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Which is more energy-efficient: dehumidifier + fan vs. air conditioner - Answers for Hanoi

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Which is more energy-efficient: dehumidifier + fan vs. air conditioner
HanoiFan posted July 25th, 2011 at 11:29 am to Help!.
Viewed 53199 times. Answered 26 times.

Our power bills are ridiculously high because we have the AC on 24-7. Would I save on my power bill if I run a dehumidifier and fan vs. running the air conditioner? I find my lack of comfort is more related to the high humidity.

I've also heard that dehumidifiers also give off heat. Is that true? Anyone find cheap, energy-efficient dehumidifiers in Hanoi? I really don't want to spend $200! Thanks.

Answers (jump to newest answer)

July 25th, 2011 at 1:42 pm

You're right about dehumidifiers give off heat, so running that plus a fan wiill not make you feel any better, but drier.

Energy-wise, a dehimidifier consumes about 150W/h, that is about 1/10 of a 12000BTU AC. You do the math!

I've been to a lot of Western houses/apartment, and I found they're not energy efficient, they run AC on empty rooms, open the door, running it too cold, in large rooms....

A fan + AC about 28C is very economic, I have to tell you! (of course keep the rooms sealed!)

Drink!
July 25th, 2011 at 3:50 pm

If you're here for the long haul, it's worth replacing your air conditioners with Inverter units. These use substantially less power than conventional binary compressor units. I found switching to Inverters saved something like 60-70% on the power bill.

Running a fan in an air-conditioned room is not energy efficient at all! In a still room, the cold air will settle near the ground whilst the hot air will rise to the ceiling. This is exactly what you want, as you don't need the air at the ceiling level to be cooled. Allowing the cool air to settle low in the room means the AC will be doing less work and costing you less to run. However, if you're constantly mixing the air up, the air conditioner must cool the room from ceiling to floor, which means it will have to work harder.

It's also a good idea to have the head units mounted low in the room, for the same reason. If they're very high, the thermostat will be high too. In particular, if you are in a room with high ceilings and a high mounted head unit, that means the AC will be working like buggery to cool space far above your head.

July 25th, 2011 at 6:25 pm

Agree to all Vegas' thermo theory, but in reallife, I always find it's better to use an additional fan.
1. If you're in a large room, and fan will help spread cold air more evenly
2. After the room is cool, the hot-cold different is minimal.
3. Air flow is blowed directly to area need; or to area too far from AC.

I dont know, may be someone with better knowledge can shed light on this!

July 26th, 2011 at 6:19 am

Have to agree with Vegas, running a fan in an AC'd room is counter productive and inefficient

Drink!
July 26th, 2011 at 7:19 am

To carry on this fascinating topic:

"but in reallife, I always find it's better to use an additional fan"

Maybe that's because it's what you're used to, and of course there's nothing wrong with that, but it's not energy efficient. See, even Dab agrees with me! So it must be right.

As for your points 1 and 3; they can be dealt with at the same time. If you're in a large room, you should have an air conditioner of a capacity to match. In that case, you won't need a fan to spread the cold air, or direct it to the place of need, as the room will be evenly and adequately cooled. If you have an air conditioner of insufficient size in a large room, then your fan might blow a bit of cold-ish air in a direction of your choosing, but it will still mix up the warm and cold air, and thus make the air conditioner's job even more impossible.

2) I'm not exactly sure what you mean by this.

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July 26th, 2011 at 8:18 am

"Beer"

I enjoy this. Think carefully before you answer. What is the purpose of the fan blower in the air conditioner and why does it have a speed setting?

A carefully placed fan in the room improves...... I'll stop now.

"Beer"

July 26th, 2011 at 8:49 am

Thanks Grant!!!

My reason is, because the AC fan is not very powerful, an additional fan will complete the job.

But yes, If I set my AC alone to 28, I'd still feel hot. With a fan, I can leave it at 29, and feel cold.

