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Old 8th April 2013, 15:00   #2911
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Default Re: Which home/office AC (air conditioner) to buy ?

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Originally Posted by Thad E Ginathom View Post
I have always been curious about the "Dehumidify" mode on my 7-yr-old Samsungs. No modern, high-tech there, just basic, temperature-controlled (the only sensors are thermostats) air cooling and drying. And, as is usual with basic split systems, no drawing in of external air.

So what is the "De-humidify" function doing and how? The only thing I can say about it is that it also seems (subjective sensing) to make the room colder! Maybe, somehow, it attempts to keep the temperature of the air below its dew point --- but I do not think it has any sensor sophisticated enough to know what that is.

.
Exactly. My 7 year old Carrier window ac also has this "Dry" mode. As per the user manual, it simply runs the compressor for a short while even after the set temperature is achieved. Basically, maintaining the temp slightly lower than set point.
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Old 8th April 2013, 15:35   #2912
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Default Re: Which home/office AC (air conditioner) to buy ?

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it simply runs the compressor for a short while even after the set temperature is achieved.
Thanks. I don't think there was any explanation in the Samsung manual.
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Old 8th April 2013, 21:42   #2913
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Default Re: Which home/office AC (air conditioner) to buy ?

Friends, with the temperatures soaring it is just getting impossible to only survive on the Fan. Help me choose a good economical AC which cools down in lesser time and cools down the room of 18*12 ft.
I have never used an AC at home nor have ever run through choosing one.
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Old 9th April 2013, 09:19   #2914
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Default Re: Which home/office AC (air conditioner) to buy ?

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Friends, with the temperatures soaring it is just getting impossible to only survive on the Fan. Help me choose a good economical AC which cools down in lesser time and cools down the room of 18*12 ft.
I have never used an AC at home nor have ever run through choosing one.
You need a 2 tonner ideally, Now depending on the Moolah available you have a vast range available. Please let us know whether you are looking at a spilt or window, and budget constraints.
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Old 9th April 2013, 14:30   #2915
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Default Re: Which home/office AC (air conditioner) to buy ?

Friends,
How about Whirlpool 3D 1 tonner 5star. I bought one today and just realised that it does not have a japanese compressor. Hope it do have the Cu tubes as mentioned.
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Old 9th April 2013, 19:36   #2916
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Default Re: Which home/office AC (air conditioner) to buy ?

Hi, could you share the make of the compressor.

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Friends,
How about Whirlpool 3D 1 tonner 5star. I bought one today and just realised that it does not have a japanese compressor. Hope it do have the Cu tubes as mentioned.
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Old 9th April 2013, 21:48   #2917
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Default Re: Which home/office AC (air conditioner) to buy ?

Sorry not sure which one it is ,whirlpool india says the compressor as 'others' .
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Old 10th April 2013, 11:42   #2918
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Default Re: Which home/office AC (air conditioner) to buy ?

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Originally Posted by Thad E Ginathom View Post
Thanks. I don't think there was any explanation in the Samsung manual.
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Originally Posted by anuragn View Post
Exactly. My 7 year old Carrier window ac also has this "Dry" mode. As per the user manual, it simply runs the compressor for a short while even after the set temperature is achieved. Basically, maintaining the temp slightly lower than set point.
Right.
Dry mode on AC
The way it works is by keeping the air flow ultra low.
This increases the residence time of air over the cooling coils, and condenses the water. The water is then drained from the tray. This removes the moisture from the air

So how does the ac ensure the air flow is ultra low? By switching off the fan. While the compressor is still running!

So in dry mode - the compressor is always running, the fan switches on and off - to maintain a certain factory set temperature (based on the dew point).

Does this actually lower the humidity? Yes in absolute terms (removes XXX grams of water from air) No in relative terms (bringing the RH down from 80% to 40%).


How a dehumidifier or dry mode should actually work
Human beings don't care about absolute humidity. What we feel on our skin the dew point of water (or the wet bulb temperature), which depends on relative humidity as well as the dry bulb temperature.

AC works by conditioning the air. Practically speaking all it does is cool the air. Cooling the air raises the relative humidity of the parcel of air that has been cooled. To the point that water starts condensing on the cooling coils. This water is collected and drained off.

The cold air at higher humidity is then warmed back to the desired temperature by the warm air outside. Not by mixing, but by heat exchange (like the radiator coil at the back of old fridge). This raises the temperature of the erstwhile cold air, raising the temperature reduces the relative humidity.

Please note if this raising of temperature occurred in the presence of the condensed water that was collected, the condensed water would simply evaporate and raise the humidity.


So what should you do?
1. The dry mode is not really a mode to dehumidify, all it does is cool the air further.
2. You never know how low the dry mode is going to cool the air, that means it may become uncomfortably cold for you (also think about electricity consumption).
3. Use the normal cool/chill mode. Play around with temperature set point and fan speed. Higher fan speed for more perceivable cooling, lower fan speed for more water condensation and thus slightly better removal of humidity.
4. Always use ceiling fan!

Last edited by alpha1 : 10th April 2013 at 11:52.
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Old 10th April 2013, 12:09   #2919
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Default Re: Which home/office AC (air conditioner) to buy ?

Err but then how are you sure it is not Japanese.
I asked about the make because Whirlpool has been using compressors(in their airconditioners) from Sanyo, Panasonic and other Japanese manufacturers. Wanted to know if they have moved to generic vendors.


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Sorry not sure which one it is ,whirlpool india says the compressor as 'others' .
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Old 10th April 2013, 12:32   #2920
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Post Re: Which home/office AC (air conditioner) to buy ?

