The quiet truth

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How can Mitsi make this claim? How can I unit provide full capacity output on quiet mode fan speed when the airflow drops considerably?

http://www.bdt.co.nz/aircon/info_quiet_truth.asp

The Quiet Truth about Heat Pumps.


Isn’t it time you got the true story on heat pumps?

Heat pumps are a great way to enjoy a comfortable home all year round, but some manufacturers are keeping quiet about their systems’ real ability to… well, keep quiet. These manufacturers often claim that a feature known as ‘Quiet Mode’ (or Sleep-Mode) makes theirs the quietest heat pumps available. But what they’re not telling you is that in order to achieve its low decibel level, ‘Quiet Mode’ must operate at a greatly reduced airflow... with a reduced comfort level to match. In contrast, Mitsubishi Electric’s whisper quiet heat pumps are tested under normal operating conditions to maintain a comfortable room temperature*. So you get all the comfort you need, without the noise. And quietly, that’s the whole truth and nothing but the truth.

*MSZ-FB25VA on low fan speed at maximum capacity, as at 1st March 2008.

[Brian_UK]

How can Mitsi make this claim?

Because they're selling to Australians/New Zealanders ??

Runs and hides in corner wearing fireproof suit.

[Greengrocer]

I think what we have here is a play on words & some "new labour" style spin!!
Unless the laws of physics have changed a unit that is rated for 2.5kW on high speed (12.1 m3/min) cannot achieve 2.5kW with only 4.5m3/min airflow on low speed. Granted the TD will increase dramatically but the overall capacity must reduce as well. A maketing ploy for the unitiated reader I'll venture.

[Brian_UK]

I wonder also whether it is a difference in fan and volute design reducing the noise levels.

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I wonder also whether it is a difference in fan and volute design reducing the noise levels.

Not sure what you mean Brian?

As surely if the airflow on Low was high enough to provide full duty 2.5kw of cooling then when it is placed on high your going to get more duty out of it?

[nike123]

Not sure what you mean Brian?

As surely if the airflow on Low was high enough to provide full duty 2.5kw of cooling then when it is placed on high your going to get more duty out of it?

No, you are not!
Heat transfer is limited by refrigerant mas flow and size of evaporator/condenser coil and fin surface.Therefore, when you reach maximum heat transfer to air at coil fins, further increase in air flow will not increase amount of heat absorbed or radiated thru evaporator/condenser.

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I wonder also whether it is a difference in fan and volute design reducing the noise levels.

No, you are not!
Heat transfer is limited by refrigerant mas flow and size of evaporator/condenser coil and fin surface.Therefore, when you reach maximum heat transfer to air at coil fins, further increase in air flow will not increase amount of heat absorbed or radiated thru evaporator/condenser.

Manufacturers design the capacity on a high fan speed. They are also stating that on low fan speed you get the same capacity as you would at high fan speed... how do you figure this out?

Greengrocer has already said... and I agree, that on lower fan speeds your going to get higher TD but because of the lower airflow your going to get less cooling. Unless the air off temperature is crazy low then your not going to get the capacity.

Normally cooling out put reduces with lower fan speeds. You increase the speed of the fan and you get higher output.

The same should be in this case if they are saying you get the full capacity at low then surely more airflow is going to produce more cooling.

[nike123]

Normally cooling out put reduces with lower fan speeds. You increase the speed of the fan and you get higher output.

That is correct if you have designed that full capacity is achieved at highest speed setting.

The same should be in this case if they are saying you get the full capacity at low then surely more airflow is going to produce more cooling.

Than nobody will be putting bigger compressors in units. By that theory, only air flow increase will be enough to make bigger capacity unit. Units of different capacities will be of same dimensions and with same compressors and only difference will be in air flow. Doesn't that sound odd to you?

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That is correct if you have designed that full capacity is achieved at highest speed setting.

Than nobody will be putting bigger compressors in units. By that theory, only air flow increase will be enough to make bigger capacity unit. Units of different capacities will be of same dimensions and with same compressors and only difference will be in air flow. Doesn't that sound odd to you?

yes it does sound odd to me, but it also sounds odd that they are claiming the unit provides full capacity in low fan speed? How is this possible? If its rated at 2.5kw on high fan speed?

[stefs_cruiser]

does it say they achieve full capacity or rated capacity?
They could reduce airflow but crank the compressor up, and end up at rated capacity(not full capacity)

But I think they don't have a quiet mode, but are trying to get the point accross that the unit is quiet within normal operating characteristics...In fact I think they are having a dig at a company that does have and promote a quiet function...

[TRASH101]

Nike has given the answer already for quiet running i.e. design for evap td at an air volume which suits the sound power levels for the fan. Therefore an increase in fan speed reduces the evap td proportionally to the increase of air volume(depending on evap design and face velocities it may reduce capacity).

Mitsubishi however claim that their whisper unit conditions a greater volume of air at a percieved noise level in comparison to other manufacturers equipment. They have probabley got a new fan and not a lot else.

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does it say they achieve full capacity or rated capacity?
They could reduce airflow but crank the compressor up, and end up at rated capacity(not full capacity)

But I think they don't have a quiet mode, but are trying to get the point accross that the unit is quiet within normal operating characteristics...In fact I think they are having a dig at a company that does have and promote a quiet function...

yes.... look at the small print.

In contrast, Mitsubishi Electric’s whisper quiet heat pumps are tested under normal operating conditions to maintain a comfortable room temperature*.
*MSZ-FB25VA on low fan speed at maximum capacity, as at 1st March 2008.

[nike123]

Manufacturers design the capacity on a high fan speed. They are also stating that on low fan speed you get the same capacity as you would at high fan speed... how do you figure this out?

In cooling mode, air has water vapor and for water vapor to condense, there is heat to be extracted to change state. That latent heat is providing same capacity of AC with reduced speed of air but at expense of sensible heat ratio.
In heating mode reduced speed means high TD (over 30K and you could end up with 55°C or more air discharge temperature, but at expense on compressor life.

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At expense of compressor life does not sound good at all.

Does it not ramp down if on low fan speed so as not to produce as much heat.

[nike123]

At expense of compressor life does not sound good at all.

Does it not ramp down if on low fan speed so as not to produce as much heat.

Yes it ramp down when condensation temperature reach safety level (for example: 56-58°C and it stop compressor if reach 61°C). But, these levels are high in comparison with normal condensation temperature when condenser dT is 5-10K (normal air flow for usual condensers in refrigeration) as oppose to ~30K in this example. And, by ramping down, mas flow of refrigerant is reduced and therefore capacity lowered.

[Brian_UK]

Not sure what you mean Brian?

As surely if the airflow on Low was high enough to provide full duty 2.5kw of cooling then when it is placed on high your going to get more duty out of it?

I mentioned noise levels not duties because the Mitsi data in your link does not give airflow rates but talks about noise levels.