I have a power meter if some one is a big fan of Myth Buster;-)

Ps. Vegas, 2. I mean Convection will be minimal when the whole room get cold, hot air temp = cool air temp (maybe!?) With no fan, maybe you'd feel cold from the knee down, but not from the torso up!?

Drink!
July 26th, 2011 at 9:47 am

The main purpose of a fan in an AC is not to circulate air, unlike a pedestal fan. The fan speed influences how much air is directed out of the machine. If the compressor is powerful enough, it can cool a larger volume of air, so if the AC fan is on high, the room will cool down more quickly. Of course, if the fan in the AC unit is too strong, then the air blown out of the unit will be warmer.

July 26th, 2011 at 10:03 am

Ah my peasant friends down in central Hanoi, bitching about a couple of extra dong to keep cool.

Up here is Tay Ho, we only use punkawallah's, they are more than a match to LG and Panasonic. I wouldn't want to watch my local polo match and drink my Pimm's without one. Tally Ho.

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July 26th, 2011 at 11:51 am

I kinda agree with Quyda...an AC unit running with a localised fan aimed directly at you makes the temperature appear lower than it is (wind chill. I run the AC at 27/28 with the fan on too. If I didn't run the fan I would need the AC on at 22/23. I would bet that running the AC at 28 with a fan is cheaper than running AC only at 22. It therefore can be more efficient to run the fan and AC at the same time.

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July 26th, 2011 at 11:52 am

(wind chill)

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July 26th, 2011 at 12:13 pm

"Beer"

The purpose of the AC fan is draw air across the heat exchanger as it will not efficiently naturally circulate (otherwise you may as well chuck a lump of ice in a bucket). It then directs cold this air across the room where it falls and if not disturbed tends to sit there as the draft from the fan is usually fairly low but enough to force it stay there. Adding a fan on the opposite side of the room breaks the bubble effect and directs the air back across the room at floor level. This air hits the wall and has nowhere to go but up and back through the AC to be cooled further. This increases the AC's efficiency as it is chilling pre-cooled air. The AC will reach the thermostat set temp faster and run less.

It's also the reason for having oscillating louvers on the front of AC units. It helps break the bubble of cool air by creating moving drafts rather than steady ones. This helps distribute the cool air more evenly rather than sitting in pockets in the room.

"Beer"

July 26th, 2011 at 1:12 pm

I still don't understand how an air conditioner works, much less all this talk about convecting, punkawallahs, and compressors. Just do this the pop psychology way:

Are you ...

down with the people? - Stay in shade, drink tea, and fan yourself.

spoiled westerner? - Close your doors, crank the air con and all fans, while enjoying an iced tea.

somewhere in between? if it's under 30degrees, fans and open windows. if it's over 30degrees, bite the bullet and turn on the air con.

Any questions?

July 26th, 2011 at 2:57 pm

Air conditioners can only work in an enclosed space, you wouldn't dream of running one with all your windows and doors open ? Using a powerful fan has the same effect as this, in that the air conditioner cannot function properly.

Use one or the other but not both and save the rain forest.

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July 26th, 2011 at 3:28 pm

"Beer"

Ummm....I can't argue with that logic.

"Beer"

July 26th, 2011 at 4:22 pm

...and then there's that old idea from another AC&Bills thread, way back when, switch suggests, to first cool the room then switch over to the "Dry" setting.

and the logic behind this is?

I know many people who open all the doors and windows and have the A/C running flat out, set to 16.

...an enclosed space, with/without a floor/pedestal fan, is not the equivalent to an open room.

Next someone will tell me that ceiling level vents are a waste of time and can only make the AC work that much harder. ;-)

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July 26th, 2011 at 4:25 pm

"Beer"

'Ceiling level vents are a waste of time and can only make the AC work that much harder.'

Job done.