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Originally Posted by alpha1 View Post
So what should you do?
1. The dry mode is not really a mode to dehumidify, all it does is cool the air further.
2. You never know how low the dry mode is going to cool the air, that means it may become uncomfortably cold for you (also think about electricity consumption).
3. Use the normal cool/chill mode. Play around with temperature set point and fan speed. Higher fan speed for more perceivable cooling, lower fan speed for more water condensation and thus slightly better removal of humidity.
4. Always use ceiling fan!
Since there is no thanks-button, Thanks!

The same thoughts were going on in my mind and I have been experimenting with various setting of my Daikin Inverter along with the ceiling-fan on/off, and by noting the actual electricity units consumed. I also have a Casio-Hygrometer to note down the actual temperature and RH% achieved.

In general the inverter-technology is extremely energy efficient compared to even 5* normal ones and is also deadly-silent!

Last edited by manim : 10th April 2013 at 12:34.
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Old 10th April 2013, 12:42   #2921
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Default Re: Which home/office AC (air conditioner) to buy ?

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Since there is no thanks-button, Thanks!

The same thoughts were going on in my mind and I have been experimenting with various setting of my Daikin Inverter along with the ceiling-fan on/off, and by noting the actual electricity units consumed. I also have a Casio-Hygrometer to note down the actual temperature and RH% achieved.

In general the inverter-technology is extremely energy efficient compared to even 5* normal ones and is also deadly-silent!
Yes of course, the VFDs (variable frequency drive) have been used by industries for decades now. In fact I am surprised what took so long to bring these to consumers segment.
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Old 10th April 2013, 14:20   #2922
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Default Re: Which home/office AC (air conditioner) to buy ?

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In general the inverter-technology is extremely energy efficient compared to even 5* normal ones and is also deadly-silent!
I looked into the documentation and was surprised to find that they use Nd-Fe-B permanent magnets in the motor. Far more efficient that using coils. Also, Nd magnets are the most powerful (and expensive) there are, so the size will also be compact. Impressed to say the least.
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Old 10th April 2013, 15:09   #2923
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Default Re: Which home/office AC (air conditioner) to buy ?

alpha1, thanks, that is a good explanation.

I have repeatedly failed to explain to my wife that, if she wants colder air, she should turn the AC fan speed (in house or car) down. The longer the air takes to pass through the cooling coils, the cooler it is going to get. Unfortunately she still persists in thinking that High is the best setting for everything. I'm afraid that a lot of people who grew up with ceiling fans simply associate strong draught with cooling.
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Old 11th April 2013, 13:08   #2924
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Default Re: Which home/office AC (air conditioner) to buy ?

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Originally Posted by Thad E Ginathom View Post
alpha1, thanks, that is a good explanation.

I have repeatedly failed to explain to my wife that, if she wants colder air, she should turn the AC fan speed (in house or car) down. The longer the air takes to pass through the cooling coils, the cooler it is going to get. Unfortunately she still persists in thinking that High is the best setting for everything. I'm afraid that a lot of people who grew up with ceiling fans simply associate strong draught with cooling.
Actually, she may be right in her way.


This is getting into mathematical thermodynamics, which cannot be reproduced here (looks like I need to sit with a pen and paper after a decade) ... but what happens is that the there are two systems:
A. {Parcel of air <=> Air inside room}
b. {Parcel of air <=> cooling coils}

The temperature of the air inside room goes down faster if the parcel of air is colder, or if the parcel of air is larger (but not as cold as earlier case). Case 1 is achieved by lowering the AC fan speed. Case 2 is achieved by increasing the AC fan speed.

All heat transfer in these cases is practically via Convection.
It so happens that heat transfer coefficient (proportional to Nusselt number) improves with higher Reynolds number (speed of flow)
[heat transfer coefficient proportional to cube root of speed of flow in case of laminar flow]
[almost linearly proportional to speed of flow in case of turbulent flow]

What this means is that faster the flow, better is the heat transfer.
Since in case 1, the parcel of air is smaller, it gets cooled to lower temperature.
In case 2, the parcel of air is larger, hence it gets cooled to higher temperature.
BUT because the heat transfer was better in Case 2, the Mass x Temperature of Case 1 is higher than Mass x temperature of Case 2.

This means the quantum of "coldness" is higher in Case 2.
And thus, Case 2 can cool the air inside the room better.


(This holds true similarly for the water heater system where you are mixing the VARIABLE rate of hot water with FIXED rate of cold water! The more water flow, the better heat transfer occurs)


HOWEVER, for the purpose of reducing humidity, you need to cool the parcel of air (whether large or small) to its dew point. This happens more efficiently in the Case A (where the parcel is small and the temperature goes down lower).


But then why does your wife feel the way she feel (which means colder when the AC fan runs faster).
Casting the placebo effect aside ...
This is because human being are pretty sensitive to humidity when the dry temperature is high. But when the dry temperature drops (lets say to about 25 deg C), our sensitiveness to humidity decreases, and hence we no longer care about it.


(*Phew*)


Now we know why a fan gives relief. Its not just because it increase the sweat evaporation and thus makes us feel better, but its also because faster flow leads to better heat transfer.

Last edited by alpha1 : 11th April 2013 at 13:25.
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Old 11th April 2013, 14:37   #2925
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Default Re: Which home/office AC (air conditioner) to buy ?

Wow, alpha1 --- a really great explanation!

As with many things husband/wife, the answer is compromise. But, thanks to you, I now I have a better understanding of her point of view.
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