - a temp setting, as most of these aircon units do not even have a humidity sensor - that's why a lot of people come to the conclusion that the "dry" function does not work properly:
if you set it to - lets say 28ºC and "dry" - but the room temp is 27 or below, the unit will only work as a fan, with the compressor not running and no cooling/dehumidifying effect.
only more expensive systems have proper dehumidifying functions, and will re-heat the air after the moisture is condensed out...
and if you really want proper "air conditioning" by that I mean full control of temperature and humidity independent of each other and the outside weather conditions you'll have to get a top of the range machine, i.e. the Daikin Ururu Sarara for 18,000 HK$ and above per piece :(
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