"Beer"

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July 27th, 2011 at 8:52 am

But we digress....

any other thoughts on whether a dehumidifer + fan would be cheaper to run vs. an air conditioner

July 27th, 2011 at 8:57 am

cheaper to run?
In general, Yes.

...determine the wattage of your DH+F and compare with wattage of AC. The one with the bigger number will use more power, hence will be more expensive to run.

More effective?
depends on your desired comfort level.

Cooking at home
July 27th, 2011 at 9:03 am

When I used to live in the Mekong Delta we would just use a fan and a wash bucket of ice when we needed to cool down. Worked surprisingly well.

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July 27th, 2011 at 9:21 am

"Beer"

Yes it is cheaper. Will you feel as cool as an AC? No.

Second hand de-humidifier was recently posted in the classifieds for $150. Your room/house better be sealed very well or the whole thing is pointless.

"Beer"

July 27th, 2011 at 9:58 am

Not sure if it's different in apartments, but we haven't used a dehumidifier at all since we came here. We find the aircon units do an excellent job at cooling and moisture reduction.

Of course it helps that we now have a monstrous new apartment block over the road that successfully blocks most of the afternoon sun...

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July 28th, 2011 at 11:59 am

Hi,

I heard if you run your AC on DRY MODE --- it saves costs and effectively dries and cools in doing so....

Try it.

July 28th, 2011 at 1:40 pm
Good Answer HanoiFan marked this as a good answer

I can't find the thread where Dry Mode was mentioned, but here's some stuff relating directly to this thread.

Used in conjunction with an air-conditioner, fans can cut energy costs.
[NYTimes]

Air Conditioner Tips
...variable speed air handler, which will improve comfort and efficiency and allow continuous air filtering at minimum energy cost. Never use continuous ventilation when the air conditioner is in use, because it will degrade humidity control.
[ACEEE | Cooling]
...air conditioning without proper humidity control is disastrous in itself...

Most air conditioning in the tropics is set at too low a temperature for human comfort: 23°C is probably plenty low enough if you have adequate dehumidification.

In some countries like Hong Kong, freestanding domestic dehumidifying units are readily available in all appliance stores. The amount of moisture these small machines can pull out of the air is quite amazing: You must remember to empty the tub daily, or arrange the position of the machine to allow a permanent drain pipe to outside.
[CBH Technical Library]

Last One,
Air Conditioner

Settings / Operation

What is Cool Mode?

In Cool Mode, the fan runs continuously and the compressor turns on and off only as needed to maintain the set temperature.

What is Fan Mode?

In Fan Mode, the fan runs continuously and the compressor is off.

What is Dry Mode?
Dry Mode is a function that will reduce the humidity in the room, making it more comfortable. It is good to use in the Spring and/or Fall when the temperature is not hot enough to run the cool mode, but the humidity is a little high. The fan and the sealed system will run, but the unit will not blow out cold air. As the air passes through the air conditioner, the humidity will condense on the evaporator so that the air comes out drier.

This is not intended to replace a dehumidifier or act as a dehumidifier. The capacity to dehumidify is much lower on an air conditioner than it is on a dehumidifier.

What is Energy Saver Mode?

The Energy Saver Mode is a function that is intended to decrease the energy consumption of the unit. When this mode is set, the unit will cool the room as normal. What you will notice is that when the compressor shuts off, the fan will too. While the compressor is off, the fan will turn on and off every 2-3 minutes so that it can check the temperature in the room. Once the temperature rises, the compressor will turn on with the fan and cool the room.
[LG Knowledgebase]

Drink!
July 28th, 2011 at 3:34 pm

The 'energy saving' setting on standard binary compressor AC units does bugger all in terms of saving energy. If you want to save money on your AC bills, get an inverter system. It'll save you a packet.

clock iconThen Some Time Passed...
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April 21st, 2013 at 2:01 am

For those of you, like me, not familiar with an "inverter system" this wiki link may be useful:

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

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